Chair Force Engineer

Tuesday, February 20, 2007

Path of the DynaSoar

Jon Goff has two good posts (here and here) about the difficulties that went into designing the Space Shuttle, the impossibility of building a fully-reusable shuttle during the 70's, and a possible way ahead.

I have long shared a similar belief. The group that sent Apollo to the moon must have felt very confident in their abilities, but they stretched too far in designing a spacecraft as long as a 737, with a design goal of flying into space every two weeks. If they had attempted building a smaller, reusable spaceplane before proceeding with the space shuttle, they'd have learned some lessons on how to do it. They'd probably go into the shuttle development with lowered expectations for the shuttle, and design the shuttle accordingly.

Specifically, I think the X-20 DynaSoar represented a painful missed opportunity. I came to this belief shortly after Columbia disintegrated, motivated by my admiration of the X-20's hot structure TPS. The metallic TPS and heat-absorbing structure of the DynaSoar would have likely been more robust than the shuttle's tile-on-aluminum construction, at the expense of a much heavier vehicle.

The X-20 DynaSoar went through many changes over its lifetime, but it appeared to have found direction prior to the December 1963 cancellation. Its original billing as a space bomber and recon platform doomed it in the eyes of defense secretary Robert McNamara, who felt that Manned Orbiting Laboratory was a more prudent use of defense dollars. In a military sense, he was justified. But X-20 was still important, in terms of establishing technologies and operational procedures for a reusable manned spaceplane. While X-20 achieved much knowledge that was applied to the shuttle, there was so much more to be learned if X-20 had proceeded with its planned 1967 launch.

I don't like playing "what if" with history, as there are too many variables to truly know how history would have proceeded had a different choice been made. I would say that the following would have been likely outcomes if DynaSoar had been built and flown:
--The shuttle would have been designed for a lower flight rate, with more realistic turnaround times
--The shuttle would not have been designed for large Air Force payloads, and may not have gotten Air Force support at all
--The shuttle would have probably been built with a hot structure and metallic TPS
--Upon seeing the difficulties of operating a reusable spaceplane, NASA may have opted to continue with an Apollo Applications Program utilizing the Saturn IB, Apollo CSM, and small space stations / mission modules instead of pursuing the shuttle

DynaSoar represented the first development spiral of a real reusable spacecraft. Subsequent spirals could have brought us farther down the path to a true RLV, through such steps as:
--Enlarging the DynaSoar glider to carry the engine and propellants for orbital insertion and de-orbit
--Replacement of the SRB's on the Titan booster with liquid-fueled, flyback boosters
--A further enlargement of the glider to include a larger crew and a useful payload
--Development of an all-reusable system with at least one flyback booster (staging around Mach 6) and a spaceplane that could fly all the way to orbit with a useful payload and return safely to earth.

I think most engineers agree that a true RLV was out of reach during the 1970's when the shuttle was designed. It's probably within reach now, but we need to work our way up to that point. Spiral development was the answer then, and it's still the answer today. The problem in the early 70's was a lack of development money. Today, we can find the money if the market sees a need for an RLV. We're caught in a classic chicken-and-egg dilemma: we need an RLV to open space for commerce, but the market doesn't currently exist to justify spending on an RLV. But a first step has to be the development of a reliable manned spaceplane that can be launched on an expendible rocket and returned to flight in a safe manner.

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