Chair Force Engineer

Wednesday, July 19, 2006

Doom, Gloom, and the Space Shuttle

The Encyclopedia Astronautica Blog has a noteworthy piece about the Space Shuttle's flaws, and why we shouldn't have expected much better than the shuttle we got. Mark Wade is totally right in assessing the foam issue as an inherent flaw in the system. He's also hitting the nail on the head by saying that if there is (God forbid) another shuttle disaster, it will not be the foam or the SRB seals that will doom "The Albatross."

The discussion on the flaws of a fully-reusable shuttle, while pointing out the difficulties of such a design, should not discourage us from seeking a true reusable launch vehicle. He identifies many real problems, but none of them are insurmountable.

1) The thermal stresses associated with constant pressurizations and depressurizations of the cryogenic tanks is an interesting problem worthy of extensive study. If cryogenic fuels are deemed to be a showstopper, it's always possible to design a rocket with storable fuels like kerosene and hydrogen peroxide, or hydrazine and nitrogen tetroxide.

2) The shuttle's heat shield is undeniably fragile, but it's not the only means of thermal protection for a spaceplane. The X-20 DynaSoar used a hot structure of exotic metals like Rene-41 steel, Columbium, and Molybdenum. The X-33 program developed metals that could be used for a passive thermal protection system.

3) Intact abort modes are unrealistic for any reusable launch vehicle. There is always the airliner philosophy of "make it so safe that the escape system is unnecessary." Mark Wade's point is that rockets will not be safer than 99% reliable using the current technologies, so I will propose a realistic escape system. The crew should fly in a small orbiter, mounted axially atop the rocket. Abort motors could free the orbiter, which would glide to a landing (or make a parachute-assisted splashdown.) Northrop Grumman proposed a similar design in a 2002 "Space Launch Initiative" proposal that I was enamored with. NG had two identical winged rockets, mated back-to-belly. The rocket on the top of the stack (when viewed horizontally) carried an HL-20 style orbiter on top of its nose.

It's funny that there was one program which actually solved all three problems: the X-20 DynaSoar. After all, the Titan III rocket used solid and storable liquid propellants. The DynaSoar glider was sized for a single man and a small payload; it could be jettisoned away and perform a landing in the event of a booster failure. It also had a metallic hot structure.

As I've stressed on many occasions, the 1963 cancellation of DynaSoar was the most short-sighted move in American space history (perhaps even worse than the end of Project Apollo.) DynaSoar would have taught us what techniques worked (and which ones did not) in our quest to build reusable spaceplanes. It also would have given American engineers some humility, teaching them that spaceplanes could not be flown routinely without a lot of effort. For the engineers who put men on the moon, the space shuttle must have seemed simple at first. If they ever believed this, they couldn't be further from the truth.