STS-3xx

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 during that Shuttle's investigation board. No mission of this type was launched before the Space Shuttle program ended in 2011.

==Procedure== The orbiter and four of the crew which were scheduled to fly the next planned mission would be retasked to the rescue mission. The planning and training processes for a rescue flight would have allowed NASA to launch the mission within a period of 40 days of its being called up. During that time, the damaged (or disabled) shuttle's crew would have to take refuge on the International Space Station (ISS). The ISS was able to support both crews for around 80 days, with oxygen supply being the limiting factor. Within NASA, this plan for maintaining the shuttle crew at the ISS was known as Contingency Shuttle Crew Support (CSCS) operations. Up to STS-121 all rescue missions were to be designated STS-300.