Conference 7.286::space

     Can some one please tell me just what is the Orian type propulsion,
    is it some kind of rocket?? What about Nuclear rockets, I have never
    heard anything about them. Why are the banned?? do they produce
    fallout, nuclear contamination or something??
    
    
                                     Jack

    	ORION nuclear rockets were originally conceived in the late
    1950's as interplanetary vehicles for the next decade.  Later on,
    Freeman Dyson "took over" the concept and modified it for interstellar
    travel.  The idea is that 300,000 nuclear bombs would be stored
    in the ship, and ejected out its rear one bomb every three seconds, 
    where they would detonate just behind the ship and create shock
    waves, which would strike a huge "pusher plate" - essentially "kicking
    along" the ORION craft to Alpha Centauri (4.3 light-years away) in
    130 years.  Not incredibly fast, but much better than what any chemical
    rocket could achieve.
                       
    	The United Nations' 1963 Outer Space Test Ban Treaty - which
    made it illegal to explode nuclear devices in Earth's atmosphere,
    oceans, or space (only underground is still allowed) - effectively
    ended any real testing of ORION, but planners still hold out for
    the future implementation of the craft, as it is one of the few
    starships which could be built with today's technology.  There
    are problems with ORION, but this discussion should be reserved
    for the Star Probe Note 212.
                           
    	Larry
    

    A non-nuclear Orion vehicle was actually flight tested, using high
    explosives.
    
    gary

    	When did this occur, who did the test, where in space did this
    test take place, and what were the results?
    
    	Larry
    

    The UN 1963 test band was actually a scientific discover of what
    happens when nuck bombs are set off in the earth's atmosphere. 
    The US and Russian , as the rumor goes, found out about it about
    the same time.  The results was a political decision , maybe a good
    idea as it was a sign of good faith but based on scientific reason.
    
    This is just a rumor, does anyone know how true it is?
    
    Also the ORION type space craft has only been used in SF books
    as far as I know with Nuck power (footfall by larry niven etc)
    
    jb
    

     Sorry I got off the subject, I just had never heard of the ORIAN
    Before. I now know why, it's sounds like a pretty far fetched and
    dangerous idea.
    
    
                                              Jack

    re .4
    
    I cannot find a reference in my library so its probably buried in
    an old AW&ST somewhere. If I remember correctly, the non-nuclear
    test was called 'Putt-Putt' and was powered by small high-explosive
    charges. It was an atmospheric test and was successful in that it
    flew (how well I don't know). Funding was from DARPA.
    
    It dates from the era of 'lets build one and fly it' rather than
    the current 'lets simulate it to death first' attitudes.
    
    gary
        

I think Freeman Dyson mentioned in his autobiography "Disturbing the 
Universe" that they tested a model of the Orion at General Atomic in 
San Diego in the early Sixties.  Another place that might discuss it 
is John McPhee's book about Ted Taylor, "The Curve of Binding Energy".
Taylor had the rare job of conceptual A-bomb designer.  He designed 
the largest and smallest fission bombs ever set off.  He and Dyson 
were the ones behind Orion.

Back to laser launching, though: How do you keep the exhaust from 
blocking the laser beam?  Or does the laser go in the side?  If it 
does, how do you keep the window in the fuel tank from burning up?

/jlr

     	The book mentioned in the previous reply sounds fascinating,any
    chance of details such as publisher etc as I'd like to get hold
    of it
    
    			Dennis

Newsgroups: sci.space
Path: decwrl!nsc!voder!lewey!evp
Subject: Re: Laser Launched Rockets and Reactors in Space
Posted: 12 Feb 87 04:47:00 GMT
Organization: American Information Technology, Cupertino, CA
Posted: Wed Feb 11 20:47:00 1987
 
in article <[email protected]>, [email protected] (Mark Muhlestein) says:
% 
%> > ...  Beam the laser down, and have the rocket ride the beam up.
%> > Since clouds are primarily a low-atmosphere phenomenon (and the
%> > ones higher up are thin), the rocket could be equipped with standard
%> > jets to get above the atmospheric junk.  Then fire up the laser,
%> > and sail off on a light beam...
%> 
%> ... 
%> Oh well.  Now for the hard part.  Building and launching the laser booster
%> and its power supply.  What kind of a power supply do you need? ...
% 
% How feasable would it be to have a satellite in geosynchronous orbit
% either:
% 
% 1) generate energy from a large array of solar cells to power a laser?
% 
% 	or
% 
% 2) build a really big solar reflector (dynamically focussable paraboloid)
%    and power the rocket directly?
 
 
I'll try to tackle some of these questions.
 
================
 
First question is: how much power are we talking about?  Answer: a
whole lot.  Using the space shuttle as a model, we can get some
ballpark estimates.  At takeoff, the shuttle weighs almost exactly
2.0e6 kg, including solids and fuel.  A lot of this is just a crude
way of getting it above the atmosphere, and not really accelerating it
to orbital velocity.  Assume for a moment that we have a nice friendly
first stage that can get it up to 100000 ft and mach 3.  We now drop
the shuttle and fuel tank and let the orbital laser have at it.  This
gives us a starting mass something below 1.0e6 kg -- I used 640e3 kg
for my analysis only because that's as much as the current main
engines can push at 1g.  (3 engines, 2091kNt vacuum thrust each.)  By
the time you reach orbital velocity, the reaction mass is all used up,
and the shuttle (with cargo) masses about 165000 + 30000 = 195e3 kg.
The average mass over the time of acceleration is therefore
(195e3+640e3)/2 = 417e3 kg. 
 
We are trying to accelerate 417e3 kg to orbital velocity -- 7.6
km/sec.  The energy needed to accomplish this is (m*v^2)/2, or about
12e12 joules.  If we are doing the work at 3g, which is the top limit
for the shuttle (due to cargo constraints), our time to orbit is 7.6
km/sec divided by 3*9.8 m/sec^2 or 259 sec: about 4.3 minutes.  During
this time, the average power is 12e12 joules divided by 259 seconds,
or 46.4e9 watts.  A typical commercial nuclear power plant generates
one gigawatt -- we need 46 of them. 
 
As an aside, the laser beam generates some momentum itself.  The
momentum of a photon is equivalent to its energy divided by C, so the
beam applies a total of 12e12/300e6 = 40e3 kg-m/sec of momentum to
both the laser and the shuttle -- about 156 Nt (or 35 pounds) of
thrust during the time power is supplied.  Considering how much a
46GWt power plant must weigh, this is fairly small, but with
continuous use it could cause major changes in the orbit. 
 
================
 
Second question: how about solar power?  The "solar constant" is the
power density of solar radiation at the earth's orbital distance --
1340 Watts/m^2.  Assuming perfect conversion, you need 12e12/1340 =
8.96e9 square meters of collection area, or a circular collector 100km
in diameter.  Naturally, if you can find a way to store up 12e12
joules when you're not firing the laser, you can cut your power
requirements considerably.  (This is not an option if your collector
is a simple reflector.) 
 
Again, the beam applies a small but significant thrust to the
collector.  In this case, since we are reflecting the light instead of
generating it onboard, the momentum imparted is doubled.  We have a
fairly decent solar sail here (if it's light weight). 
 
================
 
Enough ramblings.  The point is, you need a whole heap of energy to
get a shuttle into orbit -- a substantial fraction of the world's
current energy generating capacity for a few minutes.  If you ever get
an opportunity to see a launch in person, you'll understand just how
much power that amounts to. 
 
-- 
Ed Post -- hplabs!lewey!evp
American Information Technology    (408)252-8713

Newsgroups: sci.space
Path: decwrl!hplabs!sdcrdcf!psivax!nrcvax!nrc-ut!iconsys!mmm
Subject: Re: Laser Launched Rockets and Reactors in Space
Posted: 10 Feb 87 03:38:52 GMT
Organization: 
 
How feasable would it be to have a satellite in geosynchronous orbit
either:
 
1) generate energy from a large array of solar cells to power a laser?
 
	or
 
2) build a really big solar reflector (dynamically focussable paraboloid)
   and power the rocket directly?
 
I really don't have the background to do the relevant calculations,
but it seems that if you had a manufacturing capability in space
(probably lunar), either of these might be a cost-effective solution. 
They could be centered over the eastern coast of any equatorial area
with lots of empty ocean to the east for minimum danger in case of
mis-pointing. 
--  
	Mark Muhlestein @ Icon International Inc.
 
{ihnp4,decvax,seismo!ut-sally}utah-cs!utah-gr!uplherc!nrc-ut!iconsys!mmm

Reply to Note 247.1 by PRANCR::HUNTER 

What about Nuclear rockets, I have never heard anything about them. Why are the
banned?? do they produce fallout, nuclear contamination or something??
    
                                                                     
        Nuclear rockets work by rapidly heating the propellant by
        passing it through a radioactive core. It is basically a
        Nuclear Power Plant squirting itself across the sky.

        Can you imagine the public (much less the Greens) response to
        the idea? Especially with the relatively underreported Soviet
        nuclear-powered satellite crash as a precedent.

        My memory is that the propellant is not made radioactive due
        to the extremely short time it is in the core.

        Jack Wickwire