Astronauts on the International Space Station's Expedition 39 crew focused Tuesday (April 15) on preparing for a contingency spacewalk to be conducted in the next week or so.
Rick Mastracchio and Steve Swanson spent their day preparing for the 2.5-hour spacewalk to replace the failed multiplexer demultiplexer (MDM).
The backup computer relay system, located in the S0 truss, assists in providing insight into the truss systems, the operation of the external cooling loops, the operations of the Solar Alpha Rotary joints and the Mobile Transporter rail car.
Swanson performed a full end-to-end checkout of his spacesuit with its new fan separator pump installed. During the checkout, a cranky CO2 sensor was discovered and is now being investigated.
Mastracchio, meanwhile, gathered and configured the tools he and Swanson will use during the excursion.
Swanson and Mastracchio also participated in an on-board training session for the spacesuit "life jacket," known as the Simplified Aid For EVA Rescue, or SAFER. Should a spacewalker become untethered during a spacewalk and begin floating away from the space station, the small nitrogen-jet thrusters of SAFER would propel the astronaut back to safety.
The two NASA astronauts joined up with station commander Koichi Wakata for an audio conference with ground team that is finalizing procedures for the spacewalk.
Wakata assisted with spacewalk preparations, completing a flush of the water inside the cooling loops of the spacesuits and the airlock.
The date of the spacewalk is contingent on when a SpaceX resupply mission launches.
If SpaceX launches Friday (April 18), the spacewalk will be conducted Wednesday (April 23). If SpaceX launches Saturday, the contingency spacewalk moves earlier to Sunday (April 20).