Astronaut Piers J. Sellers Working on the ISS

When your home computer breaks, it’s an inconvenience. When a computer on the International Space Station breaks, it’s a potential disaster—not only because there’s no repairman handy, but also because you might depend on that system to stay alive, and because it’s installed on a $100 billion floating island in the sky.

On Tuesday, two astronauts on the ISS will venture forth into the harshest environment humankind has ever known in order to fix a computer.

The computer (called a multiplexer-demultiplexer) that usually controls the station’s radiators, solar arrays, cooling loops, and other hardware crapped out on Saturday morning, for reasons unknown. A backup system has kicked in to keep everything working smoothly, and the station and crew were never in any danger, says a NASA press release.

Still, the space agency likes redundancy, so it wants to the get the other system operational again as well. So they’ve scheduled an unplanned spacewalk for Tuesday starting at 8am EDT. You can watch along here:

Station commander Peggy Whitson has already prepared a space relay box, and it should take about two hours for her and flight engineer Jack Fischer to swap in the replacement.

NASA’s coverage of the spacewalk begins at 6:30am on Tuesday.