Space Forum / Shuttle / November 2007

snip

"incompletely sucessful"
What a ridiculous statement, you work for a politician right?

It did not use the same booster as the Gemini project.  A Titan 2 (Gemini)
is not the same an a Titan 3M.

http://www.astronautix.com/lvs/titan2.htm
http://www.astronautix.com/lvs/titan3m.htm

Jeff

Dang!  I knew I forgot to do something yesterday!   :-)

Parallel staging, or "tandem stacking" as you put it, is not the only
dimension of the problem here. The ice formation/foam shedding only
happens because of the use of cryogenic fuels in the tank, and it is
only a hazard because the orbiter TPS is fragile. And the orbiter TPS is
fragile because it is optimized for heat capacity, and it must be
optimized for heat capacity because the orbiter is quite dense at
re-entry... *because* it carries its ascent propellant externally.

Thus the astute designer sees that this is a multi-variable problem, and
that parallel staging is a variable that cannot be analyzed in
isolation, because it is dependent on so many other choices. Choice of
propellant, internal versus external propellant tanks, etc. Had the
orbiter been equipped with internal propellant tanks, the peak entry
temperatures would have been lower and a more robust TPS could have been
employed, negating the debris problem. Had the external tank used
non-cryogenic propellants, propellant temperatures would have been
higher and ice formation would not have been as much of a problem,
allowing less insulation (or none) on the tank, thus eliminating the
debris problem at the source.

Of course, there are tradeoffs with all these alternative approaches.
Non-cryogenic propellants would have had lower Isp, necessitating more
propellant mass (though not necessarily larger tanks, due to higher
propellant density). Internal propellant tanks would have made vehicle
controllability during landing a more difficult issue. We have never had
the chance to learn the devils in the details of all these alternative
designs, because we have never had the funding to investigate them. In
the absence of real-world examples, the wishful thinking of armchair
designers leads to a "grass is always greener" mentality: *every*
alternative must be better than what has been tried already, because we
know all too well the disadvantages of what we have tried, but of the
road not taken, we can see only the advantages.

And *that* was the result of the decision that the space shuttle must be
an "operational" vehicle, capable of carrying payloads. Because, the
Mathematica analysis went, in order to be economical, that operational
vehicle would need to be capable of 50-60 flights per year. And since
the entire US launch market at the time was only 50-60 flights per year,
that meant that vehicle needed to be able to carry every existing
payload - civilian and military - to meet that flight rate and therefore
be economical. But the size of vehicle necessary to carry all those
payloads introduced design difficulties that made it impossible to meet
the flight rate. Therein lies the paradox.

The real mistake of the space shuttle was not that of attempting a
reusable vehicle, nor a winged vehicle, nor a parallel-staged vehicle.
The real mistake is that we attempted to build an "operational" vehicle
before we had any real idea of what "operability" means in a space
vehicle. The alternative - the real "road not taken" - would have been
to build small experimental vehicles, starting from suborbital and
working our way up, that explore all the different "corners" of the
design trade space resulting from this multi-variable problem, and
learning, one painful step at a time, what works and what doesn't. Since
these experimental vehicles would neither have carried payloads nor
flown operational missions, there would be no attachment to them; they
would have flown for a few years each and then retired and replaced with
the next X-vehicle, just as happened with all the previous X-vehicles up
to and including the X-15.

That approach may or may not have resulted in a truly economical launch
vehicle by 2007, but it would surely by now have given us a better
picture of what works and what doesn't that the road we chose. By
attempting an "operational" reusable vehicle that by definition would
have to replace all the existing "operational" expendable vehicles, we
locked ourselves into a path that was difficult to reverse and was
expensive enough that we could not afford to replace it in parallel with
flying it, necessitating another long and painful gap in our experience
base.

And because that one vehicle represents the whole of our operational
experience for the last generation, its failure has led many to
overgeneralize. The space shuttle is a (partially) reusable, winged
vehicle with parallel staging using a cryogenic propellant tank. And it
failed to meet its cost, schedule, and reliability goals. Therefore, the
reasoning goes, all reusable vehicles are bad, all winged vehicles are
bad, all parallel-staged vehicles are bad, all cryogenically fueled
vehicles are bad. This is nonsense. Were the emotionally charged names
to be replaced with faceless variable names, any competent mathematics
professor would reject this logic as faulty, and rightly so.

Leopold Stotch ha scritto:

Reading this thread, I can give my 2 (euro)cents ?

In my opinion, the Space Shuttle concept is (was to be) an excellent
concept, well implemented for his times, but essentially too ahead of
the time. Not only technologically, but also on the level of space
capabilities. I mean, STS concept is useful when one has a strong foot
in LEO space, that is, having somewhat much more than a lone space station.

I'm watching also what happens on private sector and also I think Mr.
Rutan make the same mistake. SpaceShip One was a magnificent bird, but
substantially the horizontal stages concept is more ahead of times than
STS in 1970s/1980s

In my opinion sticking back to capsule concept for a little while is
perhaps the most sound decision.

Of course, in this question, that is, how to cope with Earth's gravity
well, the ultimate solution is an horizontal SSTO, that is, a
spaceplane, but this require substantially a long period of
technological growth....

Best regards from Italy,
Dott. Piergiorgio.

And your experience with such matters is what?

D.

Shuttle II would be a step backwards.  Until launch rates (40-60 per
year) can support an RLV, ELV's are the way to go.  A crew RLV would
be viable before any cargo one (too many varying payload weights to
optimize for).

Why would you want to launch an expensive comsat on a launch vehicle that
you know is less reliable?

Note that fast package delivery is generally done using cargo versions of
the same commercial airliners used to fly people.

Jeff