Spacewalkers Make Quick Work of Replacing MDM

International Space Station (ISS) crew members Rick Mastracchio and Steve Swanson made quick work of their task today of replacing a failed computer on the outside of the ISS. They were back inside, mission complete, in just 1 hour and 36 minutes.

The two NASA astronauts conducted a contingency (as opposed to planned) spacewalk to replace a Multiplexer-DeMultiplexer (MDM) that failed just before SpaceX launched its CRS-3 cargo mission to the ISS.  The MDM that failed is a backup unit and the primary unit was working fine so NASA determined the SpaceX launch could proceed as planned.  The MDM controls some of the robotic equipment needed to move SpaceX’s Dragon spacecraft to its proper location on the ISS.  Dragon arrived at ISS on Sunday and was successfully berthed to an ISS docking port using the primary MDM.

However, NASA wanted to be sure a new backup was installed as quickly as possible, hence the spacewalk today.  The new MDM was up and running before the spacewalkers returned to the airlock.  The failed MDM will be returned to Earth so engineers can examine it.

Spacewalks typically last 5-7 hours, but on occasion are shorter in order to accomplish a very defined task or because of a problem that requires early termination.   Last year’s spacewalk where European astronaut Luca Parmitano’s helmet filled with water from the spacesuit’s cooling system ended after 1 hour and 32 minutes when it became apparent that something was quite wrong.   NASA has determined that the problem was silica particles that clogged a filter, but are still investigating the source of the particles. Mastracchio wore the same spacesuit today that Parmitano was wearing last July.  It has a new filter and the water system has been flushed several times.  No problems were evident today (it also was used in a December 2013 contingency spacewalk), but NASA still has not cleared that spacesuit or the other U.S. spacesuits aboard the station for regular use in planned spacewalks.