Storms delay Endeavour astronauts
Endeavour's six crew are scheduled to touchdown at NASA's Kennedy Space Center in Florida at 10:16 pm (0316 GMT), but the weather outlook included rain showers and overcast conditions near the coastal runway.
Similar conditions were forecast at the shuttle's backup runway at Edwards Air Force Base in California, complicating efforts to end a flight that equipped the International Space Station with Tranquility -- a habitable module -- and a new observation deck offering stunning views of space.
The Endeavour crew had additional landing opportunities late Sunday and Monday in Florida and California. Conditions were forecast to worsen at Kennedy on Monday, but improve at Edwards.
The spacecraft carries enough supplies to remain in orbit until Tuesday, if necessary. NASA also has the option of diverting Endeavour's astronauts to a landing strip in White Sands, New Mexico.
"There are a lot of options we can look at," LeRoy Cain, chairman of NASA's mission management team, told reporters.
"The likelihood of all three sites being severely 'no go' is pretty unlikely."
Endeavour's return will reduce to four the number of shuttle flights remaining in a campaign by NASA and its partners in Europe, Russia, Japan and Canada to finish the construction of the orbital laboratory under way since 1998.
The new module houses most of the critical life support systems for the station's US, European and Japanese segments, as well as water recycling hardware, exercise equipment and a computer operating post for the station's robotic arm.
The new compartment's most distinguishing feature is a roomy dome about the sized of a small bus with six windows arrayed along the sides and another on top that offer the astronauts superb views of the Earth.
Endeavour's visit to the orbital outpost united 11 astronauts for three spacewalks and repairs to the internal water recovery system, hardware that recycles urine from the astronauts and moisture in the breathing air into drinking water.
The recovery system is an essential part of a strategy to keep the space station continuously staffed with half a dozen astronauts.
Endeavour commander George Zamka, pilot Terry Virts and astronauts Steve Robinson, Bob Behnken, Kay Hire and Nicholas Patrick awoke late Saturday and spent much of the night testing the shuttle's flight control and communications systems for landing.
After departing the space station late Friday, the shuttle crew examined Endeavour's heat shielding with cameras and lasers fitted to an inspection boom held by the shuttle's robotic arm.
An assessment of the imagery by Mission Control was still under way late Saturday.
Other than indications of a few minor debris impacts on the cockpit windows, there were no obvious signs of damage to the shielding that protects the spacecraft from the heat buildup that accompanies the spacecraft's high speed descent to Earth.
"Endeavour's performance has been just outstanding," said Cain.
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