STS-3xx

Contingency Space Shuttle rescue mission designations

Space Shuttle missions designated STS 3xx (officially called Launch On Need (LON) missions) were rescue missions which would have been mounted to rescue the crew of a Space Shuttle if their vehicle was damaged and deemed unable to make a successful reentry. Such a mission would have been flown if Mission Control determined that the heat shielding tiles and reinforced carbon carbon panels of a currently flying orbiter were damaged beyond the repair capabilities of the available on orbit repair methods. These missions were also referred to as Launch on Demand (LOD) and Contingency Shuttle Crew Support. The program was initiated following loss of Space Shuttle Columbia in 2003. No mission of this type was launched during the Space Shuttle program.

STS 400 was the Space Shuttle contingency support (Launch On Need) flight that would have been launched using if a major problem occurred on during STS 125, the final Hubble Space Telescope servicing mission (HST SM 4). Due to the much lower orbital inclination of the HST compared to the ISS, the shuttle crew would have been unable to use the International Space Station as a "safe haven", and NASA would not have been able to follow the usual plan of recovering the crew with another shuttle at a later date. The rescue mission would have been launched only three days after call up and as early as seven days after the launch of STS 125, since the crew of Atlantis would only have about three weeks of consumables after launch.

Three different concept mission plans were evaluated: The first would be to use a shuttle to shuttle docking, where the rescue shuttle docks with the damaged shuttle, by flying upside down and backwards, relative to the damaged shuttle.

After its most recent mission (STS 123), Endeavour was taken to the Orbiter Processing Facility for routine maintenance. Following the maintenance, Endeavour was on stand by for STS 326 which would have been flown in the case that STS 124 would not have been able to return to Earth safely. Stacking of the solid rocket boosters (SRB) began on 11 July 2008. One month later, the external tank arrived at KSC and was mated with the SRBs on 29 August 2008. Endeavour joined the stack on 12 September 2008 and was rolled out to Pad 39B one week later. Since STS 126 launched before STS 125, Atlantis was rolled back to the VAB on 20 October, and Endeavour rolled around to Launch Pad 39A on 23 October. When it was time to launch STS 125, Atlantis rolled out to pad 39A. On Thursday, 21 May 2009, NASA officially released Endeavour from the rescue mission, freeing the orbiter to begin processing for STS 127. This also allowed NASA to continue processing LC 39B for the upcoming Ares I X launch, as during the stand down period, NASA installed a new lightning protection system, similar to those found on the Atlas V and Delta IV pads, to protect the newer, taller Ares I rocket from lightning strikes.

STS 134 was the last scheduled flight of the Shuttle program. Because no more were planned after this, a special mission was developed as STS 335 to act as the LON mission for this flight. This would have paired Atlantis with ET 122, which had been refurbished following damage by Hurricane Katrina. Since there would be no next mission, STS 335 would also carry a Multi Purpose Logistics Module filled with supplies to replenish the station. The Senate authorized STS 135 as a regular flight on 5 August 2010, followed by the House on 29 September 2010, and later signed by President Obama on 11 October 2010. However funding for the mission remained dependent on a subsequent appropriations bill. Nonetheless NASA converted STS 335, the final Launch On Need mission, into an operational mission (STS 135) on 20 January 2011. On 13 February 2011, program managers told their workforce that STS 135 would fly "regardless" of the funding situation via a continuing resolution. Finally the U. S. government budget approved in mid April 2011 called for $5.5 billion for NASA's space operations division, including the Space Shuttle and space station programs. According to NASA, the budget running through 30 September 2011 ended all concerns about funding the STS 135 mission. With the successful completion of STS 134, STS 335 was rendered unnecessary and launch preparations for STS 135 continued as Atlantis neared LC 39A during her rollout as STS 134 landed at the nearby Shuttle Landing Facility. For the STS 135, no shuttle was available for a rescue mission. A different rescue plan was devised, involving the four crew members remaining aboard the International Space Station, and returning aboard Soyuz spacecraft one at a time over the next year. That contingency was not required.