Discovery heads for Earth, scheduled to touch down on Saturday

For a mission whose main objective was the transportation of a Japanese laboratory, it was only fitting that farewells were said in Japanese. That is exactly how astronauts aboard the Discovery bid goodbye by saying ''sayonara'' as the space shuttle left the International Space Station (ISS) for its return journey to earth.

Discovery undocked from the ISS early yesterday, ending a nine-day stay and headed for a Saturday morning landing at Kennedy Space Center. Shuttle commander Mark Kelly, in a brief farewell message to the three space station crewmembers, said sayonara and that he hoped the shuttle astronauts left a "better, more capable space station than when we arrived."

NASA gave shuttle Discovery's astronauts some well-deserved time off today as their flight wound down and the international space station was left further and further behind. On the other hand, NASA engineers on the ground are evaluating results of a laser scan for damage to Discovery's wings and nose.

The analysis, to uncover any signs of damage, began as soon as the first images hit the ground and continued all night. NASA expects to complete the work by early Thursday evening and, hopefully, conclude that Discovery can re-enter safely on Saturday.

The hours-long survey with the 100-foot inspection pole typically is done the day after liftoff, to give engineers plenty of time to scour the images for any hint of launch damage to the wings and nose cap, particularly vulnerable during re-entry. Another briefer inspection usually is done after undocking, to check for any impacts from micrometeorites.

However, this time round, the payload was so large (the Japanese Kibo laboratory) that there wasn't room for the inspection boom. The previous shuttle crew left its inspection boom at the space station in March, and Discovery's astronauts retrieved it as soon as they got there. Therefore, the two aforementioned inspections are being combined into one before re-entry.(See: Action-packed Day 2 for discovery astronauts)

Experts are of the opinion that Discovery appears to have sustained very little damage during its launch and its time in orbit. "I certainly was very pleased with what I saw," lead shuttle flight director Matt Abbott said.

Tetsuro Yokoyama, deputy manager of the project for the Japanese space agency, said the sight of video of the Kibo science module with the Earth below it in the background overwhelmed him. "There is no more beautiful sight," he said.

Garrett Reisman, who was leaving after having spent three months aloft, offered his snickers stash to his replacement, astronaut Greg Chamitoff. The latter will be on the ISS for six months before being replaced.

The Discovery mission has been considered a complete success. Besides installing the billion-dollar Kibo, the astronauts delivered a new pump that fixed the space station's broken toilet, replaced an empty nitrogen gas tank and performed some detective work on a mysteriously clogged, solar wing rotating joint that has hampered energy production for months. (See: International Space Station update: Both Kibo and toilet operational)

"We go into every one of these missions, we plan for the worst and we hope for the best. I don't know if it was statistics or what, but on this particular mission, we got the best," said Kenny Todd, a space station manager.

The addition of Kibo represents "a crowning achievement," not only for Japan but all the space station partners, Todd said. "It's going to go a long way toward helping us implement the science programme that's been laid out for us."