NASA inked a nearly $1 billion contract extension with United Space Alliance (USA) that keeps the Houston-based company supporting space shuttle launches an additional six months through March 2011.

NASA’s plans call for retiring the space shuttle from service after conducting two more flights to the international space station, the second of which currently is the STS-134 mission scheduled for February 2011. However, legislation now before Congress would add a logistics flight that NASA officials have said would not occur until June 2011.

The June mission would make use of a space shuttle orbiter NASA plans to have on standby to rescue the STS-134 crew should they be unable to return home in their orbiter. While that launch-on-need mission, dubbed STS-335, previously was in process for an April launch, NASA — anticipating congressional direction — has slowed preparations so that Space Shuttle Atlantis will not be ready to fly the STS-335 mission until June.

The $909.5 million cost-plus contract extension, which begins Oct. 1, covers mission design and planning, astronaut and flight controller training, system integration, flight operations, vehicle processing, launch and recovery, vehicle sustaining engineering, and flight crew equipment processing.