Conference 7.286::space

    I think nobody is interested in doing this, because everybody thinks
    that in 40 or 50 years the technology will have improved to the
    point where we will be able to gather data in a much better way.
    Technology is changing so fast that it doesn't make sense to plan
    this far into the future.
        John Sauter

    Maybe, but the British Interplanetary Society (love that name) ran
    such a study a few years back. I think it was Project Daedelus.
    They extended technology forward somewhat rather than use 'state
    of the shelf'. If I recall correctly power was supplied by
    matter/antimatter engines, accelerating the vehicle to around 0.1c
    
    You may be able to get copies of their final report. I read parts
    of it in their magazine a few years back.
    
    I know you said 'ignoring politics' but... 
    I can't think of any political system in the world today that would
    be prepared to invest the $$$ required for such an undertaking when
    the results will take 50 years to get back. I think the first mission
    to the stars will require some sort of breakthrough, either scientific
    or political.
    
    Still, it is interesting to contemplate.
    
    gary

    I do believe that the technology to reach the stars exists in todays
    technology and is not exorbitantly expensive. Ion drives are relatively
    cheap and easy to make, and ideally suited to a long term mission
    such as this.
    Only a political breakthrough is necessary.
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

      How does the Ion drive work?

      George

    the ion drive.
    
    This is, of course, a very simplified explanation but here goes;
    Start with a quantity of mercury, heat it a bit to get it vaporizing,
    now pass the vapor through some ionizing radiation, and accelerate
    it through a field out the back end of the ship.
    
    Exactly like an electron gun in a CRT only backwards.
    
    Anyway, I saw a picture of a whole bunch of these things once. NASA
    was developing them for the Halley intercept in the early 70's.
    They even actually worked!                      
    
    Oh yes, you use mercury because it is very dense, and vaporizes
    pretty easily.
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    	This is NOT to stop the discussion here, this is simply an "arrow"
    for more information on this topic:
    
    	There is plenty on "real" (non-STAR WARS) starships in Note
    
    			MTV::SF (Science Fiction)
    			# 211, 224, and 324.
    
    	They're very informative - but let's get some technology feedback
    in here, too!
    
    	Larry
    

    Probably a communication laser would be a better way of communicating
    over interstellar distances than conventional radio.  (I was reading
    about there being some actual work going on on com lasers recently.
    Perhaps in Space World?)
    
    Burns
    

    40 or 50 years ... that means a 36 to 46 year trip.
    
    if we sent a rocket in 1990 @ .1C, would it arrive first, or
    would a second rocket sent in 2010 at .3C beat it ?
    
    							Bruce

    That's really the rub. A.E. van Vogt wrote a story decades back
    called "Far Centaurus" in which a man was placed in suspended
    animation on a ship and sent out to Alpha Centauri, taking some
    inordinate number of years. When he got there an woke up, he
    found a thriving Earth colony already there. Seems that FTL was
    discovered shortly after he left.
    
    Perhaps nothing so dramatic as that will happen, but technology
    can improve radically in a short amount of time. I'd rather see
    the money spent on near space (from Mars on in) projects instead.
    
    --- jerry

    Re .8 and .9
    
    Yes things can certainly develop a lot, very quickly. 
    And they always will, but if you keep wainting for something 
    better. You will never do nothing. (Lets wait until we can 
    do it at .3, .4, .7, FTL and so on forever)
    
    Besides which, thecnology builds on itself, for example if
    had waited until we had realy efficient rockets before trying
    to put anything in orbit. We still be completly Earth bound.
    How would have we learned how to build rockets, the suttle,
    satelites, planetary explorers. 
    The way to learn how do do something is to do it. From each
    new experience we learn, and are able to do it better afterwards.
    
    Sure a .3 C space probe could get there that much faster then
    a .1 C, but we will never be able to build it unless we learn
    how to build a .1 C first. 

    Well, in this particular case there is a bit more structure in which
    to balance technology advance vs. "let's do it!".
    
    Specifically:  If there's reason to believe that we could build
    a 0.1c ship today, then we could launch by around 1990.  It would
    arrive in the vicinity of Alpha-C around 2033 (if memory serves...)
    - about 47 years from now.
    
    Let's say in ten years we could built something that travelled at
    an average of 0.2c (not all that much an advance, one might think).
    Launch it a couple of years later (less latency, given that the
    effort was already underway, unlike today...) in 1998.  Arrival
    at Alpha-C (or is it Proxima-C that's about 4.3 light-years away?)
    21.5 years later in 2019-2020.
    
    Under those assumptions, it would seem to make sense to be patient
    up front - or we'd need to be much more patient later on (or just
    build the second probe anyway and write off the first).
    
    Of course, the specific figures are strictly out of a hat.  But
    the point is that at relatively small fractions of c a SMALL
    improvement in average speed makes a LARGE difference in arrival
    time, and makes a bit of patience while technology advances a
    good bet.
    
    Conversely, once one can build a probe to run at a good fraction
    of c, there's very little reason for further delay (at least for
    relatively close targets) unless a break-through in practical
    trans-light transportation is really imminent.
    
    The analogy with earlier space efforts has problems:  in those
    cases, once our abilities exceeded the threshold required for
    orbit, it made sense to start gaining experience immediately
    and develop in parallel, whereas with inter-stellar distances
    and an apparent UPPER limit to speed advances it makes more
    sense to optimize around not starting soonest, but getting
    there soonest (with a more advanced craft than we can build now).
    
    		- Bill
    

    I'm really happy that they built the Voyager probes when they did
    instead of waiting for a more powerful propulsion system....
    
    We don't have to wait 50 years for the payoff from an early star
    probe. Equip it to make observations and experiments along the way.
    We will see the first closeup of the Oort cloud (the presumed cloud
    of comets far out around the sun), first samples of interstellar
    matter, not directly influenced by the sun and other goodies.
    One important thing is parallax measurements of the distances to
    the nearest stars. With the current baseline we have, only 2 AU,
    parallax measurement is only good for a few dozen light years.
    Imagine what distances we can measure and the precision we will
    get when the base line grows to 1, 2, 3 and 4 light years and on.
    Our understanding of the universe depends very much on accurate
    measurements of nearby stars, that can then be used for comparison
    with more distant objects.
    
    If we build a faster probe, we can tell the first one not to bother
    to slow down, just move on instead to even larger distances. Perhaps
    someone can figure out a 'grand tour' of stars to fly by. (Although
    I read somewhere that the first star probes would be flybys anyway.)
    
    It will take a long time before we launch manned interstellar trips.
    A large number of unmanned probes launched in different directions
    can help us a lot in learning about the nearby space and perhaps
    save us from unexpected dangers. Such probes launched today, would
    supply exactly the information we need 50 years from now, when we
    decide where the first manned trip should go.

    Of course it could happen sooner. Although it seems more rational
    to explore and exploit the moons, planets and asteroid belt first,
    who knows where history will take us. Parallel effort is probably
    the best approach.
    
    							Bjorn

Re .11:

While it may be true that the initial increases in unmanned interstellar
probe speeds are the most important, note that in the case of manned
probes which rely upon time dilation to get the crew to the destination
in a single human generation (or less), it is the attainment of very
high speed which is important.  The difference in speed between a probe
which delivers a crew to Alpha Centauri in 20 years, and one which delivers
a crew to the Andromeda nebula in 20 years is relatively small.

Re .12:

You are probably less likely to "see" the Oort cloud than you are to
"see" the asteroid belt.  I assume that there are various instruments
which can detect individual comets, or some effect which would
represent the aggregate of all the comets in a region.  But you make
it sound like there is some cosmic neon sign saying "Eat at Sarek's"
which is spelled out in glowing comets.
				/AHM

    You mean there isn't even a MacDonalds out there? I'm chocked!

    						:-)
    
    						Bjorn

    True, the 'closeup' of the Oort cloud may consist of a quick flyby
    of one or two iceballs, if we can find them. 100 billion comets
    spread out over that volume would make them very hard to find.
    (No irony intended, the volume of the presumed Oort cloud is HUGE.)
    However, the composition of gases in that volume of space may also
    contain clues.
    
    There MUST at least be Real Estate agents out there :-)
    
    						Bjorn

    	Thanks to the possibilities of the Bussard Ramjet and the Lasersail
    Starships, there will at least be FUEL out there in interstellar
    space!
    
    	Larry
    

    re: .13, first paragraph.  I think you picked a poor example. To reach
    Alpha Centauri in 20 years of ship-board time would not require a very
    large fraction of C, since Alpha Centauri is less than 5 light years
    away.  To reach the Andromeda galaxy (M 31) in 20 years of ship-board
    time would require a very large fraction, since M 31 is something like
    a million light years away. 
        John Sauter 

    	The Andromeda Galaxy is TWO million light years away.
    
    	If a manned starship was sent to the Andromeda Galaxy at 0.99
    percent of the speed of light (186,000 miles per second), it would
    take two million years to get there, but due to time slowing down
    for the ship, the crew would only age 28 years.  
    	Assuming the starship came right back to Earth after reaching
    Andromeda (what, no exploring?!), the crew would be 56 years older
    than when it left, and Earth would be four million years older!
    
    	Unless the crew wanted to be aged old men and women (or deceased),
    they would probably have to sent off either as young, sophisticated
    children reared by advanced mobile computers, or put in as adults
    in suspended animation.
    
    	Larry
    

    re .18
    
    How would you only age 28 years while traveling 2 million years
    at the speed of light.  Does travelling at the speed of light have
    an effect on aging?  If so, how?  I thought that the reduced aging
    theory was the product of some imaginative si-fi writer.
    
    Please enlighten me.
    
    Mark    

    Re .19
    
    No, it isn't si-fi. The time compression formulas come straight
    out of the theory of relativity.
    
    The way that the energy, velocity, and time variables relate. 
    State that the closer you come to the speed of light, the more
    energy you expend and the more time slows down. Until finaly,
    to get to the speed of light you need infinite energy and time
    stops completly.
    
    

Re .17:

Yes, I see what you mean.  Pick something a few thousand light years
away as an example, instead.
				/AHM

    re .21
     
    Thanks for the explanation.
    
    Does the term infinite energy mean that the speed of light is not
    attainable?
    
    Mark

    re .22: Yep, that's right.
    
    BTW, notice how everything neatly fits together:  Relativity says
    that someone cruising in a ship at .99C should not be able to notice
    (in certain ways).  Thus in order for him/her to travel 1 million
    earth-based light years in 20 ship-years, the ship-measured distance
    also must get shorter.  And it does.  That is the Lorentz contraction.

    If you think about it, energy works that way too.  Suppose you are
    pouring a constant amount of energy into the drive.  How can you
    be accelerating more and more slowly as you approach the speed of
    light?  Because to the ground based observer since time is slowing
    down, you are spreading the same amount of energy over a longer
    time, thus giving a smaller acceleration.
    
    Neat, huh?
    
    Burns
    

    	In regards to the fact that time does slow down on a starship
    moving at 0.99 percent lightspeed, there is an interesting discussion
    of the topic in MTV::SF Note 228.
    
    	Just remember that much of the so-called "far out" concepts
    in Science Fiction are BASED on real physics (Relativity being a
    prime source and example).
    
    	Science Fiction has also inspired many machines and concepts
    we have and plan for today - starships being one of them.
    
    	Larry
    

An observer in the starship will see the distance to objects in the
direction of travel also shorten. This makes it possible for the observer to
make the trip in the 20 years or so (by the starship clock) and not have a 
problem with the speed of light. It should be pointed out however that an 
observer traveling at the constant velocity of .99C (from our reference frame) 
will also see time slow down in our (the Earth's) reference frame. That is from
the Special Theory of Relativity. The fact that the observer is younger than 
us when the starship returns is due to the ACCELERATION (and deceleration) 
making  the starship a non inertial reference frame. That is from the General 
Theory of Relativity (which I am a bit more shaky working with).

    The reason that infinite energy is needed to move a mass at the
    speed of light is because while time slows down and space shortens,
    mass increases. So at lightspeed, the object has infinite mass,
    and thus infinite energy is required to move it.
    
    And it should be pointed out that the Lorentz contraction has been
    proven experimentally. The half-life of sub-atomic particles has
    been shown to increase as their velocity is increased.
    
    --- jerry

    Some confusion here (mine or yours, not sure).  Here's my opinion:
    
    .25--The time contraction is due to speed, not acceleration.
    To keep the situation in the realm of Special Relativity, assume
    instantaneous velocity change from an Earth-based frame to nearly
    the speed of light, travel to M 31, instantaneous reversal of velocity,
    travel back to Earth at the same speed, and instantaneous stop.
    The travel time as measured by Earth-based clocks would be 4 million
    years.  The travel time measured by ship-based clocks would be much
    less, the exact amount depending on the exact speed.  Thus, the
    time-contraction effect does not depend on acceleration.
    
    .26--The Lorentz contraction is a spatial contraction, it does not
    involve time.  There is a time contraction, but I don't know its
    name.  As I understand it, the time contraction effect was used
    to predict not a change in half-life but a change in the frequency
    of radiation emitted.  Detecting a change in half-life would be
    much harder, because particles moving at nearly the speed of light
    don't hang around for very long, so to make a measurement you would
    need something with a very short half-life.  You couldn't create
    such an object and then start to accelerate it, because the
    acceleration process takes time, and the object would be decayed
    to nearly nothing by the time you got it injected into the final
    stage of the accelerator.  Therefore, you would have to create the
    particle using precursers already moving at nearly the speed of
    light.  I don't think the state of the art in particle accelerators
    has gotten this far yet.  The advantage of using radiation is that
    a particle radiates all the time.  Half-life is a measure of decay:
    the event happens only once per object.
        John Sauter

re. 27-  The Special Theory of Relativity states that there is no preference
between inertial reference frames. This means that the reference frame of
a starship (with the starship at rest in its own frame by definition) watching 
the galaxies go by at the speed of .99c is exactly equivalent to someone at
rest with respect to the reference frame of the galaxies (ie. Earth). The 
starship traveler will see the same things happening in the Earth's reference 
frame as we see happening in the starship's reference frame, ie. the 
contraction of lengths and the elongation of time. This means that the 
starship traveler will also see us aging much more slowly than him. The special
Theory does not address anything beyond this point. This means that the Special
Theory does not address anything about which person would be younger when they
get back together, only that both observers see the other aging more slowly.
If we start accelerating (deceleration is a negative acceleration) one of the 
frames to allow the two observers to start in the same frame and end in the same
frame of reference, then we must go to the General Theory to find out what 
happens.  It says that an acceleration is equivalent to a gravitational well and
time will pass more slowly. It therefore follows that the person that was 
accelerated will be younger. (it should be pointed out that the Earth is not a
true inertial reference frame but for our purposes here it is close enough.)

re 26 - Time and space can not be separated. They must be taken as one. That is
the basic premise of Relativity. If we look at space-time as four vector with
-ict as the fourth orthogonal coordinate, then what we see in the Lorentz 
transformation is a rotation (assuming velocity in the z direction) of part
of the z vector component into the -ict vector component. 
 
 Life times of sort lived particles from secondary cosmic rays are what was
used to test Relativity. A cosmic ray hits a particle in the Earth's atmosphere
this will create a whole number of different particles, some with a half life
short enough so that their whole existence can be seen on one photographic 
plate. Its half life will be with respect to the reference frame of the center 
of mass of the collision (the cosmic ray and the particle hit). We then can 
measure the half life in the Earth's reference frame and find that the half
life is increased by just the right amount.

above i = the square root of -1
      c = the speed of light
      t = time

    Don't mean to split hairs, but...
    
    RE: .22 asks if this infinite mass/energy thing means that you can't
    go faster than the speed of light.
    
    RE: .23 replys "Yep, that's right."  --  wrong.
    
    Many times in this discussion and others that I have been involved
    in, disregard the fact that this involves the THEORY of relativity,
    not the LAW of relativity.  It is a theory, and shoud be discussed
    as one.
    
    So, theoretically you can not go faster than the speed of light,
    but it has not been proven.
    
    jim (just my opinion...)
    

    re:.27
    
    The way I remember my physics classes, there are three Lorentz
    Equations. One defines temporal contraction, one spatial contraction
    (which, as .28 points out, is essentially the same thing), and
    the last mass expansion.
    
    I don't recall where I read of the decaying-particle experiments
    of time compression (it was some time ago), so I cannot look it
    up. However, I don't see the problem you bring up. The particles
    involved don't need to be "nearly" at the speed of light. Accel-
    erating a particle just a few tenths of lightspeed should give
    you a measurable change in decay rate. I've been mostly out of
    touch with the field for a while, but the last I recall, the
    highest speed a particle accelerator has managed is getting an
    electron to something like 0.7c.
    
    --- jerry

Re .30:

Does anyone know the speed of light in water?  (Perhaps it is simply
related to the index of refraction?  It's been a while since Optics). 
That would give a lower bound on the speed of the (electrons?) emitted from
spent Uranium fuel rods.  The deceleration of the particles to below
the local speed of light in the medium causes Cherenkov radiation (a
neat blue glow, in this case).
				/AHM/THX

> Does anyone know the speed of light in water?  (Perhaps it is simply
> related to the index of refraction?  It's been a while since Optics). 

Yes, the speed of light is directly related to the refractive index.

I think the following is correct:

	 c in air
	----------  = refractive index
	c in water


jb

    re: .30 and others--I'm not too sure of my facts; it's been a long
    time since Physics 101, and ``facts'' may have changed since then.
    Therefore, I will defer to the opinions of others.
        John Sauter

    
    	I agree with re .29, the theory of relativity is just that 
    	a theory. And has not been proven to hold in all cases.
    
    	Specificaly, it was based and only has been tested so far.
    	In the behavior of atomic particles as seen from our multi-
    	atomic selves point of view. And when all the energy used
    	was suplied from outside the particles in question, like for
    	example when we acelarate protons and electrons, or look
    	at photons.
    
    	Never has it been tested using an internaly powered multi-
    	atomic object acelarating itself to relativistic velocities.
    	Like the star probe, for all we know it could reach C and
    	keep on going regardless of relativity considerations. 
    	

A few years ago, I had heard that the theory was to be tested by flying an
extremely accurate clock (cesium-atomic?) in passenger seats on airliners
for a period of time.  I had also heard that an experiment was tried during
at least one of the Apollo missions.  Granted, these are not "relativistic"
velocities - but does anyone know the results of these experiments?

    Yup, atomic clocks. Relativity was confirmed.     -Tom R.

    	So let's get building a starship and find out!
    
    	Larry
    

Re .34:

1.  Please name two other scientific "theories" (or "laws", your choice)
which *have* been completely proven to your satisfaction.  (And which
therefore you are absolutely certain will never be disproven or modified).

2.  One of the first confirmations of one of the theories of Relativity
happenned decades ago when it was used to explain an anomalous precession
of the perihelion of the planet Mercury.  I would not call Mercury "an
atomic particle".
				/AHM/THX

    Sheesh, you people are starting to sound like lawyers.  How about
    adding a disclaimer, like "currently accepted beliefs state one
    can never reach (exceed) the speed of light ... actual milage may
    vary and should not be construed as a commitment by Carl Sagan."
    
    I'm happy to accept the theory that one cannot exceed the speed
    of light IN THIS PHYSICAL MANIFESTATION OF THE UNIVERSE.  Naturally,
    this doesn't rule out hyperspatial drives, etc., which I'm suprised
    no one has brought up.  A neat Sci-Fi story (I forget the name)
    had an interesting premise:
    
    The scene was the Mission Control Room at Houston.  The U.S.'s
    first probe to Alpha Centauri was just beginning its approach
    to orbit one of the planets (don't mince words, I know it really
    happened several years before and the radio waves were just now
    being received).  The mood was subdued, since a few years prior
    to this time an alien visitor from A.C. landed on Earth in order
    to apologize for destroying our space probe.
    
    I guess the point I'm trying to raise is that one can never tell
    WHAT advance in science may make today's state-of-the-art obsolete.
    As someone mentioned, thought, that's not a reason to wait for
    that advance rather than using what we have now.
    
    Sure would be nice if that joint US-USSR Mars mission happens in
    my life time (would be even nicer to go along!).
    

Associated Press           Mon 15-SEP-1986 17:59         Comet Mission

    NASA Scientists Consider Sending Probe Far Beyond The Planets

                            By LEE SIEGEL

                          AP Science Writer

PASADENA, Calif. (AP) - NASA is considering sending a spacecraft on a
50-year,  100  billion-mile voyage to try to determine the age of the
universe and learn if a comet cloud surrounds the solar system.

If approved, the mission would  be  the  first  designed  to  explore
interstellar  space,  said  Aden and Marjorie Meinel, astronomers and
optical scientists at  Jet  Propulsion  Laboratory,  which  runs  the
unmanned  space  exploration program for the National Aeronautics and
Space Administration.

The proposed  mission  is  called  TAU,  which  stands  for  thousand
astronomical  units. An astronomical unit is the distance between the
Earth and sun, or about 93 million miles.

The nuclear-powered TAU probe would take 50  years  to  travel  1,000
astronomical units, or nearly 100 billion miles. Pluto, the outermost
planet, is about 3.3 billion miles from the sun.

The  TAU  project  was  conceived  by  JPL director Lew Allen, former
director of the National Security Agency. He  asked  the  Meinels  to
organize  a  team  to work on the idea, said laboratory spokesman Jim
Doyle.

The probe might be launched between 2000 and 2010 at a cost of up  to
$1 billion. Its major task would start 10 years after launch, when it
would  begin  precisely measuring interstellar distances that now can
only be estimated, the Meinels said.

By determining the distance to a  star  or  galaxy,  astronomers  can
learn how long ago the objects emitted the light being observed. Such
measurements  of  the  most distant objects in space, called quasars,
"then leads to the age of the universe," now estimated at roughly  20
billion years, Mrs. Meinel said

The  voyage  "will  contribute  to the big picture of the universe by
giving a truer distance scale and a truer time scale and age back  to
creation," she said.

Her  husband  said  the  spacecraft  also  will  try  to  confirm the
existence of the vast Oort cloud, perhaps a trillion comets  believed
to  enshroud  the solar system at about 4 1/2 trillion miles from the
sun.

Meinel said the inner part of the Oort cloud may extend to  within  1
trillion  miles  from  the  sun.  The  TAU  probe  would  travel only
one-tenth that distance, but might detect the  cloud  as  the  comets
pass in front of distant stars, causing a blinking effect, he said.

The  probe  also  could  look back at the solar system, a unique view
that would help scientists trying to determine if there  are  planets
orbiting distant stars, Mrs. Meinel said.

Mrs.  Meinel  said  TAU  also  might  search for unknown stars; study
interstellar gas, dust and magnetic fields; and examine  cosmic  rays
generated by the so-called big bang that gave birth to the universe.

The  Meinels  said  they  will  brief NASA officials in Washington on
Thursday.

The spacecraft would be powered by a nuclear  reactor,  which  Meinel
said  is  being developed for the Reagan administration's space-based
anti-missile defense system.

Thrust 40 times greater than conventional  rocket  engines  would  be
provided   by  an  ion  propulsion  system  that  uses  a  stream  of
electrically charged xenon atoms to bring the probe to  225,000  mph,
much faster than any existing spacecraft.

The probe would send data to a space station for relay to Earth.

Mrs.  Meinel said astronomers are only able to accurately measure the
distance of objects up to  400  light  years  away,  or  about  2,350
trillion  miles.  Distances  to  farther  objects, such as most other
stars in our Milky  Way  galaxy  and  to  other  galaxies,  are  only
indirect  measurement  estimates  based on assumptions that sometimes
prove wrong, she said.

The Voyager 1 and 2 probes and one of Pioneer  spacecraft  eventually
will  travel  into  interstellar space. They were designed to explore
planets and moons.

                  <<< MTV::$1$DUA4:[NOTES$LIBRARY]SF.NOTE;1 >>>
                            -<  Arcana Caelestia  >-
================================================================================
Note 362.181                       SF Myths                           181 of 182
PROSE::WAJENBERG                                     70 lines  16-SEP-1986 09:29
                  -< More Than You Wanted to Know About FTL >-
--------------------------------------------------------------------------------

    Like most really interesting issues, the possibility of FTL travel
    is not that simple.
    
    First, it is not true that no object can travel at the speed of
    light.  Photons can qualify as objects and they seem to travel at
    the speed of light.  (No, I'm not being ironic.  Sometimes people
    propose that photons cannot reach c, which we should then re-name
    the "limiting velocity" or some such.  But so far, they seem to
    travel at c.)  until recently, neutrinos were thought to travel
    at lightspeed, though that has been thrown into doubt by some new
    theories.  Gravitational radiation is also thought to travel at
    lightspeed.
    
    The necessary condition for traveling at lightspeed is a zero
    rest-mass. This falls out of the mechanics of Special Relativity
    fairly directly; zero rest-mass is equivalent to travel at lightspeed
    (or to non-existence of course).
    
    If you start with a non-zero rest-mass, the equations blow up at
    light-speed.  In particular, no finite quantity of energy suffices
    to accelerate a non-zero mass from below light-speed up TO light-speed
    (or beyond it).
    
    But suppose we imagine some kind of discontinuous quantum-jumps
    from one state of motion to another?  Might not one such jump leap
    from one side of the light barrier to the other, by-passing the
    problem of infinities cropping up in the equations?
    
    Such a leap would not encounter the problem of infinities, but it
    would have another problem, which is mathematical or interpretational
    depending on how you look at it.  This is a problem involving imaginary
    numbers.
    
    The Lorenz transformations are the main tools of Special Relativity.  
    They are equations that describe how events look in one frame of
    reference, given how they look in another frame.  These equations
    have square roots in them, and when the velocity of one frame is
    faster than light relative to another frame, the quantities under
    the square roots go negative, so that the square roots (and the
    whole value of the transformation) become imaginary.
    
    If you jumped an ordinary object to the far side of the light barrier,
    it would appear to you to have imaginary mass, to have imaginary
    length in the direction of travel, and to have events happening
    at imaginary rates.  Most people find this unacceptable, since we
    have no interpretation for what these imaginary numbers mean in
    terms of real-life sensory observations.
    
    Accordingly, some theorists have imagined "tachyons," objects that
    always move faster than light.  Tachyons have imaginary mass, length,
    and rates in their own rest-frames.  Consequently, they look sane
    when viewed from the low side of the light barrier.  (If they ever
    are viewed.  So far, no one has ever seen a tachyon or any direct
    evidence for one's existence.)
    
    So what does life look like to the tachyon itself?  So far as I
    know, no one has addressed this question.  (Nor do I know of anyone
    addressing the question of what life looks like to a photon, which
    has different but equally bizarre problems.)  At a guess, a tachyonic
    observer considers all its own measures real and regards our own
    proper measures as imaginary.  This is a second level of relativizing,
    slapped on top of the canonical one, and is speculative.
    
    Even if you regard the tachyon as impossible (lots of people do),
    you still haven't disposed of FTL entirely.  In General Relativity,
    people have imagined wormholes, rotating universes and multiply-
    connected spacetimes all of which allow time-travel and therefore
    FTL travel as a special case.
    
    Earl Wajenberg

    re .31:
    
    > The deceleration of the particles to below
    > the local speed of light in the medium causes Cherenkov radiation (a
    > neat blue glow, in this case).
    
    As I understand it, cherenkov radiation is emitted by a particle
    traveling faster than the speed of light in the local medium.
    Not by the particle decelerating in the medium.
    It's kind of like light's version of a sonic boom.
    
    It is also proposed as a method of finding tachyons, look for Cherenkov
    radiation in a vacuum.
    
    The neat blue glow is related to the how much faster the particle
    travels than light. Thus, particles that were just "a little bit"
    faster than light would probably give off red photons.
    
    re .29:
    
    Just because something is titled "The Theory of ..." does not mean
    it is any less valid than a "law". You are confusing the use of
    the word "theory". Common usage of "theory" means something like
    "this might be right", the scientific usage means something like
    "this is a description of the way things work". "theorem" and "theory"
    have the same roots, "theorems" are statements of truth, not
    conjecture. Relativity has passed every test thought up to disprove
    it. Relativity is not "just a theory". 
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    re .42: But just like Newton's laws of gravity, it may well be found
    in a few years that there are some circumstances under which relativity
    does not explain everything.  Then a new hypothesis will be presented
    of which relativity and the laws of gravity are a subset.
    
    Burns

    re .43:
    
    > Then a new hypothesis will be presented
    > of which relativity and the laws of gravity are a subset.    
    
    true, but I doubt that the next theory will actually negate anything
    in Relativity. 
    
    As for FTL travel, there are ways to interpret the imaginary values
    that crop up. You also run into problems even if you disregard the
    problem of accelerating past the speed of light.
    
    The problem is with the observation of cause and effect. If one
    event is caused by another through the use of FTL then two observers
    A and B in frames of reference that have some relative velocity
    between them (less than c) may not agree on which event caused which.
    Based on the supposition that any experiment should produce 
    similar results for all observers (in inertial frames), and since
    FTL violates this, then relativity says that FTL is impossible.
    
    Now before anyone says this supposition is wrong, remember that this
    is the basis of relativity. All inertial reference frames measure
    the speed of light to be exactly the same value. This was the "problem"
    of the Michelson-Morley Experiment. It is this fact
    that yields all the other wierd effects of Lorentz contraction and
    red-shift and time dialation.
    
    Now maybe there is a way to get around this but it will require
    a cleverer person than I.
                                   
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    What is the scenario ("thought-experiment") in which FTL travel
    reverses the perception of cause and effect between two observers?
        John Sauter

    re .45:
    
    the following is a note that I've already posted in both SF and
    STAR_TREK. I wouldn't really call it a "thought-experiment" it is
    a straight-forward outcome when one uses space-time diagrams to
    figure out the distortions between two moving frames.
    
    (please disregard my glib comments at the end of the note, that
    was for the benefit of the file into which it was originally submitted)
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
      
    
    
                 <<< HBO::$1$DUA4:[NOTES$LIBRARY]SF.NOTE;1 >>>
                            -<  Arcana Caelestia  >-
================================================================================
Note 228.23                  Fast clocks run slow...                    23 of 23
CACHE::MARSHALL "beware the fractal dragon"          50 lines  22-AUG-1986 09:43
                            -< The effects of FTL >-
--------------------------------------------------------------------------------

    There is a discussion somewhere in SF about FTL travel and its physical
    interpretation, but I can't find it right now, so I'm putting this
    here, since this note is about time dialation. The following was
    written for a similar discussion in STAR_TREK.
    
    sm
    
                  <<< THEBAY::DRC0:[NOTES$LIBRARY]STAR_TREK.NOTE;1 >>>
                                 -< Star Trek >-
================================================================================
Note 40.88                        Time travel!                          88 of 88
CACHE::MARSHALL "beware the fractal dragon"          35 lines  22-AUG-1986 06:18
                           -< all done with mirrors >-
--------------------------------------------------------------------------------

    finally decided to dig out my Special Relativity book and see what
    he (A.P.French) has to say about FTL.
    
    	For suppose an event P(x,t) could cause an event Q(x+dx,t+dt)
    	through the agency of a signal having a velocity u > c. Then 
    	the time interval between the events as viewed in some other
    	frame moving with velocity v would be given by:
    
    		dt' = g(dt - v*dx/c^2)
    		    = g*dt(1- u*v/c^2)

        		       {	    /--------------/ }
    			       {where g = \/ (1 - v^2/c^2)   }
    
    	Thus if u > c, we could find a range of values of v ( < c) such
    	that dt' and dt were of opposite sign. All inertial observers
    	with velocities greater than (c^2)/u could conclude from their
    	observations that event P was caused by Q, rather than the other
    	way round.... it would make the laws of physics appear different
    	to different observers - at least as long as we have a basis
    	for knowing the direction in which time is advancing, as judged,
    	for example, by our own ageing.
    			            (SPECIAL RELATIVITY, A.P.French. p118)
                                    
    Whew. What he is saying is that suppose we have two ships, one that
    can move FTL, the other just very fast. Now send the FTL ship to
    Alpha Centauri at 2*c. There will be some speeds for the second
    ship, where it *appears* that the other one arrives at A.C. before
    it left Earth.
    
    But I say, so what. Appearances are always deceiving. No *physical*
    paradoxes are created, only perceptual paradoxes. But magicians
    do that all the time.
    
    sm

    re: .44
    
    >> Then a new hypothesis will be presented
    >> of which relativity and the laws of gravity are a subset.
    
    > true, but I doubt that the next theory will actually negate anything
    > in Relativity.
    
    I don't know why I have a bug about this whole thing, but I do.
    This sounds just like when people (bright, professional, important
    people) stated, as fact, that one could not go faster than the speed
    of sound and could not land on the moon or go into space...
    
    I don't see any reason that a new theory (proven or supported) couldn't
    negate portions of relativity.  I don't propose to know how or where,
    just that it is feasable.  The theory of relativity knocked some
    holes in the law of gravity.  None that affect its use in the common
    usage of the law, but at the subatomic level it doesn't work.  The
    work that is being done in investigating a possible *new force*,
    if proven, will shoot major holes in the law of gravity.
    
    Jules Vern died knowing that men would go to the moon.  He did not
    die a fool, though many people of that time would argue that.  He
    didn't allow popular oppion or 'laws' of nature sway his conviction.
    If I should die now, I would die knowing that men would build FTL
    devices.  I would not die a fool, I would die with a vision.  And
    I am thankfull for that, right or wrong.
    
    jim
    

    re .47:                                      
    
    > This sounds just like when people (bright, professional, important
    > people) stated, as fact, that one could not go faster than the speed
    > of sound and could not land on the moon or go into space...

      These "impossibilities" were thought so only for engineering reasons
    NOT because of any fundamental physical laws.
    
    > I don't see any reason that a new theory (proven or supported) couldn't
    > negate portions of relativity.  
    
    I used the word "negate" very carefully. Are you? Relativity is
    really quite simple, it is the implications that are far reaching.
    Just about the only thing in the theory to negate is the assertion
    that the speed of light is constant for all inertial frames. This
    fact has been demonstrated quite often. This is fundamental to the
    universe, it is not a problem of tensile strength or whatever.
    
    > The theory of relativity knocked some holes in the law of gravity.
    
    Name one. Relativity added to the law of gravity, it did not put
    any "holes" in it.
    
    > None that affect its use in the common usage of the law, 
    > but at the subatomic level it doesn't work.
                   
    This is not true. The law of gravity works at the subatomic level,
    it is just swamped out by the immensely stronger forces present
    at those scales. And Relativity has nothing to do with this anyway.
    
    > The work that is being done in investigating a possible *new force*,
    > if proven, will shoot major holes in the law of gravity.
    
    If proven, will not "shoot holes" in anything. It will just be an
    ADDED force, the present forces will still act as we know them.
    This assumes there is any validity to this "new force", which is,
    for good reasons, seriously doubtful.
    
    What would you say if I said that I imagine it will someday be possible
    to square the circle with just a ruler and compass? Am I a visionary?
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    When Einstein's theories of Relativity were introduced, it was found
    that the equations for energy were only first-order approximations.
    The equation for the kinetic energy of a moving object had been
		   2
	    KE = mv

    After relativity, the equation was found to contain additional terms
    that "blew up" as the velocity approaches c.  (I don't remember the
    exact form.  I'll check on it.  Anyone else, feel free to beat me to
    the punch! :^)

    Given conditions that are extreme enough, it is possible that the
    theories of Relativity could show themselves to be "just" high-order
    approximations of a more accurate theory.  We have to consider what
    environments would provide the necessary conditions.

    There are environments which the Theories of Special and General
    Relativity may not adequately describe.  One that comes to mind
    is the vicinity of a gravitational singularity (ie. a black hole).
    Stephen Hawkings is an authority on the physics of black holes.
    Could someone find out what his theories have to say about the 
    validity of Relativity inside the event horizon of a black hole?

    Another extreme environment might be a spacecraft accelerating to
    velocities that are a significant fraction of c.  The Lorentz
    equations predict that the observed mass of the spacecraft will
    increase towards infinity as its velocity approaches c.  As its
    mass increases, its density increases until it reaches the point
    where its apparent mass would begin to distort the spacetime near
    it (or at least that is what an earthbound observer might see).
    Should it not also be true that the pilot of the spacecraft will
    observe similar spacetime distortions?  It is unclear what happens
    when velocities large enough to produce such effects are reached.
    There's room for a lot of speculation.

    BTW, uniform acceleration is different from a gravitational field,
    but more on that later.

	Thanks,

	 /~~'\
	W o o k
	(  ^  )
	 \`-'/
	  \_/

    "Einstein's general theory of relativity is probably one of the
    two greatest intellectual achievements of the twentieth century.
    It is, however, incomplete, because it is what is called a classical
    theory; that is, it does not incorporate the uncertainty principle
    of the other great discovery of this century, quantum mechanics."
    
    	- Stephen Hawkings, "The Edge of Spacetime".
    		 _American_Scientist_, Vol 72, July-August 1984
    			pp 355-9.
    
    Note that black holes are a result of general relativity, but when
    quantum is applied to a black hole, it (the black hole) tends to
    dissipate. Thus quantum relativity (as yet unfinished) removes the
    singularities that crop up in plain relativity.
    
    Now before anyone jumps up to say "AHA! There's the loop-hole,"
    ...
    oh what the heck, maybe that IS the loop-hole...
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    re .49:
    
    >    BTW, uniform acceleration is different from a gravitational field,
    >    but more on that later.
    
    Okay, lets hear it. I'll bet you are mistaken.
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

Re: < Note 212.51 by CACHE::MARSHALL "beware the fractal dragon" >
                             -< oh yeah? sez who? >-

    >re .49:
    >
    >>    BTW, uniform acceleration is different from a gravitational field,
    >>    but more on that later.
    
    >Okay, lets hear it. I'll bet you are mistaken.

    Hi, Steve!  I knew you'd want to hear this one.  Hear me out before you
    tell me I'm full of ca-ca :^)
    
    The difference is that gravitation produces a field the strength of
    which falls off as radius squared.  By uniform acceleration (as in a
    spacecraft) I mean that every part of the accelerating body is
    accelerating at the same rate.  In most cases, the difference in the
    force of gravity between the bottoms of your feet and the top of your
    head is so small that we might as well be in a uniform field.  This is
    not the case, however near a black hole.  As you approach the
    singularity, the gravitational gradient between the top of your head and
    the bottoms of your feet become great enough so that you're literally
    ripped to shreds!  In a truly uniform field, no matter how high the
    acceleration is you will not experience any force as long as you are in
    free-fall.  So free-falling into a black hole means getting stretched by
    the field gradient while "free-falling" into an extremely intense, but
    uniform field just means going very fast.
    
    Well, Steve, how did I do?  I think that there are some experiments
    where they (scientists) measured the difference between the force of
    gravity at the top of a tower and at the bottom.  It was small, but
    detectable.  I was very surprised myself when I realized that there are
    indeed subtle differences in the two concepts.  It made me think that
    there might be just enough to provide a loophole to relativity.  After
    all, I do want to go to Alpha Centauri (or at least Proxima :^)
    
    BTW, if anyone misinterpreted my use of "uniform acceleration" I
    apologize fully.  Though there does seem to be some indication that
    gravity might affect heavier objects somewhat differently than lighter
    ones, but I'm not entirely sure what the most recent research is.  I
    believe it had something to do with a new repulsive force that depends
    on mass somehow.  Maybe someone else has more info.
    
	Thanks,

	 /~~'\
	W o o k	    Is the field through the center of a torus uniform?
	(  ^  )
	 \`-'/
	  \_/

Re: < Note 212.52 by CURIUS::LEE "Elen s�la lumenn omentilmo!" >
                         -< (Says me! That's who! ;^) >-

    >The difference is that gravitation produces a field the strength of
    >which falls off as radius squared.  By uniform acceleration (as in a
    >spacecraft) I mean that every part of the accelerating body is
    >accelerating at the same rate.

    Oops!  I didn't mean to imply that accelerating in a spacecraft was
    equivalent to uniform acceleration.  I was just trying to differentiate
    between a gravitational well and "free-space", ie. far from
    gravitational wells.
    
	 Sorry,
	  ___
	 // \\
	W O O K
	(  ^  )
	 \ _ /
	  \_/
     

    The fact that the gravitational field generated by a spherical body
    is a gradient that falls off as the square of the distance is not
    material to the discussion of General Relativity.
    
    This is not the nature of gravity, but the nature of radiation from
    a point source. A line source's field will will be inversely
    proportional to the distance, and a plane source will be constant
    throught all space. So...
    
    Imagine a *very* large disk of some dense material, say lead.
    Make it real big, radius equal to that of the sun. now put an enclosed
    room at the center of the disk. There will be no experiment you
    can perform in that room that will tell you whether you are in a
    gravitational field, or uniformly accelerating. The two are equivalent.
    As the sensitivity of your instruments go up, I'll just make the
    radius of the disk larger.
    
    (you may remember this experiment being mentioned in the book 2010)
                             
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

Re: < Note 212.54 by CACHE::MARSHALL "beware the fractal dragon" >
                              -< a common error >-

    >Imagine a *very* large disk of some dense material, say lead.
    >Make it real big, radius equal to that of the sun. now put an enclosed
    >room at the center of the disk. There will be no experiment you
    >can perform in that room that will tell you whether you are in a
    >gravitational field, or uniformly accelerating. The two are equivalent.
    >As the sensitivity of your instruments go up, I'll just make the
    >radius of the disk larger.

    I agree that according to the theory of General Relativity, the two are
    equivalent.  What I am arguing is that the experiment you imagine does
    not take into account what would happen to your "*very* large disk" as
    you make the radius larger and larger.  Eventually, gravity would pull
    the disk into a sphere.
    
    There seems to be a fundamental conflict between theory and reality.
    In theory, one can make the disk arbitrarily large, but in reality, one
    is constrained by the material(s) used to make the disk.  Certainly,
    gravitation accelerates particles, but to verify such acceleration as
    being uniform requires an experiment that we are unable to perform.
    I'm not saying that this makes the theory invalid, but it does allow
    room for speculation.
    
    I don't think what I'm saying is an error in thinking per se, but
    rather a different perspective from which to examine a question.  I
    understand and respect the power that thought experiments like the one
    you used have in exploring the limits of a theory, but I don't think
    they can be used to prove that some speculation is incorrect.  They
    only indicate directions in which experimenters can explore in order to
    find ways of testing the validity of their theories.
     
	Thanks,

	 /~~'\
	W o o k
	(  ^  )
	 \`-'/
	  \_/

    The point of my "very large disk" thought-experiment was only to
    show that the difference between acceleration and gravity is not
    a "fundamental" one, but a geometric one.
    
    It does not matter whether or not I could actually build that disk.
    The nature of the Gravitational Field equations insures that the
    result I predict will indeed happen. The field is exactly equivalent
    to an electric field. The inverse-square relationship is a result
    purely of the geometry of a point source. The fundamental nature
    of the field that produces this is that the field be conservative.
    
    "field lines" cannot disappear in free space, they must terminate
    on a field source (charge for electric fields, mass for gravitational
    fields) Thus, a constant number of field lines must pass through
    any closed surface surrounding the source. 
    
    Gravity fields are conservative (this has been shown) thus obey
    the same requiements of field lines as electric fields.
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

Newsgroups: net.space
Path: decwrl!ucbvax!slb-test.CSNET!DIETZ
Subject: Bootstrap Starships
Posted: 2 Oct 86 21:22:00 GMT
Organization: The ARPA Internet
 
Here are a couple of ideas for engines for interstellar travel. Both
are based on the idea of generating energy by interacting with ambient
matter, and using that energy to eject reaction mass, much like the
tether/engine combination mentioned previously. 
 
In the first design, a collector is used to generate energy from
passing interstellar gas.  I assume the vehicle is travelling at a
good clip (.1 c, say) before this engine is turned on.  The generator
is a thin foil a few atoms thick.  On either side of the foil I place
a sparse grid negatively charged with respect to the foil.
Interstellar hydrogen atoms will hit the foil and be ionized. Their
nuclei will pass unhindered through the trailing grid. The electrons,
which are much less energetic, will oscillate between the grids,
losing energy in the foil, eventually stopping there.  Electrons can
be drawn off the foil to do useful work, like driving an ion engine. 
The electrons are eventually ejected out the back to neutralize the
gas atom nuclei. 
 
Some problems: the foil will lose mass by sputtering, and the vehicle
will have to travel light years to get significant acceleration
because the interstellar gas is thin.  However, the idea does seem
more feasible than ramjets of various kinds. 
 
By turning off the ion engine and the electron gun we can let the
generator become very negatively charged.  Gas nuclei will be
accelerated up to the vehicle's speed.  The generator acts as a
parachute. 
 
 
A second design is for ultrarelativistic flight.  It interacts with
the cosmic background radiation.  At high speeds the spacecraft
perceives a temperature gradient: the radiation is hotter in front
than behind.  This gradient can be used to drive a heat engine, and
the energy used to expel reaction mass.  The low density of the CBR
means this engine is best used for long trips at very high speeds (for
intergalactic travel). 

Newsgroups: net.space
Path: decwrl!nsc!voder!aitnet!evp
Subject: Re: Bootstrap Starships
Posted: 8 Oct 86 06:52:20 GMT
Organization: American Information Technology, Cupertino, CA
 
 
$ 
$ Here are a couple of ideas for engines for interstellar travel.
$ 
$ In the first design, a collector is used to generate energy from
$ passing interstellar gas....
$ Interstellar hydrogen atoms will hit the foil and be ionized.
$ Their nuclei will pass unhindered through the trailing grid.
$ The electrons, which are much less energetic, will oscillate
$ between the grids, losing energy in the foil, eventually stopping
$ there.  Electrons can be drawn off the foil to do useful work...
$ 
$ A second design is for ultrarelativistic flight.  It interacts with
$ the cosmic background radiation.  At high speeds the spacecraft
$ perceives a temperature gradient: the radiation is hotter in front
$ than behind.  This gradient can be used to drive a heat engine...
 
TANSTAFFL. Both schemes ignore the momentum of the particles you are
extracting energy from.  Both electrons and photons deposit their
momentum in the spacecraft they strike the collection surface.  The
energy extracted is really coming from the spacecraft velocity as it
slows downdue to "equal and opposite" reaction to the impinging
particles.
-- 
Ed Post   {hplabs,voder,pyramid}!lewey!evp
American Information Technology
10201 Torre Ave. Cupertino CA 95014
(408)252-8713

    I agree with .56, where Steve showed that homogenous gravity can
    be realized and thus there will be no way to tell gravity and
    acceleration forces apart in a closed laboratory. Since there is
    still some noise about edge effects of his big disk, try this:
    
    There is actually a way to arrange mass to generate a perfectly
    homogenous gravity field, a way that does not require building
    infinitely or unacceptable large massive discs.

    Take a spherical body (planet) with the same density throughout.
    Dig a spherical cavity within it, off center from the center of
    the planet. The gravity inside the cavity will be perfectly uniform.
    It will NOT converge towards the center of the planet.

    If you don't believe that, read on:

    1. The gravity inside a homogenous body will be proportional
       to the distance from the center. (Outside it will decrease
       as 1/r^2 but inside it will be proportional to r.)

    2. The presence of the cavity is mathematically equivalent
       to 'overlaying' the planet with a virtual smaller planet with
       negative density (but the same magnitude as the planet's).
       Inside a negative mass the gravity will repel proportionally
       to the distance from the center.

    3. The gravity at a point inside the cavity will consist of
       two components, one pointing towards the center of the
       planet, proportional to the distance to the center, and
       one pointing away from the center of the cavity, proportional
       to the distance from the cavity center. The same proportionallity
       constant is used for both components.

    4. Add those two vectors together, the sum will be proportional
       and paralell to the vector between the center of the cavity
       and the center of the planet FOR ALL POINTS WITHIN THE CAVITY.
       Thus the gravity inside the cavity is perfectly homogenous.
       (Of course air or lab equipment inside the cavity will disturb
       the perfect homogenity, but so would air and lab equipment
       on board an accelerating rocket.)
       The special case we all know about is when the cavity is
       at dead center of the planet, then the gravity inside it
       be zero everywhere.

    A real planet like Earth is not homogenous (it is more dense
    in the center and there are irregularities) so a spherical
    underground cavern will not contain a homogenous gravity field.
    However, it is my gut feeling that by modifying the shape of
    the cavity slightly we can compensate for that. That way a
    homogenous gravity field can be realized within a limited
    volume at a reasonable effort, right here on Earth, with
    equipment available today.

    						Bjorn
    

Newsgroups: net.space
Path: decwrl!decvax!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Re: Bootstrap Starships
Posted: 13 Oct 86 17:40:19 GMT
Organization: The ARPA Internet
Posted: Mon Oct 13 13:40:19 1986
 
In Vol. 7, No. 9 of Space Digest, Paul Dietz proposed some "Bootstrap
Starship" ideas.  I am very reluctant to criticize this sort of
article because this is **exactly** the sort of thing I like to see in
Space Digest.  I compliment Paul for using his head.  However I don't
think his idea will work.  My embarassing question about his design is
"where does the energy come from?".  Paul's obvious answer would be
that it is coming from the surrounding interstellar medium.

I shall focus on his second design since it's easiest to criticize. 
You have a vehicle going at about 10 psol (percent speed of light). 
The front is interacting with the interstellar medium (hydrogen at
about 0.1 particles per cubic centimeter).  The front will heat up. 
In Project Daedalus it was assumned that the front of the vehicle
would have a temperature of around 200 deg. Kelvin.  We could assume
that the rear would be at almost 0 deg. Kelvin.  In theory the Carnot
efficiency would be near perfect.  However all of your energy would
actually be coming from original kinetic energy lost due to drag.  We
can calculate power by assuming a disc of 55 meters radius travelling
at 10 psol (relativistic effects are insignificant), and assume an
interstellar medium as originally described.  From the vehicle's frame
it sees particles streaming in at 10 psol.  The mass of intersellar
medium impacted on the forward shield of the vehicle for one second
would be 1.118e-8 grams.  From this we may estimate the energy
available in one second based on KE=(1/2)*M*(V**2).  This calculates
to be 5.355 kilowatts. This would be very useful for powering such on
board systems as a navigation computer.  However it is insignificant
in terms of the vehicle's total kinetic energy.  This is extremely
**fortunate** by the way, for if drag was significant then
intersteller travel would indeed be impossible.  A side point is
**if** the 1.118e-8 grams/sec. could be converted entirely into energy
by some magic way then you would have approximately  one megawatt of
power, or 1350 horse power, which is remarkably little.  You might use
this to push out a reaction mass but then you have the embarassing
question of where do you get the reaction mass from?  It was a good
attempt Paul, but you'll have to try again. 
 
                       Gary Allen



Newsgroups: net.space
Path: decwrl!decvax!ucbvax!LLL-MFE.ARPA!ATTENBERGER%ORN.MFENET
Subject: fusion engines
Posted: 14 Oct 86 15:49:00 GMT
Organization: The ARPA Internet
 
Posted: Tue Oct 14 11:49:00 1986
  
Paul Koloc writes:
   What we need is to develop the technology of fusion to do really
   significant things beyond LEO.  DoE has demonstrated it can't make a
   workable commercial fusion power generator...
   ... prototype fusion engines could be operating just after
   three years.  These engines if based on PLASMAK(TM) technology, would
   burn hydrogen(protium) boron (eleven) which generates pure helium(four)
   and no radiation.

Actually DOE has done a responsible job of allocating scarce funds. 
The main problem is that congress lost interest in fusion when the the
oil glut began.  Also it is a long way from a prototype fusion engine
(just a hydrogen-boron pellet being hit by a laser) to an engine which
can actually lift a payload.  We need better lasers and a good way to
keep the containment vessel from eroding.  I would prefer to see all
of our pennies for space research being spent on shorter term
missions, with fusion engines developing as best they can via military
funding for laser research. 

> A side point is
> **if** the 1.118e-8 grams/sec. could be converted entirely into energy
> by some magic way then you would have approximately  one megawatt of
> power, or 1350 horse power, which is remarkably little.  You might use
> this to push out a reaction mass but then you have the embarassing
> question of where do you get the reaction mass from?

    You don't need any reaction mass, just use photons. ** IF ** you
    have reaction mass to spare, so much better, but you get max available
    thrust by throwing the mass out at the speed of light, which can
    only be done with a photon drive. But with so little mass/energy
    available the thrust is not impressive.
    
    						Bjorn


Newsgroups: net.space
Path: decwrl!decvax!ucbvax!LLL-MFE.ARPA!ATTENBERGER%ORN.MFENET
Subject: fusion engines
Posted: 14 Oct 86 15:49:00 GMT
Organization: The ARPA Internet
 
Posted: Tue Oct 14 11:49:00 1986
  
Paul Koloc writes:
   What we need is to develop the technology of fusion to do really
   significant things beyond LEO.  DoE has demonstrated it can't make a
   workable commercial fusion power generator...
   ... prototype fusion engines could be operating just after
   three years.  These engines if based on PLASMAK(TM) technology, would
   burn hydrogen(protium) boron (eleven) which generates pure helium(four)
   and no radiation.

Actually DOE has done a responsible job of allocating scarce funds. 
The main problem is that congress lost interest in fusion when the the
oil glut began.  Also it is a long way from a prototype fusion engine
(just a hydrogen-boron pellet being hit by a laser) to an engine which
can actually lift a payload.  We need better lasers and a good way to
keep the containment vessel from eroding.  I would prefer to see all
of our pennies for space research being spent on shorter term
missions, with fusion engines developing as best they can via military
funding for laser research. 

    

Not to get back to the subject or anything, but:

Does anyone know the details of Robert Forward's Star Wisp proposal 
for an interstellar probe?  All that I've heard is that it is a
sphere of fine wires a few meters across, with a controlling chip on 
it somewhere. It's accelerated by shining a very powerful microwave beam
(on the order of gigawatts) on it.  The wires reflect the beam and so 
the sphere is repulsed.  Its total mass is only a gram.  It can be 
accelerated up to relativistic speeds, and so get to other stars 
within the working careers of its designers.  Does anyone know how it 
sends data back?  If it decelerates at the other end?  How the beam 
is generated?

/jlr

    RE 212.62 -

    I just wanted to put in this information about where to find 
literature on starships; I do not mean to "cut off" your inquiry about 
the starship you mentioned.  I myself am fascinated with starships, 
and unfortunately I know very little about the Star Wisp - let's hope 
somebody does, and will post that information in this note.

    Larry


Newsgroups: net.space
Path: decwrl!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Nuclear Fusion Pulse Propulsion Systems -- available literature
Posted: 17 Oct 86 13:26:45 GMT
Organization: The ARPA Internet
 
    Someone asked about source material on Nuclear Fusion Pulse rockets
for interstellar travel.  The best source is the Project Daedalus
final report produced by the British Interplanetary society.  To
acquire a copy write: 
 
 
               The British Interplanetary Society 
               27/29 South Lambeth Road
               London SW8 1SZ
               England
  
 
    Also the Journal of the British Interplanetarey Society (JBIS),
Interstellar Studies (red cover series) often describes this style of
propulsion along with Bussard ram scoop and antimatter propulsion
schemes.  The JBIS is hands down, the best source of information about
the engineering on interstellar travel. 

    There is also a paper floating around entitled: "A Laser Fusion Rocket
for Interplanetary Propulsion" by Roderick A. Hyde, 27 Set. 1983 from
Lawrence Livermore National Laboratory (Larry Labs), reprint number
UCRL-88857.  Roderick Hyde is a nuclear weapons designer who designs
starships when he isn't designing a bigger and better thermonuclear
warhead.  Supposably, most of his major innovations on starship design
are classified (Q-Clearance).
    Also "Astronautica ACTA" will on occasion produce something on
interstellar travel.  The most exciting stuff with respect to
interstellar travel is being done by Sandia National Labs.  Sandia is
working on an inertial confinement scheme based on high energy neutral
particle beams rather than lasers.  This sort of system could easily
be adapted into a one million sec. specific impulse propulsion system.
    Word has it that the Nova, Novette inertial confinement scheme at
Larry Labs is a loser and only good for bomb work.  It'll never be
useful for producing electrical power or propelling a spacecraft. 
 
                                   Gary Allen

    re "Starwisp":
    
    i don't suppose that this is what triggered the question, but there
    was just recently a cover-story in _New_Scientist_ (sorry I don't
    have publication date, I'm home, atricle in SHR library) titled
    "Ride a laser to the stars". 
    	As I recall, Starwisp is a two-dimensional net (not a sphere)
    and is driven by a MASER. There is also a description of a manned
    round-trip voyage to Eridani (sp?) 10ly (light years) in 20 years 
    (each way).
    
    	one interesting feature of Starwisp is that at each wire junction 
    would be a microchip and some sensor, during the flyby of
    Alpha-Centauri, a lot of information would have to be taken very
    quickly and stored until it can be transmitted back to earth. 
    
     I was going to enter some extracts from the article when I first
    read it, but it was very superficial, and not worth the effort (I
    am not a touch typist)
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

Newsgroups: net.space
Path: decwrl!decvax!ucbvax!slb-test.CSNET!DIETZ
Subject: How dense is the interstellar gas near the sun?
Posted: 18 Oct 86 18:24:00 GMT
Organization: The ARPA Internet
Posted: Sat Oct 18 14:24:00 1986
 
Additional comments on "bootstrap starship"...
 
For all of those who asked "Where does the energy come from?", the
answer is: from the reaction mass.  Initially the reaction mass and
spaceship are comoving, but when one dumps the reaction mass so it is
stationary.  Its kinetic energy stays with the ship. The background
gas is not an energy source, it's a momentum sink. 
 
It was commented that, even at .1 c, the power density of the
interstellar gas is low.  Quite right; I said that in the first
message.  A very large, thin collector is needed; one also needs a
long acceleration path (light years long). 
 
The biggest problem with my first scheme was the need to ionize the
gas by impact with a foil.  Sputtering could destroy the foil too
quickly for it to be useful.  Is this necessary? 
 
It has recently been suggested (Bertaux et. al., Astron. Astrophys.
150(1), 1985;  Reynolds, Astron. J. 92(3), 1986)  that the local
interstellar gas is substantially ionized.  Estimates of density based
on Lyman backscattering by neutral hydrogen may therefore be too low.
Bertaux et. al. conclude that in the immediate solar neighbor
interstellar neutral hydrogen and helium concentrations are .03 - .06
cm**-3 and .015 - .020 cm**-3, respectively.  The ratio of neutral
hydrogen to helium is substantially below the "cosmic" ratio,
suggesting that substantial amounts of the hydrogen have been ionized.
These figures imply that from 60 to 85% of interstellar hydrogen in
the solar neighborhood is ionized (perhaps more if helium is also
substantially ionized).  In this model, the local hydrogen density is
0.2 cm**-3. 
 
Ionized gas is a *lot* easier to couple to than neutral gas.  The
heavy foil I suggested for the first version could be replaced by some
scheme using very sparse charged grids, or perhaps by superconducting
cables coupling to magnetic fields embedded in the interstellar
plasma.  Such collectors would be mostly empty space. 

    re .62:
    
>    Does anyone know how it [Starwisp] sends data back?
    
    The mesh itself can act as both an antenna and as an energy storage
    medium.  
    
>    If it decelerates at the other end?
    
    No it doesn't. But there is a way to let a larger craft decelerate. 
    
>    How the beam is generated?
    
    Remember a few years back people were talking about solar power
    sattelites that would beam energy back to earth by microwave? One
    of those (a big one) would be enough to power starwisp, however
    a huge fresnel lens would have to be constructed to collimate the
    beam. This huge fresnel lens would also be a very large mesh of
    wire but instead of aa single disk would be a series of concentric
    rings of mesh and gap. This would act to focus the beam on Starwisp.
                                     
                                                                        
    re my last entry:
    
    one interesting statistic is that our ship could be accelerated
    to .5c in just .4 light-years. 
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    OK, so we can send it.  But why?  What kind of information can a
    one-gram mass of silicon and chicken wire send back to earth?  How
    could sensors, transmitters, etc., fit within that somewhat restrictive
    weight limit?
    
    I suspect that the gross mass of the spacecraft is too low for
    usefulness by at least three orders of magnitude.

    re .67:
    
    why the cynicism? Actually, a several gram mass of "silicon and
    chicken wire" could send back quite alot of useful information.
    Look at what came back from Uranus. No one can know what new things
    are there to be discovered until we go there and see.
    
 >   How could sensors, transmitters, etc., fit within that somewhat 
 >   restrictive weight limit?    
    
    The same way a VAX fits into similarly small package inside a
    chip of silicon. Robert Forward who designed the thing, did not
    want to just blow a piece of tissue paper out there.
    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    
    
                                                  

    Not cynicism - just trying to inject some "reality" into the
    discussion, so that perhaps someone might come up with modifications
    to the idea to make it more feasible.
    
    I had thought the original reply setting forth the Whisp idea said
    ONE gram, not a few.  After a while, a "few" becomes a kilogram
    - hence the three orders of magnitude.
    
    Yes, a VAX fits on a chip - but we then have to add many pounds of
    "immaterial" stuff to make it do something useful.  I would assume that
    we would want data on the target system - such things as the presence
    of planets, the presence of life/intelligence/etc., characteristics of
    its star, radiation, gasses and particles in the system.......all this
    takes mass for sensors, mass data storage and intelligence (the n-year
    response time means control & search functions would have to be locally
    managed), etc.   Also consider the power (and power densities)
    necessary to generate a radio (or light) signal of sufficient power to
    be received reliably on earth (or earth orbit). I suspect that the best
    technology of the near (10yr? 20yr?) future would require payloads on
    the order of a kilogram, not a gram.
    
    Finally, if the spacecraft is moving at relativistic speeds (no
    deceleration at end of flight), how much time in its reference frame
    would it have in the vicinity of the target system to collect data? 
    
    If all this is so, how can the Whisp idea be used/modified to build a
    successful probe.  Is there something I am not considering in reasoning
    about spacecraft mass which would mean that it would be lighter? 

    	The Star Wisp, as it is presently designed, could at least be
    built for use as a TEST VEHICLE for a more advanced Star Wisp capable
    of carrying a "more useful" payload of instruments.
    
    	Larry
     

    The article I saw said a few grams. This may be on the light side
    but think of what you don't need, you don't need batteries, the
    microwaves provide the power. RAM chips are getting denser all the
    time you don't need printers or cabinets or CRT's. The web is the
    sending antenna with a lens here the size proposed, the wisp would
    not need to send a very strong signal, Voyager's signal is incredibly
    weak. 
    All StarWisp is is miles of very fine wire and a pile of chips.
    Some of those chips would be processors, some sensors, some RAM,
    and there would be lots of them, but I doubt they would weigh in
    at a kilo. 
    I think you expect it to need a "Voyager" at the center in order
    to take all those measurements. No, the 'instruments' are much
    different from what has gone before, it would be a very distributed
    system, thousands of photodiodes spread over a square mile, each
    with its own associated processor and RAM. maybe include a diffraction
    grating to do spectrometry. each chp would be very small and very
    light, even thousands would not add up to more than a few grams.
    The hard part is spinning wires small and strong enough.
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

    Okay, attached below are some excerpts from the article I read. This 
    should clarify my previous replies. Obviously, the person who said it 
    would weigh ONE gram was mistaken. 
                                                   
                  /
                 (  ___
                  ) ///
                 /                    
    
    	from _NEW_SCIENTIST_, pp31-35, 2 October 1986.

			"Ride a laser to the stars", 
					
					by Robert L. Forward and Joel Davis

	...
		Starwisp is simply a sail made from hexagonal mesh of wire, 
	one kilometre in diameter, weighing only 20 grams. There would be a 
	microelectronic cicuit at each of the ten trillion intersections of 
	the mesh. These semi-intelligent chips would not only work as computer 
	elements in a ten-trillion-component parallel processing supercomputer; 
	the chips would also be sensitive to light, and would function as tiny 
	pinhole cameras.

		The propulsion system for Starwisp...would consist of a 
	20 gigawatt microwave beam from a solar-powered satellite in orbit 
	arouond the Earth. ... The beam would be turned on and focused on the 
	sail by a special kind of lens called a Fresnel zone lens.

		The lens would be huge: 50,000 kilometres wide or four times 
	the diameter of the Earth. It would be a complex of wire-mesh rings 
	alternating with empty rings. The radii of the rings would be adjusted 
	so that the microwaves passing through the empty rings would be in 
	phase at the focal point of the Fresnel zone lens.

	...

		Seventeen years later, Starwisp would have travelled 
	three-quarters of the way to Proxima Centauri. The next part of the 
	mission would begin as mission control turned the microwave beam on 
	again. A powerful pules of energy would be sent streaming to the 
	spacecraft, arriving as Starwisp arrives, four years later. The beam, 
	though spread out, would still be strong enough to "turn on" Starwisp's 
	ten trillion microcircuits. The circuits would use the wires of the 
	mesh sail as microwave antennas to collect the energy of the beam. Each 
	circuit would adjust its internal clock to the phase of the microwave 
	beam. Then, acting as the photoreceptors in the retina of this 
	artificial 'eye', the ten trillion semi-intelligent chips would 
	analyse the light coming from the objects in the Proxima Centauri 
	system.
		At a velocity of 60,000 kilometres a second, Starwisp would 
	make the fastest flyby in history. ... Starwisp would race through the 
	Proxima Centauri system, covering about nine billion kilometres, 
	equivalent to the diameter of Neptune's orbit, in just 40 hours. 
	During that time, the energized superchips of Starwisp would produce 
	25 high-resolution images a second, close to the frame rates [of TV]. 
	Using the timing information from the microwave beam, the mesh would 
	reconfigure itself as a directional antenna and broadcast the data 
	back to Earth

Newsgroups: net.space
Path: decwrl!ucbvax!SU-AI.ARPA!REM%IMSSS
Subject: why Mercury (liquid metal) used for ion rocket?
Posted: 31 Oct 86 00:19:06 GMT
Organization: The ARPA Internet
 
B> Date:         Fri, 10 Oct 86 10:22:46 EDT
B> From: ST401385%[email protected]
B> To: space digest <[email protected]>
B> Subject:      Specific Impulse
 
B>      Yes, but with an ion drive, one is typically more concerned
B> about getting the most performance out of the ENERGY source, which
B> is usually the limiting factor instead of the reaction mass.
B> A fixed voltage ion drive will give a fixed energy per unit charge, E.
B> E=1/2 mv**2, so momentum transfer (mv) is SQRT (2mE).
B> To optimize this per unit reaction mass, we want the smallest molecular
B> weight possible.  To optimize this per unit ENERGY, we want the
B> HIGHEST molecular weight possible.  That's why mercury or cesium is
B> typically used.
 
I don't believe this. In deep space, you have months to reach your
target. During that time, your solar collector or atomic pile can
generate more energy than you need for your delta-vee, but the only
fuel you can carry with you is what you could launch, which is limited
by your launch booster. (Assuming you don't have a space station with
re-fueling center, which would allow a different strategy of
accumulating fuel from lots of launches to power a single deep-space
probe.)  Therefore if there were no engineering problems you would
pick the lightest ion so you could pack the largest number of
molecules in your ion-fuel tank for a given Earth-launch mass. But
there are indeed engineering problems: Hydrogen requires pressure
containers whereas mercury is a compact liquid at normal temperature
and pressure. Other atomic materials are like Hydrogen, or solid.
Mercury is the only atomic liquid available. Compounds would have to
be broken into parts (they'd break apart anyway if you tried to use
them as ion fuel) and you'd have to get rid of the parts you're not
using or else have equipment to handle all the parts with their
different particle masses and different ionization characteristics, a
big hassle equipmentwise. 
 
I have no experience in this area, this is just brainstorming, would
like to hear from an expert to judge our difference of opinion. 

              ################################################

Newsgroups: net.space
Path: decwrl!ucbvax!slb-test.CSNET!DIETZ
Subject: Fusion?
Posted: 31 Oct 86 21:15:00 GMT
Organization: The ARPA Internet
 
Geoff,
 
  In regards to that Technology Review article about fusion: it was a
critique of *magnetic confinement* fusion; specifically, tokamaks and
magnetic mirrors.  Inertial confinement fusion does not suffer from
the same problems, since the first wall can be a liquid lithium alloy
or ceramic pebble blanket, and the reaction vessel need not contain a
high vacuum.  Also, it's not clear if Lidsky's complaints apply to
D-He3 reactors, since these can use direct conversion and avoid the
major costs of steam turbines and generators. 
 
  There's a form of fusion power that is possible today.  It's
possible to excavate large cavities in salt domes by circulating
water. Fill the cavity with high pressure steam, add some impurities
to make the steam cloudy, and detonate about 100 kilotons of bombs per
day. That's about 5 gigawatts of heat, not counting heat from
radioactive decay products.  Fissile material for the bombs can be
bred separately or in-situ by surrounding the bombs with breeding
blankets.  This scheme has obvious safety problems, but requires no
new science. 
 
  Small scale inertial fusion may be closer many think.  Light ion
beam fusion is close to the power levels needed for ignition (although
delivering the beam to the target is more problematical). There's been
a report that "hohlraum" targets (in which driver energy is converted
to thermal x-rays which then drive the fuel element) have been tested
by using thermal x-rays from underground bomb explosions. 
 
  These two schemes can be combined by using multi-stage fuel
elements. A small pellet with about a gigajoule of energy output is
used to generate x-rays to detonate a 300 gigajoule (say) pellet. 
Detonate one every 5 minutes in a cavity to generate a gigawatt of
heat.  This scheme might make it practical to deliver the initial
driver energy by means of disposable conductors.  It might also make a
reasonably low-tech "mini-Orion" engine for moving asteroids, if
detonated behind a pusher plate.  Where one draws the line between
large fuel pellets and small hydrogen bombs is unclear; would such a
rocket violate the Outer Space Treaty? 

Re .72, .earlier:

A 20gm spacecraft would mass about the same as a stack of 4 U.S. nickels (5
cent pieces).  Or 8 U.S. dimes (10 cent pieces).

That's not a lot of mass to play with, even given VLSI techniques.
				/AHM

Re .42:

>    As I understand it, cherenkov radiation is emitted by a particle
>    traveling faster than the speed of light in the local medium.

Yes, although .31 implies this.  (How else could a particle decelerate to
less than the local speed of light unless it was originally traveling
faster than it?)

>    Not by the particle decelerating in the medium.

But the particle *does* decelerate.  That's where the energy for the
radiation comes from.
				/AHM/THX

    There is an interview with Robert Forward in the lastest Space World,
    including a fairly complete explanation of who StarWisp works. 
    20gm is the right figure.  The "pictures" are taken by zillions
    of light-sensitive LSI circuits the size of a cell at each
    intersection.  They are decoded into a picture through the magic
    of computers/math back on earth.  They are transmitted via some
    technique whose name I don't remember which essentially gets power
    from a microwave beam sent from earth and also uses the beam as
    a homing device to send the info back.
    
    If I think of it and get a chance, I'll type in the relavent portion
    of the interview.
    
    Burns
    

    Some excepts from the interview about Starwisp
    
    ..I dreamed up an interstellar vehicle that will take color televeison
    opictures of a star and its planets as it goes by.  And it only
    weighs 20 grams.  An ounce is 28 grams, so this thing could be folded
    up, stuck in an envelope and amiled for 22cents.  The basic design
    is a wire mesh.  Its built like a lady's veil except its a half-mile
    across and its maide out of very fine wire--about the spacing of
    a veil...At each intersection of these wires is a tiny microcircuit
    about the size of a wavelength of light.
    
    Now, if I spread this out in space and us a solar power satellite
    that can produce 10 gigawatts of microwave power, the beam bouncing
    off the wire mesh will cause it to move.  It accelerates at 115
    Gs.  It gets up to 2/10 C in less than a week.
    
    This piece of wire mesh is moving out throught space with its
    microcircuits, and it's pushed toward Alpha Centauri.  After 20
    years it gets there, but before it gets there--4.3 years earlier--we
    have to remember to beam microwaves at Alpha Centauri.  Satartisp,
    being out there, won't accelerate anymore because the microwaves
    are spread all over the place.  Instead, each little microcircuit
    will use the wires that surround it as an antenna and will capture
    that microwave power--its about 10 watts over teh whole antenna--and
    use it to power the microcircuits so they turn themselves on.
    
    One of their components is a photodetector that looks in whatever
    direction it happens to be facing--we design the thing so the
    photodetectors look in all directions.  All of a sudden this 1/2
    mile piece of mesh has become an electric eye that looks around
    at everything it can see.  Most of the time the little eyes will
    be looking at black, because it is empty space.  Occasionally, they
    will be looking at a planet.  And by using a technique called speckle
    interferometry, which uses the known stars in the sky to help
    unscramble the image, you can actually use thsese little microcircutis,
    working together, to reconstruct an image of the planet that is
    fly ing by.
    
    There is a technique which has been developed and used for years
    at Hughes called retrodirective antenna array.  you take a signal
    that's coming in to the antenna and as you collect the power, you
    adjust your clock so you are inphase with the microwaves that are
    coming in.  That means you now are all in step--each little
    microcircuit in step, knowing exactly what time to send the signal
    back to Earth, rather than randomly out in space.  The whole antenna,
    using the incoming beam as a reference wave, will send a retrobeam
    right back in the same direction, carrying on top of it color tv
    pictures as it flies through Alpha Centauri.
    

    -Pardon the typos, please
    
    
    burns    

It's going to take a very, very serious microwave receiver to pick up 
a 10W transmitter at Alpha Centauri, even if all the circuits are 
transmitting in phase with the incoming beam.  Did Forward discuss that?
Are we talking about a 1000 km dish in the outer solar system?

If I were doing this, I would have all the little microchips store up 
their color pictures and send them back after the wisp passes the star.
That way, the return beam can be narrowed down to an extremely narrow 
frequency band for maximum signal to noise ratio.  We wouldn't care 
if the data rate is only 1 bit/second, because the wisp has 
nothing else to do until it reaches the next star.

It would be better still if we could figure out some way to slow the 
wisp down at the other end and put it into orbit.  Perhaps it could 
get close enough to the star to brake in its atmosphere.  The wisp 
would have to have some kind of manuevering capability, though, and 
it's hard to see what could change it's velocity vector in time.

/jlr

    I believe the microwave beam was intended to be powered by some
    gigundic thing orbiting near Mercury and powered by the sun.  I
    assume one could use this for receiving as well?
    
    Re deceleration:  Forward has another concept where a laser-powered
    lightsail could decelerate by somehow separating part of the sail
    and having it reflect light back onto another piece of the sail
    to slow it down.  Don't quite understand why the front one does
    not pull with the same force as the back one pushes.
    
    Burns
    

    re .79:
    
    > Don't quite understand why the front one does
    > not pull with the same force as the back one pushes.
      
    
                                                 |
                                                 |
      *                              |
      A                              B           |
                                                 |
                                                 C
    the above is a side view                      
    A is the source, here at Sol
    B is the center of the sail that has detached from C (10km dia.)
    C is the remaining annulus, note the missing section.(100km. dia)
    
    Now, A is very far away, so illuminates B and C equally and with
    parallel rays. However, the rays that hit C are focused onto the
    backside of B.
    
    C is still being pushed away by the reflection, but now B is being
    pushed much more strongly back toward A.
    
    B cannot "pull" on C.
                                                   
                  /
                 (  ___
                  ) ///
                 /
    
                    

    re .80:  Thanks for trying, but I still don't understand.  Every
    photon which hits B on the backside has also hit C on the frontside.
    If we assume perfect reflectivity and all that good stuff, then
    the momentum transferred to B should be the negative of the momentum
    transferred to C, shouldn't it?  In fact, if any photons which reflect
    of C do not hit B, that is a net momentum gain in the direction
    away from A.
    
    Sorry I am being so dense.
    
    Burns
    

    re .81:
    
    No you are not being dense. You are correct. C continues to be
    accelerated away from A and B. However, it also is providing the
    braking energy for B. B is what ends up in orbit, C eventually
    disappears into infinity.    
                                                   
                  /
                 (  ___
                  ) ///
                 /
    

Newsgroups: sci.space
Path: decwrl!spar!freeman
Subject: Re: Star Travel
Posted: 18 Feb 87 01:20:04 GMT
Organization: Schlumberger Palo Alto Research - CASLAB
 
 
    With respect to the usefulness of the Bussard ramjet, one
interesting point is that interstellar matter is highly inhomogeneous.
 The too-low-density bug might better be reinvestigated as "how far is
the nearest high-density region of the interstellar medium?" 
 
    No, I don't know either.  About seven years ago, there was some
stuff in the professional astronomy literature that suggested that
perhaps the solar system was not too far from a dense region. However,
I have not kept track of the issue. 

Newsgroups: sci.space
Path: decwrl!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Star Travel
Posted: 17 Feb 87 17:33:42 GMT
Organization: The ARPA Internet
 

    In Vol. 7, No. 134 of Space Digest, Geoffrey A. Landis, in a
valiant effort to change the subject to something **other** than
politics or Voyager (the airplane), brought up the subject of Star
Travel.  Thanks, Geoffrey for the summary on Star Travel.  Also,
you're **right**, the subject did require changing.  One of the
propulsion schemes that was listed has caused me some depression. 

    Back in 1975, I was rummaging around the UC Berkeley engineering
library and found an obscure paper by R.W. Bussard, entitled "Galactic
Matter and Interstellar Flight", Astronautica Acta, 6, 179-194 (1960).

    In this paper, Bussard described the "interstellar ramjet".  This
is a device that collected interstellar hydrogen and then burned it in
a nuclear fusion reactor.  This marvellous machine could (according to
his calculations) achieve **relativistic** velocities.  At first
glance this very original idea look like the key to opening up the
entire galaxy to human exploration. I went through all of his math
(it's modified special relativity) and the algebra was correct. 

    However his idea had two killer bugs that were immediately
apparent. One is, he assumned an interstellar hydrogen density of
1.0E3 particles per cubic centimeter.  The other bug was he assumned
**all** of the hydrogen could be burned in a fusion reactor.  In
actuality, interstellar hydrogen (as Geoffrey correctly pointed out)
is only 0.1 particles/cc.  Also most interstellar hydrogen is protium
which is an isotope that will undergo fusion **only** within the core
of stars through a nuclear catalytic cycle (the so called Bethe
cycle).  I then performed a calculation myself and determined that the
electromagnetic field strengths necessary to attract the hydrogen
would cause structural failure of the vehicle (by orders of magnitude)
even if it was made out of diamond.  These are the obvious killer bugs
for Bussard's idea.  Others are errosion of the vehicle by
interstellar grains, drag on the vehicle from noncombustable hydrogen
and the galactic magnetic field, the problem of converting the energy
of the fusion reaction into thrust, and many others. 

    Unfortunately we must assign the Bussard Ram Jet to that pile
where one will find such other clever ideas like the perpetual motion
machine, the FTL drive, and the anti-gravity drive.  It is depressing
to see that despite being able to rigorously prove the Bussard Ram Jet
is unworkable, one will never the less find science fiction novels
based upon this idea, (i.e. Larry Niven's novels) and articles written
about it in professional journals, i.e. BIS and AIAA.  Alot of people
haven't gotten the word that this idea simply doesn't work.  People
have been kicking antimatter around for sometime.  I'll let another
reader of Space Digest attack this one since it's pretty easy to shoot
down.  I see only two hopes for star travel:  One is through nuclear
fusion to nonrelativistic velocities.  The other is through some new
"rabbit out of the hat" via a new unified field theory.  Because of
the "Fermi Paradox", I suspect that there are no new "rabbits" in the
hat.   The Fermi Paradox is:  "We are on the verge of being able to
travel to the stars.  The sun is a common star and the earth is not
unusual. Therefore life in the galaxy must be common.  If we can
travel to the stars then the bug eyed monsters must be able to do it
also.  However there are no bug eyed monsters, ergo the paradox."  The
Fermi paradox tells us that speeds of greater than 10 Psol (percent
speed of light) are unobtainable for a manned vehicle.  At
nonrelativistic speeds one would **not** expect a civilization to
expand beyond 50 light years from its home star (by galactic scales
this is a tiny distance).  With this sort of radius limitation, the
entire galaxy could be filled with intelligent life but the various
civilizations would never physically encounter each other except in
rare cases.  Unless "flying saucers" are real (which I seriously
doubt), we may conclude that only through enormous nuclear fusioned
propelled "Arks" can a species travel to the stars.  I strongly
suspect that only a fairly large and healthy interplanetary
civilization could foot the bill for an Ark and even then for only two
or three Arks.  This *is* an argument for space industrialization. 
However I find it a rather depressing one. 

                               Gary Allen

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!ucbcad!ames!lll-lcc!seismo!ut-sally!utastro!ethan
Subject: Re: Star Travel
Posted: 17 Feb 87 21:34:45 GMT
Organization: U. Texas, Astronomy, Austin, TX
 
In article <[email protected]>, [email protected] writes:

> At nonrelativistic speeds one would **not** expect a
> civilization to expand beyond 50 light years from its home star (by
> galactic scales this is a tiny distance).
 
You`re going to have to help me with this one.  Why 50 light years?
After all, a generation ship going 1% of light would cross the galaxy
in 4 million years.  The Universe is about 10 billion years old so
this seems like a workable speed.  I assume you've factored in
something you haven`t been explicit about. 

"More Astronomy                Ethan Vishniac, Dept of Astronomy
 Less Sodomy"                  {charm,ut-sally,ut-ngp,noao}!utastro!ethan
  - from a poster seen         [email protected]
    at an airport              University of Texas

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Expansion in space is limited to 50 light years
Posted: 18 Feb 87 21:56:11 GMT
Organization: The ARPA Internet
 

    An interstellar civilization to expand beyond 50 light years
radius from its home star.  This caused some readers to ask the
obvious question, "Why?"  Unfortunately the argument supporting this
assertion is complex. 
 
    The basic assumptions are that starships can never travel faster
than ten percent of the speed of light, and are enormously expensive. 
I'm assumning that the only way one could get men to another star
would be through a nuclear fusion propelled "Ark" which was about the
size of an L-5 type colony, and required over a hundred years to
complete one voyage.  Such a vehicle would probably cost over a
trillion dollars to make and could be constructed or serviced only by
a large and vigourous **interplanetary** civilization.  Since these
Arks would represent virtually no financial return upon completion,
the constructing civilization would look upon making these ships as
only a "luxury activity" for disposing of surplus wealth (like the
Egyptians building the Great Pyramid or the Athenians building the
Parthenon).  It is doubtful that any single civilization could justify
building more than three of these ships. 
 
    There are many stars in the galaxy.  Within a twenty light year
radius around the sun there are 88 stars.  However stars of spectal
type K5V up to M stars are unable to support life, ref:  Journal of
the British Interplanetary Society, Vol. 39, No. 9, pg. 416.  This
leaves only six stars that **might** support life.  Chances are even
if they do have life, the planet might be an ocean planet, or a
dinosaur planet, or with terrestrial incompatible life, i.e. left
handed helix versus right handed helix protein molecules.  Based on
this we may optimistically assume a sun-like star density of 1.8e-4
stars/cubic light year.  For a 50 light year radius this means 94
stars, that **could** have "earths" which **might** have life which
**maybe** interesting. 
 
    Here comes the punch line:  Interstellar expansion is a process
limited by laws-of-scale.  If a healthy interplanetary civilization is
only capable of making three Arks then only civilizations on the
frontier of the interstellar expansion will be in a position to
produce Arks.  The stars within the volume of the interstellar
expansion will already be several centuries old and have depleted
their interstellar capacity.  The volume of a sphere grows as a cube
of the radius, but the surface only grows as a square.  Therefore the
surface-to-volume ratio of the interstellar expansion will diminish
with radius.  If we assume that each hop from star to star takes a
century and it takes another century before another hop is possible
then it will be 800 years before humans are 50 light years away.
However within 800 years the inner home worlds will have changed
totally.  The typical life span for a nation or empire is about 500
years. If you have a frontier thickness of 1 light year then there
will be about 6 frontier stars to service 94 interior home systems.
The trillion dollar cost will cause much controversy on where to send
the Ark.   It will become more and more tempting to send the Ark
**back** to the ancient home worlds than to send it outwards to some
world that probably is a dead loss.  With 94 known stars to choose
from, it is much more likely that the cost of your Ark will be
justified by going *in* than by going out.  It is this basic scaling
law, coupled with the slowness and extreme cost of interstellar travel
that will limit outward expansion.  Of course this whole argument is
false **if** you can travel fast enough that relativistic time
dialation is possible.  Then the "Fermi Paradox" really is a paradox. 

                   Gary Allen 

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!ucbcad!ames!ucla-cs!rutgers!dayton!viper!dave
Subject: Re: Star Travel
Posted: 19 Feb 87 07:55:09 GMT
Organization: Lynx Data Systems, Minneapolis, MN
 

    The first "bug" is a real problem.  Of course, there is always the
possibility of denser clouds of matter that the ship can fly through. 
 
    The second "bug" may be have a solution.  Just because "protium"
only undergoes fusion naturally in the core of stars doesn't imply
that it is impossible to do it any other way.  Muon catalyzed fusion
is one possibility. 
 
 >I then performed a calculation myself and determined that the
 >electromagnetic field strengths necessary to attract the hydrogen would
 >cause structural failure of the vehicle (by orders of magnitude) even if
 >it was made out of diamond.
 
     Depends on the design.  You don't have to assume that the vehicle
is enveloped by the field. 
 
 >These are the obvious killer bugs for Bussard's idea.
 
     Not obvious.  Certainly problems to be solved.
 
 >Unfortunately we must
 >assign the Bussard Ram Jet to that pile where one will find such other
 >clever ideas like the perpetual motion machine, the FTL drive, and the
 >anti-gravity drive.
 
    Hardly.  There is nothing in THEORY that makes Bussard's idea
impossible -- only engineering problems.  It may well be impractible
to do, but there is nothing (except possibly the low density of
hydrogen) that makes it impossible. 
 
 >It is depressing to see that despite being able
 >to rigorously prove the Bussard Ram Jet is unworkable, ...
 
    Many other things have been "rigorously" proven to be unworkable
-- such as flying past the speed of sound. 
 
 >People have been kicking antimatter
 >around for sometime.  I'll let another reader of Space Digest attack
 >this one since it's pretty easy to shoot down.
 
    What is wrong with anti-matter?  Certainly if one had a supply of
anti-matter, it would be a very consentrated source of energy. Since
we know how to make anti-particles, and we can have an almost
unlimited supply of energy (solar-power) to make them with, the
problem really is only in storage; and there are several possible ways
to do that. 
 
 >Because of the "Fermi Paradox", I suspect
 >that there are no new "rabbits" in the hat.   The Fermi Paradox is:  "We
 >are on the verge of being able to travel to the stars.  The sun is a
 >common star and the earth is not unusual.
 
    Earth is unusual in at least two ways:  it has a huge moon, and
it is the only planet we know that has life on it.  The later may be a
circular argument, but there may be some other factor that we haven't
discovered yet that makes life unusual. 
 
 >The Fermi paradox tells us that speeds of
 >greater than 10 Psol (percent speed of light) are unobtainable for a
 >manned vehicle.
 
    I don't know where you got that figure, but there are other
reasons to think that there are no other intelligent species nearby. 
For instance, we are capable of communicating by radio out to several
hundred light-years and yet we haven't picked up any signals.  Why is
this?  It has nothing to do with the possibility of star-travel. 
 
 >At nonrelativistic speeds one would **not** expect a
 >civilization to expand beyond 50 light years from its home star
  
    Why is that?  If the species survives it will keep on expanding.
 
    Of course there is the argument that no species ever, or rarely,
survives developing the ability to destroy itself. If so, let us hope
that we are a rare species. 

                      | David Messer - Lynx Data Systems
If you can't convince |   amdahl  \
them, confuse them.   |   ihnp4   --!-- dayton --!viper!dave
   -- Harry S. Truman |   rutgers /   \ meccts /

    re .80-.82 :  AHA!!!  The reflector is *DETACHED*!  That is the
    key point that I did not understand!
    
    Burns

    Some of the previous replies, seem to be sujestion that a limit
    in the stellar expantion of a race exists.
    
    I don't know about that, but they seem to be basing their arguments
    in the current technological state, and so on...
    
    For example: 
    	Arcs are very very expensive, and nobody could build many of
        them due to this.
    
    	. Need not be true, with a not too big advance in technology
          there need be only one initial cost to build any number of
    	  Arcs you desire.
    
    	  For example, put an automactic Arc building factory in the
    	  astoroid belt. Producing one Arc every X time period.
    
    	Arcs need be gigantic.
    
    	. Not really, even if Faster Then Light Travel is ever found
    	  How abount Hibernation/Suspended animation techniques. This
          are certainly feasable enough. (If animals do it, we will
          eventualy be able to reproduce it al will)
    
    	Arc building expenses will never be paid back.
    
    	. Arc people could pay the money back, if they needed to.
    	  By selling information, star charts, scientific info,
    	  novels, si-fi books, etc...
    
    	And so on ... 
    		for many of these ***limitations*** 
    			and ***restraints*** that seem to pop up.
    
    	The sentinel,
    			Gil

Newsgroups: sci.space
Path: decwrl!decvax!necntc!husc6!husc2!chiaraviglio
Subject: Re: Star Travel
Posted: 20 Feb 87 06:27:50 GMT
Organization: Harvard Univ. Science Ctr., Cambridge, MA
 
In article <[email protected]>, [email protected] (David Messer) writes:
[Name of ">  >" person lost]

>  >                                   . . .Also most interstellar hydrogen
>  >is protium which is an isotope that will undergo fusion **only** within
>  >the core of stars through a nuclear catalytic cycle (the so called Bethe
>  >cycle).
	. . .
> The second "bug" may be have a solution.  Just because "protium"
> only undergoes fusion naturally in the core of stars doesn't
> imply that it is impossible to do it any other way.  Muon
> catalyzed fusion is one possibility.
 
    Unfortunately, research to date has shown that with the exception
of deuterium-tritium mixtures, muon-catalyzed fusion will not work
because the muon tends to get trapped in orbit around the fusion
product before it has catalyzed enough fusions to pay for itself.
Additionally, I think it also showed that it won't work period for
pure hydrogen-1 (makes sense -- helium-2 is unstable, and probably
won't decay to deuterium unless the protons are pulled even closer
together than a muon could achieve).  Additionally, muon-catalyzed
fusion requires low temperatures (1500`K is optimum -- above that the
muonic molecule-ions begin to not be able to hold together), and in an
interstellar ramjet the captured hydrogen would certainly be very hot
due to the high speed of the ship; in order to capture it without
heating it you would have to extract its relative kinetic energy, do
the fusion, and then somehow put the extracted kinetic energy back
into the exhaust without losing too much due to various inefficiencies. 

    The source for all of the information in this paragraph not
directly related to the interstellar ramjet is an article in the issue
of NATURE early in the fall that had a picture of bubbles or bits of
styrofoam circulating in air vortices (can't remember the exact date
of the issue, although if someone really wants I suppose I could dig
through all those back issues). 
 
>  >It is depressing to see that despite being able
>  >to rigorously prove the Bussard Ram Jet is unworkable, ...
>  
> Many other things have been "rigorously" proven to be unworkable --
> such as flying past the speed of sound.
 
	Hear, hear!  So has FTL travel, for that matter. . . .
 
>  >People have been kicking antimatter
>  >around for sometime.  I'll let another reader of Space Digest attack
>  >this one since it's pretty easy to shoot down.
>  
> What is wrong with anti-matter?  Certainly if one had a supply
> of anti-matter, it would be a very con[c]entrated source of energy.
> Since we know how to make anti-particles, and we can have an
> almost unlimited supply of energy (solar-power) to make them
> with, the problem really is only in storage; and there are
> several possible ways to do that.
 
    Exactly.  An antimatter/matter reaction system is an excellent
battery.  Of course, if we could find some way to catalyze proton
decay or do something like that we might not even have to settle for a
battery. . . . 
 
	-- Lucius Chiaraviglio
	   [email protected]
	   seismo!tardis.harvard.edu!lucius
 
Please do not mail replies to me on husc2 (disk quota problems, and
mail out of this system is unreliable).  Please send only to the
address given above. 

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!ucbcad!ames!rutgers!seismo!mnetor!utzoo!utgpu!water!
Subject: Re: Star Travel
Posted: 20 Feb 87 06:10:40 GMT
Organization: U. of Waterloo, Ontario
 
In article <[email protected]> [email protected] (David Messer) writes:

>In article <[email protected]> [email protected] writes:
>
> >In actuality, interstellar hydrogen (as Geoffrey correctly
> >pointed out) is only 0.1 particles/cc.
> 
>The first "bug" is a real problem.  Of course, there is always the
>possibility of denser clouds of matter that the ship can fly
>through.
 
    The density of hydrogen is greater very close to stars :-). But
seriously, while passing a star (not too close), one could
conceiveably collect hydrogen for fuel, or even modify the magnetic
field so as to drastically increase the energy output, and convert
energy to antimatter (as previous poster made reference to). 
 
> >... if it was made out of diamond.

This idea appeals to me $-). Also has many nice properties.
 
>Since we know how to make anti-particles, and we can have an
>almost unlimited supply of energy (solar-power) to make them
>with, the problem really is only in storage.

    Yeah!  Presumably, with the technology for creating the Bussard
field, one could create a very good magnetic bottle for the antimatter
(and keep it far away from the crew :-) and create a magnetic shield
for the crew. (See some of Larry Niven's stories for related stuff). 
 
    By the way, Bussard was smart enough to patent his design. That's
why Niven refers to it as a Bussard ramjet. Keep this in mind if you
plan on building one of your own (no smiley face; they have made
alloys which become superconductors at liquid nitrogen temperatures). 
 
Brian Dickson
(BiPeD)

Newsgroups: sci.space
Path: decwrl!ucbvax!LOCUS.UCLA.EDU!bilbo.spear
Subject: Re: Star Travel
Posted: 2 Mar 87 22:23:41 GMT
Organization: The ARPA Internet
 
    In the interest of alternate viewpoints, I have to disagree with
Gary Allen's statement that the only means for interstellar travel are
long-duration ships at non-relativistic velocities.  He mentions the
possibility of some as yet undiscovered result from unified theory
research, but that this is unlikely, due to something called the
"Fermi Paradox" (I hadn't heard of it before).  The "Fermi Paradox",
as stated by Mr. Allen is: 
 
    We are on the verge of being able to travel to the stars.  The Sun is a
    common star and Earth is not unusual.  Therefore life in the Galaxy
    must be common.  If we can travel to the stars then the bug eyed monsters
    must be able to do it also.  However there are no bug eyed monsters, ergo
    the paradox.
 
    In geologic time, we are on the verge, in human time, perhaps we
aren't so close.  And although Sol is verifiably a common star, we as
yet have no evidence that Earth and the Sol system are not unusual. I
personally believe that they are relatively common, but there is no
hard evidence for it.  As far as bug-eyed monsters, who says we are
not currently the most advanced civilization in the Galaxy (someone
has to be first), or that others have come and gone long ago, or that
there are some out there, that simply don't want us to know about
them?  Whatever, this isn't much of a paradox, and I see no reason to
take it seriously.  Perhaps it wasn't.  In that case, (in a whiney
voice) "never mind". 
 
    Also, I personally like the STAR TREK antimatter propulsion idea,
perhaps because it seems so "neat".  Since I'm not a physicist, I
don't know the physics behind it, by in the letter to which I'm
replying, it was stated as being easy to "shoot down" (heh-heh,
Klingons have been trying that for 20 years :-)).  Perhaps the Bussard
Ramjet is provably unworkable, but does antimatter necessarily follow
suit?  I seem to recall that the bumblebee couldn't fly, until certain
previously known "truths" were found to be in error.  And that was
dealing with Newtonian physics.  Antimatter deals with something that
is still in it's infancy; perhaps some known "truths" are not as
"true" as they seem.  The conditions involved are so far beyond
normal, everyday common sense, that it's still mostly theory.  Who's
to say that some modern Einstein won't find the key?  It seems pretty
likely. 
 
    As far as either of these theories (or any other for that matter),
being used or ignored in SF stories or professional journals, well, SF
is expected to do the impossible, it's part of the thrill of the
genre.  In professional journals, the technologies still find use,
either as teaching tools, or as experimental platforms to study the
physics involved.  It makes no difference if the idea, as stated,
works or not.  What is important is the ideas it can set in the minds
of the people seeing it. That is, after all, where any hope of space
travel will come from. 
 
    It is a grave (literally) mistake to believe that the current
knowledge of the sciences involved are infallible.  Earth has seen
human technology beyond the wheel and inclined plane for several
centuries, and relativistic physics for less than one.  We feel fairly
comfortable with technology now, although mistakes are still made. 
How can one expect physics to be perfect? 
 
Brad Spear

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!LOCUS.UCLA.EDU!lcc.bill
Subject: Space propulsion systems.
Posted: 6 Mar 87 21:15:36 GMT
Organization: The ARPA Internet
  
    While we're on the subject of interstellar travel, I thought I
would dig out my FORECAST OF SPACE TECHNOLOGY: 1980-2000 from NASA
(Government Printing Office), and would spew some info about propulsion
systems at the Net.  While the document does not give fun numbers like
Isp, it gives some amusing ones, like: Cost-to-develop-system
(couldn't be off by more than 1E2 :-} ) 
 
    Most of the numbers relate to year 2000 technology (as seen from 1976). 
     
                                Thrust      Weight   Conversion    cost to
                                Velocity    Power     Efficiency   Develop
Types of propulsion             (M/Sec)    (Kg/Watt)    (pct.)     $1.0 E6
---------------------------      -------    -------     ------    ---------
 
e Bombardment Electrostatic
---------------------------
Primary Hg Propellant             2.9 E4    3.5 E-3     70%          10
Primary light gas Propellant      2.1 E5    1.5 E-3     70%          10
Auxalliry Hg or Cs Propellant     2.9 E4    1.3 E-2     70%          10
 
Coiloid Electrostatic Thruster
------------------------------
Glycerol Propellant               1.9 E4    2.5 E-3     60%           2
Cesium Propellant                 1.0 E5    9.0 E-2     65%           4
 
Electromagnetic Accelerator
---------------------------
QuasiSteady (10 kW)               1.0 E4    1.0 E-3     40%          35
Steady (1 mW)                     1.0 E4    1.5 E-4     50%          35
 
Beamed Energy Driven Thermal      1.0 E4    1.5 E-4     20%        1500
----------------------------
 
Solar Sails                       3.0 E8    7.0 E-5 (1+r/2) cos^2 b  21
-----------    [can't get much faster^^^^]          r = reflectance
 
Solar Electric Propulsion
-------------------------
Hg Propellant                     4.0 E4    2.0 E-4     70%          55
 
Liquid Propellant Rocket
------------------------
Pump Fed                          5.5 E3    6.0 E-6     95%          90
Pressure fed primary              3.6 E3    3.0 E-6     95%           7
Pressure fed auxilary             3.0 E3    5.0 E-6     85%          00
 
Solid Propellant Rocket
-----------------------
Propellent Mass=1E2 Kg            2.9 E3                              1
Propellent Mass=1E4 Kg            2.9 E3                             10
Propellent Mass=1E4 Kg            2.9 E3                            150
 
Detonation Propulsion             7.0 E3    1.0 E-5     50%          10
---------------------
 
Metastable Chemical (H-H2)
--------------------------
Magnetic Stabalized 1E3 Mass      9.0 E3                             70
Magnetic Stabalized 1E5 Mass      1.7 E4                            150
Solid Matrix Stabalized 1E3 Mass  5.0 E3                             70
Solid Matrix Stabalized 1E5 Mass  5.0 E3                            150
 
Solid Core Nuclear Rocket                                      Engines only
-------------------------                                      from here on
F= 7 E4 N                         9.0 E3    7.0 E-6 < @  100%       400
F= 3 E5 N                         9.0 E3    6.5 E-6 < @  100%       700
F= 1 E6 N                         9.0 E3    7.0 E-6 < @  100%      1200
 
Dust Bed Nuclear Rocket
-----------------------
F= 2 E4   N                       1.1 E4    7.0 E-5 < @  100%       600
F= 4.5 E4 N                       1.1 E4    3.0 E-5 < @  100%       850
 
Nuclear Light Bulb Rocket
-------------------------
F= 5 E5   N                       2.0 E4    6.0 E-6 < @  100%       900
F= 1 E6   N                       3.0 E4    4.0 E-6 < @  100%      1250
 
Nuclear Gas Core Rocket
-----------------------
F= 2.5 E5 N                       4.0 E4    1.0 E-5 < @  100%       600
F= 4.5 E5 N                       6.0 E4    7.0 E-6 < @  100%       850
 
Nuclear Electric Propulsion
---------------------------
Thermonic (120/240 kW)            4.0 E4    3.0 E-2     65%         900
Thermonic (1 MW)                  6.0 E4    2.0 E-2     70%        2100
MHD (1 MW)                        4.0 E4    2.0 E-2     65%        1500
MHD (10 MW)                       6.0 E4    1.0 E-2     70%        1500
 
Fusion Rocket Engine
--------------------
Jet Power (200-1000 MW)           1.0 E6    1.0 E-3     25%        7000
 
Fusion Microexplosions            1.0 E5    1.0 E-4     15%        1800
----------------------
 
Anti-matter
----------
  
    I don't know if the GPO still has the document, or if there is an
updated version of the report (I got mine in 1978), but it is a great
little book that talks about all aspects of the space program, from
life support to information processing to propulsion. The number on
mine is NASA-SP-387. 
 
    Have fun pushing some of these numbers through your equations.
 
(bill)
 
"Necessity is the plea for every             William J. Fulco
infringement of human freedom.               TransIntelligence Systems
It is the argument of tyrants;
it is the creed of slaves."            ARPA  [email protected]
              -Wm Pitt                 UUCP: {ihmp4,sdcrdcf}!ucla-cs!lcc!bill
 
==> Standard Disclaimer about my vs. anyone-I-associate-with's opinions <===

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!slb-test.CSNET!DIETZ
Subject: Re: Star Travel
Posted: 7 Mar 87 13:50:00 GMT
Organization: The ARPA Internet
 
Gary Allen said:
 
>   It is depressing to see that despite being able
> to rigorously prove the Bussard Ram Jet is unworkable, one will
> never the less find science fiction novels based upon this idea, (i.e.
> Larry Niven's novels) and articles written about it in professional
> journals, i.e. BIS and AIAA.  Alot of people haven't gotten the word
> that this idea simply doesn't work.
 
    I notice that Niven in his latest book (FOOTFALL, with Pournelle)
uses a variant of the Ramjet in which energy is supplied by onboard
fuel. The advantage of this scheme is that protium doesn't have to be
fused, and need not be compressed to high densities (perhaps it would
not have to be compressed at all, if some kind of very large thin mesh
accelerating system were used). 
 
>   People have been kicking antimatter
> around for sometime.  I'll let another reader of Space Digest attack
> this one since it's pretty easy to shoot down. 
 
    Oh?  There are certainly handling problems, extremely good vacuum
is needed to prevent runaway warming of solid antihydrogen pellets,
making the stuff is very inefficienct (.1%, at best), and the reaction
chamber design is a challenge, but I didn't think there were any
fundamental show-stoppers. 
 
    I should note that if antihydrogen is difficult to store in a
starship, (meaning: the mass of the containment system is large
compared to the mass of the fuel) we could conceivably manufacture
antilithium. The key step here is making antineutrons by stopping
positive pions in antihydrogen, followed by carefully planned fusion
reactions. 
 
    Antimatter has an enourmous pricetag, so one wouldn't use it
unless one wanted to travel relativistically and light sails or some
other trick were not usable. 
 
>  I see only two hopes for
> star travel:  One is through nuclear fusion to nonrelativistic
> velocities.  The other is through some new "rabbit out of the hat" via a
> new unified field theory.
 
    What about light sails?  Certainly pointing accuracy is a big
challenge. Does sail erosion kill this?  Given that we can see the
stars, I wouldn't expect the sail to be shredded too quickly. 
 
>  At nonrelativistic speeds one would **not** expect a
> civilization to expand beyond 50 light years from its home star (by
> galactic scales this is a tiny distance).
 
    Gary is making the dubious assumption that all colonization
flights must originate from the system in which the civilization first
developed. Why cannot colonies grow until they are of comparable size,
then themselves send out ships?  In 10 light year steps at .1 c with
10,000 year layovers, the galaxy can be colonized in about 100 million
years. Note that 10,000 year layovers is very conservative: if a
civilization grows from 100 to 1 trillion members in that time, the
doubling time is 300 years. 
 
> we may conclude that only through enormous nuclear
> fusioned propelled "Arks" can a species travel to the stars.  I strongly
> suspect that only a fairly large and healthy interplanetary civilization
> could foot the bill for an Ark and even then for only two or three
> Arks.
 
    I also suspect a large interplanetary civilization is needed, but
said civilization (if the resources available in our system are any
indication) will likely contain trillions of inhabitants.  The
material and energy resources available to such a civilization are
more than enough to build many arks.  Would they?  Unanswerable (and I
do *not* want to start arguing about the motivations of hypothetical
aliens), but the United States spends $10 billion per year on space,
so a civilization 10,000x larger with technology 100x more productive
might spend the equivalent of 1E16 dollars per year on starships (at
current energy prices and .1% efficiency, that would buy about a ton
of antimatter per year). 

Newsgroups: sci.space
Path: decwrl!jumbo!stolfi
Subject: Re: Fermi paradox
Posted: 7 Mar 87 17:00:28 GMT
Organization: DEC Systems Research Center
X-Edited: last by stolfi on Sat Mar  7 08:58:40 1987 PST
 
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
 
Steve Willner proposes four explanations for the Fermi paradox:
 
>   1) No colonizing civilizations have arisen in our Galaxy.  
>   
>   2) Natural forces or their own activities have killed off all
>   previous colonizing civilizations.  
>   
>   3) Unrecognized factors make colonization impossible after all.  
>   
>   4) Nearby space has been colonized, but for some reason we
>   aren't aware of it.  
>   
>   ...  anyone can come up with another one.  
 
    Here is another explanation:
 
5) By the time a civilization becomes sufficiently advanced to
colonize space, it necessarily loses the interest to do so, because: 
 
  5a) it discovers that happiness can be pursued more effectively by
  direct brain stimulation; or 
  
  5b) it discovers that conquering space is a rather stupid idea.
  
    (Er, hm, maybe you will say it is included in 1) or 2) or 3)
above. Mumble.) 
 
    The more I think about them, the more these explanations sound
plausible.  I already tried to explain my reasons on net.space a few
months ago, apparently without much success.  Let me try again: 
 
5a) Consider how much time and energy Terrans already spend to
    pursue purely "artificial" pleasures/satisfactions: TV, movies,
    electronic games, novels, spectator sports, food
    flavors/colors/sweeteners, alchool, drugs, pornography, etc.
    etc.  Unhappiness about one's environment is increasingly being
    "cured" by tinkering with the brain (with drugs, psychoanalysis,
    TM, or whatever) rather than straightening the environment.
    As the technology of these things advances, as their cost
    decreases, and as they become more alluring, they will surely
    consume an ever increasing fraction of mankind's resources.  
 
    Right now space fans get a bit more bang for their buck from
    Lucasfilm than form NASA.  Although NASA has been trying to catch
    up :-), the gap will only grow bigger.  The day Lucasfilm will
    offer week-long personalized interactive 3-D movies with total
    sensory stimulation featuring Luke and Spok and ET and C3PO for
    under $10, who will care anymore for REAL (=dull, difficult,
    expensive, slow, uncertain, dangerous, tiresome, painful, etc.)
    space exploration?  
  
5b) A few centuries ago, when farming was much more labor-intensive
    and wars were fought by soldiers, population growth was the obvious
    goal of nations and individuals alike.  Persons born in those times
    would be unable to imagine a scenario where people go to great
    lengths to avoid children, rich nations have negative population
    growth, and poor nations try their best to follow the same path.  
 
    Many other ideas have similarly been changed from obvious winners
    into equally obvious losers, by technological progress and a better
    understanding of economy and politics.  Slavery has been replaced
    by salaried labor.  Cannibalism, dueling, and religious sacrifice
    are out of fashion.  Racial segregation is disappearing.
    Expansionist nations seem to have found it easier to manage an
    empire through puppet governments and economic devices, rather than
    outright invasion and territorial annexation.  
 
    In the light of those examples, it seems quite possible that at
    some point in the future we will discover that unbounded
    colonization of space is a dumb idea, for reasons that we just
    cannot see at present.  If that is true, every intelligent
    civilization will sooner or later reach the same conclusion
    (or learn it from its nearest neighbors).  
  
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Jorge Stolfi ([email protected], ...!decvax!decwrl!stolfi)
DISCLAIMER: The above opinions are posted by weight, not by volume.
Some data compression may occur during transmission.  A few spelling
errors are normal and do not render the message unfit for consumption.
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
  

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Star Travel, Light Sails, and Antimatter
Posted: 9 Mar 87 08:49:32 GMT
Organization: The ARPA Internet
 
    In an earlier posting I claimed that there are only two hopes for
star travel, namely:  nuclear fusion (IFR systems), or a Grand
Unification Theory "rabbit out of the hat". 

    Paul Dietz raised a third possibilty: Light sails propelled by a
laser.  This is an idea Robert Forward has been promoting.  However I
don't think it'll work for two reasons:  1) The laser light will
red-shift as the light sail accelerates away from the laser.  Since
light momentum is inversely proportional to wavelength, then as the
light red-shifts it will be delivering less momentum to the vehicle.
2)  Beam divergence is dependent on laser rod width divided by length.
 
    Therefore the light beam from a finite laser **must** diverge. All
you can do is minimize this divergence.  Your laser will probably be
throwing out terrawatts in order to have any effect.  Let's assume a
laser rod diameter of one meter and a sail diameter of 10 km. Assume
the light sail is one light year away (Alpha Centuri is a little over
4 l.y. away).  How long must the laser be to illuminate only the sail
and not empty space?  Answer:  The laser must be 1.0e9 km long.  The
other obvious problems are: How would you construct such a laser? 
Where would you get the energy?  How do you build the sail?  How do you
accurately track the sail when it is over a light year away? 

    I'm afraid this idea can be set next to the Bussard ramscoop as a
no-starter. By the way, I really do believe in solar sails for travel
**within** the orbit of Jupiter.  With one solar sail you could fly
back and forth to Mars as many times as you like since it consumes no
fuel.  However solar sails are limited by a dimensionless number
called "lightness number".  This puts a definite upper bound on
payload. 

    Paul commented briefly on antimatter.  Paul surprized me by not
examining the problem of the high energy gamma rays that are produced
by antimatter reactions.  This is only the number three problem.
Number one:  How do you make the stuff?  Number two:  How do you store
the stuff? (remember quantum theory proves that no container is 100%
effective). The problem with the gammas strikes me as an absolute show
stopper. Not only will you be required to have tons of shielding but
you'll have to somehow convert this deadly energy into useful thrust.
On top of that you'll have vigorous photon disintegration occuring
within the thrust chamber.  The gammas will be literally eating away
your starship.  I'm still convinced that nuclear fusion is the only
currently viable means for getting out of the Sol system and for
economicly industrializing the Sol system. 

                                             Gary Allen

Newsgroups: sci.space
Path: decwrl!sun!amdcad!amdahl!meccts!viper!dave
Subject: Re: Star Travel, Light Sails, and Antimatter
Posted: 9 Mar 87 18:17:46 GMT
Organization: Lynx Data Systems, Minneapolis, MN
  
    You make two assumptions here that may not be valid.  1) That the
light-sail system needs to be useful at light-year distances, and 2)
That it needs to illuminate only the sail.  The first assumption is
invalid if enough acceleration can be obtained at a closer distance.
The second assumtion is simply invalid; given power to spare (and we
have that with solar-power) you can simply build enough lasers so that
the amount of light falling on the sail remains useful.  This also
handles your objection to the red-shifting of the laser light. 
 
 >The other obvious problems are: How would you
 >construct such a laser?  Where would you get the energy?  How do you
 >build the sail?  How do you accurately track the sail when it is over a
 >light year away?
 
    If all the problems were solved, there wouldn't be any need to
discuss it.  If ideas could be dismissed because they have unsolved
problems then we wouldn't get anything done. 
 
    I'm afraid this idea can be set next to the Bussard:

 >I'm still convinced that nuclear
 >fusion is the only currently viable means for getting out of the solar
 >system and for economicly industrializing the solar system.
 
    I am surprised that you feel this way -- after all, there are
problems with fusion as well. 

                      | David Messer - Lynx Data Systems
If you can't convince |   amdahl  \
them, confuse them.   |   ihnp4   --!-- dayton --!viper!dave
   -- Harry S. Truman |   rutgers /   \ meccts /


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!slb-test.CSNET!DIETZ
Subject: Laser Sails, Antimatter
Posted: 9 Mar 87 22:17:00 GMT
Organization: The ARPA Internet 
 
 Response to Gary Allen:
 
> The laser light will red-shift as the light sail accelerates away from
> the laser.  Since light momentum is inversely proportional to
> wavelength, then as the light red-shifts it will be delivering less
> momentum to the vehicle.
 
    But more energy.  A photon reflected off the sail is red shifted
twice, so it ends up with only (1-b)/(1+b) of its original energy, b =
v/c, v = speed of the sail.  The fraction of energy transfered to the
vehicle is 2b/(1+b), which approaches 1 as v --> c (assuming all
photons are reflected at 180 degrees; photons reflected at slightly
lower angles in the sail's frame of reference get abberated forward in
the laser's frame of reference, as does radiated waste heat). 
 
    Thrust does go down.  This is a consequence of the fact that it
takes more energy to accelerate a fast moving object than a slow
moving one.   However, since thrust is typically limited by sail
heating, we can increase laser power as b increases.  If the sail is
always kept at its maximum temperature, beam power in the sail's frame
of reference will be constant, so thrust will be constant (assuming
sail reflectivity is independent of frequency; I think (?)
reflectivity typically increases with increasing wavelength.) 
 
>  Beam divergence is dependent on laser rod
> width divided by length.  Therefore the light beam from a finite laser
> **must** diverge.  All you can do is minimize this divergence.  Your
> laser will probably be throwing out terrawatts in order to have any
> effect.  Let's assume a laser rod diameter of one meter and a sail
> diameter of 10 km.  Assume the light sail is one light year away (Alpha
> Centuri is a little over 4 l.y. away).  How long must the laser be to
> illuminate only the sail and not empty space?  Answer:  The laser must
> be 1.0e9 km long.
 
    Gary's beam divergence analysis is totally wrong (I suggest he
apply the same reasoning to radar antennas).  Gary's 1 meter aperture
would suffer extreme diffraction spreading.  The transmitter will
likely use a phased array of smaller lasers.  The lasers beams might
be put in phase by using a remote reference laser placed perhaps 1000
AU downrange from the transmitter. It transmits a reference beam that
is phase conjugated and amplified. This is similar to the scheme
proposed for aiming microwaves from a powersat. The sail is perhaps
300 km wide, as is the laser array.  With a wavelength of .3 microns,
the beam can in principle be focused out to about eight light years. 
 
>  The other obvious problems are: How would you
> construct such a laser?  Where would you get the energy?  How do you
> build the sail?  How do you accurately track the sail when it is over a
> light year away?  I'm afraid this idea can be set next to the Bussard
> ramscoop as a no-starter.
 
    These are difficult problems, but they are not obviously
impossible. Certainly they are not in the same league as the problems
with the original Bussard Ramjet, where theoretically impossible
material strengths and nuclear reactions are required. 
 
    Tracking can be done by flying the vehicle on a preplanned course
with active self guidance (tiltable sections in the sail provide
maneuvering).  This only requires that the beam not change direction
suddenly, not that it track a distant target.  Energy can be supplied
by many very large solar powersats, or by something better if it is
developed. This requires a large investment, but no rabbit tricks. 
 
    Other problems I mention for sake of honesty:  mechanical coupling
of thrust from the sail to the vehicle, stiffening the sail,
destruction of sail components by sputtering, deflection of the beam
by the gravity of planets in near-solar space, security (that laser
could do major damage anywhere in the solar system if used as a
weapon) and, of course, deceleration at the end.  The last probably
imposes the strictest upper limit on speed, although for long trips
one might coast most of the way at high speed then slow down gradually
by deploying a thin mesh plasma brake.  Travelling to Alpha Centauri,
it may be possible to slow down in Alpha C's plasma tail, since the
interstellar wind is coming from Centaurus and the plasma tail should
be pointing nearly in our direction. 
 
    Gary also commented on antimatter:
 
> Paul commented briefly on antimatter.  Paul surprized me by
> not examining the problem of the high energy gamma rays that are
> produced by antimatter reactions.
 
    Clearly, these can be stopped by shielding.  This imposes a limit
on the power density of the engine, since waste heat will have to be
expelled, but imposes no crippling limit on exhaust velocity (if one
is willing to tolerate low thrust).   Gary may not realize that most
of the energy produced in antimatter annihilation comes off as charged
particles (pions mostly) or neutrinos, with only a fraction as gamma
rays from neutral pion decay and positron annihilation. 
 
>  This is only the number three
> problem.  Number one:  How do you make the stuff?  Number two:  How do
> you store the stuff?  (remember quantum theory proves that no container
> is 100% effective).
 
    Antimatter is made in accelerators, by bombarding targets with
energetic protons.  Much cleverness is needed to collect, sort and
cool the antiprotons that are produced, but this is only (!) an
engineering problem. Efficiencies of up to .1% have been talked about
(this is far above current efficiencies, but current antiproton
factories are not designed with very high efficiency in mind; an
efficient factory would use a superconducting linac rather than a
synchrotron to produce the primary beam, and would capture many more
of the antiprotons).  Whether these factories will have exorbinant
capital costs is not clear. 
 
    How do we store antimatter?  Neutralize the antiprotons with
positrons and collect the atoms to form solid antihydrogen.  Suspend
and move the antihydrogen by its diamagnetism (all this in
microgravity anyway).  Very good vacuum and low temperatures are
required, but I don't see why (perhaps bulky) containment chambers
cannot be designed.  Gary's final comment aside, 100% effective
confinement is not needed -- only 99.99...% effective confinement. 
How many nines we need will tell us how hard the task will be. For a
starship, antilithium hydride is probably needed to reduce tank mass. 
 
>   The problem with the gammas strikes me as an
> absolute show stopper.  Not only will you be required to have tons of
> shielding but you'll have to somehow convert this deadly energy into
> useful thrust. 
 
     And I suppose the radiation from a fusion rocket is not "deadly"?
 Energy from photons escapes to space or gets radiated as waste heat. 
One uses the charged particles produced to heat larger quantities of
normal matter, which is expelled as a plasma.  The hard part is
getting the antimatter to react fast enough before it gets blown out
the nozzle. 
 
> On top of that you'll have vigorous photon
> disintegration occuring within the thrust chamber.  The gammas will be
> literally eating away your starship.
 
    Photons will cause some transmutation in the reaction chamber, but
with low aspect ratio shields the rate of such reactions should be
much lower than the rate of fuel consumption.  Carry several changes
of shielding mass, if necessary; the mass wouldn't be that great. 
 
    I personally feel light sails are more feasible than antimatter
rockets (if only because they are much more efficient, when antimatter
production efficiencies are included).  Neither concept can be judged
to be obviously impossible at this point. 


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!DFVLROP1.BITNET!ESG7
Subject: Some comments on anti-matter storage
Posted: 10 Mar 87 11:40:27 GMT
Organization: The ARPA Internet
 
    In an earlier posting I attacked Paul Dietz's idea of a laser
propelled light sail by going through a beam dispersion analysis based
on a single rod laser.  Paul correctly pointed out that this analysis
was wrong since the laser light would come from a phased array of
lasers and not from a single rod.  

    However Paul then went on to say that this array could be focused
to 8 light years (which I find very hard to believe).  Electrical
engineers out there in ARPA-Land a question for you:  Is such a tight
beam possible?  Since Paul has fair-and-squarely shot me down on my
single rod analysis I shall counter-attack in another area.  Paul
claimed that anti-hydrogen could be stored in a vacuum container by
being suspended through paramagnetism.  I will not address the
question of heating and melting of the anti-hydrogen by magnetic eddy
currents (though this is a problem).  Instead I'll show that this is
impossible due to vacuum constraints.  The best vacuum known is in
interstellar space which is 0.1 particles per cubic centimeter.  The
interplanetary vacuum is 1000 particle/cc.  Low Earth orbit vacuum at
120 km is 1.0E11 particles/cc.  The best current artifical vacuum is
at about 1.0E10 particles per cc.  Let us assume that through the
marvels of technology an artificial vacuum of 1000 particles/cc is
possible (a seven orders of magnitude improvement).  One **might**
achieve such a vaccum inside a diamond container heated to several
thousand degrees and then cooled to near zero degrees kelvin.  One
could take this container to interstellar space, open-and-close it and
then bring it back to Earth (I don't think it's possible to
artifically pump it down). The 1000 particles/cc would represent a
free molecular carbon gas. 

    Now let us place a tiny dust mote of frozen anti-hydrogen into
this container and suspend it in the center.  Let the anti-hydrogen
have a surface area of 1.0E-11 square meters. Assume that the carbon
gas is at 1 degree Kelvin (in truth it will be much hotter).  The
thermal velocity of the gas will be 1 meter/sec. From this we
calculate that 1.0e-3 particles/sec will impact the anti-hydrogen
delivering 1.0e-5 ergs/sec. Assume that most of the heat is absorbed
in the anti-hydrogen.  The only means of dumping the heat is through
black body radiation.  Assume that the hydrogen is a perfect black
body (a generous assumption).  By Stefan's law the hydrogen must have
a temperature of greater than 50 degrees kelvin in order to reject the
accumulating heat from the matter/anti-matter reactions.  The boiling
point for hydrogen is 21 degrees kelvin.  Of course the paramagnetism
will have been lost when the anti-hydrogen melted.  We observe that a
thermal runaway will occur in this problem. The black body radiation
must impinge on the walls of the vacuum container which will liberate
even more carbon. Also there will be outgassing of the anti-hydrogen
which will heat the walls of the container and liberate even more
gaseous carbon. 

    In summary the idea doesn't work because a perfect vacuum in a
closed container is impossible.  Possible fixes for this problem would
be to make a hunk of anti-aluminum and suspend that in the center (it
is also paramagnetic and has a much higher melting point).  How do you
make anti-aluminum?  Answer:  I don't have a clue. Another fix is to
suspend the antimatter in front of the spacecraft and insist that the
spacecraft doesn't leave interstellar space. However this seems rather
silly to have a spaceship that can't leave interstellar space. 
Apologies to Captain Kirk and Mr. Spock, but it looks like antimatter
storage doesn't work. 

                                    Gary Allen


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!cbatt!gatech!hubcap!beede
Subject: Re: Star Travel, Light Sails, and Antimatter
Posted: 10 Mar 87 03:46:58 GMT
Organization: Clemson University, Clemson, SC
 
    In article <[email protected]>, [email protected] says:

> . . . .  2)  Beam divergence is dependent on laser rod
> width divided by length.  Therefore the light beam from a finite laser
> **must** diverge. . . . .
> . . . .  Let's assume a laser rod diameter of one meter and a sail
> diameter of 10 km.  Assume the light sail is one light year away (Alpha
> Centuri is a little over 4 l.y. away).  How long must the laser be to
> illuminate only the sail and not empty space?  Answer:  The laser must
> be 1.0e9 km long.  . . .
 
    I am not a physics type, but is there a fundamental reason that we
need to use a single large rod?  E.g., a bundle of .1mm rods 1e5km in
length (long, but not any billion K) would have a length to width
ratio equal to that in the example.  Surely the engineers could
overcome a minor difficulty such as stiffening such a beastie {-:, and
keeping it oriented. 
 
Mike Beede		   UUCP: . . . ! gatech!hubcap!beede
Computer Science Dept.          
Clemson University
Clemson SC 29631-1906

Newsgroups: sci.space
Path: decwrl!ucbvax!GALILEO.S1.GOV!ota
Subject: Star Drives
Posted: 10 Mar 87 17:11:29 GMT
Organization: The ARPA Internet
 
    I'm a bit surprised that neither Paul Dietz nor Gary Allen appear
to have read Robert Forward's work on either antimatter drives or
lightsails.  I must agree with Dale Amon that you read his work.  I
have two old papers on this subject, but I have seen a recent Air
Force study that Forward wrote on antimatter and THE FLIGHT OF THE
DRAGONFLY covers the lightsail idea and is also more recent. 
 
    I'll summarize some of the interesting tidbits from these old
papers:
 
Robert L. Forward, "Antimatter Propulsion", Hughes Research Laboratories -
    Malibu, Research Report 549, November 1981.
 
    The main trick with avoiding gammas is to have the magnetic nozzle
do most of it work before the charged pions decay.  You have 70 nsec
of time to do this which means about 21 centimeters of space. 
 
    The technique for cooling and storing the neutral antihydrogen is
to use what Forward calls "resonant radiation cooling and capture". 
This is discussed in the March 87 SciAm. 
 
Forward, "Roundtrip Interstellar Travel using Laser-Pushed Lightsails",
    Hughes Research Laboratories - Malibu, Research Report 550, January 1982.
 
    The basic idea here is to put the laser near Sol, perhaps pumped
directly with solar radiation.  The diameter of the actual laser is
not critical.  This laser could use a laser from the lightsail as a
guide beam for tracking and distortion correction.  A similar scheme
is being investigated for the SDI using phase conjugation to correct
for atmospheric distortion. 
 
    The laser beam is directed to a final transmitting lens between
the orbit of Saturn and Uranus.  This lens is a Fresnel zone plate
which alternates zones of vacuum (index 1) and plastic (index ~ 1.5). 
This lens has a diameter of 1000km and masses 560,000 tons, assuming a
wavelength of 1um.  This combination has a spot size of 98km at 4.3 ly. 
 
    To accomplish the deacceleration at the other end the lightsail is
cut 1/3 of the way out from the center to leave two sails.  The inner
one has an area of 1/10 and deaccelerates in the light reflected by
outer part.  The outer ring has 9/10 the original area and continues
accelecerating.  Because of the ratio of areas and masses the inner
sail deaccelerates at 10 times the rate that the outer reflector
accelerates. The two stage system only works one-way.  A three stage
system would allow a round trip mission. 
 
    Anyway, this is a very brief summary.  You are encouraged to go
out and check the original material.  THE FLIGHT OF THE DRAGONFLY has
a technical appendix and should be available in most bookstores. 
 
	Ted Anderson


Newsgroups: sci.space
Path: decwrl!decvax!tektronix!uw-beaver!cornell!rochester!seismo!mnetor!utzoo!
Subject: Re: Star Travel, Light Sails, and Antimatter
Posted: 10 Mar 87 22:44:35 GMT
Organization: U of Toronto Zoology
 
> The laser light will red-shift as the light sail accelerates away from
> the laser...
 
    This demonstrates that lightsails have problems when velocities
start to get up to a substantial fraction of the speed of light. 
True, but there is a lot that can be done at velocities where the
losses are modest. 
 
> ...  2)  Beam divergence is dependent on laser rod
> width divided by length.  Therefore the light beam from a finite laser
> **must** diverge.  All you can do is minimize this divergence...
 
    As Forward has pointed out, you use a lens.  (In any case the
issue is complicated because you probably use multiple lasers.)  His
calculations were for a Fresnel zone plate made out of -- as I recall
it -- quarter- wavelength plastic and vacuum.  It's 1000 km across and
spins slowly to retain its shape.  It will focus most of the beam
energy onto a 1000-km sail out to about 40 light-years.  All errors
are inversely proportional to the focal length, which is monstrous, so
the lens does not need to hold its shape with high precision. 
 
> ... Where would you get the energy?
 
    Presumably solar energy.  Mercury is valuable territory. 
 
> How do you build the sail?
 
    Presumably robotic construction, it will be too big and too flimsy
to use human labor efficiently.  If you postulate self-reproducing
machinery, in particular, a 1000-km sail is trivial. 
 
> How do you accurately track the sail when it is over a
> light year away?...
 
    You don't.  All you do is keep the beam pointed in pretty much the
right direction, with maybe an occasional correction.  The spacecraft
moves to stay in the beam, not vice-versa.  The key problem is not
sail tracking but pointing stability. 
 
> ... the problem of the high energy gamma rays that are
> produced by antimatter reactions...
 
    Troublesome but solvable, probably.  The engine itself will need a
pretty heavy-duty cooling system.  The crew quarters will quite simply
need shielding.  A combination of a long ship and shadow shielding can
get the mass down to where it's manageable.  I've seen a
properly-shielded proposal for an antimatter-powered ship capable of
90+% of the speed of light, and the shielding problems of more modest
vessels pale beside that one. 
 
> ... Number one:  How do you make the stuff?
 
    To get enough for in-Sol-system work and the beginnings of
development for interstellar spacecraft, a factory with the size (and
power demand) of the Hanford uranium-enrichment complex will do.  For
serious interstellar work, you probably want large, specialized power
satellites in solar orbit. It sure would help if somebody could come
up with a really efficient way of making antimatter, but the ways
we've got will do in a pinch.  It just needs a pretty large-scale
effort.  (Again, self-replicating machinery would make an enormous
difference.) 
 
> Number two:  How do
> you store the stuff?  (remember quantum theory proves that no container
> is 100% effective)...
 
    Quantum theory turns up other interesting things, too.  There has
been a suggestion that at really low temperatures -- like 0.0001 K --
antimatter could be handled with normal matter, because the wave
functions don't overlap enough to produce a reaction.  I'm not enough
of a physicist to check that one.  The studies funded by outfits like
the USAF have concluded that storing the stuff is not an insuperable
problem; low temperatures, hard vacuum, and handling by magnetic or
electric fields will suffice. 
 
> The problem with the gammas strikes me as an
> absolute show stopper.  Not only will you be required to have tons of
> shielding but you'll have to somehow convert this deadly energy into
> useful thrust...
 
    The gammas are sheer waste, nothing can be done about them.  But
in case you're not aware of it, the proton-antiproton reaction does
*not* yield gammas immediately.  A large fraction of the energy is
temporarily in the form of charged particles, which a magnetic nozzle
can handle.  Please read some of the work that has been done before
denouncing it as impossible. 

"We must choose: the stars or	  Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	  {allegra,ihnp4,decvax,pyramid}!utzoo!henry

    A mirror out with the outter planets would create some interesting
    launch window problems based on the orbit of the mirror and amount
    of time when it was within a certain tolerence of being in a straight
    line between the laser (also orbiting at a different velocity) and
    the target star (actually the spacecraft itself).
    
    Burns
    

Newsgroups: sci.space
Path: decwrl!pyramid!amdahl!meccts!viper!dave
Subject: Re: Star Travel, Light Sails, and Antimatter
Posted: 11 Mar 87 16:52:50 GMT
Organization: Lynx Data Systems, Minneapolis, MN
 
    In article <[email protected]> [email protected] (Henry Spencer) writes:

 >> How do you build the sail?
 >
 >Presumably robotic construction, it will be too big and too flimsy to use
 >human labor efficiently.  If you postulate self-reproducing machinery, in
 >particular, a 1000-km sail is trivial.
 
    If you postulate self-reproducing machinery almost ANY large
engineering problem is trivial. 
 
 >I've seen a properly-shielded proposal
 >for an antimatter-powered ship capable of 90+% of the speed of light, and
 >the shielding problems of more modest vessels pale beside that one.
 
    It seems to me that you would need on the order of five times as
much "fuel", half of which is antimatter, as payload to achieve 90% of
C.  It must be an interesting design to handle that much antimatter
with so little structure. 
 
 >"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
 
I choose the stars.   :-)

                      | David Messer - Lynx Data Systems
If you can't convince |   amdahl  \
them, confuse them.   |   ihnp4   --!-- dayton --!viper!dave
   -- Harry S. Truman |   rutgers /   \ meccts /


Newsgroups: sci.space
Path: decwrl!pyramid!amdahl!meccts!viper!dave
Subject: Re: Some comments on anti-matter storage
Posted: 11 Mar 87 17:12:00 GMT
Organization: Lynx Data Systems, Minneapolis, MN
 
    In article <[email protected]> [email protected] writes:

 >Paul claimed that anti-hydrogen could be stored in a vacuum
 >container by being suspended through paramagnetism.  I will not address
 >the question of heating and melting of the anti-hydrogen by magnetic
 >eddy currents (though this is a problem).  Instead I'll show that this
 >is impossible due to vacuum constraints.
 >One **might**
 >achieve such a vaccum inside a diamond container heated to several
 >thousand degrees and then cooled to near zero degrees kelvin.  One could
 
    I don't know why you decided on a diamond container other than to
make it sound expensive.  Does anyone know what the vapor pressure of
diamond is compared to, say, gold? 
 
 >take this container to interstellar space, open-and-close it and then
 >bring it back to Earth (I don't think it's possible to artifically pump
 
    Why bring it back to Earth?  I think the eviromentalists would
quite rightly object to manufacturing of antimatter on Earth. 
 
    (Nice antimatter you have there...  Be a shame if you were to drop
it... :-) 
 
 >Another fix is
 >to suspend the antimatter in front of the spacecraft and insist
 >that the spacecraft doesn't leave interstellar space.  However this
 >seems rather silly to have a spaceship that can't leave interstellar
 >space.
 
    No sillier than having water-ships that can't leave the ocean.
Space is big (really big), if one has to build one's starship in the
orbit of Pluto, it really wouldn't make a whole lot of difference to
travel time needed between stars. 

                      | David Messer - Lynx Data Systems
If you can't convince |   amdahl  \
them, confuse them.   |   ihnp4   --!-- dayton --!viper!dave
   -- Harry S. Truman |   rutgers /   \ meccts /


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!ucbcad!ames!lll-lcc!seismo!mcvax!enea!tut!intrin!pl
Subject: Re: Fermi paradox
Posted: 11 Mar 87 12:20:36 GMT
Organization: Intrinsic Oy, Tampere, FINLAND
 
    In article <[email protected]> [email protected] (Jorge Stolfi) writes:
 
>Steve Willner proposes four explanations for the Fermi paradox:
 
    Here's yet another candidate:
 
n) The space around us is fully inhabitated, but measures are taken to
   keep us from knowing it, because such knowledge is considered harmful
   for a growing-up civilization.

Petri Launiainen        : Phone:
Intrinsic Oy            :   (int) 358 31 132800
Aleksis Kiven katu 11 C : UUCP:
33100 Tampere,  FINLAND :   [email protected]


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!BUASTA.BITNET!POUND
Subject: Interstellar matter
Posted: 12 Mar 87 18:33:00 GMT
Organization: The ARPA Internet
 
    In V7 # 160 Jay Freeman writes:

  > The too-low-density bug might better be reinvestigated as
  > "how far is the nearest high-density region of the interstellar
  >  medium?"
 
    And in V7 #161 Keith Lynch sez:

  > Nobody knows the density of interstellar dust grains.
 
    (Obviously Keith has no friends who are radioastronomers...)
 
    In order that we may finally put the Bussard Ramjet to sleep, here
are the numbers: 

    (note: M* = solar mass = 2 E+33 gm, pc3 = cubic parsec, kpc = 1000 pc)
 
    In a 1 kpc survey about Sol, the long-dead COPERNICUS satellite
found these densities: 
 
        HII(=H+)            .003 M*/pc3
        HI(=neutral H)      .031 M*/pc3
        H2(=molecular H)    .007 M*/pc3
 
    Note that 1 M*/pc3 = 40.3 H atoms/cc = 6.8 E-23 gm/cc.
 
    Typical ISM dust grain density:   0.002 M*/pc3
 
    Typical properties of interstellar clouds (cf. _Astrophysics II_,
Bowers and Deeming, 1984): 
 
        Type            Kinetic Temp      density       Composition
                                         (atoms /cc)
 
   Diffuse Clouds         50-150 K        10-1000       mostly HI
                                                        mass=400 M*
                                                        radius = 5 pc
 
   Molecular Clouds        3-10 K         10^3 - 10^6   mostly H2,
                                                        molecules (CO),
                                                        and dust
                                                        m = 300 M*
                                                        r = 1 pc
 
    The nearest clouds are on the order of a *kpc* away.  Nobody's
gonna use a Bussard Ramjet in the near future. :-(  
 
|   Legalize        |           Marc Pound--Boston Univ. Astro Dept
|   Henry Spencer!  |           pound@buasta (on a variety of networks)


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!FINHUT.BITNET!FYS-TS
Subject: Bussard Ramjets
Posted: 13 Mar 87 08:35:23 GMT
Organization: The ARPA Internet
  
    I have not been following the Digest in a while, so my comments
may be out of date, but anyway: 
 
1. How does one achieve braking to halt in a solar system with a BRJ?
   If I picture the situation correctly, in order to brake down the
   magnetic scoop would have to remain in the direction of motion and
   simultaneously the thrust would have to be to the direction of the
   scoop. Two questions arise: how does the outgoing, most probably
   high-temperature and ionized fusion-product plasma interact with
   the magnetic field of the scoop and secondly, is it possible, that
   after expelling the fusion-products, the 'ashes', to the direction
   of movement, at sometime the scoop eventually begins to collect
   the 'ashes' along with hydrogen, which eventually would change
   the realtive amount amount of fusionable fuel in the scooped stuff,
   thus maybe reducing the efficiency of the fusion plant?
 
2. Those discussing about laser-powered lightsails, someone suggested,
   that the tracking of the ship and the sail would be done preprogrammed.
   It would be nice to read, what magnitude of angular accuracy would be
   needed at the solar system end, to keep the laser beam on target even
   about 4-7 light-years distance away. Additionally, Robert Forward
   suggested using the same laser for braking to halt at the target solar
   system. If the beam does not go on target, the ship can not stop.
   It would be nice for a manned vehicle... Some other questions arise,
   what is the scattering due interstellar medium, does the solar wind
   of other stars have effect(probably not), etc...
 
    Well, that much for this time.
 
Tero Siili
Helsinki University of Technology, Finland


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!R20.UTEXAS.EDU!CS.VANSICKLE
Subject: Forward's antimatter article in New Destinies
Posted: 13 Mar 87 16:34:25 GMT
Organization: The ARPA Internet
 
    A more easily obtainable artice by Robert L. Forward on the
engineering of antimatter space drives is in NEW DESTINIES, Volume 1,
Spring 1987, Baen Books. It should be in your local bookstore in the
Science Fiction section. 
 
Larry Van Sickle
[email protected].#Internet
Computer Sciences Department
U of Texas at Austin


Newsgroups: sci.space
Path: decwrl!ucbvax!DFVLROP1.BITNET!ESG7
Subject: More comments on Star Travel
Posted: 13 Mar 87 15:31:35 GMT
Organization: The ARPA Internet
 
    In SPACE Digest Volume 7 : Issue 162, Henry Spencer responded to
some earlier remarks made by me concerning Robert Forward's laser
driven light sail. 
 
>> ... Where would you get the energy?
>Presumably solar energy.  Mercury is valuable territory.
 
    A major problem here will be dumping the waste heat.  If we assume
that our laser is pumping out a terra-watt and is operating at 10
percent efficiency then we have to reject 9 terra-watts. If the
radiator is made of steel then it will have a surface area of greater
than 14.7 square kilometers in order not to melt (that's a square
steel plate that is 2.4 miles by 2.4 miles).  This radiator will have
to be in the shadow of the collector or a sun shield.  Building such a
device on Mercury would be ill-advised because it would only worsen
heat rejection. 
 
>> How do you build the sail?
>Presumably robotic construction, it will be too big and too flimsy     
>to use human labor efficiently.  If you postulate self-reproducing     
>machinery, in particular, a 1000-km sail is trivial.
 
    A 1000-km sail is trivial as is a 1000-km frensel lens and a 14.7
square km radiator??  Henry, your credibility is showing.  I got a
better thing to postulate:  Let's postulate that if we close our eyes,
clap our hands, and wish real hard then an FTL-drive will appear out
of thin air.  A self-reproducing machine with full AI capability
already exists (it's called a human being).  I doubt you'll ever make
a machine that is cheaper than that.  However by your own admission
this sail is too big and flimsy for humans to make. 
 
>> How do you accurately track the sail when it is over a
>> light year away?...
>You don't.  All you do is keep the beam pointed in pretty much the
>right direction, with maybe an occasional correction.  The spacecraft
>moves to stay in the beam, not vice-versa.  The key problem is not sail
>tracking but pointing stability.
 
    Now that's a pretty thin come back.  You're a bright guy Henry,
you know that the position error of the beam will grow as you get
further away.  There will be jitter on board the laser due to
machinery and buffeting from the solar wind and light pressure (the
intensity of which is almost totally chaotic).  Your sail is supposed
to have a pretty heafty velocity vector and is quite fragile (so no
large delta Vs).  Of course you can fix that by letting the beam
diverge but that defeats the whole idea. 
 
                        --- Commentary ---

    There is too much wishful thinking in these ideas and not enough
hard science.  I want to see us get to the Stars as much as anyone
else in this news group.  However Science Fiction masquerading as real
engineering proposals isn't going to get the job done.  Let's increase
the signal-to-noise ratio on the issue of Star Travel and make the
subject respectable.  Too many times have I read someone claim that
some whacky idea was plausible and all that remained was the
engineering details.  Those engineering details are often 99.999999%
of the problem. Look at nuclear fusion, the problem is "trivial".  All
you got to do is drop a speck of tritium-deuterium into a container
and zap it with a laser. The minor details of the laser, radiation,
heat extraction, etc. are "simple" engineering details and not worthy
of our concern.  What utter Hogwash.  If we can't crack the "trivial"
engineering details of Inertial Containment Fusion, then what hope is
there for these other crazy ideas.  Come on guys, get some perspective
on the problem. 

                            Gary Allen

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!sdcsvax!ucsdhub!hp-sdd!ncr-sd!ncrcae!ece-csc!mcnc!
Subject: Re: Some comments on antimatter storage
Posted: 12 Mar 87 08:20:08 GMT
Organization: ENEA DATA Svenska AB, Sweden
  
    Wouldn't it be possible to store the antimatter in a magnetic
bottle (a la fusion chamber), and have a quite (sufficiently) good
vacuum in it?  If we assume that it IS possible to store it that way,
how do we get a good vacuum? Well, I thought, couldn't you just
generate two magnetic fields, shaped like half-spheres, that intersect
each other? Projection like this: 
 
      / \
     /   \
    (     )
     \   /
      \ /

    OK, not very good half-spheres.  Anyway, at first the distance
between the two parantheses :-) would be 0, then you just turn up some
dial that makes the two fields (that still intersects, thus making a
closed space) grow apart from each other.  *Nothing* in between. 
Great.  Very vacuum.   This of course assumes that the fields really
can shut out ordinary matter; but even if they can only shut out
certain types of matter, like certain particles, why couldn't you just
fill the area *outside* and directly next to the fields with just, and
nothing but, those very particles?  That way nothing else would even
have a go at coming inside the fields, right?  Then how you get the
antimatter inside is another story. 
 
    Is this possible. If not, why not?
 
    Looking forward to (non-flaming) comments.
 
/Peter (turbo) Svenson	pesv@enea (UUCP)   [email protected] (ARPA)
-----------------------------------------------------------------------------
"Zen can make you help other people, or, failing that, at least get
them off  your back." 


Newsgroups: sci.space
Path: decwrl!ucbvax!slb-test.CSNET!DIETZ
Subject: Plausible arguments; antimatter; Forward; 50 light year limit.
Posted: 14 Mar 87 13:48:00 GMT
Organization: The ARPA Internet
 
    Dave Chassin wrote:
 
> I see a serious lack of 'scientific method' here. Many people have
> been basing arguments solely on plausibility. This is ridiculous
> reasoning, and I think it achieves nothing. I would and do reject
> any line of reason which concludes: 'and this seems plausible'.
 
    This is correct, except that plausible arguments can be used as
counterexamples when someone has claimed to prove something.  In this
case, Gary Allen claimed that interstellar colonization was
impossible, but plausible scenarios where it is highly likely can be
given. The plausible scenarios are nothing but tales, of course.  No
certainty is possible short of observing actual colonization or the
lack thereof, since we cannot predict the psychology or sociology of
unknown aliens, nor be sure of the feasibility of star travel until it
is accomplished.  
 
    Gary Allen's analysis of antimatter heating in imperfect vacuum
had several flaws.  (1) Gary assumed that all the energy generated in
annihilations on the tiny solid hydrogen mote will be deposited in
that mote.  Gary's mote had a surface area of 1E-11 meters, for a
diameter of slightly under 2 microns.  The gamma radiation produced in
annihilation will travel meters in antihydrogen, and the charged
particles centimeters at least.  So only a small fraction of the
energy released is deposited in the antihydrogen.  (2) Gary claimed
that heating of the vacuum chamber wall will lead to runaway
outgassing.  With proper design this will not happen: at a fixed
background gas density, the energy hitting the wall per unit area can
be made arbitrarily low by increasing the radius of the container.
Also, particles ejected from the container wall by the impact of
radiation can be made to have an arbitrarily small chance of hitting
the antimatter mote, again by increasing the radius of the container. 
  
    Ted Anderson was surprised I hadn't read Robert Forward's work.  I
have read some of it.  I thought phased array lasers would be more
reliable than a single large laser directed through a zone plate. 
Also, I don't have Forward's book with me.  I thought the
self-deceleration mirror trick was unworkable, but on second thought I
now see that by having the vehicles track the beams rather than vice
versa the idea may work. Ted did suggest using a reference beam from
the lightsail and phase conjugate.  I don't see how this can work,
given the time delays involved.  
 
    Finally: Gary Allen made explicit his assumptions that went into
his 50 light year limit on colonization.  These assumptions seem
debatable, to say the least... 
 
>    The basic assumptions are that starships can never travel faster than
> ten percent of the speed of light, and are enormously expensive.
 
    We've already handled the first.  About the second, expense is
relative to the capabilities of a society.  A starship requires a
trivial fraction of the material and energy resources available in a
star system.  Even making antimatter requires tiny (on an astronomical
scale) solar energy collectors.  The effort required is large compared
to *today's* capacity, but that's about as relevant as saying travel
to the moon is impossible because cavemen didn't have the capability.
(Rockets will never be launched because one launch consumes as much
energy as the campfires of all the tribes produce in 10 years --
clearly ridiculous!) 
 
    In my previous plausible scenario, a society might spend $1E16 per
year on starships.  Even taking Gary's $1E12 figure for the cost of an
Ark, that's 10,000 launches per year.  Gary's assertion that no
society could build more than three of these ships is clearly
contradicted in this scenario, by many orders of magnitude .  (I
wonder were Gary got the $1E12 figure?  The small space colonies
should be much less expensive than that. Perhaps most of the cost is
in fuel?)   Note also in my scenario that individual productivity is
assumed to be 100x higher than today, so individual income could
perhaps be $3M/year.  If 30,000 people save ten years of income,
that's about $1E12. 
 
    Gary goes on to state that stars of spectral type K5V to M are
unable to support life.  Wrong -- planets around those stars are
unable to evolve life.  Gary depends heavily on the assumption that
building a civilization away from planets, and on barren planets, is
impossible. Strange, given that he is advocating L5-style Ark
spaceships and has advocated lunar colonies.  Note that Gary's
argument that space colonies are too expensive (they require much
shielding) is hardly relevant when there is no habitable planet to
live on instead, and also hardly relevant to societies much more
technologically advanced than our own. 
 
    Gary argues that civilizations on the edge of the expanding sphere
will more likely send their colonists back rather than forward. This
seems implausible.  Either those old systems have depleted their
resources, in which case you wouldn't want to go there, or they have
not, in which case they will have a large entrenched population. Gary
mentions that the average lifetime of a civilization or country is 500
years.  After that every individual gives up and dies, I suppose? 
 
    The issue of starship feasibility seems to bring out a lot of
silly arguments on the part of the less responsible SETI advocates (I
do not necessarily place Gary in this class).  For example, Drake has
argued against the possibility of starships by arguing that the energy
demanded would be better used by the society to increase the standard
of living -- this from a man who works in a profession that, by that
standard, would not exist.  Sagan (I think?) wrote an article on
starships arguing they were infeasible.  His argument showed that the
starship would require ridiculously large waste heat radiators. 
Unfortunately, he assumed the radiators would work at 300 degrees K!  
Sagan and Newman wrote a paper purporting to show (via application of
the diffusion equation) that colonization of the galaxy would take too
long for the wave to have reached here. Unfortunately, their use of
the diffusion equation was mathematically inappropriate (the
population density gradient at the edge of the colonization sphere was
too large; colonization is more like an explosion). Etc., etc. 
 
    Responsible SETI advocates simply say speculation without
experimentation is scientifically sterile, so let's listen and keep
out minds open.  That's my position.  If I were a betting man I'd bet
they find nothing, but that's true of much research, and SETI isn't
expensive.  Proposal: look at distant galaxies, where galaxy-spanning
civilizations may be detectable. 


Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!SAIL.STANFORD.EDU!REM%IMSSS
Subject: Refuting ESG7's ideas opposed to building arks.
Posted: 14 Mar 87 20:04:28 GMT
Organization: The ARPA Internet
  
<ESG7> Date: Mon, 09 Mar 87 09:44:24 MEZ
<ESG7> From: ESG7%[email protected]
<ESG7> Subject: Star Travel, Light Sails, and Antimatter
 
<ESG7> In an earlier posting I claimed that there are only two hopes for star
<ESG7> travel, namely:  nuclear fusion (IFR systems), or a Grand Unification
<ESG7> Theory "rabbit out of the hat".  Paul Dietz raised a third possibilty:
<ESG7> Light sails propelled by a laser. ...
 
<ESG7> How would you construct such a laser?
<ESG7> How do you build the sail?
 
    Mere engineering problems. A technology capable of living and
working in space, and of tapping the energy of Sol and the materials
of the Sol system, might find a way to engineer a billion-mile-long
laser and a thousand-mile-across sail.  There's nothing physically
impossible about such engineering tasks as far as I know, just they
are way beyond 1987 technology, might have to wait until 2037. 
 
<ESG7> Where would you get the energy?
 
    Obviously from Sol.  Virtually *all* of Sol's energy is radiated
into deep space, where it essentially wasted, a wee bit slightly
heating the Oort Cloud, and the rest going out out out ... into the
void. 
 
<ESG7> How do you accurately track the sail when it is over a light year
<ESG7> away?
 
    You don't!!
 
    You just aim the lightbeam along the trajectory you want the craft
to travel (you compute where the target star will be by the time your
craft gets there), and you have machinery on the craft to track the
beam instead of vice versa. 
 
Re antimatter:
 
<ESG7> How do you make the stuff?
 
    One easy way is to bombard a target with lots of gamma rays
(generated by a gamma-ray laser, which of course is solar-powered),
and selectively collect the stuff that flies out the back. The
antiprotons or anti-electrons (positrons) or whatever you want are
collected, and the rest are returned to the gamma-ray target to try
again. This device is grossly energy-inefficient, but relatively
simple to engineer and who cares if we waste all the solar energy
anyway since we're wasting a lot more now by not tapping it at all
(except the teensy bit which happens to hit Earth or some other
planet). If we ever start running short on gross energy output from
Sol (like if we have a complete Dyson sphere around it and there's
none left unused), then we can design something more efficient. 
 
<PFD> Date:     Mon, 9 Mar 87 18:17 EDT
<PFD> From: "Paul F. Dietz" <DIETZ%[email protected]>
<PFD> Subject:  Laser Sails, Antimatter (Response to Gary Allen:)
 
<PFD>   Travelling to Alpha Centauri, it may be possible to slow down in
<PFD> Alpha C's plasma tail, since the interstellar wind is coming from
<PFD> Centaurus and the plasma tail should be pointing nearly in our
<PFD> direction.
 
    Furthermore, if we know ahead of time which exact direction the
plasma tail is pointing, we might deliberately aim for the tail
instead of the star, to get maximum decelleration, then tilt the sail
to provide both braking and transverse force, thus ride the tail in to
the star. 
 
<ESG7> Date: Wed, 18 Feb 87 11:34:07 MEZ
<ESG7> To: [email protected]
<ESG7> From: ESG7%[email protected]
<ESG7> Subject: Expansion in space is limited to 50 light years
 
    (Why is the date on this message so old?? If it is a mistaken
repeat transmission, forgive my castigating you again for an old
message.) 
 
<ESG7>    In a previous posting I made the assertion that one would not expect
<ESG7> an interstellar civilization to expand beyond 50 light years radius from
<ESG7> its home star.  This caused some readers to ask the obvious question,
<ESG7> "Why?"
 
    I ask it again. Your message here doesn't answer it in any correct
way, since it is based on a false assmption. 
 
<ESG7>    The basic assumptions are that starships can never travel faster than
<ESG7> ten percent of the speed of light, and are enormously expensive.
 
    That's not the problem, I accept that premise, >0.1C is difficult
and possibly not worth the effort. Also ... 
 
<ESG7> I'm assumning that the only way one could get men to another star
<ESG7> would be through a nuclear fusion propelled "Ark" which was about the
<ESG7> size of an L-5 type colony, and required over a hundred years to
<ESG7> complete one voyage.
 
    Maybe not the only way, but the most reasonable way we currently
envision, so let's go with that.  But ... 
 
<ESG7> Since these Arks would represent virtually no financial return upon
<ESG7> completion, the constructing civilization would look upon making these
<ESG7> ships as only a "luxury activity" for disposing of surplus wealth
<ESG7> (like the Egyptians building the Great Pyramid or the Athenians
<ESG7> building the Parthenon).  It is doubtful that any single civilization
<ESG7> could justify building more than three of these ships.
 
    There you go talking about financial return to parents instead of
setting seed upon the wind. Do you expect your children to support
you? (You would analyze financial return before conceiving children,
and only if they will pay you back more than you invest in their
upbringing would you ever conceive them??) No, your children are your
survival machines for your genes and perhaps some of your ideas and
morals etc. It's the same with these interstellar arks. Did you miss
the earlier postings, or am I seeing an old message that you sent
before the postings arrived at your site? 
 
    Have you ever watched a nature series on PBS? (NATURE, PROFILES OF
NATURE, PLANET EARTH, LIVING PLANET, et. al.) Have you seen how those
primitive creatures assure their survival by sending out millions of
eggs or spores?  Some sea creatures even give off thousands of
fully-formed children (not eggs or spores)!  We should do the
analagous thing on an interstellar scale if we want to survive. 
 
<AG> Date: 19 Feb 87 15:37:25 GMT
<AG> From: [email protected]  (Andre Guirard)
<AG> Subject: Re: Expansion in space is limited to 50 light years
<AG> To: [email protected]
 
(In reply to ESG7)
<AG> This assumes that financial return is the only "coin" for which a
<AG> civilization considers projects worthwhile.  I and, I'm sure, many
<AG> others on this newsgroup have a much more important "payoff" in mind
<AG> when we support space exploration: species survival.
 
    Yes.

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!SAIL.STANFORD.EDU!REM%IMSSS
Subject: Antimatter storage; how good a vacuum?
Posted: 15 Mar 87 09:03:52 GMT
Organization: The ARPA Internet
 
<ESG7> Date: Tue, 10 Mar 87 12:29:19 MEZ
<ESG7> From: ESG7%[email protected]
<ESG7> Subject: Some comments on anti-matter storage
 
<ESG7> The best vacuum known is in interstellar space which is 0.1 particles
<ESG7> per cubic centimeter.  The interplanetary vacuum is 1000 particle/cc.
<ESG7> ... The best current artifical vacuum is at about 1.0E10 particles per
<ESG7> cc.
 
    What on Earth (literally) are you talking about??  I thought we
were talking about some 50-100 years in the future when we're living
and working in space? What makes you think the ability to force air
out of a vessel into Earth's atmosphere is relevant? 
 
<ESG7> Let us assume that through the marvels of technology an artificial
<ESG7> vacuum of 1000 particles/cc is possible (a seven orders of magnitude
<ESG7> improvement).
 
    No marvel is needed; merely open your vessel to interplanetary
space. With ionization and electromagnetic pumping of the ions out to
interplanetary space (instead of into Earth's atmosphere as you seem
to imply) and free electrons we should be able to achieve several
orders of magnitude better than the ambient (interplanetary)
semi-vacuum. 
 
<ESG7> One **might** achieve such a vaccum inside a diamond container heated
<ESG7> to several thousand degrees and then cooled to near zero degrees
<ESG7> kelvin.  One could take this container to interstellar space,
<ESG7> open-and-close it and then bring it back to Earth (I don't think it's
<ESG7> possible to artifically pump it down).
 
    Why would you ever want to bring your container back to Earth?
Surely you don't think we're going to try to store massive amounts (a
few grams) of antimatter anywhere near or on Earth, do you?  We're
trying to get hazardous or polluting industry off Earth into space!
[That doesn't sound like a solution to me! - LK] 
 
<ESG7> Another fix is to suspend the antimatter in front of the spacecraft
<ESG7> and insist that the spacecraft doesn't leave interstellar space.
<ESG7> However this seems rather silly to have a spaceship that can't leave
<ESG7> interstellar space.
 
    By your logic it would be silly to have an airplane that can't
travel on freeways or a ocean-liner that can't leave water, after all
what good does it do to have a plane or ship that can't deliver door
to door?  What ever happened to the idea of a shuttle craft?  The big
trans-star ship keeps away from dense matter, and the local shuttle
commutes between the trans-star ship and the local planet or
space-colony. 
 
<ESG7> Apologies to Captain Kirk and Mr. Spock, but it looks like antimatter
<ESG7> storage doesn't work.
 
    Credit for STAR TREK for having a starship which never landed
itself on planets, but either beamed people down&up (probably not
possible), or used a shuttle craft.  STAR TREK was sort of right on
that point, I think. 


Newsgroups: sci.space
Path: decwrl!ucbvax!DFVLROP1.BITNET!ESG7
Subject: And the Star Travel debate rages on....
Posted: 16 Mar 87 11:27:05 GMT
Organization: The ARPA Internet
 
    The Star Travel debate is attracting a lot of interest.  This is
great, since the subject is certainly interesting.  However, some
readers' responses bordered on being random.  I would like to
encourage these people that before they hose out some emotional flame
onto the net, that they proof read it before to see if their argument
is comprehensible (many weren't).  As usual, the most well thought out
and technically correct responses come from Paul Dietz.  Paul made a
couple of statements that were incorrect: 
 
> Gary Allen claimed that interstellar colonization was impossible,
 
    I've never claimed that interstellar travel is impossible.  In
fact in an earlier posting I described a way to travel to the stars by
means of an interstellar "Ark" and based my 50 light-year colonization
limit on this vehicle.  I am confident that interstellar travel **is**
possible through Inertial Fusion Rockets (IFR) of the type described
by the British Interplanetary Society and Rod Hyde of LLNL.  However,
I do think that interstellar travel by Bussard Ram Scoops, antimatter
rockets, or laser driven light sails is impossible. [I disagree
strongly here with Allen. - LK] 
 
>Gary Allen's analysis of antimatter heating in imperfect vacuum had
>several flaws.  (1) Gary assumed that all the energy generated in
>annihilations on the tiny solid hydrogen mote will be deposited in that
>mote. Gary's mote had a surface area of 1E-11 meters, for a diameter of
>slightly under 2 microns.  The gamma radiation produced in annihilation
>will travel meters in antihydrogen, and the charged particles          
>centimeters... only a small fraction of the energy released is         
>deposited by the antihydrogen.  (2) Gary claimed that heating of the   
>vacumm chamber will lead to runaway outgassing....                     
>the energy hitting the wall per unit can be made arbitrarily low       
>by increasing the radius of the container.
 
    I redid the calculation assumning a ten percent absorption of the
energy.  Unfortunately the temperature of the anti-hydrogen is still
at the one atmosphere boiling point.  The calculation was a simple
order of magnitude analysis to prove impossibility.  Except for the
assumption of energy absorption, I always made assumptions favorable
to the anti-hydrogen remaining frozen.  However it still melted. Of
course, if you make the container really big then there will be less
wall interaction.  However we're talking about a fuel tank inside a
star ship.  This has to be reasonably compact.  Also we have not
addressed the problem of transport of the fuel from the tank to the
combusion chamber or handling during manufacture.  Both problems are
far more difficult than simple storage.  Also another reader mention
the possibility of easier handling of antimatter at low temperature.
This is news to me.  However this point is irrelevant, since the
antimatter will be heated to a much higher temperature by the energy
of collision and then its wave function could see the colliding
particles wave function causing mutual annihilation.  I should also
point out that Paul's observations on the difficulty of absorbing
energy raises grave questions about how one extracts thrust from a
matter/antimatter reaction. 
 
>Finally: Gary Allen made explicit his assumptions that went into his
>50 light year limit on colonization.  These assumptions seem debatable,
>to say the least...
>>    The basic assumptions are that starships can never travel faster  an
>> than ten percent of the speed of light, and are enormously expensive.
>We've already handled the first.  About the second, expense is relative
>to the capabilities of a society.
 
    Paul has not handled the first problem.  In arguing for antimatter
rockets and Forward's light sails, Paul has not demonstrated
feasibility nor has he shown the capability of relativistic
velocities. Expense is relative, but a trillion bucks is still a
trillion bucks. If you divide a tillion dollars over the entire
American population you will be giving every single person $4000. 
Would you pay $4000 so someone elses grandson could make it to
Tau-Ceti?  I'd pay $4000 for my grandson (and $40,000 for myself). 
However I'm a space fanatic. From John Q. Public, you'd be lucky to
get forty cents. 
 
>Gary goes on to state that stars of spectral type K5V to M are unable
>to support life.  Wrong -- planets around those stars are unable to
>evolve life.  Gary depends heavily on the assumption that building a
>civilization away from planets, and on barren planets, is impossible.
 
    Paul, you're the one that's wrong.  It's clear that I meant these
stars couldn't evolve life.  Of course they can support life that
travels to it, but what idiot civilization would send a star ship to a
barren system?  We got plenty of dead worlds in the solar system, and
it costs a whole lot less to stay here.  The extreme expense of star
travel is justified only if you can go to an Earthlike world. 
 
>Gary mentions that the average lifetime of a civilization or country is
>500 years.  After that every individual gives up and dies, I suppose?
 
    No, but they could (and probably will) do something much worse.  A
society could regress and become no-growth.  It could renounce
technology and become an agricultural society concerned with religious
contemplation and such burning philosophical issues as: "How many
angels can dance on the head of a pin?"  The Romans inherited geometry
and science from the Hellenistic Greeks.  What did they do with it? 
Answer:  Almost nothing.  The Medieval Europeans also inherited this
same Hellenistic tradition.  What did they do with it?  Answer:  Almost
nothing.  We can thank our stars for the Renaissance. 
 
    Another point people kept raising in arguing against the 50
light-year limit theory was the concept of "carrying the seed". 
"Carrying the seed" works for the first three times you've travelled
to the stars. But what do you do **after** you've carried the seed? 
Sure, I'd like to have a son and a daughter, but do I really want ten
thousand sons and daughters?  The "seed" argument doesn't work for
unbounded interstellar growth.  Many people argued against the three
star ship limitation, saying that the Sol system has lots of
resources, (Why should one be content with just three star ships?). 
However these enormously expensive ships won't be built for economic
reasons.  They'll be built for idealogical reasons, i.e. carrying the
seed, scientific research, etc.  However, after your home world has
done it three times and your daughter planets have each done it three
times, then the thrill will be lost.  The home world will be insulated
from the frontier by its colonies.  It'll feel that it has done its
part and leave star travel to the colony worlds.  Others argued
against the 1 light-year frontier thickness.  This is an insignificant
point.  If you argue that the frontier is 10 light-years thick, then
the radial limit upon expansion is only slightly increased, if at all.
The law-of-scale concerning the frontier volume servicing the home
world volume would still stand. 

                              Gary Allen                                

Newsgroups: sci.space
Path: decwrl!decvax!necntc!husc6!husc2!chiaraviglio
Subject: Re: Laser Sails, Antimatter
Posted: 16 Mar 87 22:24:05 GMT
Organization: Harvard Univ. Science Ctr., Cambridge, MA
 
    In article <[email protected]>, [email protected] 
("Paul F. Dietz") writes: [about how to store antimatter in solid form]

> For a starship, antilithium hydride is probably needed to reduce tank mass.
 
    I think you want antilithium antihydride, or anti-(lithium
hydride). Antilithium hydride would be very bad. . . .  :-) 

	-- Lucius Chiaraviglio
	   [email protected]
	   seismo!tardis.harvard.edu!lucius
 
Please do not mail replies to me on husc2 (disk quota problems, and
mail out of this system is unreliable).  Please send only to the
address given above. 

Newsgroups: sci.space
Path: decwrl!ucbvax!cartan!obnoxio
Subject: Re: Space Travel ... and Antimatter
Posted: 18 Mar 87 11:01:04 GMT
Organization: Brahms Gang Posting Central
Responding-To: [email protected] (Henry Spencer)
 
    Gary Allen left a few points uncriticized.  I think I'll jab at them.
 
    In article <[email protected]>, henry@utzoo (Henry Spencer) writes:

>> ... the problem of the high energy gamma rays that are
>> produced by antimatter reactions...
>
>Troublesome but solvable, probably.
 
    With probability > .01, I suppose.
 
>The engine itself will need a pretty
>heavy-duty cooling system.  The crew quarters will quite simply need
>shielding.  A combination of a long ship and shadow shielding can get the
>mass down to where it's manageable.
 
    Down to where it's manageable?  Hahaha.  Now *why* is this man
laughing? 
 
>I've seen a properly-shielded proposal
>for an antimatter-powered ship capable of 90+% of the speed of light, and
>the shielding problems of more modest vessels pale beside that one.
 
    Why do I hear people throw off .9c without blinking?  Grr, it
worries me. You say this ship is capable of .9c?  Do you know what
this entails?  Have you done the physics?  (For the lazy, just look it
up in J Ackeret "Zur Theorie der Raketen" Helv Phys Acta 19:103
(1946)) 
 
    In units where c=1, to obtain final velocity v, assuming utter
perfection energy-wise, the ratio of payload to entire ship is
sqrt((1-v)/(1+v)). Assuming one wants to decelerate back to zero at
the end, one must square this quantity.  This gives 5.26%.  If one is
travelling at constant acceleration a, the distance travelled is
(cosh(aT)-1)/a).  (T here is proper time; it works out that the
payload ratio is exp(-aT).)  This works out to be, for acceleration
measured in "g"s, 8.5/a light years (plus coasting). 
 
    Now this is almost believable.  But what about the real world?
(There's *always* something, isn't there?) 
 
    If fraction eff of emitted energy is useful, and the rest is just
dumped (this includes inefficiencies and stage separations, etc), we
must raise this ratio to the 1/eff power.  (This conveniently turns
out to be equivalent to the case of wasteless exhausts with relative
velocity eff.) 
 
    So, our payload ratio becomes .00004% for eff=.2, and
.000000000016% for eff=.1.  Frankly, I think anyone seriously
expecting eff>.2 to be achieved is a raving lunatic.  ("Scotty, could
you beam this 'engineering' difficulty into a wall?"  "Aye aye,
Captain!") 
 
    Anyway, that's uh, a LOT of fuel you've got there.
 
    Now, if one were planning to return ....
 
    So let's look at v=.1.  Here for eff=1.0, we get a payload ratio
of 82%. Not bad.  When eff=.2, we get 37%, and when eff=.1, about 14%.
This may even be plausible.  I'll believe it when I see it, of course.
After all, eff=.01 gives us a ratio of .0000002%. 
 
    Oh, you were really talking about being properly shielded?  I
haven't thought about the gamma rays, but what about interstellar
space grains? I mean, you run into a teensy little gram at .9, and
it's like being hit by a 20 kiloton nuke blast, the size of the
Hiroshima atomic bomb of 1945.  You know, as in "BOOM".  That's a LOT
of shielding to provide for.  And there's still that immense payload
ratio.  (Yes, I know the typical grain is believed to be about 1e-15
g.  Somehow I don't like the idea of learning about the atypical dust
grains the hard way.) 
 
    Even if you restrict .9 to the intergalactic medium (and pray a
lot), just getting there is going to take a while.  And to make
matters worse, one is going to have to practically *crawl* through the
Oort Cloud of comets.  At .0001 or less. 
 
    Note that I don't think interstellar travel is impossible.  Just a
lot harder and far more expensive than I think most of you want to
realize. Nothing less than planetoid-sized and extraordinarily slow
arks seems feasible according to known physics. 
 
>> Number two:  How do
>> you store the stuff?  (remember quantum theory proves that no container
>> is 100% effective)...
>
>Quantum theory turns up other interesting things, too.  There has been a
>suggestion
 
    Wow.  An actual suggestion.  THIS is why you people believe in
interstellar travel?  Because of suggestions of how physics *might*
turn out?  Gag me with a gluino.  (And to think that I thought that
the unswerving faith in the of-course solvability of the "mere"
engineering difficulties was stupendous.) [This guy gets a bit too
rude here for my tastes - LK] 
 
>that at really low temperatures -- like 0.0001 K -- antimatter
>could be handled with normal matter, because the wave functions don't
>overlap enough to produce a reaction.  I'm not enough of a physicist to
>check that one.
 
    I'm not enough either, but it sure sounds like wishful thinking.
Apparently it's close enough for government work, and of course as
always it's close enough for SF. 
 
    Come on.  There is *always* the zero point energy minimum, even at
absolute zero.  *This* is what quantum mechanics tells us.  And its
size is inversely proportional to the mass of the object in question. 
 
    As a first guess, I would expect a kind of van der Waals analogue
of a force to develop between nearby hydrogen and antihydrogen atoms,
encouraging the electron and positron to annihilate each other. 
 
>The studies funded by outfits like the USAF have concluded
>that storing the stuff is not an insuperable problem; low temperatures,
>hard vacuum, and handling by magnetic or electric fields will suffice.
 
    Someone should tell the physics community!
 
    One of the interesting side results that I've seen noted from the
method of stochastic cooling was experimental confirmation of the
stability of antiprotons.  Before, they had linear beams of
antiprotons that travelled at near the speed of light for a fraction
of a second kind of hard to catch them.  Stochastic cooling allowed
circular beams to be kept going (at worthwhile beam densities).  And
it was just last year that the first published accounts of successful
antiproton traps came out.  They could actually count how many
antiprotons they had. 
 
    Or has the USAF stuff been kept classified all these years?  Just
how long have they kept antimatter stored?  And how much? 
 
    Sorry, I just can't be impressed by toys.
 
>But in case
>you're not aware of it, 
 
    Well, I am.
 
>the proton-antiproton reaction does *not* yield
>gammas immediately.
 
    Of course not.  Protons are rather complicated objects.  This has
been known for nearly two decades now. 
 
    But does this make a difference?
 
>A large fraction of the energy is temporarily in the
>form of charged particles, which a magnetic nozzle can handle.
 
    A "magnetic nozzle"?  Now what is that?  And how can it handle
reaction times on the order of 1e-23 to 1e-10 seconds?  (You did say
"temporarily"?)  And just how does it aim a mixture of positive and
negative particles of various masses and momenta in the same
direction?  (Hmm, let me guess: "very quickly!") 
 
    Yes indeed, this sounds like a classic way to revolutionize all of
modern high energy physics.  Perhaps they should tell someone.... 
 
>Please
>read some of the work that has been done before denouncing it as impossible.
 
    OK.  Here's a compromise: I will simply denounce it as science
fiction. That way no one can accuse me of exaggerating. 
 
    Note that I don't think the storage of vast amounts of
antihydrogen is impossible.  Just very very difficult, with nothing
exotic about it either. 
 
    Humph.  I've got a much more practical suggestion for getting to
the stars. First, find a good-sized collapsar (say this big ---> .
<---) .... 
 
ucbvax!brahms!weemba	Matthew P Wiener/Brahms Gang/Berkeley CA 94720
 
    PS - I've changed my mind.  I give the derivation of the equations
for a relativistic rocket with inefficiencies--those for hyperbolic
motion are too well known and hence omitted: 
 
			<-de- * ==|===M====>
 
Let
	M denote the rocket rest mass,
	dM the change in rocket rest mass,
	de the exhaust energy,
	dx the wasted energy,
	eff the efficiency ratio de/(de+dx),
	v the Earth-frame speed of the rocket,
	dv' the change in the rocket's speed, in the rocket-frame
	dv the corresponding Earth-frame change,
	B the factor 1/sqrt(1-v^2).
 
Computing to first order in the rocket's frame, we get
 
		de + dx + dM = 0		(conservation of energy)
 
		de = M dv'			(conservation of momentum)
 
		dv' = B^2 dv			(relativistic addition)
 
This yields:
 
		eff dM/M + B^2 dv = 0,
 
    Which is easily solved to give M_final/M_init =
sqrt((1-v)/(1+v))^(1/eff) for a trip starting at velocity 0, ending at
v.  This value is squared for stopping, and squared again if a round
trip is planned. 
 
    More generally, in case of fuel emitted with velocity w<1, one
replaces "de" by "b dm" in the energy equation, and "de" by "w b dm"
in the momen- tum equation, where dm is the rest mass of useful fuel,
and b=sqrt(1-w^2). This is equivalent to replacing "eff" by "eff w" in
the final results. 


Newsgroups: sci.space
Path: decwrl!ucbvax!SAIL.STANFORD.EDU!REM%IMSSS
Subject: laser beam to interstellar sailboat
Posted: 18 Mar 87 11:07:04 GMT
Organization: The ARPA Internet
 
<OTA> Date: Tue, 10 Mar 87 09:11:29 PST
<OTA> From: [email protected]
<OTA> Subject: Star Drives
 
<OTA> This laser could use a laser from the lightsail as a guide beam for
<OTA> tracking and distortion correction.
 
    This wouldn't work over interplanetary distances, much less
interstellar, because of the long speed-of-light feedback delay. Let's
go back to pre-aimed beam with the light sail tracking the beam not
vice versa, since that involves no long servo delay, ok? 
 
<HS> Date: 10 Mar 87 22:44:35 GMT
<HS> From: [email protected]  (Henry Spencer)
<HS> Subject: Re: Star Travel, Light Sails, and Antimatter
 
<HS> All you do is keep the beam pointed in pretty much the right
<HS> direction, with maybe an occasional correction.  The spacecraft moves
<HS> to stay in the beam, not vice-versa.  The key problem is not sail
<HS> tracking but pointing stability.
 
    Yup.  Note the "occasional correction" must be a sudden change in
the second derivative of angle, not in absolute angle nor first
derivative, lest the sail suddenly lose track of the beam (literal use
of word "track" here). 


Newsgroups: sci.space
Path: decwrl!ucbvax!NRL-SSD.ARPA!mike
Subject: Re: Star Travel/ Fermi Paradox
Posted: 18 Mar 87 13:48:10 GMT
Organization: The ARPA Internet
  
    I've been biting my tounge and not saying anything through this
entire discussion of why star travel isn't possible, but I've finally
had enough of it. 

    Folks, why is it that we always seem to assume that there are no
real improvements to be made???  Examples: Nobody wanted to believe
that Earth consisted of anything besides Europe, Africa, and Asia for
centuries until some guy named Columbus came along and rubbed their
noses in it.  Then there's always "Man doesn't have wings, therefore
he can't fly"; once again, we had to have our noses rubbed in it.  "It
is impossible to fly the Atlantic solo and unrefueled." (How many
times do you have to rub a dog's nose in it???  Maybe we need to get
knocked over the head with a baseball bat.)  "The speed of sound is an
absolute barrier."  Oh really?  Ask General Yeager about that one.
"Man cannot survive in outer space."  Hmmmm.  Seems to me we went from
90 minutes in orbit to landing a man on Luna in a grand total of about
12 years and that includes the time we spent designing the original
MERCURY capsules. 

    Gary, Jorge, I realize you guys have good arguments for the Fermi
Paradox, etc, but I really don't see any evidence that this time will
be any different than any of the ones I mentioned above.  Newtonian
physics sufficed for centuries, until we started getting more
sensitive equipment, and started noticing that there seemed to be
problems at very high speeds, etc., and still apply for 99.9999
percent of all the things that man needs.  What's to say that
Relativistic models don't break down at some point either???? The
whole point is, let's quit wasting time finding reasons not to do
things, and start finding solutions to the problems. 
  
Mike Stalnaker      'Always listen to the experts.  They will tell you what 
[email protected]    cannot be done, and why.  Then you can go do it.'
(301) 258-5130 				-Paraphrase of Robert A. Heinlein.
		     "I've never met a paradox that couldn't be paradoctored."
						     --Robert A. Heinlein.
 
 
Newsgroups: sci.space
Path: decwrl!ucbvax!OZ.AI.MIT.EDU!MINSKY
Subject: SPACE Digest V7 #167, interstellar travel
Posted: 18 Mar 87 14:04:00 GMT
Organization: The ARPA Internet
  
    We have been considering interstellar travel without taking into
account any technical progress first.  Let us assume that in, say,
10,000 years we achieve a nanotechnology in which we can make
computing elements each from a small number of well placed atoms.
(Let's neglect sub-atomic structures for the moment.)  This will
permit us to make computers that contain 10**18 element per cubic
millimeter.  This should be able to simulate a very powerful brain. 
 
    Second, suppose that in this 10,000 years we make progress in AI.
Then that cubic millimeter could be programmed to contain something
much like ourselves, complete with the contents of a billion books. 
 
    Now reformulate the interstellar travel problem so that the goal
is to accelerate payloads of the order of a few milligrams.  There may
be a few problems about power sources, but 10,000 years should help
with that.  There may also be some shielding problems, but advances in
redundancy and self-repair should make that inconsequential. 
Decellerating, landing on planets, and converting back into animals,
are also interesting little problems. 
 
    The basic point is that the launch vechicle will be 10**9 times
smaller, at the start, than the kinds that have been considered here,
and hence need not constitute such expensive projects. 

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!slb-test.CSNET!DIETZ
Subject: Making antimatter by neutron-antineutron oscillation
Posted: 21 Mar 87 15:13:00 GMT
Organization: The ARPA Internet
 
    On the subject of manufacturing antimatter...
 
    One speculative phenomenon in some grand unified theories is
neutron-antineutron oscillation. Free neutrons would oscillate into
antineutrons (and back again) if there is a tiny mass difference and
if the theory allows some kinds of baryon-number changing
interactions. 
 
    Current experiments place a lower limit on the oscillation time T
of 10^6 seconds. After t seconds (t << T) a free neutron will be found
to be an antineutron with probability (t/T)^2.  10^6 seconds is a bit
long to be useful, since the neutron mean lifetime is about 900
seconds. 
 
    However, these experiments were done on Earth. There may be a weak
intermediate range force sensitive to baryon number (this is very
controversial) or perhaps there are contributions from quantum gravity
that might cause antimatter to experience a stronger attraction to the
earth than normal matter (this will be tested soon at CERN).  This
could change the energy of a neutron relative to an antineutron near
Earth and suppress oscillation. The oscillation time might then be
more like 3x10^3 seconds, in which case we might (in space)
optimistically change about 10% of the free neutrons to antineutrons.
If making a free neutron costs 10 MeV (from fusion, say) this would be
some 10,000 times more efficient than the most optimistic accelerator
based scheme, and might even be a net source of energy. 
 
    Perhaps one could also use resonant enhancement of the
oscillation, using a magnetic field interacting with the particles'
magnetic moments. A similar phenomenon has been proposed for solving
the solar neutrino problem by resonantly converting electron neutrinos
to other flavors as they pass through Sol. 

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!CSV.RPI.EDU!weltyc
Subject: Antimatter storage, how good a vacuum?
Posted: 2 Apr 87 14:38:39 GMT
Organization: The ARPA Internet
             
   <ESG7> Another fix is to suspend the antimatter in front of the spacecraft
   <ESG7> and insist that the spacecraft doesn't leave interstellar space.
   <ESG7> However this seems rather silly to have a spaceship that can't leave
   <ESG7> interstellar space.
 
    This really is a silly statement.   The extra cost of making a
vehicle capable of entry (where there is an atmospere involved), or
simply capable of landing/takeoff (even if there isn't an atmosphere)
makes it ridiculous to consider giving those capabilities to an
interstellar - or even interplanetary craft.  All space flights to
date have made this distinction.  Of course there would be some kind
of shuttle (call it what you will), a smaller craft with the ability
to takeoff and land, and enter an atmosphere.  In simplest terms, just
think of the extra weight the big ship would have if it had to be able
to land....and the extra fuel to push that extra weight... 
 
*** Posted April 2 (my messages seem to be coming about a month after
                    I post them)
 
					-Chris

Newsgroups: sci.space
Path: decwrl!decvax!ucbvax!slb-test.CSNET!DIETZ
Subject: Antimatter; Gary's Claims
Posted: 10 Apr 87 12:56:00 GMT
Organization: The ARPA Internet
 
    Some more responses to Gary Allen...
 
    Gary Allen acknowledged that he had overestimated the energy
deposited in a tiny piece of solid antihydrogen by annihiliation
products. He then recalculated the equilibrium temperature, assuming
10% of the energy would be absorbed as heat.  He argued he had made
many assumptions favoring cooling.  However, even 10% energy
absorption is much too high: if annihilation radition travels meters
in antihydrogen, and the pellet is microns across, perhaps 1E-6 is a
better estimate to the heating efficiency. 
 
    Gary also only considered thermal radiation as a means of cooling.
There is at least one other: sublimation. This would be inappropriate
if the pellet is to be stored indefinitely (unless the escaping vapor
could be trapped, cooled and recondensed) but a continuous flow of
antimatter is desirable in a starship. One has to run the engines,
after all. Is the heat of sublimation of solid hydrogen high enough
for this to be important? 
  
    Gary stated that the best vacuums attained on Earth were around
1E10 cm**-3, but electron storage rings typically operate at a
nanotorr or so (about 3E7 molecules/cc). It is also not clear why
vacuum conditions attainable on Earth are at all relevant to
conditions attainable in space. He stated that the thermal velocity of
a carbon atom at 1 deg. K is 1 m/sec; it is actually about 37 meters
per second (did he mean a millikelvin?). I expect the vapor pressure
of many solids to be nil at low temperatures, and radiation from
annihilation will mostly be absorbed deep in the structure (or go
right through), so it won't sputter many atoms. More of a worry would
be adsorbed gas, but that can presumably be baked off in space. 
 
>> Gary Allen claimed interstellar colonization was impossible.
>I've never claimed that interstellar travel is impossible. 
 
    I said colonization, Gary, not travel.  Gary claimed colonization
beyond 50 light years was impossible. 
 
    Gary's 50 light year colonization limit has an immediately obvious
flaw:  Stars move! Even if Gary's scenario is correct and colonization
runs into a wall at 50 light years, the stars in that colonized volume
will continue moving relative to one another. At 30 km/sec (and some
nearby stars move faster than that relative to us), a star will move
50 light years in 500,000 years. I suppose Gary is assuming that the
civilizations around all the colonized stars will die out or stagnate
permanently in less than O(1 million) years. 
 
>>>    The basic assumptions are that starships can never travel faster  an
>>> than ten percent of the speed of light, and are enormously expensive.
>>We've already handled the first.  About the second, expense is relative
>>to the capabilities of a society.
>Paul has not handled the first problem.  In arguing for anti-matter
>rockets and Forward's light sails, Paul has not demonstrated feasibility
>nor has he shown the capability of relativistic velocities.  Expense is
>relative, but a trillion bucks is still a trillion bucks.  If you divide
>a [trillion] dollars over the entire American population you will be giving
>every single person $4000.  Would you pay $4000 so someone elses
>grandson could make it to Tau-Ceti?  I'd pay $4000 for my grandson (and
>$40,000 for myself). However I'm a space fanatic.  From John Q. Public,
>you'd be lucky to get forty cents.
 
    I have handled the first problem, in the sense that I have shown
that Gary has not proved light sails to be impossible. I'm not saying
they are certainly feasible, only that they don't contradict the laws
of physics as we currently understand them (as FTL does), and don't
seem to require theoretically impossible materials (as the original
ramjet does). Gary seems to be taking the position that unless we can
demonstrate now how to solve all the engineering problems, the
problems are inherently unsolvable. Gary's attitude would be
appropriate if someone were proposing to build, right now, a
relativistic starship, but is inappropriate when attempting to set
limits on what will be technically feasible in the far future. 
 
    Gary's comment about $4000 per person is plain obfuscation. Gary
assumes that the starship would be built by a civilization of size
comparable to the current American population. This assumption is
absurd -- even today, the US population is only 5% of the world
population. The solar system can support many orders of magnitude more
people. 
  
    If, for example, a 2.5 trillion person economy builds one starship
per year, and that starship costs $1E12, that's 40 cents per person
per year -- just the level Gary said I'd be lucky to get from John Q.
Public. Even today, NASA's yearly budget is around $40/US citizen,
some 100 times this figure, and future productivity and real incomes
are likely to be much higher.  What data we have shows that Gary's
claim about the likelihood of obtaining funds (at least from the
government) is simply false. 
 
    Is my assumption about 2.5 trillion people living in space
optimistic? Hardly! Assume each person requires 1000 tons of material
for living space, associated productive capacity, and so on (a quite
generous assumption). That's 2.5E15 tons of material, or, if that
material has a density of 2 gr/cc, a cube of material 110 km on a
side. The large asteroids could easily supply that; very much larger
populations are possible if the material in moons and planets can be
fully exploited (I think it eventually will be; a planet is a terribly
inefficient way to use matter). I assume materials are efficiently
recycled. 
 
    Is my assumption about 2.5 trillion people necessary? No! Assuming
we can bring the world population to 10 billion people, at an average
per-capita income 10x that of the current US level. Scaling NASA's
("WASA's"?) current budget proportionally, that budget would be some
$4 trillion per year. Scaling the Soviet space program would give an
even larger figure. 
 
> Paul, you're the one that's wrong.  It's clear that I meant these stars
> couldn't evolve life.  Of course they can support life that travels to
> it, but what idiot civilization would send a star ship to a barren
> system?  We got plenty of dead worlds in the solar system, and it costs
> a whole lot less to stay here.  The extreme expense of star travel is
> justified only if you can go to an Earth-like world.
 
    Gary is showing his planetary chauvinism. Why should a system
without life bearing planets be considered "barren"? If the vast
majority of persons in the starship building civilization are living
in space habitats, would they consider the lack of a lifebearing
planet a strong argument against colonization?  We certainly have many
dead worlds in this solar system, and they will be studied and used. 
But why should this prevent colonization of other "barren" systems? 
 
    Gary asks: why should an "idiot" civilization colonize a system
without lifebearing planets? Many reasons: to determine if it really
is lifeless (how would you tell for sure without visiting?), to gain
further data on the formation, evolution and properties of stars and
planets, to conduct large scale engineering projects in an unpopulated
star system, to conduct experiments in terraforming, as a stepping
stone to more distant systems, as insurance against disaster, for
political prestige, for ideological reasons, to prevent others from
colonizing the system, for military reasons, etc. 
 
    Gary again claims the cost of building a starship is extreme.
Nonsense! To a large space-inhabiting civilization utilizing the
resources available in this solar system, the per-capita cost of
building one starship is TRIVIAL. It could very well be the case that
the capacity would exist to build many more starships than there are
reachable target stars, in which case arguments about the
undesirability of "barren" star systems lose credibility. 
 
> No, but they could (and probably will) do something much worse.  A
> society could regress and become no-growth.
 
    How Gary can make such pronouncements about the probable behavior
of civilizations is beyond my understanding. We can't make any such
predictions about our species, let alone hypothetical aliens about
which we have zero data. If Gary insists on doing so, it would be
intellectually cleaner to just assume that all civilizations destroy
themselves or stagnate before any starships can be sent out. 
 
    An equally valid (that is to say, entirely speculative and
unsupported by evidence) prediction about the future behavior of
civilizations is that they would become less materialistic and more
concerned with the gathering of knowledge.  Such a civilization would
eagerly send colonists to on interstellar trips for the knowledge such
trips would provide. 
 
> If someone can come up with a counter-argument recognizing the above
> five points then the discussion will be worthwhile.
 
    Gary's point 1 [volume of sphere increases faster than the surface
area] is true but I don't understand what it has to do with anything.
So what if there are many more interior systems than frontier systems?
There is no claim being made that all population growth on interior
systems need be exported, and there is no plausible motivation for
sending ships only to already colonized systems. Moreover, assuming
starships have limited range, once the colonization sphere becomes
large enough most of the interior systems are unreachable from the
frontier. In the limit the radius of curvature of the colonization
sphere is much larger than starship range, 1/2 of the systems
reachable from a frontier system will already have been colonized, and
each frontier planet need colonize only 1+epsilon new star systems to
keep the wave going. 
 
    Point two is really two points: starships tax the resources of a
star system (doubtful) and starships are inevitably slow (not proven,
and, indeed, not provable, unless Gary is willing to correctly predict
all relevant future technological and scientific advances.) 
 
    Point three [that systems producing starships are eventually
insulated from the frontier] is true, but irrelevant (see point 1
above and point 5 below). 
 
    Point 4 [that star travel is ideologically motivated and will
provide no economic return] may be true, but there could be other
reasons (political, for instance), and the relative cost will be so
low for a large civilization that the lack of economic return wouldn't
be important (after all, what's the economic return from particle
physics? from today's space programs? from organized religion?).
Enough of today's government spending (and personal spending, for that
matter) is ideologically motivated that this is no counterargument. 
 
    Moreover, point 4 is sensitive to the level of interest rates. In
an economy with low interest rates it may well be economically
feasible to send colonists to nearby star systems. The export from the
colony would be information: scientific, or even entertainment
programs.  That the original investors would not live to see the
project completed is not an objection, since stock can be traded
before that point. 
 
    Point five [that the home system will change significantly as the
radius of colonization expands] is irrelevant. Once a system is far
from the colonization front, what it does is unimportant to the
progress of the wave, since it is no longer a source of starships. As
an explanation of the Fermi paradox, this hypothesis is also
methodologically dubious: lacking a scientific theory of alien
sociology, such explanations cannot be proved, and in the absence of
observation of alien societies no such theory can be formulated. 
 
Paul Dietz

Date: Thu, 23 Mar 89 16:42:23 EST
From: Glenn Chapman <[email protected]>
To: [email protected], [email protected],
        [email protected]
Subject: Room Temperature Fusion - possible indication?
 
    A very astounding breakthrough just may have been made in nuclear
fusion.  According to both the Financial Times (Mar 23, pg. 1, 26, and
22) and the Wall Street Journal (Mar. 23, b1 & b8) two scientist will
announce indications of room temperature fusion of heavy hydrogen
(deuterium) inside a solid material today at the University of Utah. 
These are not off the wall guys - the FT points out that both are
experimental experts in electrochemistry (Dr. Martin Fleischmann of
Southampton University UK, Dr. Stan Pons of University of Utah). 
Fleischmann is also a fellow of the Royal Society in London.  I will
summarize the articles but suggest that you get hold of the FT one
(the WSJ was written by someone who really does not know the details).
I have added some physics info to make it more understandable. 

    The process they are using consists of the following.  Consider an
electrochemical cell (like a battery) with a platinum electrode, a
heated palladium electrode in a bath of heavy water (deuterium oxide).
 Flow current from the palladium (negative electrode) to the platinum
electrode (positive one).  At some current the deuterium flow into the
palladium, combined with the effect of the material itself, causes the
deuterium nuclei to come together and fuse into helium 3 plus a
neutron (with 3.27 MeV of energy) or tritium plus hydrogen (with 4.03
MeV, 1 MeV = 1.6E-13 Joules of energy). (My speculation the fusion
processes here are not certain). 

    To show the real strangeness here note that the repulsive forces
from the positive charges on the two nuclei normally require
temperatures of 50 - 100 Million degrees to overcome (high temp. mean
the atoms are travelling very fast and so when they collide they
overcome the repulsion to get close enough together to have fusion
occur).  This room temp. result is obviously very unusual.  What
really indicates that fusion has occurred is that the FT article
states they saw fusion products, gamma rays, tritium and neutrons,
none of which are generated by chemical processes. It is especially
the neutrons that are important - that shows that fusion occurred. 
People at the UK Atomic Energy Authority say they know of the work and
are treating it seriously.  The article has been submitted to the
British science journal Nature.  Just my own speculation but one thing
that may agree with this is that there is a material called Zeolite
which stores hydrogen at densities higher than that of liquid
hydrogen. This shows that solids can force hydrogen atoms closer
together than they normally would be. 

     There is a news conference that will be held today at U of Utah.  If
there is anyone who can get more information on this please send it to me.
 
                                                      Glenn Chapman
                                                      MIT Lincoln Lab
                                                      [email protected]
 

               <<< LDP::LDP$16:[NOTES$LIBRARY]ASTRONOMY.NOTE;4 >>>
                         -< Astronomical Discussions >-
================================================================================
Note 612.5  Is there a "Mr. Fusion" home energy supply in your future?    5 of 5
MTWAIN::KLAES "N = R*fgfpneflfifaL"                 282 lines  29-MAR-1989 15:09
                          -< Gleanings from the net >-
--------------------------------------------------------------------------------
    Here's more from the sci.physics list on room temperature fusion.
High-lights: a rumored confirmation of the experiment at Los Alamos, a
back-of-the-envelope calculation that the entire world's inventory of
palladium would make for a reactor only as powerful as a single
fission plant. 
 
[On the last one, a message, which I didn't save, from Paul Dietz --- whose
speculations that the effect stems from deuterons trapped in the palladium
lattice fuse by tunneling together was confirmed in Tuesday's NYT ---
discussed alternate ways of forming your palladium which might make for a
more efficient reaction --- e.g., instead of using palladium wire you use a
thin film of palladium clad to a neutron-reflecting, heat-sinking substrate.] 
 
Oh my, we live in exciting times.  I still think fire was a bigger
discovery, though....
  
From: [email protected] (John Scott McCauley Jr.)
 
[ This to some might be a repost. My normal machine phoenix is up and
down so I tried posting some details from prep.ai.mit.edu. As
it hasn't got to phoenix yet, I am reposting ]
 
I just received a preprint of the Jones and Palmer publication.
It is called 'Observation of Cold Nuclear Fusion in Condensed Matter',
S.E. Jones, E.P. Palmer, et al (Depts Physics and Chemistry, BYU),
J. Rafelski (Dept Physics, U. Arizona), dated March 23, 1989.
 
It is 16 pages long and gives a lot of details about their setup.
 
This is a *real* paper and not a press release -- it shows data
and probably gives enough info to be duplicated it in the lab.
  
    Here are some highlights:
 
'We have observed deuterium-deuterium fusion at room temperature during
low-voltage electrolytic infusion of deuterons into mettalic titanium
or palladium electrodes. The fusion reaction
	d + d -> helium-3(0.82 MeV) + n (2.45 MeV)
is evidently catalyzed as d+ and metal ions from the electrolyte are
deposited at (and into) the negative electrode. Neutrons having approx
2.5 MeV energy are clearly detected with a neutron spec. The
experimental layout is portrayed in Figure 1.'
 
Only the neutron branch was measured -- the T + p is assumed to
have the same cross-section.
 
Estimated reaction rate for cold fusion is about 1e-23 fusions/
deutron pair/second.
 
This may explain high levels of Tritium in volcanos.
 
They are trying other setups.
 
The paper is *very* cautious about applications of this for power
generation. Last sentence in paper:
'... while the fusion reaction rates observed so far are small, the
discovery of cold nuclear fusion in condensed matter opens the
possibility of at least of a new path to fusion energy.'
  
Here are some of my own personal observations+guesses.
 
Cold fusion can happen. The reaction rate of Jones & Palmer
is too small right now to be of use. It is far lower
than the tokamak was  two decades ago. However, the technology is
not exotic. In 20yrs or less we know whether or not this
technology will work. This is about the same time as tokamaks,
if not shorter.
 
The Fleschman and Pons experiment seems to be producing the same
effects. However, there is an interesting question left for dreamers.
The Jones & Palmer group base their reaction rate on neutron count.
However, if the Helium-3 + neutron branch is being suppressed by spin
alignment, say, then the Jones and Palmer group will have
underestimated the fusion reaction rate! To find the total reaction
rate, one must also measure the fusion reaction rate of the Helium-4 +
gamma branch. [supposedly the F&P experiment observed equal numbers of
Tritium and neutrons, i.e. the T + p and He-3 + n have equal
cross-section]. One could use calorimeters or measure gammas to find
the total reaction rate. It is just possible that the Fleschman and
Pons group did that and saw a huge discepency between the reaction rates. 
 
It is also possible that Fleschman and Pons are producing an
electrochemical effect (read battery) and this is upsetting the calorimeter
measurements.
 
	Wait till the papers come out,
 
			Scott
 
P.S. Be careful you have adequate amounts of neutron shielding if
     you try this. As was said before, safe doses of neutrons are
     on the order of nanowatts for 2.5 MeV energies.
 
From: [email protected] (andrew)
 
I cross-post this for your delectation, since it is about physics and
research, and you can hang it over your front door in a frame and show
your grandchildren (let's hope!)...
 
>From [email protected] Tue Mar 28 17:41:29 1989
From: [email protected] (Nanotechnology Newsgroup Nexus)
Newsgroups: sci.nanotech
Subject: Fusion Now!
Organization: Rutgers Univ., New Brunswick, N.J.
Approved: [email protected]
  
I have just received a call from a (previously Very Skeptical) friend
in a nationally known research lab who says that people at Los Alamos
have succeeding in duplicating Fleischman & Pons' results.  "Looks
like it's real after all."  He says the scientific community is
"abuzz" with the news.
 
I'm reminded to some extent of the story of how after the Wright
brothers first flew, they were virtually ignored by the world at
large, and particularly the scientific community, who had seen so many
hoaxes and failed attempts.  Then a few years later a respected
European scientist was travelling through Ohio, when in the fields
near Dayton he saw this huge creature in the air.  "My God, what is
that thing?"  The reply: "Oh, it's just those crazy Wright boys and
their flying machine." ...
 
--JoSH
 
From: [email protected] (Donn Seeley)
Subject: tidbits from the Salt Lake Tribune coverage of the fusion story
Keywords: news leaks, competing BYU research, patents, LANL work, lithium
 
I've naturally been curious about this story as it has developed; one
of the aspects that puzzled me was the timing of the announcement.
One reason for the timing is that there apparently were some leaks
prior to last week.  The 3/25 edition of the Tribune quotes Pamela
Fogle, director of news services for the University of Utah:
 
	'We thought long and hard about the news conference,' she
	said.  The story was starting to leak out of the university and
	many of the leaks had inaccuracies, she said, so U. officials
	decided it couldn't wait.
 
At the same time I have to wonder about the reported competing research
at Brigham Young University, and whether Pons and Fleischmann wanted to
claim credit first.  Another story in the same edition states:
 
	Brigham Young University officials confirmed Friday that BYU
	physicist Steven Jones had also submitted a manuscript on 'cold
	fusion' research to Nature.  Unlike the U. researchers, Dr
	Jones has declined to discuss details until it has been
	published.
 
	BYU spokesman Paul Richards said he understood both manuscripts
	were submitted with the hope they would appear side by side in
	Nature...
 
	Mr Richards stressed that BYU's research has been carried out
	independently of the U. project, and Dr Jones has been working
	on cold fusion for several years.  ...
 
	Dr Jones is also scheduled to present his paper in May at an
	American Chemical Society meeting in Baltimore.
 
	Most of his fusion work has used [muons] to catalyze the fusion
	reaction, but an abstract on the Baltimore talk indicates he
	will also speak on research very similar to the U. experiment,
	in which fusionable material was imbedded in palladium metal.
 
	'We have also accumulated considerable evidence for a new form
	of cold nuclear fusion which occurs when hydrogen isotopes are
	loaded into crystalline solids without muons,' the abstract said.
 
	Mr Richards said he does not believe BYU has applied for any
	patents on their research, as the U. has, 'but I know we're
	planning to.'
 
	He couldn't say if those plans would be affected by the U.'s
	application.  'We don't know because we haven't seen what they
	are doing.'
 
	'If they have some kind of a comprehensive patent, that could
	cause some problems for us,' he added.  'We have documented
	notes going back to '85 and '86, and we hope that would have
	some bearing.'
 
The patent issue is interesting too.  Here are some details on the
University of Utah's patent process from another article:
 
	James Brophy, U. vice president for research, told regents the
	patent rights for the research belong to the university.
 
	If the patent holds up, Dr Brophy said the two researchers will
	get a third of any royalties, the U. chemistry department will
	get a third because that's the academic department Dr Pons is
	affiliated with [he's the chair -- DMS], and the remaining
	third will go to the university itself.
 
The Tuesday (3/28) edition contains some more tantalizing hints that
others have successfully duplicated Dr Pons's experimental results:
 
	Researchers at Los Alamos National Laboratories may have
	already confirmed the results of the University of Utah's
	nuclear-fusion studies, according to the U. professor who made
	the studies.
 
	Stanley Pons said he heard Monday that the New Mexico
	laboratory had repeated his experiments with success.  'I'm
	very positive about that possibility,' he said, adding that he
	was still encouraging other scientists to wait until his paper
	is published in May.
 
	Los Alamos officials would not confirm the report Monday afternoon.  
        'Nothing yet,' said Jeff Schwartz, public affairs officer.  ...
 
	Dr Pons couldn't say whether Los Alamos scientists had directly
	measured neutrons, but he suspected they had.
 
Here we have to trust Dr Pons for the veracity of the report.  If
true, then both BYU and LANL may have duplicated the experiment, but
frustratingly, neither BYU nor LANL have yet said as much to the press.
 
The same interview gives some more clues about the process:
 
	One problem in scaling up [to larger reactors] would be getting
	the fusionable material into the metal rods, he said.  'It
	takes a long time to charge the big rods up,' he said,
	estimating that a one-inch diameter rod could take up to a year
	and a half.  That might be reduced by casting the rods in a
	deuterium environment, he added.  ...
 
	He said a neutron emitted in the fusion process undergoes a
	secondary reaction which emits a gamma ray, which they have
	measured.  'The gamma ray is of the predicted energy.'
 
	While the experiment has been portrayed in such elegantly
	simple terms, Dr Pons said there is really far more going on
	that they haven't researched fully.  Those complications
	include the role of lithium in the fusion reaction.  Lithium is
	added to the heavy water solution to help electricity flow in
	the electrode.
 
	'We have maintained that the deuterium-deuterium reaction is
	not the main heat producer...  There are other components in
	the system...  Lithium is a fine candidate right now as far as
	I'm concerned.'
 
It's amusing that Dr Pons is so devoted to the University of Utah in
spite of the state's shaky commitment to higher education.  He lives
here for much the same reasons that I live here:
 
	...  The North Carolina native said he came to the university
	five years ago because 'it's just one of the best departments
	in the country.'
 
	A skier and hiker, Dr Pons said he is 'very happy' in Salt
	Lake City.  'I love the mountains and I love the life here.
	I'm very impressed with the whole city.'
 
A political flap has arisen as a result of the fusion announcement.
Legislators are battling over whether to increase university funding to
support further fusion research.  The governor has proposed a $5
million grant, but predictably there has been conservative opposition
-- the contrary view is that work with commercial potential should be
done by commercial enterprises, not by the state.  Tuesday's political
cartoon by Bagley shows Joe Utah in his easy chair holding the sports
page in front of him, with the TV in the foreground babbling about the
fusion story; he comments to his wife: 'Just a couple more of those
deadbeat U of U professors who probably think they're too good to teach
a couple of classes...'
 
Stanley Pons was trying to teach a class yesterday, but the camera
crews were proving to be an inconvenience,
  
From:  rutgers!pnet01.cts.com!jim (Jim Bowery)
 
A quick calculation shows that if the world's entire palladium
inventory were put into a reactor producing 20watts of heat per
cubic cm, it would deliver no more power to the grid than a
single conventional fission power station.
 
Perhaps there are other materials, and perhaps there are ways to
increase the power density by orders of magnitude.  At present,
however, even if this cold fusion work is replicated, we don't
have a technology to solve global energy or greenhouse problems.
We DO have a promising new avenue of RESEARCH (not development).

        There is a new book now available on actual starship designs in 
    most mass-market bookstores.  It is titled THE STARFLIGHT HANDBOOK: 
    A PIONEER'S GUIDE TO INTERSTELLAR TRAVEL, by Eugene F. Mallove and 
    Gregory L. Matloff, John Wiley & Sons, Inc., New York, 1989, 
    ISBN 0-471-61912-4 (hardcover - $19.95).

        The authors share extensive backgrounds in aerospace engineering 
    and astronomy.  The book gives a good study of the various and varied 
    ways we may one day reach other star systems, and there is an adequate 
    supply of diagrams and mathematics to back up the engineering plans.  
    It is definitely worth a read for those who want to know what it will 
    really take to attain the 'final frontier'.

        Larry

A Book on Interstellar Travel
-----------------------------

	THE ROAD TO THE STARS,
	by Iain Nicholson,
	Westbridge Books (A Division of David & Charles)
	Brunel House, Newton Abbot, Devon
	In Canada :-
	Douglas David & Charles Limited
	1875 Welch Street, North Vancouver, BC
	ISBN 0-7153-7618-7

From the flyleaf :-

	This book reviews current and predictable technologies that will
perform a part of the human race's expansion through the galaxy. In passing it
discusses the sociological and psychological effects that will result from the
dawn of the age of man's materity, as well as pointing up the hazards and the
hindrances that will be an everyday part of interstellar exploration. Various
means of propulsion, both known and speculative, are described, and attention
is paid to the time-scales involved in interstellar travel, their effects on
terestrial society, economics and politics, and the technologies required in
order that the travellers may survive them. 

	The text is divided into three main parts: the first explains the
reasons why interstellar exploration is not only desirable but also plausable;
the second deals primarily with the technologies of transport and exploration;
and the third is concerned with the people involved, from both
sociopsychological and technological viewpoints, and closes with a discussion
of the effects that contact with other interstellar travellars may have. In
addition there is an epilogue setting the book into context via reasoned
prediction of the time-scales involved in man's progress into space over the
next ten thousand years or so. 

    	It should be pointed out that Nicholson's book was published in
    1978 and is very likely out of print.  You will probably have to go
    to a used bookstore or library to find it.
    
    	Larry
    

Article: 79427
Newsgroups: sci.space
From: [email protected] (Sam Wormley)
Subject: Re: Travelling to Alpha Centauri
Sender: [email protected] (USENET News System)
Organization: Center for Nondestructive Evaluation
Date: Fri, 10 Dec 1993 01:35:19 GMT
 
      THE UNIVERSE AND EYE
      Text by Timothy Ferris, Illustrations by Ingram Pinn, Forward by John 
       Gribbin
      Cronical Books, San Francisco  1993
      Q126.F47  1993  500--dc20  92-25619  CIP
      ISBN 0-8118-0300-7
 
      The Universe and Eye is a delightful book suitable for young readers as
      well as old. Timothy Ferris has penned a number of one- and two-page
      essays, each illustrated by an original drawing by Ingram Pinn. The
      subject matter ranges from nanotechnology to the environment to
      inflation and the big bang. Philip Morrison (book reviewer for
      Scientific American) recently praised The Universe and Eye on NPR's Talk
      of the Nation, Science Friday. This reviewer couldn't agree more. Here
      are a couple of samples:
 
      Interstellar Travel: "Interstellar travel is routine in the pages of
      science fiction tales, but most of the scientists and engineers who have
      studied the question are pessimistic about the prospect of flying to the
      stars. The cost in propellant, they note, might well exceed the total
      current energy output of the industrialized world. A starship at speed
      would have have to deflect or evade every tiny interstellar dust grain,
      each of which would pack the wallop of a cannon ball. These and many
      other high hurdles lie between here and a real-world realization of Star
      Trek.
 
      "Still, one wonders. A haunting invitation is contained in the special
      theory of relativity, which shows that the passage of time aboard a
      starship moving at nearly the velocity of light would be so much slower
      than here on Earth that astronauts could travel vast distances in
      manageable periods. If their ship could maintain a steady acceleration
      that reproduced the force of Earth's gravity, they could sail all the
      way to the Andromeda galaxy in less than thirty years of on-board time.
      But they could never return [to their own spacetime]. By the time they
      landed in Andromeda, two million years would have expired back home".
 
      Time Travel: "Theorists tilling the fertile gardens of Albert Einstein's
      general theory of relativity tell us that time travel may indeed be
      possible -- not out here in the ordinary world, where journeys into the
      past would violate fundamental laws of science and logic, but in the
      netherworld that lurks within black holes. There, on the slopes of
      steeply curving space, one might find "spacetime loops" spun in such a
      fashion that an astronaut who dove into one would emerge in the past.
      "The American physicist J. Richard Gott III, working with a conjecture
      first published by Kip Thorne, described such a scenario. "If you fell
      into a black hole you'd look for a closed time-like curve, because
      entering one would forestall your doom," Gott remarked. "If you made
      your way to an entrance you'd see, say, eleven copies of yourself. The
      first version of yourself might say, 'I've been around once,' the
      second, 'I've been around twice,' and so on. You plunge into the loop,
      fly around it, and return to see yourself entering the black hole.
      Wanting to be helpful, you call out, 'I've been around once.' You're now
      the first image of yourself that you saw when you entered. After another
      trip, again encountering your original self, you call 'I've been around
      twice.' And so on, until, after eleven times around, you leave the loop,
      only to be killed a short time later when you crash into the singularity
      at the center of the black hole."
 
                                                             -S. Wormley

Article: 79439
Newsgroups: sci.space
From: [email protected] (Henry Spencer)
Subject: Re: Travelling to Alpha Centauri
Date: Fri, 10 Dec 1993 03:14:23 GMT
Organization: U of Toronto Zoology
 
In article <[email protected]>
[email protected] (Sam Wormley) writes: 

>    Interstellar Travel: "Interstellar travel is routine in the pages of
>    science fiction tales, but most of the scientists and engineers who have
>    studied the question are pessimistic about the prospect of flying to the
>    stars. The cost in propellant, they note, might well exceed the total
>    current energy output of the industrialized world. A starship at speed
>    would have have to deflect or evade every tiny interstellar dust grain,
>    each of which would pack the wallop of a cannon ball. These and many
>    other high hurdles lie between here and a real-world realization of Star
>    Trek.
 
Ferris has spent too much time listening to Carl Sagan and not enough
reading JBIS.  Most of the problems he alludes to have solutions, things 
we can confidently expect to build within a century, if not today. 
 
There are people -- Sagan seems to be one of them -- who apparently
*want* to believe that interstellar travel is impossible.  The facts
no longer support this belief, as Enrico Fermi realized nearly half a
century ago. 
 
The energy problem is the fundamental one.  It's indeed serious... but
plot the amount of energy available to mankind versus time and you find 
there is reason for optimism.  Compare the output of one large power 
plant today to that of the industrialized world a hundred years ago. 
 
Bear in mind that there are people alive today who remember a time
when man could not fly, radio did not exist, "antibiotic" was not a
word, and most of the population were, of necessity, farmers.  The
world has changed beyond recognition in one lifetime.  We can
confidently speak of what is possible today, somewhat less confidently
of what will be possible twenty years from now... but claims that
something will remain impossible a century or a millennium from now
are meaningless blather. 
-- 
Belief is no substitute                 | Henry Spencer @ U of Toronto Zoology
for arithmetic.                         |  [email protected]  utzoo!henry

Article: 79370
From: [email protected] (Bill Higgins-- Beam Jockey)
Newsgroups: sci.space
Subject: Propulsion FAQ (was Re: Journey to A-Centauri) (long)
Date: 9 Dec 93 11:00:35 -0600
Organization: Fermi National Accelerator Laboratory
 
In article <[email protected]>, <[email protected]> writes:

> Suppose funding is not a problem.  Based on our existing knowledge/technology,
> is there anyway for earthlings to set foot on A-Centauri or any other systems?
> Clearly, our existing vechicle couldn't handle interstellar travels.
> 
> Can anyone recommend me some books/info on this subject?
> 
> Thanks.
> 
> Ken Tai.
 
[Oh, boy.  I get to use my recently developed "boilerplate FAQ answer."]
 
The Frequently Asked Questions (FAQ) list for the Usenet newsgroup
sci.space has information relevant to your question.  It is posted
every month to sci.space with a long expiration time, so you can
probably find it on your system.  If not, there are other ways to
obtain it.
 
The FAQ postings are available by anonymous FTP from the Ames SPACE
archive in ames.arc.nasa.gov:pub/SPACE/FAQ/faq*, along with more
information expanding on topics in the FAQ.
 
I append some useful sections, but you might like to read the entire
FAQ list.
 
     O~~*           /_) ' / /   /_/ '  ,   ,  ' ,_  _           \|/
   - ~ -~~~~~~~~~~~/_) / / /   / / / (_) (_) / / / _\~~~~~~~~~~~zap!
 /       \                          (_) (_)                    / | \
 |       |     Bill Higgins   Fermi National Accelerator Laboratory
 \       /     Bitnet:     [email protected]
   -   -       Internet:  [email protected]
     ~         SPAN/Hepnet:      43011::HIGGINS 
 
===================
[At this point I append a chunk of the FAQ that seems to be helpful to Ken.]
 
From: [email protected] (Jon Leech)
Newsgroups: sci.astro,sci.space,sci.answers,news.answers
Subject: Space FAQ 05/13 - References
Supersedes: <[email protected]>
Followup-To: poster
Date: 1 Dec 1993 23:15:29 -0500
Organization: University of North Carolina, Chapel Hill
Lines: 700
Approved: [email protected]
Distribution: world
Expires: 6 Jan 1994 04:15:26 GMT
Message-ID: <[email protected]>
References: <[email protected]>
NNTP-Posting-Host: watt.cs.unc.edu
Keywords: Frequently Asked Questions
Xref: fnnews.fnal.gov sci.astro:33646 sci.space:44709 sci.answers:689
      news.answers:15536 
 
[...the following is only an excerpt from tfile , which is itself part 5 of
the 13-part FAQ compiled by Jonathan Leech.]
 
    ESOTERIC PROPULSION SCHEMES (SOLAR SAILS, LASERS, FUSION...)
 
    This needs more and more up-to-date references, but it's a start.
 
    ANTIMATTER:
 
	"Antiproton Annihilation Propulsion", Robert Forward
	    AFRPL TR-85-034 from the Air Force Rocket Propulsion Laboratory
	    (AFRPL/XRX, Stop 24, Edwards Air Force Base, CA 93523-5000).
	    NTIS AD-A160 734/0	   PC A10/MF A01
	    PC => Paper copy, A10 => $US57.90 -- or maybe Price Code?
	    MF => MicroFiche, A01 => $US13.90
 
	    Technical study on making, holding, and using antimatter for
	    near-term (30-50 years) propulsion systems. Excellent
	    bibliography. Forward is the best-known proponent
	    of antimatter.
 
	    This also may be available as UDR-TR-85-55 from the contractor,
	    the University of Dayton Research Institute, and DTIC AD-A160
	    from the Defense Technical Information Center, Defense Logistics
	    Agency, Cameron Station, Alexandria, VA 22304-6145. And it's
	    also available from the NTIS, with yet another number.
 
	"Advanced Space Propulsion Study, Antiproton and Beamed Power
	    Propulsion", Robert Forward
 
	    AFAL TR-87-070 from the Air Force Astronautics Laboratory, DTIC
	    #AD-A189 218.
	    NTIS AD-A189 218/1	  PC A10/MF A01
 
	    Summarizes the previous paper, goes into detail on beamed power
	    systems including " 1) pellet, microwave, and laser beamed power
	    systems for intersteller transport; 2) a design for a
	    near-relativistic laser-pushed lightsail using near-term laser
	    technology; 3) a survey of laser thermal propulsion, tether
	    transportation systems, antiproton annihilation propulsion,
	    exotic applications of solar sails, and laser-pushed
	    interstellar lightsails; 4) the status of antiproton
	    annihilation propulsion as of 1986; and 5) the prospects for
	    obtaining antimatter ions heavier than antiprotons." Again,
	    there is an extensive bibliography.
 
	    "Application of Antimatter - Electric Power to Interstellar
	    Propulsion", G. D. Nordley, JBIS Interstellar Studies issue of
	    6/90.
 
    BUSSARD RAMJETS AND RELATED METHODS:
 
	G. L. Matloff and A. J. Fennelly, "Interstellar Applications and
	Limitations of Several Electrostatic/Electromagnetic Ion Collection
	Techniques", JBIS 30 (1977):213-222
 
	N. H. Langston, "The Erosion of Interstellar Drag Screens", JBIS 26
	(1973): 481-484
 
	C. Powell, "Flight Dynamics of the Ram-Augmented Interstellar
	Rocket", JBIS 28 (1975):553-562
 
	A. R. Martin, "The Effects of Drag on Relativistic Spacefight", JBIS
	25 (1972):643-652
 
    FUSION:
 
	"A Laser Fusion Rocket for Interplanetary Propulsion", Roderick Hyde,
	LLNL report UCRL-88857. (Contact the Technical Information Dept. at
	Livermore)
 
	    Fusion Pellet design: Fuel selection. Energy loss mechanisms.
	    Pellet compression metrics. Thrust Chamber: Magnetic nozzle.
	    Shielding. Tritium breeding. Thermal modeling. Fusion Driver
	    (lasers, particle beams, etc): Heat rejection. Vehicle Summary:
	    Mass estimates. Vehicle Performance: Interstellar travel
	    required exhaust velocities at the limit of fusion's capability.
	    Interplanetary missions are limited by power/weight ratio.
	    Trajectory modeling. Typical mission profiles. References,
	    including the 1978 report in JBIS, "Project Daedalus", and
	    several on ICF and driver technology.
 
	"Fusion as Electric Propulsion", Robert W. Bussard, Journal of
	Propulsion and Power, Vol. 6, No. 5, Sept.-Oct. 1990
 
	    Fusion rocket engines are analyzed as electric propulsion
	    systems, with propulsion thrust-power-input-power ratio (the
	    thrust-power "gain" G(t)) much greater than unity. Gain values
	    of conventional (solar, fission) electric propulsion systems are
	    always quite small (e.g., G(t)<0.8). With these, "high-thrust"
	    interplanetary flight is not possible, because system
	    acceleration (a(t)) capabilities are always less than the local
	    gravitational acceleration. In contrast, gain values 50-100
	    times higher are found for some fusion concepts, which offer
	    "high-thrust" flight capability. One performance example shows a
	    53.3 day (34.4 powered; 18.9 coast), one-way transit time with
	    19% payload for a single-stage Earth/Mars vehicle. Another shows
	    the potential for high acceleration (a(t)=0.55g(o)) flight in
	    Earth/moon space.
 
	"The QED Engine System: Direct Electric Fusion-Powered Systems for
	Aerospace Flight Propulsion" by Robert W. Bussard, EMC2-1190-03,
	available from Energy/Matter Conversion Corp., 9100 A. Center
	Street, Manassas, VA 22110.
 
	    [This is an introduction to the application of Bussard's version
	    of the Farnsworth/Hirsch electrostatic confinement fusion
	    technology to propulsion. 1500<Isp<5000 sec. Farnsworth/Hirsch
	    demonstrated a 10**10 neutron flux with their device back in
	    1969 but it was dropped when panic ensued over the surprising
	    stability of the Soviet Tokamak. Hirsch, responsible for the
	    panic, has recently recanted and is back working on QED. -- Jim
	    Bowery]
 
	"PLASMAKtm Star Power for Energy Intensive Space Applications", by
	Paul M. Koloc, Eight ANS Topical Meeting on Technology of Fusion
	Energy, special issue FUSION TECHNOLOGY, March 1989.
 
	    Aneutronic energy (fusion with little or negligible neutron
	    flux) requires plasma pressures and stable confinement times
	    larger than can be delivered by current approaches. If plasma
	    pressures appropriate to burn times on the order of milliseconds
	    could be achieved in aneutronic fuels, then high power densities
	    and very compact, realtively clean burning engines for space and
	    other special applications would be at hand. The PLASMAKtm
	    innovation will make this possible; its unique pressure
	    efficient structure, exceptional stability, fluid-mechanically
	    compressible Mantle and direct inductive MHD electric power
	    conversion advantages are described. Peak burn densities of tens
	    of megawats per cc give it compactness even in the
	    multi-gigawatt electric output size. Engineering advantages
	    indicate a rapid development schedule at very modest cost. [I
	    strongly recommend that people take this guy seriously. Bob
	    Hirsch, the primary proponent of the Tokamak, has recently
	    declared Koloc's PLASMAKtm precursor, the spheromak, to be one
	    of 3 promising fusion technologies that should be pursued rather
	    than Tokamak. Aside from the preceeding appeal to authority, the
	    PLASMAKtm looks like it finally models ball-lightning with solid
	    MHD physics. -- Jim Bowery]
 
    ION DRIVES:
 
	Retrieve files pub/SPACE/SPACELINK/6.5.2.* from the Ames SPACE
	archive; these deal with many aspects of ion drives and describe the
	SERT I and II missions, which flight-tested cesium ion thrusters in
	the 1960s and 70s. There are numerous references.
 
    MASS DRIVERS (COILGUNS, RAILGUNS):
 
	IEEE Transactions on Magnetics (for example, v. 27 no. 1, January
	1991 issue). Every so often they publish the proceedings of the
	Symposium on Electromagnetic Launcher Technology, including hundreds
	of papers on the subject. It's a good look at the state of the art,
	though perhaps not a good tutorial for beginners. Anybody know some
	good review papers?
 
    NUCLEAR ROCKETS (FISSION):
 
	"Technical Notes on Nuclear Rockets", by Bruce W. Knight and Donald
	Kingsbury, unpublished. May be available from: Donald Kingsbury,
	Math Dept., McGill University, PO Box 6070, Station A, Montreal,
	Quebec M3C 3G1 Canada.
 
    SOLAR SAILS:
 
	Starsailing. Solar Sails and Interstellar Travel. Louis Friedman,
	Wiley, New York, 1988, 146 pp., paper $9.95. (Not very technical,
	but an adequate overview.)
 
	"Roundtrip Interstellar Travel Using Laser-Pushed Lightsails
	(Journal of Spacecraft and Rockets, vol. 21, pp. 187-95, Jan.-Feb.
	1984)
 
    TETHERS:
 
	_Tethers and Asteroids for Artificial Gravity Assist in the Solar
	System,_ by P.A. Penzo and H.L. Mayer., _Journal of Spacecraft
	and Rockets_ for Jan-Feb 1986.
 
	    Details how a spacecraft with a kevlar tether of the same mass
	    can change its velocity by up to slightly less than 1 km/sec. if
	    it is travelling under that velocity wrt a suitable asteroid.
 
	"Tethers in Space Handbook, 2nd Edition", Paul A Penzo & Paul W
	Ammann. NASA Office of Advanced Program Development, 1989.
	    NTIS N92-19248/3	  PC A12/MF A03
 
	    It may be possible to obtain this handbook from:
		NASA Office of Advanced Program Development
		NASA HQ Code DD
		Washington, DC 20546
 
	NASA Conference Publication 2422
	Applications of Tethers in Space
	Workshop Proceedings Vols 1 and 2.
	[Proceedings of a workshop held in Venice, Italy, Octover 15-17, 1985]
 
    GENERAL:
 
	"Alternate Propulsion Energy Sources", Robert Forward
	    AFPRL TR-83-067.
	    NTIS AD-B088 771/1	  PC A07/MF A01   Dec 83 138p
 
	    Keywords: Propulsion energy, metastable helium, free-radical
	    hydrogen, solar pumped (sic) plasmas, antiproton annihiliation,
	    ionospheric lasers, solar sails, perforated sails, microwave
	    sails, quantum fluctuations, antimatter rockets... It's a wide,
	    if not deep, look at exotic energy sources which might be useful
	    for space propulsion. It also considers various kinds of laser
	    propulsion, metallic hydrogen, tethers, and unconventional
	    nuclear propulsion. The bibliographic information, pointing to
	    the research on all this stuff, belongs on every daydreamer's
	    shelf.
 
	Future Magic. Dr. Robert L. Forward, Avon, 1988. ISBN 0-380-89814-4.
 
	    Nontechnical discussion of tethers, antimatter, gravity control,
	    and even futher-out topics.
 
[Hey, Jon, how come this book isn't in the General section?
 
      Eugene F. Mallove and Gregory L. Matloff, THE STARFLIGHT
       HANDBOOK: A PIONEER'S GUIDE TO INTERSTELLAR TRAVEL, 1989
 
It's probably the best semi-technical introduction to interstellar
flight.  It's buried in Larry Klaes's list of interPLANETARY flight books in
part 8/13.]

Article: 80281
Newsgroups: sci.space
From: [email protected] (al jackson)
Subject: Re:Bussard Ram
Sender: [email protected] (USENET News Client)
Organization: Solar System Exploration Division, NASA JSC
Date: Tue, 21 Dec 1993 15:51:27 GMT
 
Some of the basic papers are:
 
R.W. Bussard, GALACTIC MATTER AND INTERSTELLAR FLIGHT, Astronautica
Acta, vol 6., 179 - 194. (1960) 
 
This is an amazing paper, maybe even more farsightedly than the great
interstellar flight papers by Saenger. 
 
D.P. Whitmire, RELATIVISTIC SPACEFLIGHT AND THE CATALYTIC NUCLEAR
RAMJET, Acta Astronautica , vol 2, 497 - 509. (1975) 
 
I always thought our paper on the laser powered interstellar ramjet
was a nice modification of the straight ramjet. 
 
D.P. Whitemire and A.A. Jackson LASER POWERED INTERSTELLAR RAMJET
Journal of the British Interplanetary Society vol 30, no 6 p 223 - 226
 
Carl Sagan's exposition on the Bussard ram in Communication with
Extraterrestrial Intelligence is quite good, I think there is a
reference to an Icarus paper by him that is good too. 
 
The book BOUND FOR THE STARS and what is the book by Gene Malove...
about interstellar flight...?... have very extensive references. 
 
Al Jackson
 

Article: 80462
Newsgroups: sci.space
From: [email protected] (JACKSON)
Subject: Re:Bussard Ramjet
Sender: [email protected] (USENET News Client)
Organization: Organization, City, State, etc.
Date: Fri, 24 Dec 1993 11:01:28 GMT
 
This is a follow up for whoever asked about sources of material about
interstellar flight and the Bussard Interstellar Ramjet.  The following
are the best introductions and have the most extensive biography of
technical articles: 
 
THE ROAD TO THE STARS
Iain Nicholson
William Morrow and Company, Inc.
New York, 1978
 
THE STARFLIGHT HANDBOOK
A PIONEER'S GUIDE TO INTERSTELLAR TRAVEL
Eugene F. Mallove and Gregory L. Matloff
John Wiley and Sons, Inc
New York, 1989.
 
And for whoever asked about using antimatter with an interstellar
ramjet see: 

A.A. Jackson
Some Considerations on the Antimatter and Fusion Ram Augmented
Interstellar Rocket, Journal of the British Interplanetary Society
V. 33, PP 117-120, (1980)
 

From:	US4RMC::"[email protected]" "belbruno" 25-MAY-1994 16:04:45.53
To:	[email protected]
CC:	
Subj:	Conference: "PRACTICAL ROBOTIC INTERSTELLAR FLIGHT: ARE WE READY?"

                ************  ANNOUNCEMENT  **************

      The conference entitled,

      PRACTICAL ROBOTIC INTERSTELLAR FLIGHT: ARE WE READY? 

      will be held at New York University and the United Nations

      from August 29 - September 1, 1994. 

      The principal sponsor is The Planetary Society.

      Other sponsors include The British Interplanetary Society, The
      United Nations Outer Space Office, Jet Propulsion Laboratory,
      Mission From Planet Earth Study Office - NASA HQ,
      Geometry Center, National Space Society, Space Studies Institute,
      World Space Foundation, American Astronautical Society, New York
      University, American Astronomical Society, Mondo-tronics, Inc.

      The two topics focused on are 1.) Feasibility of performing a robotic
      interstellar mission in the near term that is both affordable and has
      a short flight time, and 2.) The search of planets orbiting nearby
      stars.

       ***************************************************************
        The keynote speakers are Dr. Robert Forward, and Dr. Carl
        Pilcher, Chief, Mission From Planet Earth Study Office, NASA HQ.
       ***************************************************************

      Other main speakers include Dr. Michael Klein of JPL, Dr. Richard
      Terrile also of JPL, and Dr. David Brin.

      Sessions are divided into 1. Interstellar Flight Concepts( Astro-
      dynamics, Propulsion), 2. Engineering Aspects(Miniturization,
      Electronics, Communications, Attitude Control) 3. Extra-solar
      Planetary Systems(Results, Methods), 4. Intermediate Prestellar
      Destinations(Heliopause, Oort Cloud, Gravitational Lense of the Sun)

                              *******
      A public event is planned to be held at the United Nations on the
      evening of the 30th which is sponsored by The Planetary Society.
      It will be held in the Dag Hammarskjold Auditorium at 6-9:00 PM.
      All technical sessions will be held at New York University in
      Greenwich Village.
                              *******

      The Organizing Committee is Edward Belbruno(Chair, Geometry Center),
      Louis Friedman(Planetary Society), William McLaughlin(JPL),
      Gregory Matloff(NYU), Thomas McDonough(Caltech), Gary Bennett(NASA),
      Bruno Augustine(Rand),Giovanni Vulpetti(British Interplanetary Society),
      Seth Potter(NYU)
      *****************************************************************

      For information on registration, abstract submittal, program, please
      contact Dr. Edward Belbruno at The Geometry Center; University of
      Minnesota; 1300 South Second Street; Minneapolis MN 55101, or
      call (612)626-1845, FAX (612)626-7131, e-mail [email protected].

      Abstract submittal deadline is July 15, 1994.
      Early Registration Deadline is July 15, 1994.

      The Registration fee prior to July 15 is $150, and $190 after July 15.
      Registration includes four days of technical sessions at NYU, Public
      event at the UN, and a dinner.  Checks made payable to Innovative Orbit
      Design at the above address.(10% discount if a member of a cosponsoring
      organization.)      

% ====== Internet headers and postmarks (see DECWRL::GATEWAY.DOC) ======
% From: [email protected] (belbruno)
% Newsgroups: sci.space.news
% Subject: Conference: "PRACTICAL ROBOTIC INTERSTELLAR FLIGHT: ARE WE READY?"
% Date: 25 May 1994 12:35:28 -0700
% Organization: The Geometry Center, University of Minnesota
% Approved: [email protected]
% Distribution: world
% Originator: [email protected]
% Apparently-To: [email protected]

Article: 3227
From: [email protected] (Kev OBoyle)
Newsgroups: sci.space.tech
Subject: Re: Interstellar propultion system
Date: 25 Aug 1994 17:22:02 -0400
Organization: America Online, Inc. (1-800-827-6364)
 
In article <[email protected]>, [email protected] (MATTHEW
JONES) writes:
 
>In the Guardian (UK newspaper) today, it was reported that a Uni of
>Wales guy called Miguel Alcubierre, had a workable (!) warp drive
>theory, where the drive system inflates spacetime behind the craft,
>while simultaneously contracting it in front. The craft experiences no
>adverse relativistic effects apparently, as it travels, as far it is
>concerned in a bubble of normal spacetime, while traveling at
>super-light speed!
 
Damn!! I'm a never published science fiction author/hobbist (really a
computer consultant), and that was my idea!!!  One of the really cool side
effects of this concept (which I call "Gravity surfing") is that in a
region of space where external gravitational sources are distributed
evenly then the colapsed space infront of the traveler would appear to be
more massive than the inflated space behind so in effect the ship could
freefall  toward the carrot of "dense" space and as it moves forward so
does its target. (also, the premise of a good artifical gravity system).
So, how many people know whats missing here??  
 
...The mechanism. We are talking about bending space/time: No small
feat there!  I concocted a method where certain atomic nuclei like Fe
(which is extremely well ordered and dense)  are set to spin in a
magnetic field and bombarded with protons.  When the protons hit the
Iron Atom the atom spins asymetrically for a moment producing a micro
gravity wave. Through some-- admittedly black box-- MAZER effect the
gravity wave is propagated and magnified through several strata of
spinning iron nuclei until a large curve in space is produced. Voila,
Warp Drive.  Anyhow, it works for me (but I'm not a physicist). 
 
A more conventional star ship would probably employ several different
technologies.  Built propperly, A small Ion driven vessel could utilize
gravity assist and a mile wide gossimer parasol (which of course has
wonderful magneto-electric properties) to exit the helio-pause via moon
based Laser cannon and solar wind, then invert the parabola of the parasol
(or face the opposite direction whichever is easiest) send an oscelating
magnetic field through it and scoop up all the interstellar particles in
its path with this. The Particles would then be focused  and excelerated
(again using electro Magnetics ).  Finally, just as they are being ejected
out of the back of your ship, you'd burn them with Ions (or photons) so
they yield forth every ounce of inertia.  Your parasol acts as a radiation
shield stearing energized particles into the engine and you can fly around
at about 1/4 the speed of light.  The big thing is leaving the helio-pause
with enough inertia to engage the RAM scoop.  
 
I'd love to get feedback no any of these ideas.
 
E-mail me at:    kev oboyle @ AOL.com
 
Oh, also, I'd REALLY appreciate any more info on the Miguel Alcubierre
Warp Drive.
 
Thanks,

Kevin O'Boyle
Kevin M. OBoyle