Almost Back in the Saddle?

Well, NASA has released a status report on the Space Shuttle return-to-flight effort, called NASA's Implementation Plan for Space Shuttle Return to Flight and Beyond--Revision 2. Overall, those responsible for making the Space Shuttle as safe as possible and for getting it flying again in order to complete the International Space Station and retire by 2010, to make way for the new Crew Exploration Vehicle, are confident that they have a handle on the situation. Repeated delays in the projected next flight of the Space Shuttle notwithstanding, the report professes that risks are finally reaching the point of being fully understood--and mitigated. The return-to-flight is now projected for March 2005 at the earliest.

According to public spokesmen, problems with the External Tank are the primary schedule drivers. It was foam insulation debris from the outside of the tank that fell and damaged Columbia's thermal protection on the underside of the left wing, creating the chink in the armor that the superheated atmosphere penetrated on reentry. Some of the foam is being replaced by electric heating systems, while other areas may simply end up being redesigned.

Another potential obstacle that is being tackled preemptively as part of the return-to-flight schedule are the flex hoses (of which there are more than 200 on each orbiter), which have demonstrated a tendency to crack.

One particularly innovative bit of progress is the scheme for on-orbit repair of damaged thermal protection tiles. A technique has been worked out whereby a Space Shuttle docked at the International Space Station can reorient into a "belly-up" position so that spacewalking astronauts and the robotic arm of the ISS will have access to any damaged tiles.

Early on, it was widely recognized that the concept of tile repair while in orbit was itself extremely daunting. Nonetheless, a joint project among NASA, the United States Air Force Research Laboratory, and teams in industry have developed a multifaceted repair concept. There is provision for plugging small holes in the wing's leading edge, putting a rigid wrap over larger damaged panels, and even for filling cracks. Despite the challenges of applying such materials in a situation of near-vacuum and weightlessness (a simple caulking gun just won't cut it), the repair kit ought to be ready for action by the next launch in March 2005, if not a few months sooner.

Perhaps most dramatic, though, is the concept of a Shuttle-to-Shuttle rescue operation. Should a problem be identified for a Space Shuttle already in orbit, the idea is to accelerate the preparation of another Shuttle so that it can rendezvous with the Shuttle in distress before its life support gives out. Considering that the established turnaround time on Space Shuttle missions is measured in months rather than days, this magnitude of an acceleration is no small thing to ask. It will be interesting to see what goes into creating such a capability. And of course, there will also be the matter of how to rendezvous and dock two Space Shuttles; conceptually it isn't anything terrible, but it's never been done before, will require new airlock and docking hardware to be installed on the vehicles, and will doubtless involve some tricky maneuvers. The Space Shuttles, after all, have enormous vertical stabilizers that already complicate maneuvers around the International Space Station; having to choreograph the maneuvers of two Space Shuttles for docking with one another, and avoid damage to either of them, will be a delicate ballet, indeed.

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