STS-134 (Endeavour / final flight)

Background

Space Shuttle Endeavour was the youngest orbiter in NASA's fleet, built as a replacement for *Challenger* following the 1986 disaster and first flown in 1992. Over nearly two decades of service, it accumulated a record of landmark missions: the first Hubble Space Telescope servicing flight, the delivery of major components to the International Space Station, and the first mission to carry a crew of seven on a long-duration ISS increment. By 2011, NASA had committed to retiring the entire shuttle fleet, and STS-134 was designated as Endeavour's sixteenth and final spaceflight. That distinction gave the mission a ceremonial weight that was amplified by its scientific cargo — the Alpha Magnetic Spectrometer, known as AMS-02, a particle physics instrument whose story of development spanned more than a decade and whose potential discoveries were expected to shape fundamental physics for years to come.

Commander Mark Kelly, a veteran of three previous shuttle flights, led a crew of six. Pilot Gregory H. Johnson had flown once before, on STS-123. Mission specialists Michael Fincke, Andrew Feustel, and Gregory Chamitoff each brought deep spaceflight experience, while Roberto Vittori flew as a payload specialist representing the European Space Agency, making him the first ESA astronaut to fly aboard Endeavour. The crew had trained extensively for both the station assembly work and the delicate installation of AMS-02, an instrument that had never been designed for on-orbit servicing — meaning its placement on the Station's S3 truss segment had to be executed with precision from the start.

Launch and Ascent

Endeavour lifted off from Launch Complex 39A at Kennedy Space Center on 16 May 2011, after a launch attempt earlier in the month had been scrubbed due to a technical fault with an auxiliary power unit heater. The delay drew widespread public attention, partly because of the presence of astronaut Mark Kelly's wife, U.S. Representative Gabrielle Giffords, who had been critically injured in an assassination attempt just months earlier and traveled to Florida to watch her husband's launch.

At mission elapsed time T+8 minutes 30 seconds, the orbiter reached a stable orbit, its main engines having delivered it to the altitude needed to begin phasing maneuvers toward the International Space Station. The ascent was clean, and the subsequent inspection of Endeavour's thermal protection system using the Orbiter Boom Sensor System confirmed the vehicle was in sound condition for the mission ahead.

Rendezvous, Docking, and Station Operations

Approximately 55 hours and 33 minutes after liftoff, Endeavour docked with the International Space Station's Pressurized Mating Adapter 2. Before docking, Kelly performed the standard Rendezvous Pitch Maneuver — a slow backflip of the orbiter that allowed ISS crew members to photograph the heat shield tiles for damage assessment.

The centerpiece of STS-134's station work was the installation of AMS-02 on the Station's main truss. The Alpha Magnetic Spectrometer is a high-energy particle physics detector built under the leadership of Nobel laureate Samuel Ting of MIT. Designed to detect cosmic rays, positrons, antiprotons, and potentially signatures of dark matter and antimatter in the cosmic flux, AMS-02 is one of the most complex scientific instruments ever installed in space. The spectrometer was lifted from Endeavour's payload bay using the Station's robotic arm and carefully berthed on the S3 truss segment, where it has remained operational. Unlike most ISS experiments, AMS-02 was explicitly not designed to be returned to Earth for servicing, reinforcing the importance of a flawless installation.

The mission also included four spacewalks, conducted by various pairings of Fincke, Feustel, and Chamitoff. These EVAs, collectively totaling more than 27 hours of extravehicular activity, accomplished the installation of a new ammonia pump module, the preparation of the Alpha Magnetic Spectrometer for operations, and other station maintenance and outfitting tasks. The spacewalks were executed without major incident and reflected the crew's thorough preparation.

During the docked phase, which lasted well over two weeks of the total mission, supplies, equipment, and scientific materials were transferred between Endeavour and the Station. The crew also spent time with the ISS Expedition 27 crew, sharing both operational tasks and the awareness that this was one of the final shuttle visits the Station would receive.

Undocking, Reentry, and Landing

Endeavour undocked from the ISS at approximately T+305 hours 33 minutes into the mission. The orbiter then conducted its own inspection and final system checks as it phased away from the Station. At T+376 hours 40 minutes, Endeavour executed its deorbit burn over the Pacific Ocean, committing the vehicle to reentry. Approximately 59 minutes later, at T+377 hours 39 minutes, the orbiter touched down on Runway 15 at Kennedy Space Center, completing a mission of roughly 16 days.

Legacy

STS-134 stands as one of the more scientifically substantial missions in the shuttle program's final years. The deployment of AMS-02 has proven to be genuinely consequential: the instrument began returning data almost immediately and has since detected billions of cosmic-ray events, including measurements of positron flux at high energies that continue to be analyzed for evidence of dark matter interactions. As of its long-term operational record, AMS-02 represents one of the most productive scientific instruments on the International Space Station.

For Endeavour specifically, the mission closed a chapter in American human spaceflight. The orbiter was subsequently decommissioned and prepared for public display, eventually transferred to the California Science Center in Los Angeles, where it was placed in a permanent exhibit. For the broader shuttle program, STS-134 marked the second-to-last mission before STS-135 concluded Atlantis's career and formally ended the Space Transportation System era. The combination of Endeavour's valedictory status and the lasting significance of the AMS-02 instrument ensures that STS-134 occupies a durable place in the history of human spaceflight.