As NASA investigates why Columbia broke up during its reentry into the atmosphere on February 1, killing all seven astronauts onboard, the space agency faces some difficult choices. For more than a decade, aerospace experts had warned about the vulnerability of the aging, 100-ton space shuttles to the superheated gases that envelop the craft as they descend to Earth. If investigators determine that a breach in Columbia's heat shield or aluminum skin doomed the mission, NASA might require shuttle crews to inspect the craft's exterior before reentry and perhaps devise a strategy for repairing damage while in orbit. But if the accident's cause cannot be pinpointed or if a major redesign of the three remaining shuttles is required, NASA may have to accelerate its development of a smaller, more reliable spacecraft.

Previous efforts to replace the shuttle fleet have been expensive failures [see "Has the Space Age Stalled?" by Mark Alpert; Scientific American, April 2002]. Last November the agency committed $2.4 billion to producing a design for an orbital space plane (OSP) that could ferry a crew of at least four astronauts to the International Space Station. (With the shuttles grounded, NASA lost access to the station; only the Russian Soyuz and Progress spacecraft can ferry crews and supplies to the orbital outpost.) NASA's plans, however, are still vague; the agency has not yet decided whether the OSP will be a winged vehicle like the shuttle, a lifting body (a squat craft shaped to maximize aerodynamic lift), or a capsule like Soyuz. And even if Congress approved an additional $10 billion to build the space plane, it would not be ready to carry crews into orbit until 2012. Dennis E. Smith, manager of the OSP program, is looking for ways to speed up the schedule, but he cautions, "I don't think we can save a lot of time."

This article was originally published with the title Rethinking the Shuttle.

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