 STS-125 was the only planned shuttle mission after the "Columbia" accident to be launched into a low-inclination orbit that did not allow rendezvous with the International Space Station.Due to the inclination and other orbit parameters of Hubble, "Atlantis" would have been unable to use the International Space Station as a safe haven in the event of structural or mechanical failure.To preserve NASA's post-"Columbia" requirement of having shuttle Launch On Need (LON) rescue capability, STS-400 was the flight designation given to the Contingency Shuttle Crew Support (CSCS) mission which would have been flown by "Endeavour" in the event "Atlantis" became disabled during STS-125.