NASA astronauts Peggy Whitson and Jack Fischer are heading back outside the International Space Station a bit quicker than expected. Tuesday morning, the pair will head outside to remove and replace a data relay box that failed Saturday morning.

It’s called a multiplexer-demultiplexer (MDM) and is one of two fully redundant systems that controls a variety of hardware aboard the ISS. Systems like solar arrays, radiators, cooling loops and other hardware.

NASA stressed the crew aboard the ISS are not in danger. The backup MDM kicked in, and the station is functioning normally.

Yesterday, Whitson put together a spare data relay box and tested it to make sure it was working properly. Everything checked out. Now, Whitson and Fischer are getting all the tools ready and giving their spacesuits a thorough check ahead of tomorrow’s spacewalk.

Whitson will handle the installation of the new MDM. Interesting side note: Whitson (with help from astronaut Shane Kimbrough) installed the MDM that failed Saturday back on a March 30th spacewalk.

While Whitson is taking care of the new MDM, Fischer will install a pair of wireless communications antennas on the Destiny Lab portion of the ISS. These antennas were originally planned to be installed back on the spacewalk earlier this month, but mission control decided to postpone.

Tomorrow’s spacewalk will extend Peggy Whitson’s record for most time spent spacewalking by a female astronaut. It’ll be her 10th spacewalk. Fischer gets his second taste of the vacuum of space just a couple of weeks after his first spacewalk.

2017 has been a busy year for NASA astronauts outside the ISS. Tuesday’s spacewalk marks the sixth by U.S. astronauts this year. Already matching the number of spacewalks in all of 2015. And one behind the seven NASA spacewalks in 2011. The most spacewalks in one year by NASA astronauts at the ISS came in 2007 with 20.

ISS spacewalks

NASA will provide live coverage of tomorrow’s spacewalk starting at 6:30 am ET. Whiston and Fischer should be opening the outer airlock around 8:00 am ET. The spacewalk is expected to last about two hours.

Image credits: NASA Johnson, NASA


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