Ok, I goofed! (Hey, I said that I didn't have the books handy!)
Anyway, to answer Scott's question, a vacc suit has to supply two things.
First, it has to have a gas-tight membrane of some sort, so as to prevent
loss of oxygen. Second, it has to support the internal pressure required
(at least 3 psi for pure oxygen, 15 psi for oxy/nitro)
It turns out that *skin* will work just fine as the gas barrier. So a
skinsuit is basicly an elastic leotard that supplies the pressure required
to keep your body from doing nasty things to itself. You do have to add
some padding and the like in a few areas to round things out, plus you
need an arrangement over the chest to allow for breathing (sort of a
balloon to keep the volume unchanging). Just add a neck seal and helmet,
and you have a suit.
This actually has advantages over regular suits, as you get to use your
body's built-in cooling system instead of one of those bulky packs. Sweat
carries away a *lot* of heat when it is evaporating in a vacuum!
Such suits were built and tested in the mid-50s (I beleive it was done at
Wright-Patterson AFB). They had their own problems, such as being *very*
hard to put on or take off, and needing to be *very* formfitting. They
also needed an elastic that didn't degrade upon long exposure to vacuum.
But they were actually *worn* in a vacuum chamber during testing.
Now for Pooh Bear's comment about impulse...
Rocket efficiency is measured in terms of "specific impulse" (in this
case, specific has the same meaning as in "specific gravity", that is,
"per unit of mass").
In other words, "specific impulse" meaans "how big an impulse (momentum
change) can a unit mass of fuel cause".
The "formula" is ancient (and ignores unit balance):
Isp = (pounds of thrust) / (pounds per second of fuel consumption)
This give Isp in seconds. Another means of calculating it is to divide the
exhaust velocity by g (32.17 ft per second^2 or 9.8 m/sec^2).
As I said, there's a fundamental flaw in the way the units are expressed,
but it *does* work. With an Isp of 450, the Space Shutttle engines could
produce 450 tons of thrust with a fuel flow rate of 1 ton per second of
fuel. (450 = 450/1) From this point, calculations are easy.
I usually go by an *old* chart that NASA distributed to partically every
science classroom in the country. It listed the Isp for the following
types of rocket:
chemical 400 (theoretical max at the time)
"nuclear heating"
(ie NERVA) 800
fusion 600,000
ion ??? (can't recall)
photon 31 million
Note that from the real world we have things like the better model rocket
solid fuel engines doing about 180 (Centuri Enerjet engines in the mid
70s) and the Space Shuttle main engines doing 450 or so (and I hear that
it's unlikely that they can be improved on as far as Isp goes...
maintenance, and cost are a different matter)