STS-131 (ISS assembly flight 19A) was a NASA Space Shuttle mission to the International Space Station (ISS). launched on April 5, 2010, at 6:21 am from LC-39A, and landed at 9:08 am on April 20, 2010, on runway 33 at the Kennedy Space Center's Shuttle Landing Facility. The mission marked the longest flight for Space Shuttle Discovery. The primary payload was a Multi-Purpose Logistics Module loaded with supplies and equipment for the International Space Station. The mission also removed and replaced an ammonia tank assembly outside the station on the S1 truss. STS-131 furthermore carried several on-board payloads; this mission had the most payloads since STS-107. It is also the last shuttle mission with a crew of 7. Crew Mission payload Multi-Purpose Logistics Module Leonardo The primary payload of STS-131 was the Multi-Purpose Logistics Module (MPLM) Leonardo. The MPLM was filled with food and science supplies for the International Space Station (ISS). The MPLM also carried the third and final Minus Eighty Degree Laboratory Freezer for ISS (MELFI), Window Orbital Research Facility (WORF), one Crew Quarters Rack, the Muscle Atrophy Resistive Exercise (MARES) rack, Resupply Stowage Racks (RSRs), and Resupply Stowage Platforms (RSPs). Lightweight Multi-Purpose Equipment Support Structure Carrier The Lightweight Multi-Purpose Equipment Support Structure Carrier (LMC) carried a refurbished Ammonia Tank Assembly (ATA) to the ISS. The refurbished ATA was removed from the Space Station and returned for use on this mission during STS-128. It was swapped with an empty tank which will ride home on the LMC. TriDAR This mission was the second flight of the TriDAR, a 3D dual-sensing laser camera, intended for potential use as an autonomous rendezvous and docking sensor. TriDAR provides guidance information that can be used to guide a vehicle during rendezvous and docking operations in space. TriDAR does not rely on any reference markers, such as reflectors, positioned on the target spacecraft. To achieve this, it relies on a laser based 3D sensor and a thermal imager. Geometric information contained in successive 3D images is matched against the known shape of the target object to calculate its position and orientation in real-time. The TriDAR tracked the ISS position and orientation from the shuttle during docking, undocking, and flyaround operations. Mission milestones The mission marked: 162nd NASA crewed space flight 131st shuttle mission since STS-1 38th flight of Discovery 33rd shuttle mission to the ISS 106th post-Challenger mission 18th post-Columbia mission 35th and