The 6-member crew of space shuttle Endeavour began its two-day journey back to the Earth from the orbiting International Space Station (ISS) on Sunday 11:55 pm (EDT) after delivering a $2 billion payload - Alpha Magnetic Spectrometer particle detector or a cosmic ray detector - and a pallet of spare parts intended to tide over the orbital outpost after the shuttle program ends.

The shuttle's crew, whose commander is Mark Kelly (husband of Rep. Gabrielle Giffords), spent 12 days on board the orbiting station and completed four spacewalks to complete construction of the U.S.-side of the $100 billion outpost, a project of 16 nations that is being assembled in orbit since 1998.

The shuttle is scheduled to land on Earth on June 1, following which it will be put up on exhibit at the California Science Center in Los Angeles.

A final space shuttle mission will kick off on July 8, when Atlantis will be launched, carrying a year's worth of supplies for ISS - a contingency plan in case the commercial companies hired to take over supply runs to the station encounter delays with their new vehicles.