Today we could watch not planned spacewalk performed by crew members of International Space Station. It was sixth EVA in 2017 and another success of ISS crew.
Today Peggy Whitson and Jack Fischer left Quest airlock to perform service on MDM computer unit, which was installed outside the Station on lab’s power truss. Both MDM units installed in the same place called Tier 2 were replaced during EVA-4 during Expedition 50 on March 24 and March 30, 2017 by Shane Kimbrough, Peggy Whitson and Thomas Pesquet. After over a month one of them failed on last Saturday and NASA decided to change it today after series of test performed by Peggy Whitson on Sunday.
To remind MDM (Multiplexer-Demultiplexer) are electronic units working as a part of Command and Data Handling (CDH) system which controls ISS including power system, attitude control system and every crucial segment of the ISS. MDM's are controlling streams of data floating from various elements of the subsystems to others keeping everything connected. These continuous exchange of the data is necessary to keep Station operationable and keeping each system under control and protecting from interfering between each other.
Spacewalk began at 11:20 UTC when Peggy Whitson and Jack Fischer left Quest airlock and begun their walk to MDM computer. They were able to unplugged cables and take MDM unit out. Surprising issue started with main bolt which was not as sstable as it should. Peggy Whitson cleaned it with compressed nitrogen and reinstalled another MDM unit successfully. After finishing tests and receiving confirmation that MDM is working both NASA astronauts returned to Quest airlock and closed hatch at14:06 UTC. Whole spacewalk last only 2 hours forty minutes.