NASA astronauts all set for emergency spacewalk outside International Space Station today

New Delhi: NASA astronauts Peggy Whitson and Jack Fischer are all set to for an unscheduled spacewalk outside the International Space Station (ISS)Tuesday, May 23.

Expedition 51 Commander Whitson and Flight Engineer Fischer will replace a critical computer relay box that failed May 20.

The relay box, known as a multiplexer-demultiplexer (MDM), is one of two units that regulate the operation of radiators, solar arrays and cooling loops. They also route commands to other vital station systems.

Live coverage of the spacewalk begins at 6:30 a.m. EDT on NASA Television and the agency’s website.

While the cause of the MDM failure is not known, NASA says the crew on the station is in no danger, and the MDM failure - believed to be internal to the box itself - has had no impact on station activities. Because each MDM is capable of performing the critical station functions.

The failed relay box was installed in the space station truss March 30 during a spacewalk by Whitson and Expedition 50 commander Shane Kimbrough.

Whitson, who prepared a spare data relay box May 21 and tested components installed in the replacement, said that the spare MDM is ready to be brought outside to replace the failed unit.

During the spacewalk planned to last about 2.5 hours, Whitson will replace the MDM, while Fischer will install a pair of antennas on the US Destiny Laboratory module to enhance wireless communication capability for future spacewalks.

The spacewalk - the 10th for Whitson and the second for Fischer - will be the 201st in support of space station assembly and maintenance. It is also the sixth spacewalk conducted from the Quest airlock this year.

Whitson, who already is the leading female spacewalker in history, will be designated extravehicular crew member 1 (EV-1) wearing a suit with red stripes. Fischer will be designated as EV-2, wearing a suit with no stripes.

A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crewmembers Steve Swanson and Rick Mastracchio of NASA.