STS-131: Space Station Resupply and Ammonia Tank Replacement

STS-131 was an International Space Station resupply and maintenance mission flown by the National Aeronautics and Space Administration (NASA) using the space shuttle Discovery, and the orbiter's 38th flight. Rather than delivering an independent probe, the mission carried research racks, living equipment and maintenance spares to an already continuously occupied station, then brought back experiment materials and used equipment requiring inspection.

The Italian-built Leonardo Multi-Purpose Logistics Module was carried in the shuttle's payload bay and provided pressurized transport space. To increase carrying capacity, engineers removed about 178 pounds of noncritical hardware before the flight. NASA's annual report recorded that the module carried more than 17,000 pounds of cargo, about 7.7 metric tons; 16 research, systems and storage racks were transferred, not all of them experimental equipment.

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Commander Alan Poindexter and pilot James Dutton were responsible for flight operations. Mission specialists Rick Mastracchio and Clayton Anderson performed spacewalks; Stephanie Wilson, Dorothy Metcalf-Lindenburger and Naoko Yamazaki of the Japan Aerospace Exploration Agency took part in robotic-arm operations, cargo transfer and tasks inside the spacecraft. Seven crew members were aboard.

The flight control team at Johnson Space Center worked in shifts. The mission press kit named Richard Jones as lead flight director, Mike Sarafin as responsible for another orbital shift, and Ginger Kerrick as responsible for the planning shift. Ground engineers, shuttle crew and station personnel had to coordinate equipment movements, airlock use, power and communications. External maintenance could not be conducted independently of operations inside.

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At 10:21 UTC on April 5, 2010, or 6:21 a.m. local daylight time in Florida, Discovery lifted off from Launch Pad 39A at Kennedy Space Center. It docked with the International Space Station at 07:44 UTC on April 7. These times marked the mission's launch and arrival at its orbital workplace respectively.

After reaching orbit, the shuttle's Ku-band system failed to operate normally, affecting its rendezvous radar and high-rate data transmission. The team used the station's downlink capability to supplement the data link. Thermal protection system inspection imagery also had to be transmitted to the ground through the station before separation. The mission was therefore extended by one day so that ground teams could finish the inspection before departure.

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Mastracchio and Anderson completed three extravehicular activities totaling 20 hours 17 minutes, principally to replace a depleted ammonia tank in the station's external thermal control system. The new tank was moved from the shuttle payload bay to the station truss, while the old tank had to be secured in the payload bay for return. Robotic arms transported large components, while the astronauts handled fasteners, connectors and plumbing.

Difficulties with fastening bolts forced some work to be postponed. NASA's annual report also listed a nitrogen tank assembly valve failure, showing that completing installation and having all associated components function normally were separate matters. In addition to replacing the ammonia tank, the crew retrieved a Japanese external experiment payload. Such returned items provided physical objects for ground inspection rather than telemetry records alone.

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Leonardo carried four research racks: the Window Observational Research Facility, EXPRESS Rack 7, the Muscle Atrophy Research and Exercise System, and the third Minus Eighty-Degree Laboratory Freezer for ISS. It also carried living and storage equipment. The freezer preserved samples such as blood, urine and plants, slowing changes in their condition so they could later be returned for analysis on the ground.

The window observation facility was installed at the Earth-facing window of the Destiny laboratory, providing structural support, power and data connections for cameras and remote-sensing equipment. The muscle research system used a seat, restraints, actuators and measurement software to support research on forces and movement at several joints. A contemporary European Space Agency report recorded that the two devices had been transferred into their respective laboratories; completing delivery did not mean that the associated scientific findings had already been produced.

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On April 17, Discovery undocked from the station, flew around it to take photographs and departed. Return cargo included hardware from European fluid experiments and research samples transferred from station freezers into refrigerated return containers. This linked orbital work to ground testing and made use of the shuttle's capacity to bring back relatively large equipment.

Weather delayed the landing by another day. Discovery finally landed at Kennedy Space Center at 13:08 UTC on April 20, or 9:08 a.m. local daylight time, after a flight lasting about 15 days. It completed the principal resupply and maintenance objectives and returned Leonardo to Earth in preparation for its subsequent conversion into a permanent station module. Launch, docking, departure and landing each represented a different phase of the mission.

References: [1] [2] [3] [5]