The Space Shuttle Program - The Return To Flight

Soon after publication of the CAIB report, the NASA administrator appointed a Return to Flight (RTF) Task Group to assess the progress of the agency at implementing CAIB recommendations before shuttle flights were resumed. The RTF Task Group was an independent advisory group comprising more than two dozen non-NASA employees with expertise in engineering, science, planning, budget, safety, and risk management. Its members were granted access to NASA facilities and meetings as the agency regrouped and developed new safety strategies.

The most critical technical issue was debris shedding from the ET during ascent and subsequent damage to the orbiter's thermal protection system. The primary focus was on eliminating ET debris and using devices to detect debris impacts. The procedures were changed for applying foam insulation to the ET, and quality control and inspection programs were expanded. Equipment changes were implemented to provide a smoother surface for foam application and to impede ice formation.

NASA decided that the first two shuttle flights after Columbia would be "test" flights to assess the effectiveness of new safety changes. The orbiter Discovery was selected for the first RTF mission. More than 100 cameras were installed on exterior spacecraft surfaces and at ground locations to provide an array of observation angles during ascent. The fifty-foot-long orbiter boom sensor system (OBSS) was installed on the end of the shuttle remote manipulator system (SRMS) to allow visual inspection of the wing tips and most of the orbiter underbelly while in flight. (See Figure 4.9.) A team of image analysts was assembled at JSC to inspect the images for any signs of damage. Dozens of sensors were installed on the wing edges of Discovery to take temperature readings and record the time and location of any debris impacts.

On July 26, 2005, Discovery launched from KSC for a fifteen-day mission. The orbiter, with a seven-member crew onboard, docked with the ISS and unloaded equipment there. Three spacewalks were conducted including one in which astronauts tested new repair techniques for the thermal protection system. The shuttle landed safely at Edwards Air Force Base on August 9, 2005. NASA proclaimed the first RTF a success. However, camera footage showed that foam debris had shed from the ET during shuttle ascent. Luckily, the debris did not hit the orbiter. NASA and the public realized that the hazard that FIGURE 4.9 Orbiter boom sensor system "A Computer-Generated Image of the OBSS in Operation while Attached to the Shuttle Remote Manipulator System," in Final Report of the Return to Fight Task Group. National Aeronautics and Space Administration, July 2005. http://www.nasa.gow/pdf/125343main_RTFTF_final_081705.pdf (accessed December 28, 2005)had doomed Columbia had not been eliminated, but merely avoided by chance this time. The second RTF test flight was postponed indefinitely and is not expected to occur until late 2006.

The final report of the RTF Task Force was released to the public after the landing of Discovery. However, its findings were communicated to NASA directors prior to launch. The Task Force reported that NASA had "met the intent" of twelve of the fifteen most critical recommendations made by the CAIB. (See Table 4.3.) The other three recommendations were considered "so challenging" that NASA was unable to comply with them prior to RTF. The three problem areas were:

• External Tank Debris Shedding
• Orbiter Hardening
• TPS Inspection and Repair

The report noted, "It has proven impossible to completely eliminate debris shedding from the External Tank. The hard fact of the matter is that the External Tank will always shed debris, perhaps even pieces large enough to do critical damage to the Orbiter." Technical and time limitations also prevented NASA from successfully hardening orbiter surfaces to prevent damage from debris impacts and from proving that a damaged thermal protection system could be repaired while a shuttle was in orbit.