STS-131 (Discovery / ISS resupply)

Background

By 2010, the International Space Station had entered a phase of rapid outfitting. With its core structure complete, NASA and its partners were focused on filling the laboratory modules with the science hardware, crew accommodations, and consumables that would allow the station to realize its full research potential. The Space Shuttle's enormous cargo capacity made it the only vehicle capable of delivering the largest pieces of that puzzle, and with the shuttle program approaching retirement, each remaining flight carried an urgency that earlier missions had not. STS-131 was conceived as one of the heaviest resupply runs of the entire shuttle era, tasked with hauling a densely packed Leonardo Multi-Purpose Logistics Module from Kennedy Space Center to the orbital outpost some 350 kilometers overhead.

Discovery, one of the program's most experienced orbiters, was selected for the mission. Commanding the flight was Alan Poindexter, a naval aviator making his second spaceflight. James Dutton served as pilot, also on his first long-duration assignment. Mission specialists Rick Mastracchio, Dorothy Metcalf-Lindenburger, Stephanie Wilson, and Naoko Yamazaki rounded out the shuttle crew, while Clayton Anderson was already aboard the station as an Expedition 23 crew member. The composition of the crew carried its own historic weight: with Metcalf-Lindenburger, Wilson, and Yamazaki flying on Discovery and Tracy Caldwell Dyson already present on the station, the mission would momentarily place four women in orbit simultaneously — the most in human spaceflight history.

Launch and Ascent

Discovery lifted off from Launch Complex 39A at Kennedy Space Center on April 5, 2010. The moment of liftoff was immediately notable: three women were seated aboard the orbiter while a fourth was already circling Earth on the station. Within approximately eight and a half minutes of launch, Discovery's main engines fell silent and the vehicle was on orbit, its crew preparing for the rendezvous sequence that would culminate in docking with the station.

The historic gender milestone, though secondary to the operational goals of the mission, attracted considerable public attention. For the first time since humans had been flying in space, four women were aloft at the same moment — a quiet but meaningful marker of how thoroughly the astronaut corps had evolved since the all-male crews of the early space age.

Cargo Operations

The centerpiece of STS-131's work was the Leonardo module, a pressurized Italian-built container roughly the size and shape of a large truck trailer. Berthed in Discovery's payload bay, Leonardo had been loaded with an exceptional quantity of hardware before launch. Once the shuttle was secured to the station's docking port and hatches were opened, the crew set about systematically transferring the module's contents.

Among the items delivered were new science racks destined for the station's laboratories, a crew sleeping berth that would allow additional long-duration residents to be accommodated comfortably, and a science freezer critical for preserving biological samples collected during research on human physiology in microgravity. The full transfer of cargo between Leonardo and the station represented one of the largest single-mission deliveries of the shuttle program, with the module carrying the equipment and supplies needed to sustain an expanding crew through months of continued operations.

Three spacewalks were conducted during the docked period to accomplish external tasks, including the transfer of hardware and the replacement of aging equipment on the station's exterior. Mastracchio and Anderson served as the primary spacewalkers for these excursions, working in the vacuum outside the station while their crewmates managed operations from within.

Throughout the docked phase, the crew worked in coordinated shifts to keep cargo transfers moving efficiently. The timeline was demanding — the mass of material to be relocated was substantial — but the crew completed the handoff successfully. Once all transfers were concluded, Leonardo was reberthed in Discovery's payload bay, now carrying the hardware and samples being returned to Earth.

Undocking, Return, and Legacy

After the cargo work was complete, Discovery undocked from the station and began the sequence of maneuvers that would bring the orbiter home. The crew performed the standard separation and flyaround before moving to a safe distance. Deorbit preparations proceeded on schedule, and the deorbit burn was executed to commit Discovery to reentry. The orbiter descended through the atmosphere and touched down at Kennedy Space Center, completing a mission that had lasted roughly fifteen days.

STS-131 is remembered for what it delivered and for what it represented. On the practical side, the mission materially advanced the station's capability, filling its laboratories with hardware that would support research for years. The science racks and freezers transferred during those docked days contributed to ongoing investigations in biology, materials science, and human physiology — work that continues to inform both fundamental science and the planning of future long-duration spaceflight.

The human dimension of the mission earned it a place in the broader history of spaceflight beyond the logistical ledger. The simultaneous presence of four women in orbit, though achieved not through any formal design but through the natural convergence of crew assignments, was a genuine first. It reflected a generation of change in who was considered qualified to fly in space and who was actively doing so. Naoko Yamazaki's participation was itself notable as only the second Japanese woman to fly in space, underscoring the increasingly international character of the station program.

As one of the final flights before the shuttle's retirement in 2011, STS-131 also carries the retrospective weight of an ending. Discovery — which would go on to fly one additional mission before being retired to the Smithsonian — performed flawlessly. The mission exemplified what the shuttle program had become in its final years: a workhorse of station assembly and resupply, operating with a professionalism honed over three decades, crewed by astronauts who represented the full breadth of the people who had carried human spaceflight forward.