In a spacewalk lasting less than an hour, two members aboard the International Space Station successfully restoreda critical computer system.

A pair of NASA astronauts replaced a dead backup computer on the International Space Station during a short spacewalk Wednesday (April 23) to restore a critical computer system back to full strength.

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NASA astronauts Rick Mastracchio and Steve Swanson made quick work of their repair during the spacewalk, removing the faulty station computer and installing a spare less than an hour after floating outside the orbiting laboratory at 9:56 a.m. EDT (1356 GMT).

"It looks like a good day for you guys to take a walk in space," Mission Control radioed the astronauts as the spacewalk began. The spacewalk was slated to last only 2.5 hours. [See photos from today's spacewalk]

Mastracchio and Swanson replaced a computer known in NASA parlance as a Multiplexer-Demultiplexer, or MDM. The device is a backup computer for routing commands to systems supporting the space station's solar arrays, robotic arm rail car and other critical systems along the station's backbone-like main truss.

The 10-year-oldMDM computer failed on April 11during a standard test. The primary computer in the system is working fine, but NASA station flight controllers ordered today's repair spacewalk to restore redundancy in the system.

"Looks like we've got a new MDM," Mastracchio said as he finished the job.

A quick test showed the new computer was working fine.

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Space station astronauts step outside to replace dead computer