During its 22 years of operation, "Columbia" was flown on 28 missions in the Space Shuttle program, spending over 300 days in space and completing over 4,000 orbits around Earth. While it was seldom used after completing its objective of testing the Space Shuttle system, and its heavier mass and internal airlock made it unideal for planned Shuttle-Centaur launches and dockings with space stations, it nonetheless proved useful as a workhorse for scientific research in orbit following the loss of "Challenger" in 1986. "Columbia" was used for eleven of the fifteen flights of Spacelab laboratories, all four United States Microgravity Payload missions, and the only flight of Spacehab's Research Double Module. The Extended Duration Orbiter pallet was used by the orbiter in thirteen of the pallet's fourteen flights, which aided lengthy stays in orbit for scientific and technological research missions. "Columbia" was also used to retrieve the Long Duration Exposure Facility and deploy the "Chandra" observatory, and also carried into space the first female commander of an American spaceflight mission, the first ESA astronaut, the first female astronaut of Indian origin, and the first Israeli astronaut.