Two astronauts were able to quickly replace a faulty backup computer box during a spacewalk earlier today (April 23) at the International Space Station.

NASA astronauts Rick Mastracchio and Steve Swanson removed the box and installed a spare within an hour, according to NBC News.

Ground controllers reported that the box, also known as a multiplexer-demultiplexer (MDM) was working fine.

The old box failed to respond to commands back on April 11.

Most spacewalks talk anywhere between five or six hours, but this one lasted approximately one hour and 36 minutes.

Mastracchio and Swanson left the station's Quest airlock around 10 a.m. for what was supposed to be a 2-1/2-hour spacewalk, according to Reuters.

The device is about the size of a small microwave oven, and is one of two that control a number of important 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.

Mastracchio was in charge of switching the boxes, while Swanson cut dangling lanyards that had been in the way of the space station's Dextre robotic hand.

This was the ninth spacewalk for Mastracchio, and the fifth for Swanson, according to Reuters.

As the two worked outside, Japanese astronaut Koichi Wakata played a supporting role inside the ISS.

Astronaut and former space station crewmember Chris Cassidy said replacing the computer is "pretty straightforward," in an interview with NASA Television last week.

"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 during the interview.

The $100 billion station is a permanently staffed research laboratory that flies 260 miles above Earth.

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