Mastracchio and Anderson will conduct three six-and-a-half-hour-long spacewalks to replace an ammonia tank assembly, retrieve a Japanese experiment from the station’s exterior, and switch out a rate gyro assembly on the S0 segment of the station’s truss structure.
Discovery will carry a multi-purpose logistics module (MPLM Leonardo) filled with food and science supplies to be transferred to the station. This includes the Minus Eight Degree Laboratory Freezer for ISS (MELFI), the Window Observational Research Facility (WORF), a crew quarters rack, and the Muscle Atrophy Research and Exercise System (MARES) rack, resupply stowage racks and resupply stowage platforms. The WORF is designed to enhance the work that astronauts are able to do looking out the window of the Destiny laboratory by adding cameras, multispectral and hyperspectral scanners, camcorders and sensors. With those instruments, the crew will be able to study global climates, land and sea formations and crop weather damage like never before. Meanwhile, the MARES will provide the crewmembers with a way to assess the strength of their muscles while in space. The deterioration of muscles not used while astronauts are floating in microgravity has long been a concern for space programs. This rack will mean that the crewmembers don't have to wait until they're back on solid ground to find out how their time in space affected their health. Instead, the MARES will help them exercise seven different human joints, gauge the strength of the muscles around those joints and decide how the countermeasures designed to prevent muscle atrophy are working.
STS-131 will be the 33rd shuttle mission to the station, and the final shuttle mission with a seven person crew. This will be the final Space Shuttle mission that contains one or more "rookie" astronauts; the missions after this will have all-veteran crews. STS-131 will be the third mission in the Space Shuttle program to carry three female astronauts; STS-40 and STS-96 were the first and second. This flight will also mark the first time that two Japanese astronauts, Naoko Yamazaki and Soichi Noguchi, are in space at the same time. Assuming an on-time launch of April 5, 2010, landing is expected after a thirteen day mission on April 18, 2010.