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Rosetta was launched on 2 March 2004 from the Guiana Space Centre in Kourou, French Guiana, on an Ariane 5 rocket and reached Comet Churyumov–Gerasimenko on 7 May 2014. It performed a series of manoeuvres to enter orbit between then and 6 August 2014, when it became the first spacecraft to orbit a comet. (Previous missions had conducted successful flybys of seven other comets.) It was one of ESA's Horizon 2000 cornerstone missions. The spacecraft consisted of the Rosetta orbiter, which featured 12 instruments, and the Philae lander, with nine additional instruments. The Rosetta mission orbited Comet Churyumov–Gerasimenko for 17 months and was designed to complete the most detailed study of a comet ever attempted. The spacecraft was controlled from the European Space Operations Centre, in Darmstadt, Germany. The planning for the operation of the scientific payload, together with the data retrieval, calibration, archiving and distribution, was performed from the European Space Astronomy Centre, in Villanueva de la Cañada, near Madrid, Spain. It has been estimated that in the decade preceding 2014, some 2,000 people assisted in the mission in some capacity. In 2007, Rosetta made a Mars gravity assist (flyby) on its way to Comet Churyumov–Gerasimenko. The spacecraft also performed two asteroid flybys. The craft completed its flyby of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010. Later, on 20 January 2014, Rosetta was taken out of a 31-month hibernation mode as it approached Comet Churyumov–Gerasimenko. Rosetta's Philae lander successfully made the first soft landing on a comet nucleus when it touched down on Comet Churyumov–Gerasimenko on 12 November 2014. On 5 September 2016, ESA announced that the lander was discovered by the narrow-angle camera aboard Rosetta as the orbiter made a low, 2.7 km (1.7 mi) pass over the comet. The lander sits on its side wedged into a dark crevice of the comet, explaining the lack of electrical power to establish proper communication with the orbiter.

Columbia was named after the American sloop Columbia Rediviva which, from 1787 to 1793, under the command of Captain Robert Gray, explored the US Pacific Northwest and became the first American vessel to circumnavigate the globe. It is also named after the command module of Apollo 11, the first crewed landing on another celestial body. Columbia was also the female symbol of the United States. After construction, the orbiter arrived at Kennedy Space Center on March 25, 1979, to prepare for its first launch. Columbia was originally scheduled to lift off in late 1979, however the launch date was delayed by problems with both the RS-25 engine, as well as the thermal protection system. The first flight of Columbia was commanded by John Young, a veteran from the Gemini and Apollo programs who was the ninth person to walk on the Moon in 1972, and piloted by Robert Crippen, a rookie astronaut originally selected to fly on the military's Manned Orbital Laboratory spacecraft, but transferred to NASA after its cancellation, and served as a support crew member for the Skylab and Apollo-Soyuz missions. Columbia spent 610 days in the Orbiter Processing Facility, another 35 days in the Vehicle Assembly Building, and 105 days on Pad 39A before finally lifting off. It was successfully launched on April 12, 1981, the 20th anniversary 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, 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, 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.

Die Explorer-Serie erhielt damit die Chance, die ersten Satelliten in die Erdumlaufbahn zu heben, und war gegenüber dem Vanguard-Projekt überaus erfolgreich.