of the first human spaceflight (Vostok 1), and returned on April 14, 1981, after orbiting the Earth 36 times, landing on the dry lakebed runway at Edwards Air Force Base in California. It then undertook three further research missions to test its technical characteristics and performance. Its first operational mission, with a four-man crew, was STS-5, which launched on November 11, 1982. At this point Columbia was joined by Challenger, which flew the next three shuttle missions, while Columbia underwent modifications for the first Spacelab mission. In 1983, Columbia, under the command of John Young on what was his sixth spaceflight, undertook its second operational mission (STS-9), in which the Spacelab science laboratory and a six-person crew was carried, including the first non-American astronaut on a space shuttle, Ulf Merbold. After the flight, it spent 18 months at the Rockwell Palmdale facility beginning in January 1984, undergoing modifications that removed the Orbiter Flight Test hardware and updating it to similar specifications as those of its sister orbiters. At that time the shuttle fleet was expanded to include Discovery and Atlantis. Columbia returned to space on January 12, 1986, with the launch of STS-61-C. The mission's crew included Dr. Franklin Chang-Diaz, and the first sitting member of the House of Representatives to venture into space, Bill Nelson. The next shuttle mission, STS-51-L, was undertaken by Challenger. It was launched on January 28, 1986, ten days after STS-61-C had landed, and ended in disaster 73 seconds after launch. Prior to the accident, Columbia had been slated to be ferried to Vandenberg Air Force Base to conduct fueling tests and to perform a flight readiness firing at SLC-6 to validate the west coast launch site. In the aftermath, NASA's shuttle timetable was disrupted, and the Vandenberg tests, which would have cost $60 million, were canceled. Columbia was not flown again until 1989 (on STS-28), after which it resumed normal service as part of the shuttle fleet. STS-93, launched on July 23, 1999, was the first U.S. space mission with a female commander, Lt. Col. Eileen Collins. This mission deployed the Chandra X-ray Observatory. Columbias final complete mission was STS-109, the fourth servicing mission for the Hubble Space Telescope. Its next mission, STS-107, culminated in the orbiter's loss when it disintegrated during reentry, killing all seven of its crew. Consequently, President George W. Bush decided to retire the Shuttle orbiter fleet by 2010 in