SPACE CENTER, Houston -- With the most anxiety-ridden part of their flight still to come, the shuttle Discovery and its crew of seven set off for home yesterday after leaving the International Space Station.
Tomorrow's planned predawn reentry into the Earth's atmosphere will be the first by a space shuttle since Columbia's catastrophic descent in February 2003.
The two space station residents wished the Discovery crew a safe landing. ''It has really been a pleasure and, no, we are not glad to see you go. We would love to have you stay a little longer," said station astronaut John Phillips. ''Have a good flight."
Once undocked, Discovery looped around the space station for the first full photographic survey of the orbiting outpost since the last shuttle visit in late 2002, and then sped away into the blackness.
The departing astronauts reported they may have seen a piece of debris fly off the space station, but Mission Control assured them it was just a camera reflection.
Discovery spent nine days at the station, one more than planned because of the uncertainty over the timing of the next shuttle visit, so the astronauts could leave behind surplus food, laptop computers, and other supplies.
This shuttle mission could determine the future of the shuttle program. NASA has suspended all future shuttle flights until engineers figure out why a 1-pound chunk of foam insulation ripped off Discovery's external fuel tank shortly after liftoff on July 26 -- and fix the problem.
NASA is hoping that it can make the necessary fixes quickly enough to resume the approximately 20 flights planned before the program ends in 2010 and the shuttle is replaced by a new-generation cargo craft.
The 1-pound piece of foam, which could have caused damage of the type that affected Columbia, missed the shuttle.
It was by far the biggest piece of foam that fell off, but at least three other pieces came loose that exceeded NASA's safety limits.
Mission managers also want answers for the two pieces of thermal-tile filler that came loose on Discovery's belly and had to be removed by a spacewalking astronaut, and the torn thermal blanket under a cockpit window. The chance of the blanket coming loose during reentry and striking the shuttle is remote, engineers concluded, so it was left alone.