Discovery heads for home


CAPE CANAVERAL -- Shuttle Discovery left the International Space Station yesterday en route to a planned homecoming tomorrow at the Kennedy Space Center.

With Navy Cmdr. Mark Kelly piloting Discovery, the shuttle and its crew of six undocked from the station at 6:08 a.m. as the spacecraft flew 210 miles above the Pacific Ocean north of New Zealand. Kelly slowly eased the shuttle away before firing steering jets to separate the ships.

"Have a safe journey back, soft landings, and we'll see you on the ground in a few months," station astronaut Jeff Williams radioed as Discovery undocked.

"Thanks, Jeff," shuttle commander Steve Lindsey replied. "We enjoyed it tremendously."

During Discovery's nine-day visit, the shuttle dropped off a third resident for the station, German astronaut Thomas Reiter, along with more than 3 tons of equipment and supplies. The crew also performed three spacewalks, including one that restored mobility to a robotic arm on the station critical to continuing the outpost's construction.

After yesterday's undocking, Discovery's astronauts used a sensor-equipped boom at the end of the shuttle's 50-foot robot arm to inspect the nose of the orbiter and the right wing's leading edge for damage from orbital debris or micrometeoroids. A survey of the left wing was completed Friday.

Engineers are studying the results and plan to clear Discovery's heat shield for the flight home this morning if, as expected, no damage is detected.

"The team is working through all of that data," said John Shannon, chairman of the mission management team for Discovery's flight. "Right now, they don't see anything of concern at all."

Today, the crew will check out Discovery's flight control systems to get ready for a planned 9:14 a.m. landing tomorrow. If the shuttle is unable to land at that time because of bad weather or a technical issue, a second opportunity is available one orbit later at 10:50 a.m.

Mission managers will focus much of their attention during this morning's checkout on one of Discovery's three auxiliary power units, or APUs, that operate the ship's body flaps, brakes and steering during landing. The unit has a small leak of either hazardous hydrazine fuel or harmless nitrogen gas. Engineers have been unable to determine which.

The leaky APU will be turned on for about five minutes during today's checkout. If the leak rate doesn't worsen, the plan is to use the unit during landing as usual. However, if the rate increases, mission managers will likely decide to run the APU until its fuel supply is exhausted to minimize any hazard from a possible leak of flammable hydrazine. Only one of the three APUs is needed to land the shuttle safely.

NASA managers are not expected to activate the shuttle's backup runway at Edwards Air Force Base in Southern California tomorrow. Weather conditions are forecast to be generally favorable with some concerns about possible showers. Discovery has enough on-board supplies to remain in orbit until Wednesday.

Michael Cabbage writes for the Orlando Sentinel.

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