Discovery astronauts install huge truss to space station
Mission specialist Robert Curbeam and Sweden's first astronaut Christer Fuglesang spent six hours and 36 minutes in their extravehicular mission, installing a two-ton truss segment to the ISS among other tasks, NASA said. "Christer, you knocked yourself out," mission control told Fuglesang. "Congratulations."
The spacewalk ended at 0307 GMT as the station orbited over north Africa.
The operation was particularly sensitive because the astronauts had to move the truss within centimeters (inches) of the fragile solar arrays that provide electricity to the orbiting laboratory.
In a delicate maneuver, the 3.37-meter (11-foot) truss, called P5 spacer, was guided by the ISS robotic arm operated by US astronaut Joan Higginbotham in coordination with Curbeam and Fuglesang, who bolted the structure in place.
The modular, girder-like structure of the ISS is being assembled piece by piece. Construction of the space station resumed in September with the Atlantis mission, after a three-year hiatus following the Columbia disaster.
Discovery co-pilot Bill Oefelein directed the heavy construction work in space that extended the ISS's total length to 120 meters (394 feet).
Curbeam and Fuglesang also hooked up six cables on the ISS for electricity, commmunications and climate control.
Last on their worksheet were maneuvers to allow enough room for the new solar arrays to track the sun's rays in a 360-degree rotation.
Two other spacewalks, scheduled on Thursday and Saturday, are expected to be highly complex because the astronauts will rewire the electricity and climate control of the US-made portion of the ISS from its present, temporary set-up.
The work, during which power to half of the ISS will be switched off, includes activating the solar arrays installed by an Atlantis mission in September that will double the present electrical output of the ISS.
Curbeam and Fuglesang will work on the ISS on Thursday, and on Saturday Curbeam and mission specialist Sunita Williams will install cameras outside the ISS expected to greatly facilitate future construction work.
The Discovery mission is part of 14 shuttle flights NASA has planned over the next four years to finish the ISS by 2010, when the shuttle fleet, down to three orbiters, is to be retired.
Discovery blasted off late Saturday from Cape Canaveral, Florida -- the first nighttime liftoff in four years -- on its 12-day construction mission to the ISS. It docked on the station Monday and is to remain there eight days.
Williams replaced Thomas Reiter of Germany on the space station. Reiter arrived at the ISS in July on Discovery and will return to Earth on the same shuttle, set to land on December 21.
In a mission that has gone smoothly so far, National Aeronautics and Space Administration engineers said that Discovery's heat shield had not suffered any damage.
Two preliminary inspections carried out after takeoff and shortly before Discovery docked with the ISS had shown no damage.
Such inspections on the shuttles have become routine since the Columbia tragedy.
Columbia's heat shield was pierced by foam insulation that peeled off its fuel tank during liftoff, causing the shuttle to disintegrate during its return to Earth in February 1, 2003, killing all seven astronauts on board.