CAPE CANAVERAL, Fla., April 14 (UPI) -- In the third of four spacewalks planned during shuttle Atlantis' week-long stay at the space station, two astronauts worked in the vacuum of space on Sunday to retool the station's robot arm for work aboard a mobile base.
In a 6 1/2-hour outing, astronauts Steven Smith and Rex Walheim rewired the station's robotic crane so that it could tap a newly installed truss segment for power rather than the Destiny science laboratory. The work prepares the arm for attachment to a mobile transporter, a rail car of sorts that will run along the 44-foot-long truss.
The $190 million transporter, which was carried to the station by Atlantis, is scheduled for its first test-run on Monday. The rail car was not built for speed -- top rate is one inch per second -- but convenience.
NASA plans to expand the station's truss to the span the length of football field over the next two years, laying the foundation for additional laboratories and solar array panels to boost power supplies. The Canadian-built robot arm, which is expected to be used extensively during station construction, will be able to be rolled along the truss to different work sites.
"There are actually parking spots on the truss where (the robot arm) can stop and plug itself in to receive power and data," Smith said in a preflight interview. (Our goal) is to make sure that the train works so follow-on flights can allow the arm to walk on to that train."
Rewiring the arm took longer than expected so NASA flight managers rescheduled another task planned for Sunday's outing -- installing an access ladder from the station's airlock to the new truss -- for the final spacewalk of the mission on Tuesday.
Atlantis is scheduled to depart the space station on Wednesday and return to the Kennedy Space Center on Friday.