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Boom surveys shuttle belly
Some key shuttle inspection tools, like a boom to survey the underside of the shuttle, were successfully tested during the STS-114 mission, but more work remains. (credit: NASA)

A few lessons from the return to flight

When space shuttle Discovery landed at Edwards Air Force Base in California it was the end of the first post-Columbia test flight. It is important to stress that this was a test flight, and that all future shuttle flights will also be, to one extent or another, test flights. The August 2003 Columbia Accident Investigation Board (CAIB) report found that many of the problems with the shuttle system were due to NASA’s premature decision to declare the system “operational” back in 1982. The CAIB report explained that the “approval process (for the Shuttle) also produced unreasonable expectations, even myths, about the Shuttle’s future performance that NASA tried futilely to fulfill…”

On the STS-114 mission, as befits a dangerous test flight, Discovery was more heavily instrumented and there were more sensors, both on and off the spacecraft, than ever before. From now on every shuttle launch will be tracked and examined in microscopic detail, and this should set a precedent for all future manned space launches. Just as no airliner is allowed to operate without a set of black boxes, for the foreseeable future no manned rocket should be allowed to lift off without a comprehensive flight recording system. The development of such systems could be one way that technology from the shuttle can usefully be transferred to the future Crew Exploration Vehicle (CEV) and its associated hardware.

The orbital boom sensor system has proven itself with none of the vibration problems some experts feared. The picture of the Discovery’s underbelly gave the media something new and spectacular to report on. The tiny dents and fractures that showed up and the precautionary removal of the protruding gapfillers gave the public an extra layer of drama to an already tense story.

It is important to stress that this was a test flight, and that all future shuttle flights will also be, to one extent or another, test flights.

This not only means a bright future for the RocketCam and Ecliptic Enterprises, the company in California that makes it, but it means that NASA will have to continue to devote time and money to developing a new generation of vehicle health monitoring systems. If all goes well these will evolve into systems that, within limits, will fix problems as they arise. Such systems will be an integral part of the CEV and the more they can be tested on the shuttle, the better.

The CAIB recommendation that each future flight be tracked by an improved set of ground-based tracking cameras has been carried out to the satisfaction of the Stafford-Covey Return to Flight Task Group. The need for this capability will have an impact on future manned space flights, whose launch windows will probably be constrained by the need for daylight and good weather. This requirement could be somewhat overcome by the use of high-altitude aircraft with their own sets of cameras such as NASA’s two WB-57s. These are heavily-modified US versions of the British Canberra bombers of the 1950s. NASA should begin to look for a replacement since such aircraft will almost certainly be needed well into the 2030s.

According to the Task Group report, NASA has not met three of the fifteen CAIB recommendations. These three are inevitably the most difficult ones, perhaps, and given the nature of the shuttle they are simply impossible to fix. The first and best known of these is the requirement to prevent the External Tank from shedding pieces of foam heavier than 18 grams (0.04 lbs). (See “Foam and the limits of foresight”, The Space Review, August 1, 2005.)

A piece of foam that weighed almost a full pound fell off the ET’s Protuberance Air Load ramp. Another three or four pieces of foam that detached from the tank seem to have been less consequential, but nevertheless NASA has wisely decided to ground the shuttle until March to give itself enough time to do everything it can to fix this problem. Getting this right is not only important for the future safety of the shuttle, but is equally important for the future of the shuttle-derived heavy-lift vehicle that the senior management at NASA hopes to use for future exploration of the Moon and Mars.

NASA was able to get the shuttle back into orbit, but in doing so they found that they had a lot more work to do. By rescheduling the next mission for March of next year, NASA is giving itself what should be plenty of time to make real progress.

If NASA decides to go with an in-line “stick” configuration for this launcher the foam problem will not be so urgent; the cargo carrier will be above any foam-insulated portions of the vehicle. However, an alternative design, featuring a side-mounted cargo pod with or without the engines attached, would be subject to foam strikes, just as the orbiter now is. Since the pod would not be returning to Earth, the foam-shedding problem might not be critical, but a large strike might wreck the aerodynamics of the craft and do mission-critical damage to it. A permanent fix for this problem would be a wise future investment, and the Exploration Systems Mission Directorate might want to consider ways to support the operations people in their “tiger team” effort.

The other two CAIB objectives that were not met are orbiter hardening, which may be impossible, and thermal protection system inspection and repair, particularly the repair part. The Task Group found that “…NASA has satisfied the inspection portion of this recommendation.” The actual repair systems that were flown on STS-114, though, were “only for emergency use and cover a limited range of potential damage.” They have not yet been proven effective and it will take a lot more work before even they are more than a set of last-ditch emergency options.

Aviation Week referred to Discovery’s flight as a “Tarnished Triumph”, and this is about right. NASA was able to get the shuttle back into orbit, but in doing so they found that they had a lot more work to do. By rescheduling the next mission for March of next year, NASA is giving itself what should be plenty of time to make real progress, both for fixing the foam shedding problem and improving the in-flight repair tool kits. The open question is, will they use this time wisely, or will it be wasted?


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