Endeavour flew its final mission in May 2011, delivering a landmark physics experiment to the International Space Station. The crew of six installed the Alpha Magnetic Spectrometer, a large particle detector designed to search cosmic rays for antimatter and clues to the nature of dark matter, mounting it on the station's truss to run for years.
Four spacewalks completed station maintenance and outfitting. The mission was commanded by Mark Kelly, whose wife, Congresswoman Gabrielle Giffords, was recovering from an assassination attempt months earlier, lending the flight an unusual measure of public attention. Endeavour, the youngest orbiter, built to replace Challenger, retired after this flight. Its delivery of the spectrometer left the station with a premier scientific instrument that would keep gathering data long after the Shuttle era ended.
Endeavour's final flight carried a two-tonne particle physics detector and a story the press could not leave alone. The Alpha Magnetic Spectrometer, championed for decades by the Nobel laureate Samuel Ting after a prototype flew in 1998, was installed on the station's truss to sift cosmic rays for antimatter and dark matter — an instrument so expensive and so nearly cancelled that its presence aboard the last Endeavour mission was itself a political achievement.
The commander was Mark Kelly, whose wife, the congresswoman Gabrielle Giffords, had been shot in the head at a constituents' meeting in Tucson four months earlier. He had stepped away from training, then returned; she travelled to Florida and watched the launch from a rooftop, one of the more extraordinary spectators the programme ever had.
The crew made four spacewalks to finish the outfitting of the station's exterior and left the orbiter's inspection boom permanently attached to the truss, since there would soon be no Shuttle to carry one. Endeavour had been built to replace Challenger, from structural spares, and flew twenty-five times in nineteen years. The spectrometer it delivered has now recorded more than two hundred billion cosmic ray events and is still counting.
