WASHINGTON – A pair of astronauts will take an emergency spacewalk outside the International Space Station on Tuesday to replace a failed computer, NASA said on Sunday

The one of two primary device that controls U.S. systems  aboard the orbiting outpost went out of order on Saturday. Now, the $100 billion orbiting laboratory is depending on a backup system to carry commands to its solar power system, radiators, cooling loops and other equipment.

According to NASA, Station Commander Peggy Whitson and Astronaut Shane Kimbrough have been tasked with the repair of the malfunctioning computer.

On Sunday, Whitson prepared a spare data relay box that is ready to be brought outside to replace the failing unit.

The sixth spacewalk conducted from the Quest airlock this year is expected to last for two hours.