Its Job Done, Shuttle Leaves Space Station
By WARREN E. LEARY
Published: July 16, 2006
The space shuttle Discovery detached from the International Space Station early Saturday, slipping away from the research outpost after more than a week of joint operations that set the stage for future missions.
After photographs and farewells, the six-member Discovery crew and three astronauts remaining on the station closed hatches and made final checks before the shuttle undocked at 6:08 a.m., Eastern time, and slowly pulled away.
''Have a safe journey back, soft landings, and we'll see you on the ground in a few months,'' said Col. Jeffrey N. Williams of the Army, the station flight engineer and science officer.
At a late-morning news conference, Anthony J. Ceccacci, the shuttle flight director, said the separation of the two spacecraft had gone perfectly. ''We had a by-the-book undocking from the station,'' Mr. Ceccacci said.
The shuttle pilot, Mark E. Kelly, a commander in the Navy, maneuvered the shuttle to a position about 40 miles from the station, maintaining an option to return and re-dock. Discovery stayed in sight of the station while the shuttle crew completed a final round of inspections to be sure its heat shield was intact.
Using the shuttle's robot arm and a boom tipped with a pack of laser sensors and a camera, the crew spent three hours making a final survey of the shuttle's nose cap and right wing leading-edge panels, made of the reinforced carbon-carbon composite material that withstands the highest heat of re-entry. The crew inspected the left wing on Friday.
John Shannon, deputy manager of the shuttle program, said at a briefing on Saturday that the left wing had been cleared of concerns for landing, and that a determination on the other two areas should be made by early Sunday following overnight examination of the scanning data.
The surveys, done for the first time, were intended to look for signs of damage from impacts by dust-size micrometeoroids or space debris. Astronauts aboard the shuttle and the station inspected Discovery for debris damage with sensors and high-definition photography when it arrived, and National Aeronautics and Space Administration managers cleared the craft to return home.
The new scans were added to the departure routine to add assurance that all was well. If new, severe problems are detected when ground inspectors study the data, the shuttle could return to the station for repairs or to leave its crew for later rescue.
Mr. Ceccacci said it would take engineers a day to assess the new laser scans and pictures, comparing the results with similar inspections conducted July 5, the day after launching. If all is well, he said, NASA managers will give the crew final permission on Sunday to prepare to leave orbit and land on Monday.
Discovery is completing only the second shuttle flight since the Columbia accident three years ago. Columbia and its crew of seven were lost when returning from a mission because of damage to the reinforced carbon-carbon wing panels from launching debris. NASA spent more than $1 billion to redesign the shuttle system to reduce the debris hazard and to improve inspections in space.
The only remaining concern about Discovery's mission is a slight fuel leak in one of its three auxiliary power units, which power the ship's hydraulic systems for steering and braking when returning to Earth.
Mr. Shannon said Friday that two of the power units were working fine, but that questions remained about a drop in pressure in the fuel system of the third. A small leak in the suspect unit could be harmless nitrogen gas or flammable hydrazine fuel, he said.
As a precaution, he said, the shuttle crew will turn on that unit early Sunday as part of its normal testing to see if the leak rate changes. If it does, the crew could burn off the hydrazine and shut down the unit before returning to Earth to eliminate any fire hazard.
A shuttle needs only one power unit to land and could return without incident operating two for the first time, Mr. Shannon said.
More evidence is pointing to nitrogen being the source of the leak, he said Saturday, adding that he expected the suspect power unit to be cleared and the shuttle to land with all three operating.
The shuttle is scheduled to land at the John F. Kennedy Space Center in Florida on Monday, but NASA is planning for a possible landing at Edwards Air Force Base in California because of the power unit issue.
NASA officials called Discovery's mission to the station a success that should lead to resuming construction of the research outpost. The shuttle delivered a German astronaut, Thomas Reiter, to the station for a six-month mission, increasing its crew to three for the first time since the Columbia accident.
Photo: Thomas Reiter, who will spend six months on the space station, said goodbye yesterday to Piers J. Sellers, front. In the background are Stephanie D. Wilson and Pavel V. Vinogradov, the station commander. (Photo by NASA TV, via Associated Press)