Space shuttle Discovery sailed away from the International Space Station yesterday, leaving behind a third full-time crewmember on the station and high hopes that NASA can quickly resume construction of half-built outpost.
The shuttle, which arrived at the station nine days ago, is due back on Earth tomorrow to conclude only the second mission since the 2003 Columbia accident.
"Have a safe journey back, soft landings and we'll see you on the ground in a few months," space station astronaut Jeff Williams told the Discovery crew as the shuttle slipped out of its docking port.
The primary purpose of Discovery's flight was to demonstrate the successful redesign of the shuttle's fuel tank, return the space station to full staff for the first time in three years and repair the station's mobile rail cart so that assembly of the $100 billion complex can resume.
All goals were met, as well as a host of other objectives including tests to repair shuttle heat shield damage and the delivery of more than 2.5 tons of new equipment and supplies to the outpost.
"Our (goals) won't be completely accomplished until we have the crew safely on the ground," said flight director Tony Ceccacci.
Touchdown at the Kennedy Space Centre in Florida is scheduled for 3.14 p.m. tomrrow.
In addition to packing up their cabin for landing, the Discovery astronauts yesterday completed a second inspection of their ship's wings to check for damage from micrometeoroid impacts.
Analysis was under way but so far engineers have seen nothing to prevent Discovery's planned touchdown tomorrow.
NASA ordered extensive in-flight inspections as part of $1.3 billion in safety upgrades since the Columbia disaster.
Inspections earlier in the flight, conducted with the same cameras and sensors on a robot arm used during yesterday's survey, found no damage from launch debris impacts, such as what triggered the breakup of Columbia and the deaths of seven astronauts on February 1, 2003.
The only problem nagging NASA engineers is a small chemical leak in one of the shuttle's three power units used during landing.
NASA plans to test the unit today and if the leak worsens, it may be shut down, forcing the shuttle to land with just two of the power units for the first time in the programme's history.