Nasa astronauts Peggy Whitson and Jack Fischer will be stepping out for an unplanned spacewalk to repair a data relay box of the International Space Station's (ISS) computer that failed a few days ago.

The two astronauts will replace a failed computer, which is one of the two units on the ISS that regulates major power, heating and cooling systems alongside other equipment.

Whitson is tasked with replacing the main box known as a multiplexer-demultiplexer (MDM), while Fischer will install two wireless communications antennas on the Destiny Lab.

The spacewalk, which is expected to last for 2.5 hours will be the tenth of Whitson's career, and the second for Fischer. Whitson, currently the commander of the ISS expedition, has already spent more days in space than any other American astronaut.

Nasa said that despite the problems with the computer, the space station's five-person crew from the US, France and Russia is not in any danger. They have been relying on a backup system until the repairs take place. A spare electronics box to replace the failed device has already been prepared and tested.

The video streaming above shows the astronauts getting ready for the spacewalk and their communications with the control room back on Earth. Nasa regularly broadcasts such space operations mainly for educational purposes.

Nasa astronaut Peggy Whitson along with Expedition 50 Commander Shane Kimbrough installing three new adapter plates for three of the six new lithium-ion batteries on the International Space Station Nasa