Spacewalkers set out for 4th station service call

By Irene Klotz

CAPE CANAVERAL, Florida (Reuters) - Two shuttle Atlantis astronauts floated outside the International Space Station on Sunday for a fourth and final spacewalk before the shuttle departs on Tuesday.

Patrick Forrester and Steven Swanson left the station's airlock about 12:40 p.m. EDT/1640 GMT to finish work on a rotary joint so a pair of electricity-producing wing panels can track the sun for power.

The wings were installed last week during the first spacewalk of Atlantis' 13-day flight.

During the installation, the space station's primary computer network crashed, raising concerns that the still-under-construction, $100 billion outpost would have to be temporarily abandoned.

The German-built computers were provided to Russia in exchange for equipment to dock Europe's cargo ship, called the Automated Transfer Vehicle, at the station early next year.

Russian flight controllers and cosmonauts aboard the station figured out a way to bypass suspect protection circuits and successfully revived the network. The computers control steering rockets that are needed to periodically readjust the station's position in space.

NASA wants to make sure the thrusters will kick in to dampen any motion caused when the 100-ton shuttle detaches and plans a test of the system on Monday.

The shuttle has enough supplies to stay at the outpost until Wednesday if any problems arise.