In this image provided by NASA backdropped by Earth's horizon and the blackness of space, the International Space Station appears very small from the point of view of the Space Shuttle Endeavour as the two spacecraft carry out their relative separation Monday March 24, 2008. Endeavour's vertical stabilizer, orbital maneuvering system pods and payload bay are seen in this image photographed by an STS-123 crewmember onboard the shuttle. Earlier the STS-123 and Expedition 16 crews concluded 12 days of cooperative work onboard the shuttle and station. (AP Photo/NASA)
CAPE CANAVERAL, Fla. (AP) -- Clouds moved in and threatened NASA's plans to bring the shuttle Endeavour and its crew of seven back to Earth on Wednesday to wrap up "a two-week adventure" at the international space station.
"It's going to be pretty close here," Mission Control informed the astronauts two hours before the scheduled touchdown.
It was overcast much of the day, but late in the afternoon, a thick bunch of clouds moved in from the southeast. Flight controllers debated whether it was safe, with enough visibility, for the shuttle to land right before sunset or whether it would be better to try for the second and last opportunity of the day, 1 1/2 hours later.
Endeavour blasted off March 11 on an ambitious, intense construction mission that had even its commander wondering at times how everything would go.
In the end, commander Dominic Gorie and his multinational crew accomplished everything they set out to do during their voyage, which spanned 16 days and 6.5 million miles. The astronauts installed the first piece of Japan's Kibo lab, put together a giant Canadian robot named Dextre, tested a shuttle repair technique and more.
"This has been a two-week adventure," said Gorie's co-pilot, Gregory Johnson. "It's been a pleasure and an honor to be on it and although we've had wonderful events and some great successes ... we're ready to get home."
The space station is now 70 percent complete, thanks to the latest additions, with a mass of nearly 600,000 pounds.
Ten more shuttle flights to the space station - spread over the next two years - will round out the numbers. NASA hopes to have its share of the orbiting outpost finished in 2010 and its three shuttles retired, so it can focus on human expeditions to the moon.
Discovery is scheduled to fly to the space station in late May, carrying up Japan's enormous Kibo lab. The fuel tank for that mission arrived at Kennedy Space Center on Wednesday. Subsequent fuel tanks could get backed up, however, because of all the design changes necessitated by the 2003 Columbia disaster.
NASA expects to have a better idea in another month whether it can keep the year's launches on track. Space shuttles are supposed to soar four more times in 2008, which would mean six missions for the year, a flight rate not seen since 2001.
Up on the space station, meanwhile, the three occupants are gearing up for next week's arrival of the European Space Agency's supply ship, Jules Verne. The unmanned cargo carrier - the first of its kind - rocketed away from French Guiana this month with a load of food, water and clothes.
Less than a week after that, on April 8, the Russians will launch a fresh space station crew from Kazakhstan.
NASA couldn't be more pleased with this space station traffic jam.
Returning aboard Endeavour was French Air Force Gen. Leopold Eyharts, who spent 1 1/2 months aboard the space station, and Japanese astronaut Takao Doi, who accompanied his country's space station contribution to orbit.
Raising the Kibo lab's storage compartment from Endeavour's payload bay for attachment to the space station "was a great moment not only for me, but for Japan," Doi said late Tuesday. It was concrete evidence, finally, of the Japanese Space Agency's partnership in the longtime station project.