However, astronauts were expected to try again at 8:39 pm local time (0039 GMT Thursday) after a brief 90-minute delay, as weather was expected to improve, said flight director Richard Jones.

The Endeavour's mission at the ISS was the longest ever -- 16 days and five spacewalks, the most ever embarked upon in a single mission as astronauts attached a new Japanese laboratory called Kibo to the ISS.

NASA's mission control at Johnson Space Center in Houston, Texas, earlier gave the green light for the shuttle's cargo bay doors to close at 1926 GMT, the first step toward deorbiting.

The delay, announced about wo hours later, means deorbiting may not start until 7:33 pm local time (2333 GMT) with landing at Cape Canaveral now scheduled for 8:39 pm (0039 GMT Thursday).

If conditions do not improve, astronauts will try again during several openings Thursday or Friday.

"This has been a two-week adventure and it's been a pleasure and honor to be on it," shuttle co-pilot Greg Johnson told Houston after the crew got their wake-up call from control center around 1500 GMT.

Endeavour commander Dominic Gorie late Sunday described the 16-day mission as an all-around success.

"We've done awesome," Gorie said. "Every spacewalk was a win, every robotic op (operation) was a win."

His comments came after mission specialists Robert Behnken and Mike Foreman attached a 50-foot sensory boom to the outside of the space station.

ISS flight director Dana Weigel said the spacewalk, often referred to by NASA officials as an EVA, or an extra-vehicular activity, had set a new record.

"This was five EVAs ... more than we've done on any station mission," he said.

The spacewalkers also successfully installed an experiment on the outside of the European Space Agency's laboratory, which the astronauts had failed to complete during the third spacewalk on March 17.

Endeavour launched on March 11. Its mission's main tasks were to install the first part of the Japanese Kibo lab, a micro-gravity research facility that will be the station's largest module when completed in March 2009.

Japan Aerospace Exploration Agency astronaut Takao Doi, who is returning on the Endeavour, said Kibo "is going to open up a new era for Japan in the space program."

Astronauts also tested new repair techniques for the shuttle's heat shield. NASA has been testing different in-space repair techniques on the shuttle's protective layer since a crack in Columbia's heat shield caused it to explode while re-entering Earth's atmosphere in 2003, killing its seven-member crew.

Astronauts also assembled the Canadian-made Dextre robot, which is designed to undertake maintenance operations on the space station that until now required a human touch, and reduce the need for risky spacewalks.

The robot's human-like upper torso swivels at the waist, and its arms were designed with seven joints to provide it with maximum versatility. Umbilical connectors provide power and data connectivity.

Manipulated by joysticks inside the ISS or from ground control on Earth, the 1.56-tonne Dextre will conduct operations such as replacing small components on the station's exterior.

NASA wants to complete construction of the ISS by 2010, when its three-shuttle fleet is scheduled to be retired.

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