The mission’s main task was to install the AMS-02 Alpha Magnetic Spectrometer cosmic-ray detector on the Space Station that will hunt for antimatter and the mysterious ‘dark matter’.
Although AMS-02 is not a vital part of the Station, it is the last big payload to be lofted to the orbital complex by the Shuttle.
After this final flight of Endeavour, only one more flight of the spaceplane is planned. Atlantis will fly STS-135 with four astronauts in July to deliver spares and supplies to the Station to secure its capabilities in years to come and to provide a logistics backup until the commercial cargo providers will be available in 2012 – in addition to ESA’s ATV and Japan’s HTV unmanned cargo ships.
Station construction began in November 1998 with the launch of Russia’s Zarya module. Assembly was significantly delayed because of the tragic loss of Shuttle Columbia, which also resulted in the decision to retire the fleet after completion of the Station.
One more pressurised module will be attached to the Station, in 2012: Russia’s Nauka Multipurpose Laboratory Module is as big as Zarya and Zvezda. It will be installed on the Earth-facing docking port of the Zvezda module.