Space shuttle safety and the Hubble servicing mission
by Dwayne A. Day
|The decision to scrap the last Hubble servicing mission was actually mentioned in a Washington Post article a day before the actual announcement, but was overlooked by the rest of the news media.|
On Friday, January 16, NASA Administrator Sean O’Keefe conducted a previously unplanned briefing to Hubble scientists and engineers at NASA’s Goddard Space Flight Center. According to a later news article, O’Keefe had announced that his decision had been “razor thin” in favor of canceling the mission. O’Keefe stated that the decision had been made because of safety concerns. As soon as the briefing was completed, word immediately leaked to the news media and on the evening of January 16 NASA called a news conference where Dr. John Grunsfeld, the agency’s chief scientist and an astronaut who had flown on two previous Hubble servicing missions, answered questions from the press. According to press accounts, Grunsfeld stated that “To respond responsibly to the Columbia Accident Investigation Board’s recommendations that we have inspection and repair techniques would have involved the development of a tremendous amount of technology that looks like it would have been too big of a challenge.” Grunsfeld also reportedly said that new safety procedures would require having a second shuttle standing by during the servicing mission to provide a rescue capability.
Rather than providing a detailed written explanation of the factors that led to the decision to cancel Servicing Mission 4, agency officials have chosen to respond orally to congressional and press questions about the decision, and to write letters to the editor for several newspapers where critical accounts of the decision appeared. Their explanations for the cancellation of the servicing mission are provided below.
The Columbia Accident Investigation Board addressed the subject of inspection and repair of the shuttle’s thermal protection system in recommendation 6.4-1 The recommendation states:
For non-Station missions, develop a comprehensive autonomous (independent of Station) inspection and repair capability to cover the widest possible range of damage scenarios.
Accomplish an on-orbit Thermal Protection System inspection, using appropriate assets and capabilities, early in all missions.
The ultimate objective should be a fully autonomous capability for all missions to address the possibility that an International Space Station mission fails to achieve the correct orbit, fails to dock successfully, or is damaged during or after undocking.
NASA officials have explained that they will demonstrate inspection and repair capability for shuttle missions during the first two shuttle flights. It is unclear from agency statements when they plan to have fully autonomous inspection and repair capabilities ready, however. According to press accounts, because the CAIB recommends that fully autonomous capability is an “ultimate objective” and not a requirement that must be met before the shuttle returns to flight, it is up to NASA officials to determine when this objective must be met. Even the initial shuttle missions after return to flight would have some inspection and repair capability provided by the International Space Station (ISS). The Hubble mission is the only planned mission that would have no other means of inspection and repair of the thermal protection system.
On February 9, Bill Readdy, NASA Associate Administrator for Space Flight, stated in a telephone news conference that under new rules developed by the agency, NASA would need to have a stand-by rescue mission to fly to Hubble if the first shuttle suffered problems. According to Readdy, the schedule pressures and logistics problems with preparing this mission would be severe. Presumably, such a shuttle would have to be ready to launch within a relatively short time after the servicing mission, because a crippled shuttle in orbit would have limited oxygen reserves. At least one article has noted that this would provide little time to find and correct the problem that had crippled the first shuttle so that it would not happen with the rescue shuttle.
|A rescue mission for the Hubble servicing mission would be more difficult and complex than a rescue mission to the ISS, which would not have to be significantly different than the normal, planned ISS mission.|
On February 19, shuttle program manager Bill Parsons announced that for all future shuttle flights to the International Space Station NASA planned to have a second shuttle ready to fly to the space station within 45 to 90 days. The crew of a crippled shuttle in orbit could presumably use the International Space Station as a “safe haven” until the rescue shuttle arrived. However, if the crippled shuttle was unable to reach the ISS, or suffered problems after leaving the ISS, a rescue shuttle that was 45-90 days from launch would be of little value.
In letters to the editor of newspapers, several NASA officials have made several subtle points concerning the rescue mission option. First, because the Hubble Servicing Mission and stand-by rescue mission would have to be processed essentially in parallel, there would be greater strains on the workforce—more people working overtime, more resources stretched thin, and a greater possibility of overlooking problems.
Second, a rescue mission for the Hubble servicing mission would be more difficult and complex than a rescue mission to the ISS. In fact, an ISS rescue mission would not have to be significantly different than the normal, planned ISS mission. Some procedures might have to be changed and possibly some payload removed or changed, but other than heightened tension—and any changes to the shuttle in order to avoid a repeat of the problems that had crippled the first craft—a rescue mission to ISS would not be significantly riskier and could be conducted at a more normal operational pace. A Hubble rescue mission would have to be prepared for a different orbit, different abort modes, and a different payload. The rescue mission crew would have to train for an EVA transfer of the crew.
A rescue mission to a shuttle stranded by Hubble would also have additional risks. For instance, the vehicle would have to be launched in a much shorter period of time, providing little time to diagnose and correct the problem that had crippled the first shuttle.