NASA gave its final approval Tuesday for the spacewalk and insisted that the safety precautions will be ample, even though no one will be inside the space station to serve as a watchman.
Normally, two crew members go out at a time, employing the buddy system for safety reasons, while the third astronaut stays behind to watch over them and the spacecraft. But the station has had just a two-man crew since last spring to reduce the need for supplies while the shuttles are grounded because of the Columbia space shuttle disaster.
NASA was initially skeptical of the Russian Space Agency's idea for an all-hands spacewalk and agreed to the 5 1/2-hour outing only after months of safety analyses.
The Americans and Russians came up with 13 flight rules governing what to do if something breaks, the space station spins out of control, a fire erupts or some other emergency arises.
During the spacewalk, astronaut Michael Foale and cosmonaut Alexander Kaleri will retrieve some science experiments and set up others. They will also will check the exterior of the station for any signs of a blow from debris. Last November, the crewmen heard a strange metallic noise, possibly from a piece of space junk hitting something.
The space station has been abandoned briefly a few times in the three years it has been occupied, to move the astronauts' escape craft from one docking port to another. Flight controllers kept close watch over the spacecraft, and nothing went wrong. But the station has never been left unattended while the crew was outside on a spacewalk.
The Russians have left their space stations empty during spacewalks for decades. They had been pushing for this excursion since last summer because of contractual agreements with the European and Japanese space agencies, which own the experiments that need to be taken in and out.
Flight controllers routinely monitor and even run the international space station's systems, so that was not the major concern for NASA. The chief worry was safety, and all NASA's concerns were answered to its satisfaction, said flight director Sally Davis.
The crewmen overcame the final hurdle last week when they managed to squeeze into their docked Soyuz capsule while wearing bulky spacesuits. NASA wanted to prove that in an emergency, such as a fire or decompression, the spacewalkers could immediately get into their escape craft.
Medical supplies will be left inside near the hatch in case one of the spacewalkers comes in hurt.
After the Columbia disaster a year ago, NASA wanted to wait until shuttle flights resumed so a third crew member would be inside for any spacewalk. But managers changed their minds when it became apparent that shuttles were going to be grounded for much longer than anticipated.
The station's next two-man crew expects to make two spacewalks, conducting far more critical work. Station operations manager Mike Suffredini said this week's spacewalk will be fairly routine and will help NASA identify any problems for the next time.
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