Space shuttle Discovery began its two-day journey back to Earth after a successful stay at the international space station, but an iffy weather forecast left NASA unsure where and when the spacecraft will land.
NASA officials would like to have Discovery land on Friday at Kennedy Space Centre, since that would spare the agency the expense of transporting the shuttle back to its Florida home from two other possible landing sites: Edwards Air Force Base in California and White Sands Space Harbor in New Mexico.
But at the scheduled landing time, Kennedy was expected to have low clouds and possible showers, while gusty winds were expected at Edwards. White Sands had the best weather forecast on Friday, although that traditionally is NASA's last choice. During the only landing there in 1982, dust contaminated the orbiter and the brakes were damaged.
"They're kind of really in a difficult position of deciding where they want to go and when they want to go," said NASA spokesman George Diller.
If the shuttle cannot land on Friday, other attempts can be made on Saturday. Discovery must be on the ground by Saturday or it will run out of the fuel that supplies its electricity.
"Saturday is the last day we can keep it up," said shuttle flight director Tony Ceccacci.
A day after leaving the space station, Discovery's seven astronauts on Wednesday were to inspect the shuttle's heat shield using the spacecraft's robotic arm attached to a 50-foot (15-meter) boom. The inspection will look for any damage along the shuttle's nose cap and wings caused in space by micrometeoroids. Engineers on the ground should know within a day after the inspection whether Discovery can be cleared for landing.
A similar inspection was conducted on the second day of Discovery's mission. Both examinations were added as preventive measures after the Columbia disaster in 2003 killed seven astronauts. Foam from the shuttle's external tank broke off during lift off, causing a gash in a wing that allowed fiery gases to penetrate the spacecraft during re-entry into the atmosphere. Astronauts also will release three, small experimental satellites over the next two days.
During eight days at the space station, Discovery's astronauts made four spacewalks during which they rewired the station's power system, installed a 2-ton (1.8-metric ton) addition and coaxed a stubborn solar panel to fold up accordion-style into its box. "It's always a goal to try and leave some place in a better shape than it was when you came," Discovery commander Mark Polansky said on Tuesday before leaving the station. "And I think we've accomplished that."
The mission also rotated out German astronaut Thomas Reiter of the European Space Agency, who is returning to Earth after six months at the station. Replacing him is US astronaut Sunita "Suni" Williams as the third member of the shuttle crew. Several hours after Discovery's seven astronauts departed on Tuesday, station commander Michael Lopez-Alegria radioed to Mission Control that the space lab once again was "pretty roomy up here." Mission Control answered back, "And quiet." "Well, Suni's still here," said Lopez-Alegria, ribbing his new crew mate.