While the astronauts were struggling with the panel, NASA had already approved extending the mission by a day for an extra space walk, using 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.
The fourth space walk, slated for Monday, will see Discovery undock from the station Tuesday and astronauts undertake a final heat shield inspection Wednesday. Discovery would then land at the Kennedy Space Center around 3.55pm Friday (7.55am Saturday AEST). NASA is expected to prepare backup landing sites at Edwards Air Force Base in California and White Sands, New Mexico.
NASA had been considering skipping the heat shield inspection if a fourth space walk was required - 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 Monday 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.
NASA has struggled with the space station's stubborn solar panel for four days, comparing the process to folding a roadmap. Space walkers Christer Fuglesang and Robert Curbeam spent seven hours wrestling with it on Wednesday as part of an electrical refit of the station. The astronauts managed to partially retract the 37-metre panel, which had acted as a temporary power source for the station for six years, so a they could rotate a new, permanent pair of solar wings towards the sun.
The solar panel causing the problems is attached to the P6 tress segment. It is part of the station's backbone but has been temporarily attached to one arm of the station since 2000 - awaiting the P5 tress segment which astronauts installed during their first space walk on Tuesday. The P6 segment will be moved to the end of the P5 segment and the solar panel redeployed in 2007 - completing one end of the station.