In the aftermath of the 2003 Columbia accident, NASA removed the Hubble Space Telescope (HST) Servicing Mission 4 (SM4) from the Space Shuttle manifest. Reasons cited included concerns that the risk of flying the mission would be too high. The HST SM4 was subsequently reinstated and flown as Space Transportation System (STS)-125 because of improvements in the ascent debris environment, the development of techniques for astronauts to perform on orbit repairs to damaged thermal protection, and the development of a strategy to provide a viable crew rescue capability. However, leading up to the launch of STS-125, the viability of the HST crew rescue capability was a recurring topic. For STS-125, there was a limited amount of time available to perform a crew rescue due to limited consumables (power, oxygen, etc.) available on the Orbiter. The success of crew rescue depended upon several factors, including when a problem was identified; when and what actions, such as powering down, were begun to conserve consumables; and where the Launch on Need (LON) vehicle was in its ground processing cycle. Crew rescue success also needed to be weighed against preserving the Orbiter s ability to have a landing option in case there was a problem with the LON vehicle. This paper focuses on quantifying the HST mission loss of crew rescue capability using Shuttle historical data and various power down strategies. Results from this effort supported NASA s decision to proceed with STS-125, which was successfully completed on May 24th 2009
