Two NASA astronauts on the International Space Station (ISS) are preparing for an unplanned spacewalk tomorrow (Tuesday) to replace a failed data relay unit that was installed just two months ago. Peggy Whitson and Jack Fischer will begin their spacewalk about 8:00 am ET.

This will be Whitson’s 10th spacewalk, tying her with Michael Lopez-Alegria as the NASA astronaut with the most spacewalks, also called extravehicular activity (EVA). The EVA is supposed to last for about 2.5 hours. Depending on the precise duration of the EVA, she would become second or third in terms of how many hours NASA astronauts have spent on spacewalks. Lopez-Alegria currently holds that record at 67 hours 40 minutes. Russia’s Anatoly Solveyev holds the world record of 82 hours 22 minutes on a total of 16 EVAs throughout his career.

Whitson will be joined by NASA astronaut Jack Fischer on his second spacewalk. NASA TV coverage will begin at 6:30 am ET.

The failure of the multiplexer-demultiplexer (MDM) box on Saturday was completely unexpected. The ISS has two redundant MDM units and this one was just replaced on a March 30 spacewalk conducted by Whitson and NASA astronaut Shane Kimbrough. The data relay box control ISS radiators, solar arrays, cooling loops and other hardware. The other MDM is working perfectly. A software problem is thought to be the problem. Whitson, who is in command of the ISS, prepared and tested a spare MDM box on Sunday.

On the March 30 EVA, Whitson set a new EVA duration record for a woman, surpassing NASA astronaut Sunita Williams’ record of 50 hours and 40 minutes. Whitson extended her record on a May 12 EVA with Fischer. She now has 57 hours 35 minutes of time on spacewalks.



NASA astronauts Jack Fischer (left) and Peggy Whitson (right) preparing for May 12, 2017 spacewalk from the International Space Station. Photo credit: NASA