Discovery undocks from the International Space Station

Adam Turner
Wednesday, 20 December 2006 06:04

Science - Space

The Space Shuttle Discovery has undocked from the newly overhauled International Space Station and is preparing for a final heat shield inspection before returning to Earth.

Staying behind is Indian-American Sunita Williams, beginning a six month stint on the station after undertaking her first space walk this week. She ventured outside as part of an eight day overhaul of the ISS's electrical systems in preparation for further expansion of the station next year.

The STS-116 crew had a busy stay at the station. The crew continued the on-orbit construction of the station with the addition of a 2 ton segment during the first of the four space walks. The next two space walks were devoted to the rewiring of the station’s power system, leaving it in a permanent setup.

Discovery's eight day mission to the station went a day longer than planned after an extra space walk was required to fully retract a stubborn solar panel. The extended mission means the shuttle is now forced to use one of two days of emergency fuel set aside to allow for landing delays due to bad weather. Bad weather delayed Discovery's launch for two days last week, and the shuttle will now only have 24 hours of reserves for its fuel cells should weather delay its return to Earth.

Tomorrow the crew will undertake a final heat inspection, which NASA had been considering skipping despite insisting on additional safety precautions since damage to a fuel tank lead to the death of Columbia's seven astronauts during re-entry in 2003. An unplanned initial inspection of the heat shield was undertaken as a precaution last week after sensors detected "very low" impact readings. After initial fears the shuttle had been damaged by space junk or a micrometeoroid, NASA engineers advised Discovery's crew it did not need to conduct an extra inspection.

Discovery is expected to land at the Kennedy Space Center on Friday afternoon. With only one bad weather day in reserve, NASA is expected to prepare backup landing sites at Edwards Air Force Base in California and White Sands, New Mexico. Preliminary weather forecast are for possible low clouds and rain at Kennedy and high cross winds at Edwards, but White Sands is currently clear for Friday.