Conference 7.286::space

  There are a number of things that make the space effort expensive. I can
think of 3 major reasons, Mach 5+ flight, twin environment requirements, and
no economy of scale.

  Mach 5 +
  --------
  I think I mentioned once before an article I read saying that Mach 5 aircraft
were much more expensive to build and operate than Mach 3 aircraft because of
two things, the dramatic increase in heat problems that start happening around
Mach 5 and the expense of the engines. 

  Aircraft that operate below Mach 3 can be build out of cheap materials and
can use off the shelf turbo fan engines mass produced by GE or Pratt and
Whitney. Mach 5 + aircraft must be built out of very expensive materials and
need very expensive rocket engines that usually burn liquid hydrogen or solid
fuel which is both expensive and dangerous to handle. 

  Twin Environments
  -----------------
  Another things that makes space flight so expensive is that a space craft
must be able to live in two environments, flight through the atmosphere and
space. While there are amphibious aircraft, think of all the failed attempts to
build two environment vehicles.

  An attempt was made back in the 50's to build a car that was also a boat, but
in spite of many weekend boaters it was never very popular. There was also talk
back in the 60's of a combination car and general aviation aircraft but the only
flying car ever seen is in a James Bond movie. And while there are amphibious
aircraft they are generally small, expensive to operate, and have limited
use.

  By contrast, not only does a space craft have to live in two environments,
they are two harsh environments, Mach 5+ flight and space. You might be able to
put pontoons on a DC-9, but imagine if you wanted to convert one into a
submarine that could survive depths down to 1000 feet, come to the surface,
take off and fly at Mach 5. The problems would only start to approach what
a space craft has to do on every flight.

  No Economy of Scale
  -------------------
  If you look at the cost of supporting airlines in the United States and
include aircraft manufacturing and maintenance, flight crews, ground crews,
runways, hangers, ramps, and the air traffic control system. I think you'd have
a bill that exceeded space flight. One big difference is that they fly a lot of
airplanes and each one takes in revenue. 

  Imagine if you cut back the airlines and said that there were only going to
be 2 airports, LAD and Miami International, Boeing would still build 757's to
fly the route, but only one every 5 years and they would only make 10 flights
per year. 

  If you think about it, you'd still need trained engineers at Boeing to build
and maintain the aircraft, a hanger full of engineers to fix them, takeoff and
landing facilities, pilots and crews and the like yet revenue would go near
zero. That's the situation for space flight when you have 3 or 4 of each type
of space craft operating 10 times or less per year.

  So when you add those reasons together, harsh environment, twin environment,
and no economy of scale, it makes sense that it is very expensive to fly into
space relative to running an airline. 

  George 

    Re: .-1

    I'm not sure I buy that as an explanation (although I've not one
    to offer as a replacement).

    Consider, we and the Soviets got the German scientists and a few
    V2 rockets in 1945.  Just over a decade later we have Sputnik in
    orbit.  Less than a decade later we have manned lunar
    landings/returns along with a tremendous variety of military and
    non-military launch vehicles for sub-orbital, orbital, and even
    extra planetary and extra sol-system velocities and payloads.  I'm
    sure that a lot of the costs never were recorded in a ledger that
    the public saw due to the military nature of much of the impetus,
    but I'd be real surprized if, adjusted for inflation, we're
    getting as much launch capability for the dollar today they were
    getting in, say, 1968 or so.  And I would never expect efficiency
    from a military organization - steady progress, accountability,
    first-class facilities, yes; efficiency and low-cost, no.

    This was all done in the era of the slide-rule, manual drafting,
    standard structural components, manual or punched-tape machining,
    and where every step was an experiment (we blew up a lot of the
    early launch attempts).  I mean most of this was accomplished
    before IBM even came out with the 360 series mainframe or Digital
    with the PDP-8 mini.

    Now we've got number-crunchers of all sorts and prices, solids
    modeling that can ensure three-dimensional movement without
    interferences, all sorts of dynamic system modelling (finite
    element, etc.), manufacturing capabilities that are automated and
    repeatable and precise to tolerences that were unheard of outside
    the nuclear weapons industry, micro-electronics that can be
    embedded in control circuits that have more computational
    capability than was available to all of the *designers* of the
    Saturn-V, super alloys of all sorts (single-crystals, powder and
    ion depositions, super coatings), lightweight structural
    components (all sorts of composits and ceramics and hybrids), and
    I'm sure there's been major advances in various chemical fuels
    (e.g. various hypergolics and the solid fuels).  And we know a
    whole lot more about getting a payload off the ground, through an
    atmosphere safely, and back again.

    Yet progress over the 25 years since the moon landings has seemed
    to come to an absolute snail's pace while the cost per pound of
    payload remains far beyond all but the most wealthy private
    corporations and other than low-earth orbits or geo-synch
    satellites we have virtually no cost-effective bus.

	Mike

  It's not so much that space flight didn't cost much during the Apollo
program, (the costs were high even back in the 60's) it's more a matter of the
public being willing to pick up the tab. I remember hearing once that each
Saturn V launch costs something like $600,000,000 which was quite a bit back in
those days. In fact, the reason that the program was stopped after Apollo XVII
was due to cost and a feeling that the money should be "spent back here on
earth". 

  And while the cost of computers is coming down, computation power has always
been a relatively small part of the total budget. The costs of producing things
necessary to make reusable space craft remain high while the design of these
craft become more complex. Also, much of space flight is labor intensive and
the people working in the program tend to be professionals with relatively high
salaries. 

  So when you add together the high prices associated with harsh environments,
multiply environments, no economy of scale, they lead to the problems of high
development costs, labor intensive work, and no return on investment. That was
true back in the 60's and it's true today. The only difference was that back
then we were more willing, as a nation, to foot the bill. 

  George 

    
    Re .1-.3
    
    What you guys are saying is that the Space Industry needs something
    to kick start it up to the level were it would reach its own economic
    critical mass. Such as if the governament would garanty and pay for
    some VERY HEAVY Space traffic...  
    
    With lots of activity the Space Industry would be able to spread its 
    overhead over many flights/Kgs/pounds, and more importantly it could 
    then justify/afford to invest in designing and building Launch and 
    other Space systems that would benefit from the economy of scale.
    
    Such HEAVy traffic to be delivery in the form of one or more of the
    Mega-Projects of the Space Age. Examples:
    
    1.  Permanent Moon Orbital Station and Moon Base(s).
    2.  Permanent Mars Orbital Station and Mars Base(s).
    3.  Solar Power Satelites (Microwave Beaming power to Earth)
    
    Note:  These projects need not be USA only projects, better if the
    admitadly high costs were distributed among many countries.
    
    Thus would not only these very worthy goals be acomplished but as
    a side benefit. Other space related activities would become that
    much more affordable, as for example:
    
    Satellite communications, Space Zero-G Research, Space Manafacturing,
    Space Astronomy, Satellite Navigation, and so on...
    
    Launch costs would certainly come below $1000 per Kg (or $450/pound)
    And who knows maybe even below the mythical $100/Kg that would make
    it affordable for regular people like us to spend a vacation in LEO.
    
    Gil

>    What you guys are saying is that the Space Industry needs something
>    to kick start it up to the level were it would reach its own economic
>    critical mass. Such as if the governament would garanty and pay for
>    some VERY HEAVY Space traffic...  
    
    This is, of course, what happened to the aircraft industry in WW1, but
    I wouldn't like another war. Unfortunately I don't think anything else
    would be big enough, so I think we'll have to settle to slow progress.
    
    Peter

RE           <<< Note 877.4 by MAYDAY::ANDRADE "The sentinel (.)(.)" >>>
>                     -< Mega-Governament-Projects needed >-

    
>    What you guys are saying is that the Space Industry needs something
>    to kick start it up to the level were it would reach its own economic
>    critical mass. Such as if the governament would garanty and pay for
>    some VERY HEAVY Space traffic...  
    
  No, not really. Economy of scale was only one of my points.

  Remember, I also talked about harsh environments and twin environments. A
mega project would do nothing to prevent those costs.

  George

As usual George got that mach 5 thing wrong, yet again ....

George, get it through your head....  

mach 5 is a problem for aircraft continuing their flight in the atmosphere.

We are talking HOURS here.  In this case, the heat load IS a problem.

The time that a trans atmospheric vehicle would be in the atmosphere operating
at mach 5 plus is on the order of minutes (and very few at that, less than 10,
maybe 5).  The heat load of 5 minutes at mach 5 plus CAN be handled.  PERIOD.

You got one fact right and are mistakenly trying to apply that factoid to
everything.

There is a FAR mor difficult problem for air-breathing engines than heat (there
is virtually no problem for any other component of a spacecraft, FOR THE PERIOD
IN WHICH IT WILL BE IN THE ATMOSPHERE), that problem is variable geometry.  The
appropriate geometry at any particular mach number is different.  For high mach
numbers, the inappropriate geometry could blow out the engine, like a candle in
a strong wind.  The problem is calculating the appropriate geometries,
configuring an engine to meet those geometries and then executing in a real
environment (with such complicated factors as cross winds, varrying external
temp, etc.)  We still don't have part 1 correct, calculating the appropriate
geometries!

Heat load is NOT a major factor.  It is a factor, but one that can be READILY
dealt with.  Certainly not one of the top 3.

If you want to put my top 3 in they are:

1)  fluid dynamic combustion calculations.  Necessary for calculating
appropriate shapes, fuel mixes, etc.  Problem is both compute limited and set-up
limited.  setting up a complex fluid dynamic problem takes days.  Y\ou need
hundreds of runs to verify a design at a speed.  We need mach 23 speed range.

2)  Lack of viable, interesting to-do's.  space power sats are OUT.  No one
would let a weapon of that magnitude in space.  Think about what gigawatts of
microwave power could do if pointed to an inhabited area ....

3)  There really isn't one.  Actually my #2 shoudl be #1, if we have that, the
other stuff falls in place.

Tony

    Re -.1
    
    >2)  Lack of viable, interesting to-do's.  space power sats are OUT. No one
    >would let a weapon of that magnitude in space.  Think about what
    >gigawatts of microwave power could do if pointed to an inhabited area ....
    
    hm... are you sure?  Power Sats would be a lot less dangerous then current
    Nuclear Power plants and Nuclear Missiles.  And they are easy to shield
    agaisnt, unlike nuclear stuff.	Besides at the proposed Microwave beam 
    density levels they would do nothing more then warm you up a bit. 
    
    (-; Maybe we could get the military to fund this in part if we agreed
    to build them so that they can produce much higher beam power densities,
    althouh even then their military value would be near zero. 
    
    !!! Another idea, use them to warm those poor city folk, in those cold
    winter days !!!
    
    Seriously: Power Sats are not only a viable goal, but in the long term,
    they would even pay for themselves.
    
    Thus its not Mega-Space-Projects that are lacking, but as we all know,
    its the Political Will to do them.   First there was the glory of the
    space race now there is only the bad shape of the economy.
    
    	Gil

Will you *please* keep your vitriolic comments to mail.

I, for one, am growing rather tired of them.

We are not all as eminently qualified as you to talk on these topics -- for
many of us it is just a hobby, a diversion, a place to muse.   If bad data
is sent out, it can be gently corrected or ammended without resorting to
killing the messenger.

It is, after all, rocket science...


- dave

           <<< Note 877.7 by DCOPST::TONYSC::SCOLARO "One Way out" >>>

>As usual George got that mach 5 thing wrong, yet again ....
>George, get it through your head....  

 As usual those who can't argue fact try to win the argument by bashing the
noter.

>If you want to put my top 3 in they are:

  As you will see, 3 is really 2.

>1)  fluid dynamic combustion calculations.  Necessary for calculating
>appropriate shapes, fuel mixes, etc.  Problem is both compute limited and set-up
>limited.  setting up a complex fluid dynamic problem takes days.  Y\ou need
>hundreds of runs to verify a design at a speed.  We need mach 23 speed range.

  I find it really hard to believe that doing a calculation results in high
cost. If we had the computation power to do the necessary calculations back
in the 60's, how can the cost of doing these calculations be all that high
today?

  A PC running a 486 that can be obtained for $2,000 should be able to do just
about any calculation that a $1 million dollar CDC-3600 could do back in the
60's. If the costs of doing calculations are less than 1% of what they were
back then, and if the costs of calculations are a large part of the cost of
space flight, why wouldn't the total cost be coming down?

>2)  Lack of viable, interesting to-do's.  space power sats are OUT.  No one
>would let a weapon of that magnitude in space.  Think about what gigawatts of
>microwave power could do if pointed to an inhabited area ....

  How does a lack of things to do drive up cost? If it costs $100,000 to launch
a given payload, how is the cost lower if it is something worth while rather
than if it is a load of bricks? Do engineers work for less if the payload
cost is justified?

>3)  There really isn't one.  Actually my #2 shoudl be #1, if we have that, the
>other stuff falls in place.

  Hey, if 3 can be 2, why can't 2 be 1? Space costs a lot because the cost
of doing calculations is going up, worthwhile projects are less expensive to
launch that worthless projects, and 2 = 1. Now why wasn't I smart enough to
figure out all that?

  George

I humbly appologive if my tone was incorrect.

George, I respectfully disagree with your use of the hypersonic craft data.  You
are using valid data from one flight regeime and extrapolating it to another
regeime.  Extrapolation is a valid scientific tool, however, I believe the
differences between two flight regeimes invalidates the comparison.  Cooling
that is difficult for 2-4 hours is not nearly as great a challenge when it is
only required for 5 minutes.  Please let me know why you think it is.  

re calculations

The cost of each individual calculation HAS gone down dramatically.

The problem is not the cost of the calculations, but the size of the problem
that is being modelled.  

It is far easier to model a rocket engine than a scramjet!

You know inlet temperatures pressures and atomic composition of the inlet
streams in a rocket.  A scramjet has many more possible inlet conditions.  The
number of situations to be modelled, and the complexity of each situation is
vastly expanded.

It is not therefor a 'cost of calculations' problem.  

Rather it is an increasing complexity of that being modelled.  

And, I guess I should have made it clear, I was not implying that the cost of
calculations is driving the cost of the cost of space flight per see, since the
whole research endeavor is tiny compared to shuttle operational costs.  Rather,
the difficulty of the problems being moddeled for future technology orbiters
slows the rate of technical advance.  

There are (to my way of thinking) two ways to lower costs.  Improve your
technology achieve economy of scale.

re lack of things to do

Sorry, I thought I was melding into one of your points EXACTLY.  That is your
point on economies of scale.  If there is something to do, that is agreed that
we must do, that would require a large capacity, the cost of space activities
would come down.  

Re the 3-2 stuff.

I was trying to be funny and failed.  Most lists are in 3 or 10.  I couldn't
think of 3, but started that way for fun.

Tony

  The costs involved in flying at Mach 5+ are very much a factor. True the
flight doesn't last long, but where they don't stay at Mach 5 as long they fly
much faster than Mach 5 (hence the "+"). when they reenter the atmosphere. 

  As a result the craft has to be built for two environments with conflicting
requirements, hyper-sonic flight in the atmosphere and zero pressure flight in
space. If a craft were being built for one of those environments it would be
much cheaper but building for both, is more expensive just as it is in any
vehicle that attempts to operate in two different environments.

  As for the scramjet problems, the costs seem to be high even if scramjets are
not used so I don't see how those costs are responsible for space flight being
expensive. 

  It seems that we agree on economy of scale. 

  George

    re .various
    
    The duration of Mach 5+ flight on re-entry also needs to be considered.

George, 

Soo close.... :)

Yes, faster, but also at higher and higher altitude.

In the seminal article about scramjets in Scientific American, it was clearly
stated that the heat load is arbitrary!  You want less heat, you accelerate at a
higher altitude.  THERE IS NO HEAT PROBLEM FOR THE CRAFT, PERIOD.

There are design trade-off's.  There always are, every machine is a trade-off.

You can go mach 25 in the atmosphere without exotic heat removal technology. 
They could in 1986, and materials are better today.

The problem is engine design.

re two environments.....

Please explain.  Wouldn't the more rigorous environment provide the bulk of the
cost?  It is possible that the alternative environment coudl be free, if the
constraints are correct.  Your assertion that it has to cost more is, I feel
mistake.  

re scramjets


ARGH, I am having a problem making myself clear.

The problem is not the cost of computations.

It is the difficulty in birthing a follow-on technology.  

The scramjet development process has been limited by the unavailability of a
mach 8+ wind tunnel :)

Thus all development has been 'theoretical', coming from numeric calculations of
an engine simulation.  

This is a difficult process, basically new ground.

Scramjets are the logical follow-on to shuttle technology.  

And (I'm sure this statement is so benign that even George could agree with it),
IF the technological promise of scramjet-based craft is realized, the inherent
technology is vastly cheaper than present rocket technology.

Remember the two keys, technology and scale.  Scramjets could solve the
technology problem.

re reentry

I believe that the same computational techniques being used for scramjet
technology WILL enhance our understanding of airbraking.

And imagine a reversible scramjet .....  

I do not believe that a trans atmospheric vehicle will have a problem with
reentry.  The problem is achieving a transatmospheric vehicle :)

Tony

    Back to the original topic ...
    
    The hight costs problem as I see it, has more todo with the lack of
    an economy of scale then with the complexity of the technology.
    
    The fact that a Launcher's velocity has to go from 0 to 8 Km/s is
    dramatic, that is why all launching systems are so big and complex.
    
    But the fact remains that a higher Launcher activity would allow
    the fixed overhead costs (such as development, industrial capacity,
    and payload/launch/landing/control facilities) to be devided amond 
    more payload mass, bringing the cost per mass unit DOWN.
    
    In addition higher activity would also give everyone involved more 
    experience with the whole process, allowing then to find simpler 
    less expensive solutions to things.
    
    But more then anything else it would justify the development and
    utilization of new and better launching vehicles such as the NASP,
    the DC-Y, 2 Stage Shuttles, Bid Dumb Bosters, ALS, etc... that
    may never see the light otherwise.
    
    As it is governament is even reluctant to pay for "modest (-;"
    inprovements to the Space Shuttle such as the new more powerfull
    SRBs, and the new lighter External Tank.
    
    Part of the problem of-course is that the governament tru NASA
    is doing too much itself. If governament payed a private company
    to operate the shuttle, I bet Operational costs would be much lower
    then they are today. After all NASA doesn't have the profit 
    incentive to cut costs the way a private company would have. 
    
    Gil

RE: <<< Note 877.14 by DCOPST::TONYSC::SCOLARO "One Way out" >>>

>THERE IS NO HEAT PROBLEM FOR THE CRAFT, PERIOD.

Since you understand this, could you explain to me all the work that went on
under the NASP and similar program umbrellas that was concerned with dealing
with heat? I recall reading many references to such work, and I'd appreciate
it if you could clear up for my why anyone cared about such topic if it was NO
PROBLEM, PERIOD.
						-- Tom

re .16

Perhaps I should have stated it differently.  And as I look at it my wording is
dead on wrong.

The 'heat problem' was stated in the form 'a mach 5 airliner has a lot of heat
to dump'.  This is the heat problem that I was referring to.  The accumulated
heat LOAD that the aircraft is exposed to.

So I should have said 'there is no heat LOAD problem'.

That having been said.  There are surfaces that reach high temperature.  To me
this is a materials problem, not a heat load problem.  

And it is very different materials problem for a mach 5 ramjet and a mach 25
scramjet.  

The ramjet requires an area of subsonic flow in order to support combustion. 
This requires slowing a portion of the airflow by a great amount.  The specific
heat generated by a ramjet above mach say 7, is prohibitive.  Even cooling the
leading edge surfaces with liquid hydrogen placesd you in an environmnet where
there is no presently known materials solution.

A scramjet is a supersonic combustion ramjet.  This is where modelling comes in.
The specific heat generated is a variable in the equation!  (or should I say,
can be selectable by the modeller, it is not fixed by the speded you wish to go,
as a ramjet is).  Now, the better materials you have, the more relaxed the
constraint becomes, the more viable the technology.

A rocket, or even a ramjet, can be modelled in isolation.

With a scramjet, the engine is virtually the entire craft.....  

You must model the entire thing, in order to measure performance.

Tony

          <<< Note 877.14 by DCOPST::TONYSC::SCOLARO "One Way out" >>>

>In the seminal article about scramjets in Scientific American, it was clearly
>stated that the heat load is arbitrary!  You want less heat, you accelerate at a
>higher altitude.  THERE IS NO HEAT PROBLEM FOR THE CRAFT, PERIOD.

  Tony, I am trying to understand what you are talking about. As I understand,
this note is asking why the space program costs so much. I assume that means
the space program from Mercury-Gemini-Apollo, through the Shuttle and on into
the future. What does a discussion on scramjets have to do with heat problems?

  And how can you say that heat problems have never been a problem? John Glenn
had a heat shield problem on his Mercury flight, different systems were used
for heat shields on Mercury-Gemini-Apollo, the tiles on the Shuttle are
expensive, and it's not at all clear what heat problems will exist on future
craft. Did this scramjet article in Scientific American cover all of these
programs?

>You can go mach 25 in the atmosphere without exotic heat removal technology. 
>They could in 1986, and materials are better today.

  Sure, but there is expense involved. The systems have to be built and they
have to be maintained. Also, heat shields are heavy which adds to the launch
weight hence the cost of a launch.

>The problem is engine design.

  A problem is engine design.

>Please explain.  Wouldn't the more rigorous environment provide the bulk of the
>cost?  It is possible that the alternative environment coudl be free, if the
>constraints are correct.  Your assertion that it has to cost more is, I feel
>mistake.  

  Where did I say "bulk"? It is one factor. For example, if you were going to
build something to be deployed in space to move people around and not reenter
it would need no heat shield or any systems for "flying" through the atmosphere
or "landing". Conversely, to build an airplane that's not going above 30,000 feet
you don't need as good a life support system as if you are going to build a
space craft. 

  To build something that can both fly like an airplane and work in space, you
need a much more expensive craft since it has to be able to live in two
different environments and transition between them. This has been a problem
with flying and floating cars, amphibian air planes, and it contributes to the
cost of flying into space. 

>  And (I'm sure this statement is so benign that even George could agree with
>it), 

  Ok, you win

  Tony is such an ignorant fool that it's a wonder he can get out of the bed
in the morning. Clearly he is so stupid that anything he says is probably wrong
even if it were right before he said because no fact would want to agree with
an image in his moronic brain. 

  There Tony, see, I can do your type of arguing and if I haven it the past
it's only because I was trying to keep the debate above your level. But you
win, you've dragged me down to the pits of mud slinging.

>IF the technological promise of scramjet-based craft is realized, the
>inherent technology is [sic] vastly cheaper than present rocket technology. 

  This remains to be seen.

  George

Re .18

With a viable scramjet technology, and the appropriate modelling of the air
column, and understanding of aerobraking, it is concievable that 'reentry' will
pose no greater heat stress than getting there in the first place.

And that will be minimal, save for a few leading edge surfaces that receive the
greatest friction.

With scramjet technology (since you only carry fuel, liquid hydrogen, one of the
lightest elements, not oxidizer), our conventional view of reentry may be
obsolete.  

The type of reentry becomes a design parameter.  If it costs you less to do it
the conventional way, you go ahead and do it.  BUT, it is clearly feasible that
a more efficient means rather than a straign dump into the atmosphere becomes
possible.  

re multi-mode

Fine, a craft that only needs operate in space is simpler than a craft that has
to operate in the atmosphere.\

But, for a scramjet, by and large the conditions of space relax the design
criteria.  A slight leak is probably just as deadly at mach 25 in the atmosphere
as in space.

re the statement

George, I was not meaning to demean you.  I have noted your strong suspicion of
technology beyond the shuttle.  Your attitude has been 'I don't believe it will
be cheaper'.  I couched the statement with a conditional, to imply that if the
technology works AS ENVISIONED (i.e. it confounds the skeptics and works), it
will be cheaper.

If I said it wrong, or if I offended you, I appologize.

Tony 

  It's not so much that I am suspicious of technology beyond the Shuttle. I'm
sure there will be many great and wonderful systems for flight into space as
the years progress. I'm only skeptical of the claims of how cheap the scramjet
system will be since we've heard those claims before and they don't seem to be
addressing the things that have cost a lot in the past (the topic of this
note). 

  The scramjet does sound expensive.

  Reentry will still involve some sort of heat shield or extra fuel. The slower
they enter the atmosphere the longer they are exposed to heat from high speed
even if they stay high in the atmosphere. If they want to stay very high and
use the engine to slow down then it will mean extra fuel. That still comes up
as cost regardless of how they fly the reentry and the craft will still have to
be built to be both a space craft and an airplane. 

  There will be no economy of scale until and unless they prove their claim
that flying there and back is really cheap. 

  So even with the scramjet it appears that space flight will be expensive for
some time.

  George 

George,

I agree with a lot of what you say in the previous note.

But I think there is perhaps one thing you are missing.

It is only FUEL that the scramjet will have to use to slow down, not fuel and
oxidizer.

At launch, the weight of the shuttle is something like 80% ozygen (either in the
form of liquid ozugen in the ET or in the solid fuel, with only an insignificant
amount for crew use).  

The scramjet will use liquid h2 for fuel.

Thus there becomes the possibility for a real trade-off between (conventional)
heat shield weight with passive slowing and with active slowing.  Without air
breathing engines, this is a no brainer, use passive.  With air breathing
engines?  Not nearly as clear.  I believe air breathing engines switches the
equation.

IF the equation is shifted, at least as far as reentry goes, the scramjet
becomes a fundamentally cheaper system.

re designing as both airplane and spacecraft.

Maybe I'm dense on this one.  I cannot see one iota of extra cost to a trans
atmospheric vehicle from a high speed scramjet craft.

Hull  --- scramjet more stringient
manuevering engines ----  scramjet already requires, control surfaces aree not
as effective at mach 25
day - night effects  --- scramjet already has more thermal stress requirements.
reentry we have talked about.  maybe no extra hull requirements, with possibly
some extra fuel for slowing down required.

Does anyone have one I missed?

I believe scramjet based transatmospheric vehicles are inherently cheaper than
the present shuttle.

The problem of course is actually modelling one and then building it.

Tony

>>  It is only FUEL that the scramjet will have to use to slow down, not fuel
>>and oxidiser.

  Eh? Can you run a scramjet in reverse thrust, like a jet engine? It sounds
a bit of a difficult engineering proposition, especially since (as an earlier
reply points out) with a scramjet essentially the whole craft is the engine. 
How would it use *only* fuel to slow down?

  One big problem with space is that it is a government program. Even successful
(perhaps especially successful) examples of these end up with layers of
bureaucracy, political meddlers, and pork barrels to support. The original aims
get lost as more and more people get involved whose prime objective is not the
original one. Too many are more concerned with careers, salaries, fighting turf
wars etc. and other personal objectives than the real purpose of the
organisation. This sort of thing happens to all large organisations
sooner or later; I'm sure most of us could think of examples much closer to
home than NASA. In the good times when money is rolling in they get away with
it, because there are enough resources to do this and meet the overall
objectives. However this often tends to make the deterioration even more rapid.
When belts have to be tightened, too often the survivors in the organisation
are, initially at least, those who are best at defending their patch (or
covering their tracks) rather than those who are contributing most to the real
objective. The latter then suffers, badly. Private companies tend to have to
reform or go out of business, unless they have grown so strong that they can
stifle opposition before it becomes a threat. Government programs, with thouands
of voter's jobs, many $$ in contractors profits at stake, and no obvious
competitors, tend to take a lot longer to turn around or to kill off.

Ken

  There are two problems with the "scramjet" argument. First, it doesn't answer
the question proposed here as to "why space programs cost so much". It is a
proposal for what they may or may not cost in the future, but it doesn't answer
why space flight has cost so much in the past. 

  Second, the economy of scale problem means that there will be no volume to
eat up the development cost. And as .-1 says, the engine will have to be more
complex if it is used for reentry since it will have to work in reverse. A
craft with a rocket engine can turn around and fire backwards but a scramjet
will have to have additional mechanics to reverse it's thrust since it will
still have to be pointed forward to intake air. 

  As for operating in twin environments, if that is not a problem, why don't we
have flying submarines, floating cars, and tunneling trains. Even farm
impliments like tractors built to operate in the field are awkward when you try
to drive them on the road. 

  If you build a craft which only operates in space it doesn't need wings,
doesn't need any sort of heat shield, doesn't need engines that run
continually, doesn't need landing gear, doesn't have to worry about getting hit
with lightening, doesn't have to be able to float. Think about the upper stage
of the LEM compared to any space craft that flies in the atmosphere. Which
seems more complex? 

  George 

Re reverse thrust

didn't think it through entirely, I could be wrong on being ablew to use the
engine as a reverse thrust.

The point I was trying to make is that what had been thought of as a 'quick get
through the atmosphere and slow down' is not necessarily true.

Perhaps a more gradual aerobraking with powered return flight becomes attractive.

Also re multimode

George, you went general on me.  You stated a 'general rule', to address a
specific question.  I can find no additional constraint that the space
environmnet places on a mach 25 scramjet powered craft.  I will freely grant
that a craft designed for space alone would be simpler than a craft designed for
space and atmosphere.  This is however putting the cart before the horse.  It
will be a long time before humanity has many space only craft.

Tony

RE          <<< Note 877.24 by DCOPST::TONYSC::SCOLARO "One Way out" >>>

>The point I was trying to make is that what had been thought of as a 'quick get
>through the atmosphere and slow down' is not necessarily true.

  Yes, we agree on this. However, I believe that what ever system is used to
slow down will involve cost.

  - Heat shield - heavy, adds to launch cost
  - Tiles or protective skin - expensive materials
  - Retro-ROckets - Heavy fuel and O2 adds to launch costs
  - Reverse Scramjet - Technologically advanced, high development costs

  No matter how you cut it, it's expensive to return to earth and will be for
a while.

>I can find no additional constraint that the space
>environment places on a Mach 25 scramjet powered craft.  

  Sure, but that doesn't address the question here. The question is "why does
space cost so much". I presume that means compared to non-space activity.
An airline can operate a 737 much cheaper than NASA can operate a space craft
that flies in the atmosphere because the 737 doesn't need all the equipment
necessary to operate above the atmosphere.

  737          Flies below 40,000 feet         - cheap
  lifting body Dropped by mother craft,
               operates in upper atmosphere   - cheap (relatively)
  LEM          Operates only in space          - cheap

  craft that takes off and lands like a 737, flies at hypersonic speed, and
  drifts in space - expensive.

  George

    re .Scramjets
    
    Scramjets don't need to work backwards, the fact is that vehicles like
    NASP will still need OMS rockets just like the suttle does.  Scramjets
    no matter how good only operate in the atmosphere,  so  NASP would use
    its OMS for the final push up, orbit maneuvering, and the de-orbit burn.
    
    Once back in the atmosphere,  it will use air-fricton to slow it down,
    even  NASP cannot afford to do anything else. However, a small reserve 
    of hydrogen fuel could give it a bigger cross range capability as well
    as the safety of multiple landing passes.
    
    A scramjet launcher like NASP is expensive to develop, just like the 
    Shuttle was. But it is a doable thing, the only question is how costly
    it would be to operate ?
    
    Less then the Shuttle one would assUme, at the very least its one 
    integrated craft that doesn't need assembly for every flight. But what
    about the rest ... how expensive a refursbishing would it need for its
    scramjets, heat shields, OMS, ... and so on. lets not forget that the
    Shuttle too was billed as cheap to operate when they developed it.
    
    Gil