CAPE CANAVERAL, Fla., Nov. 30 (UPI) -- Shuttle Endeavour's orbital construction workers freed a mobile platform stuck on the International Space Station's railing Saturday, then hustled through a revised work plan to finish preparing the station's radiator system for service next year.
Astronauts Michael Lopez-Alegria and John Herrington floated out of the space station's airlock to begin the third and final spacewalk planned during the shuttle's week-long stay at the outpost.
Ground controllers revamped the astronauts' job list while engineers tried to figure out why a rail car stopped 10 feet short of its target. The $190 million car, which serves as a mobile base for the station's crane, was being moved along the newly installed P1 truss when it stopped. NASA had planned to use the crane to assist the spacewalkers with their primary job: attaching 33 clamps onto joints in the station's cooling system lines to prevent leaks.
After several attempts to restart the car, NASA flight directors dispatched the two spacewalkers to inspect the transporter, as well as a pair of attached cargo carts and the stations rails to see if they could find anything wrong.
"Houston, I found the problem," radioed Herrington to NASA's Mission Control Center shortly after reaching the rail car.
The astronaut discovered an umbilical caught around an antenna, preventing the rail car's wheels from moving. Herrington deployed the antenna, freeing the car and four-and-a-half hours behind schedule, it rolled into position. The delay, however, prompted NASA to pass on using the station's robot arm to assist the spacewalkers. Instead, they maneuvered themselves into position to work on the station's air conditioning system.
The shuttle crew was scheduled to spend one more day at the space station transferring equipment and gear before departing on Monday. The shuttle will be returning with NASA astronaut Peggy Whitson and her two Russian crewmates who have been stationed aboard the outpost since early June.
"I do think I'm ready to go, but it's been kind of a gradual process," said Whitson during an inflight press conference. "A month ago ... when I started packing, I was definitely not ready to go. My husband reminded me that's it's much better to leave while you still want to stay than the other way around. So I think that's good advice and I'm happy to go while I wouldn't mind staying at all."
Taking over the station's operations are commander Ken Bowersox, science officer Don Pettit and flight engineer Nikolai Budarin. Endeavour is due back at the Kennedy Space Center on Wednesday.