Astronauts conduct emergency spacewalk to replace computer system

Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer of NASA on board the space station will take an impromptu 200th spacewalk on Tuesday, May 23, at 5:30 PM to fix a broken instrument of International Space Station.

NASA's last emergency spacewalk took place in December 2015 when two United States astronauts left the station to release the brakes on a robot arm's mobile transporter.

The computer which failed is the multiplexer/demultiplexer, which was installed on 30 March. The walk will last roughly two hours, during which time Fischer will replace the MDM with a spare relay box. NASA built two into the system to maintain redundancy, and one is still functioning.

They will be replacing the multiplexer-demultiplexer (MDM) data relay box on the S0 truss that suffered a failure last week. "The antenna installation task was originally planned for the last spacewalk on May 12", said the NASA statement.

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.

And so, Whitson and Fischer will venture back outside just 11 days after completing their most recent excursion on May 12, switching their spacesuits to battery power around 8 a.m.to officially kick off U.S. EVA-43.

After the failure was reported, the space station switched over to the spare MDM, but NASA made a decision to fix it as it wants to restore redundancy as quickly as possible.

Astronauts performed a similar spacewalk in 2014.

The failed unit was installed not quite two months ago.

The tier 2 MDMs relay commands to a variety of critical station systems, including the station's guidance, navigation and control system, the lab's stabilizing gyros, the environmental control system, the station's cooling system and others. She has confirmed that the spare relay box was ready to be used as a replacement for the failed MDM.

  • Carolyn Briggs