Rockets are perhaps unique in the field of engineering in being specifically designed to come apart during normal operation (Fig. 2.7). The Saturn V Moon rocket, for example, broke into no less than eight pieces on every flight. Only one of those pieces, and one of the smallest, returned to Earth. This modular flight

Fig. 2.7 Diagram of the planned Ares I crew rocket, showing typical modular design. The only reusable parts are the solid rocket boosters and the conical crew module (courtesy NASA)

architecture worked satisfactorily, but it was exceedingly wasteful in terms of discarded hardware as well as cost. The Space Shuttle does a little better, breaking into only four pieces, but still ludicrously throwing away the most operationally important component, its propellant tank. Spaceplanes, by contrast, will specifically be designed to retain all parts, refuel almost anywhere, and return for new missions.

Spaceplanes will operate from runways, much like ordinary airplanes. They will not require extensive launch complexes, mobile service structures, or armies of launch personnel. Furthermore, they will be designed to be landed, cooled down, refueled, and reflown within hours, rather than months or years as with the Space Shuttle. Simple airplanelike operations will characterize the successful spaceplane of the future.

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