Rick Mastracchio Prepares for an Upcoming Spacewalk

ISS039-E-013244 (18 April 2014) — NASA astronaut Rick Mastracchio, Expeditionn 39 flight engineer, replaces the Enhanced Input/Output Control Unit Circuit Card of the spare External Multiplexer/Demultiplexer (MDM), in preparation for an upcoming spacewalk. He will be joined by fellow NASA astronaut and Flight Engineer Steve Swanson on the spacewalk.