Spacewalkers work on space station cooling system

By Irene Klotz

HOUSTON (Reuters) - Spacewalking astronauts installed a refrigerator-sized tank of gas needed for the International Space Station's cooling system on Wednesday, while crewmates worked inside the outpost to outfit Europe's newly arrived space laboratory.

"Welcome to spacewalking," astronaut Rex Walheim told his partner, Hans Schlegel, who was making a belated but eagerly anticipated debut spacewalk.

"It's a good feeling," said Schlegel, 56, as he worked his way out of the space station's airlock to the shuttle's payload bay.

Schlegel, of Germany, had to sit out the first spacewalk of shuttle Atlantis' mission on Monday due to an undisclosed medical condition, but was cleared for Wednesday's spacewalk. He told reporters his medical situation was a private matter.

Walheim, 45, paired with rookie Stanley Love, 42, for Monday's outing when the $1.9-billion Columbus module, Europe's first permanent space lab, was installed. The lab was brought to life on Tuesday.

During Wednesday's spacewalk, Walheim and Schlegel unbolted a 550-pound (250-kg) tank of nitrogen from a platform in Atlantis' cargo hold and then caught a ride on the shuttle's robotic crane over to the space station to install it on an exterior support beam. The nitrogen is used to pressurize ammonia coolant lines.

The astronauts placed the station's spent nitrogen tank into the shuttle and anchored it for the return trip to Earth. The new tank, unlike the old one, can be refilled in orbit.

RADIATION LEVELS

During the spacewalk, NASA for the first time used real-time data from a solar observatory to monitor radiation levels around the shuttle and space station. The sun periodically spews high-energy radiation that can be dangerous to humans outside the protective bubble of Earth's atmosphere.

"We're testing this model to see if it can be used in an operational situation," said Stephen Guetersloh, a particle physicist with NASA's Space Radiation Analysis Group at the Johnson Space Center in Houston.

The sun is in the quiet phase of its 11-year cycle, which is expected to peak in 2010 or 2011.

On Friday, during the third and final spacewalk planned during Atlantis' flight, Walheim and Love are scheduled to install a solar telescope and a materials science experiment to the outside of the Columbus module.

While Wednesday's spacewalk was under way, shuttle and space station crewmembers resumed working inside the new laboratory to set up experiment racks and equipment. The module was opened for the first time in space on Tuesday.

"We are very pleased indeed to see crew finally inside the laboratory," said Alan Thirkettle, the European Space Agency's station program manager.

(Editing by Jim Loney and Philip Barbara)