Atlantis astronauts perform historic spacewalk

Thomas Jones and Robert Curbeam outside Atlantis on Wednesday

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JOHNSON SPACE CENTER, Texas -- Two astronauts ventured from the space shuttle Atlantis to work on the international space station on Wednesday, conducting the 100th spacewalk in U.S. history.

Thomas Jones and Robert Curbeam Jr. put the finishing touches on the orbiting outpost's newly installed science laboratory Destiny during their historic spacewalk, the final one of the shuttle flight.

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They performed the bulk of the mission's objective on two previous spacewalks, mounting and installing the $1.4 billion Destiny on space station Alpha.

During Wednesday's five-hour excursion, Jones and Curbeam attached a spare communications antenna to Alpha and double-checked cables and a docking port that they attached to Destiny during the second spacewalk.

Practicing for disaster

They were to take photographs of latches that never fully locked into place on the base of the huge U.S. solar wings installed in December. Flight controllers will use the photographs to determine how they might fix the latches during a future mission.

Jones and Curbeam also simulated a disaster. The spacewalkers practiced emergency techniques that future spacewalkers could use to assist an incapacitated partner.

Each astronaut took a turn playing a debilitated crewman while the other pulled him the length of the payload bay back into the crew compartment.

On Tuesday, Alpha reached two milestones: It sped around the Earth guided by solar rather than rocket power -- and by Americans rather than Russians.

"We've reached another benchmark," radioed Mission Control.

Station flexes solar wings

On the cue of Mission Control in Houston, Texas, computers inside Destiny sent commands to four gyroscopes that were delivered by shuttle astronauts last autumn. The gyroscopes, in turn, took over the steering of the space station from fuel-guzzling Russian thrusters.

The computers and gyroscope motors were powered by electricity from giant solar wings that were installed in December. The gyroscopes help the space station save rocket thruster fuel, which is costly and burdensome to deliver.

When the gyroscopes were in control, so was NASA's Mission Control in Houston. Until that moment, flight controllers in Russia had always been in charge.

The station will alternate between thrusters and gyros for now, but once NASA has thoroughly tested the new system and declared it operational, the moment-to-moment command of the station will begin to shift from Russia to the United States.

The 800-pound (363-kg) gyros, spinning more than 6,000 times a minute, keep the station pointed in the right direction to collect sunlight for solar power.

The gyros not only are cheaper than the thrusters, they are designed to operate more smoothly and are less likely to upset delicate experiments that NASA and its international partners -- Russia, Japan, Europe and Canada -- plan to conduct on the $100- billion station.

Houston tries to clear the air

Mission directors were trying to solve one problem in setting up Destiny: its carbon dioxide-removal system was not working because of a bad pump.

Astronauts prepare to leave Atlantis for their third and last spacewalk

The five Atlantis astronauts and three Alpha residents had to rely instead on the air purifiers aboard the shuttle and the Russian segments of the space station.

The shuttle's thrusters have been used to boost the altitude of the station several times during the mission. One more reboost is planned before Atlantis departs. The shuttle should conclude its 11-day flight by landing at Florida's Kennedy Space Center on Sunday.

The space station's crew has lived on Alpha since November. They plan to return next month when the shuttle Discovery brings a replacement crew to the outpost.

The first spacewalk by a U.S. astronaut took place in 1965. Edward H. White's jaunt from the Gemini 4 spacecraft lasted just 21 minutes.

Before going back inside, Jones and Curbeam paid tribute to White -- who died in a launch pad fire in 1967 -- and all the other Gemini, Apollo, Skylab and shuttle astronauts who performed spacewalks over the decades. Moonwalks are included in the tally.

"And here we are now," Jones said. "We think in the years to come in the very near future, we'll see not only the construction of the space station completed, but spacewalkers will take their place not only in low-Earth orbit, but back on the moon and back on the asteroids and perhaps even to Mars.""

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