(Reuters) - Two U.S. astronauts floated outside the International Space Station on Wednesday to replace a failed computer that serves as a backup to critical control systems, including the outpost's solar panel wings.

Flight engineers Rick Mastracchio and Steve Swanson left the station's Quest airlock just after 10 a.m. EDT (1400 GMT) for what was expected to be a 2-1/2-hour spacewalk. They carried with them a spare computer to be installed in the central section of the station's exterior power truss.

"It looks like a great day to take a walk in space," Canadian astronaut Jeremy Hansen radioed to the crew from NASA's Mission Control in Houston.

NASA scheduled the abbreviated outing - most U.S. spacewalks last more than six hours - after the computer failed on April 11.

The device, which is about the size of a small microwave oven, is one of two that control several critical systems outside the station, including rotating the solar panel wings to track the sun and positioning a mobile base for the station's robotic crane.

Replacing the computer is "pretty straightforward," astronaut and former space station crewmember Chris Cassidy said in an interview last week on NASA Television.

"We anticipate it to go quickly, but as with anything in space operations ... you never know what's going to be thrown at you," Cassidy said.

Except for emergency repairs, such as the computer replacement, NASA spacewalks remain suspended while engineers continue to assess the spacesuit failure last year that caused the helmet worn by Italian astronaut Luca Parmitano to fill with water, nearly drowning him.

The leak was later traced to a blocked filter. NASA flew new parts to the station for astronauts to make spacesuit repairs. Before two emergency spacewalks in December to fix the station's cooling system, astronauts also outfitted their helmets with absorbent pads and snorkels for breathing if the leak reoccurred.

Those spacewalks were completed with no problems. Mastracchio, who is making his ninth spacewalk, and Swanson, on his fifth, also included the snorkels and pads in their helmets for Wednesday's outing.

A new spacesuit was among the cargo aboard the Space Exploration Technologies' Dragon capsule that reached the station on Sunday.

NASA expects to resume routine spacewalks for maintenance and less-pressing repairs in July.

The station, a $100 billion project of 15 nations, is a permanently staffed research laboratory that flies about 260 miles above Earth.

(Reporting by Irene Klotz; Editing by Jonathan Oatis)