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CAPE CANAVERAL - The shuttle Discovery astronauts bid an emotional farewell to their colleagues aboard the International Space Station today and headed into their spaceship to prepare for the journey home.
"Better go or we'll never leave," shuttle commander Mark Polansky told station skipper Michael Lopez-Alegria as he
made his way to a connecting tunnel.
"It has been a very exciting time, so it's obviously hard to let go," added Germany's Thomas Reiter, who is returning aboard Discovery after nearly six months on the station.
The crew left behind rookie astronaut Sunita Williams, who took over the slot vacated by Reiter as a member of the station crew.
Hatches between the shuttle and station were closed shortly before 2:30pm EST (0830 NZT) and Discovery was due to depart about three hours later.
After a final inspection of the shuttle's critical heat shield and a checkout of the landing systems, the astronauts are expected to land on Friday at the Kennedy Space Centre in Florida.
They left the station with a new electrical-power system so laboratories built by Europe and Japan can be added.
Nasa was prepared with spare equipment in case cooling pumps didn't start and recovery plans in case the rewiring triggered a blackout.
But it was the fairly straightforward retraction of an old solar-array wing that tripped up the mission, requiring an unplanned and hastily choreographed fourth spacewalk so astronauts could manually free tension wires, realign grommets and shake out flaps in the partly extended panel.
Nasa had allotted three to four hours for the job, which engineers had hoped to accomplished by remote command. The work spanned four days, including a spacewalk that required veteran astronaut Robert Curbeam to venture outside for record fourth time during a single mission.
He improvised with tools that had been wrapped in insulating tape to prevent electric shocks and worked in areas never intended for an astronaut's glove.
Sweden's Christer Fuglesang accompanied Curbeam on three spacewalks and Williams was Curbeam's partner for one.
Nasa needed the panel retracted so it can be repositioned on the station next year.
"I've been scared of this flight for a long time," said the station's lead flight director John Curry. "I'm very relieved."
Nasa is under a firm deadline to finish the US$100 ($145.79) billion complex by 2010 when the shuttle fleet is scheduled to be retired. At least 13 more missions are needed to complete assembly.
Discovery's crew also delivered more than four tons of equipment, food and supplies, installed a new segment to the station's metal backbone and delivered shields to better protect the station's living quarters against micrometeoroid strikes.
The extra day in space forced Nasa to make a difficult choice: give up a final check of the shuttle's heat shield, or use one of two days' emergency supplies reserved for landing delays due to poor weather or equipment problems.
Managers opted to dip into the reserves but mobilized backup landing sites in California and New Mexico, in addition to the shuttle's prime runway in Florida, for landing attempts on Friday.
- REUTERS