Space shuttle Discovery headed home

HOUSTON (Reuters) - Space shuttle Discovery undocked from the International Space Station on Monday after an 11-day stay during which astronauts made a risky repair to a solar panel and delivered a new module to the outpost.

Discovery, with pilot George Zamka at the helm, gently pulled away from the station 218 miles above the Pacific Ocean to begin a two-day journey back to Earth.

"Shuttle departing," space station commander Peggy Whitson said as she rang a ship's bell in a naval salute that is traditional on the station.

"Thank you guys for the (Harmony) module and all your help," she radioed to Discovery, referring to an Italian-built module delivered by the shuttle.

Zamka then steered Discovery around the station while crewmates snapped pictures and shot video of the orbital outpost to document its condition and the newly-repaired wing.

Once Discovery cleared the station's orbit, astronauts used the shuttle's robot arm and sensor-laden inspection boom to examine the ship's heat shield, ensuring it was safe for the fiery return through Earth's atmosphere before touchdown.

The shuttle launched from the Kennedy Space Center in Florida on October 23 and is scheduled to land there at 1:02 p.m. EST on Wednesday. The crew includes returning space station flight engineer Clay Anderson, who was replaced by astronaut Dan Tani.

The 24-foot-long Harmony module delivered by Discovery was the first new room added to the outpost in six years.

It will serve as the berthing port for European and Japanese laboratories scheduled for delivery starting in December as NASA pushes to finish the outpost before the shuttle fleet is retired in 2010.

Station expansion plans may have been saved by a risky repair improvised by NASA after a solar power panel ripped in two places while it was being unfurled on October 30.

Astronaut Scott Parazynski, on the fourth spacewalk of the mission, rode the station's robot arm, extended by a boom borrowed from the shuttle, out to the partially unfolded panel to thread it with hand-fashioned cables so it would not tear further.

With the cables, or "cufflinks" as NASA called them, in place, the panel was extended to its full 110-foot length, drawing cheers from Mission Control in Houston.

Had the repair failed, space station program manager Mike Suffredini said NASA might have had to jettison the panel, which would have caused not only a power shortage, but also stability problems for the station.

The panel was part of an 18-tonne truss the Discovery crew reinstalled from a temporary location as NASA prepares for station expansion.

Still to be repaired is a sluggish, 10-foot circular joint that rotates a separate set of solar arrays to keep them pointed at the sun for maximum electricity production.

A spacewalking Tani found metal shavings in the joint, which was installed on the station in June and had been acting up in recent weeks.

Suffredini said the station has sufficient power to support Europe's Columbus laboratory, planned for delivery on a December shuttle flight, five years behind schedule.

Until the rotary joint is repaired, it was uncertain if Japan's Kibo lab can be installed starting in February as planned, he said.

(Additional reporting by Irene Klotz in Cape Canaveral, Florida; Editing by Jim Loney)