page_title: STS-133
section_title: Cracks in the external tank
hierarchical_section_title: STS-133 / Shuttle processing / Cracks in the external tank
caption_attribution_description: English: detail of external tank crack on STS-133
context_page_description: STS-133 was the 133rd mission in NASA's Space Shuttle program; during the mission, Space Shuttle Discovery docked with the International Space Station. It was Discovery's 39th and final mission. The mission launched on 24 February 2011, and landed on 9 March 2011. The crew consisted of six American astronauts, all of whom had been on prior spaceflights, headed by Commander Steven Lindsey. The crew joined the long-duration six person crew of Expedition 26, who were already aboard the space station. About a month before lift-off, one of the original crew members, Tim Kopra, was injured in a bicycle accident. He was replaced by Stephen Bowen.
  The mission transported several items to the space station, including the Permanent Multipurpose Module Leonardo, which was left permanently docked to one of the station's ports. The shuttle also carried the third of four ExPRESS Logistics Carriers to the ISS, as well as a humanoid robot called Robonaut. The mission marked both the 133rd flight of the Space Shuttle program and the 39th and final flight of Discovery, with the orbiter completing a cumulative total of a whole year in space.
context_section_description: Additional inspection of the tank revealed cracks in foam insulation in the flange between the intertank and liquid oxygen tank. The cracks are believed to have occurred about an hour after super-cold propellants began flowing into the external tank for the 5 November launch attempt. The cracks in the tank were the first to be found at the launch pad.
  The insulation was cut away for additional inspection, revealing two additional 9-inch metal cracks on either side of an underlying structural rib called "stringer S-7-2". NASA managers then decided to cut away additional foam and observed two more cracks on a stringer known as S-6-2 adjacent to the two original cracks. They were found on the far left of removed foam on the flange area between the intertank and the liquid oxygen tank. However, these cracks appeared to have suffered less stress than the others found. No cracks were found in stringers on the right side. NASA suspected the use of a lightweight aluminum-lithium alloy in the tanks contributed to the crack problem. Repairs commenced while the shuttle remained on the pad. An environmental enclosure was erected around the known damage site to facilitate the ongoing repairs and eventually to apply fresh foam insulation. On 18 November, as part of the repairs, technicians installed new sections of metal, called "doublers" because they are twice as thick as the original stringer metal providing additional strength, to replace the two cracked stringers on Discovery's external tank.
  Scanning of the stringers on the liquid oxygen/intertank flange was completed on 23 November. NASA also performed backscatter scanning of the lower liquid hydrogen/intertank flange stringers on 29 November.
  Program managers identified the analysis and repairs that were required to safely launch the shuttle, and this analysis was reviewed at a special Program Requirements Control Board (PRCB) held on 24 November. Managers announced at that meeting that the launch window available in early December would be passed up, with a new target of 17 December set, but cautioned that the launch could slip into February 2011. After reviewing the space station's December traffic model following the realigned Johannes Kepler ATV's launch date, NASA had identified a potential launch window in mid-/late-December 2010. The 17 December 2010 date was preferred because it would have allowed the shuttle to carry more stored oxygen to the International Space Station to help it deal with oxygen generation issues, which the crew had dealt with for several months. "What we've told the agency leadership is that clearly we're not ready for the 3 December to 7 December window that's coming up next week," John Shannon, NASA's SSP manager, said in a news conference held after the special PCRB. "We'll leave the option open for a launch window for 17 December, but a lot of data has to come together to support that".
caption: The structural cracks in external fuel tank.
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