CAPE CANAVERAL, Fla. - Space shuttle Endeavour's astronauts attached the world's largest, most powerful set of solar panels to the international space station on Sunday, then watched with delight and relief as the first glittering wing unfurled.
The panel extended to its full length but was not taut, prompting NASA to put off extending the second wing until Monday at the earliest.
The astronauts' task is as monumental as the wings themselves: The future of space station construction hinges on their ability to install the $600 million solar panels, which will provide much needed power to the newly inhabited outpost.
Spacewalkers Joe Tanner and Carlos Noriega bolted the wings to the space station Sunday afternoon, and about five hours later, shuttle skipper Brent Jett Jr. was able to command the right wing to open.
''Ah, it looks beautiful,'' Noriega exclaimed as the wing finally opened after a delay caused by a computer software problem.
''More power to the station,'' said Tanner.
It took less than 14 minutes for the first folded wing to spread to its full 115 feet, and it soon began generating electricity. Some of its tension cables appeared to be slack, however, a problem that had flight controllers debating how best to proceed. NASA held off in tightening the wing, which would have been the final step.
''Since we are in a good, safe posture, there's no reason to be in a big hurry and deploy the other blanket until we absolutely understand what we saw, or what we're looking at right now,'' said flight director Bill Reeves.
A computer software problem initially left Jett unable to command the latches and retention pins on the wings to open so the panels could unfurl. New software was sent up, and Jett was able to open all the latches and pins except one on the left wing. He continued to send commands and eventually freed the stuck pin.
At the start of their 7-hour spacewalk, Tanner and Noriega had helped Canadian astronaut Marc Garneau, the shuttle robot arm operator, line up the wings for installation. The spacewalkers, positioned on either side of the attachment point, gave Garneau instructions for closing the final 3 feet.
The blue and gold-colored wings, made of silicone cells and thin Kapton layers, had been folded like an accordion for Thursday's launch aboard Endeavour.
Once attached and fully unfurled, the shiny wings will cover half an acre and make the station one of the brightest objects in the night sky. The larger the wings are, the more sunlight that can collect for conversion into electricity.
Each wing is 38 feet wide and covered with 32,800 solar cells, and has power-storing batteries and radiators at the base. The combined wingspan - 240 feet, including a connecting bar - exceeds that of a Boeing 777 jetliner.
NASA expects the solar panels to generate 65 kilowatts at peak power - four times what currently is produced by the small Russian-built solar wings already on the space station. Without this extra electricity, the space agency could not launch its Destiny science lab in January - or any other power-hungry pieces.
By the time the space station is completed in 2006, NASA will have installed three more sets of these solar wings. Each is designed to last 15 years and will keep operating even if individual solar cells are pierced by bits of space junk.
Alpha commander Bill Shepherd and his two Russian crewmates were mere observers to all the action 235 miles above Earth on Sunday. The hatches between the docked spacecraft remained sealed because of the difference in cabin air pressure.
Two more spacewalks are planned this week by Tanner and Noriega, on Tuesday and Thursday, to finish wiring the solar wings and to install other equipment on the space station. If all goes well, the two crews will meet on Friday.
Sunday's spacewalk featured something new: helmets equipped with small cameras that provided live views of what the astronauts were seeing. They were dubbed ''Joe-cam'' and ''Carlos-cam.''
''We promise to make all of our movements nice and slow and steady so nobody gets sick looking at the pictures,'' Tanner said before the flight.
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