3 spacewalks in 9 days for astronauts

Let the spacewalks begin. U.S. astronauts Michael Lopez-Alegria and Sunita Williams on Wednesday were expected to make the first of three spacewalks over a nine-day period outside the international space station.

It would mark the first time U.S. astronauts have attempted the feat in such a short period of time without a space shuttle docked at the station.

"We're going to be knocking out three, one right after another," said Glenda Laws, lead spacewalk officer.

The astronauts plan to connect ammonia loops that keep the U.S. lab cooled from a temporary to a permanent system, and to jettison a sun shade and thermal shrouds during their three trips outside the station. Besides Wednesday's trip, spacewalks are planned for Sunday and the following Thursday.

If the spacewalks go as planned, Lopez-Alegria would have little time to rest before going on a fourth scheduled spacewalk in late February.

It's not uncommon for U.S. astronauts to conduct three spacewalks over a short period of time during a visit by a space shuttle to the station _ four were carried out during Discovery's trip in December.

The extra astronauts are handy for helping the spacewalkers prepare their spacesuits and the airlock, and for operating robotic arms on the station and shuttle to provide camera views or move the spacewalkers.

Conducting a spacewalk with just a three-man crew at the space station is a much tougher task. The difficulty is magnified when trying three in such a short period of time _ a major reason it has never been done before.

Unlike spacewalks with a docked shuttle, the coordinator during the upcoming spacewalks will be at Mission Control in Houston instead of at the space station.

NASA officials said they scheduled the spacewalks so closely together because the first two are almost identical in nature, and time and energy could be saved on preparation. Timing also played a role, as the U.S. spacewalks were scheduled to take place between the last shuttle visit in December _ when the cooling system was turned on _ and the next scheduled visit in mid-March.

Lopez-Alegria and Williams will have three days to rest between each spacewalk, although Mission Control could give them more time if they need it.

"These two crew members are extremely fit and we don't think there is any reason for concern that they would have undue physical exhaustion," Laws said.

Because Lopez-Alegria has been at the space station since September, the spacewalkers haven't trained together in the practice pool at the Johnson Space Center since last July. So Mission Control has been giving them extra time to study up and practice computer simulations.

"It's a refresher in every sense of the word in what they last practiced in Houston," said Derek Hassmann, spacewalk flight director.

The spacewalkers need to be especially careful about avoiding ammonia leaks, as the toxic substance leaked out of cooling line in 2001 when astronaut Robert Curbeam was performing a similar task. Curbeam positioned himself so the sun would bake off the ammonia crystals and the shuttle airlock was vented to prevent contamination.

"We are preparing ourselves and preparing the spacewalking crew for the potential that we may have some ammonia leakage," Hassmann said. "We feel that we're ready if it does come."

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On the Net:

International space station: http://www.nasa.gov/mission_pages/station/main/index.html