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The
International Space Station
(ISS) is an internationally developed research facility, which is being
assembled in low Earth orbit. On-orbit construction of the station
began in 1998 and is scheduled for completion by 2011. The station will
remain in operation until at least 2015. With a greater mass than that
of any previous space station, the ISS can be seen from the Earth with
the naked eye, and, as of 2010[update], is the largest artificial
satellite orbiting the Earth. The ISS serves as a research laboratory
that has a microgravity environment in which crews conduct experiments
in biology, human biology, physics, astronomy and meteorology.
The
station has a unique environment for the testing of the spacecraft
systems that will be required for missions to the Moon and Mars. The ISS
is operated by Expedition crews, and has been continuously staffed
since 2 November 2000—an uninterrupted human presence in space for the
past 9 years and 75 days. As of 1 December 2009, the crew of Expedition
22 is aboard.
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The
ISS is a synthesis of several space station projects that includes the
American Freedom, the Soviet/Russian Mir-2, the European Columbus and
the Japanese Kibō. Budget constraints led to the merger of these
projects into a single multi-national programme. The ISS project began
in 1994 with the Shuttle-Mir programme, and the first module of the
station, Zarya, was launched in 1998 by Russia. Assembly continues, as
pressurised modules, external trusses and other components are launched
by American space shuttles, Russian Proton rockets and Russian Soyuz
rockets. As of November 2009[update], the station consisted of 11
pressurised modules and an extensive integrated truss structure (ITS).
Power is provided by 16 solar arrays mounted on the external truss, in
addition to four smaller arrays on the Russian modules. The station is
maintained at an orbit between 278 km (173 mi) and 460 km (286 mi)
altitude, and travels at an average speed of 27,724 km (17,227 mi) per
hour, completing 15.7 orbits per day.
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Operated
as a joint project between the five participant space agencies, the
station's sections are controlled by mission control centres on the
ground operated by the American National Aeronautics and Space
Administration (NASA), the Russian Federal Space Agency (RKA), the Japan
Aerospace Exploration Agency (JAXA), the Canadian Space Agency (CSA),
and the European Space Agency (ESA). The ownership and use of the space
station is established in intergovernmental treaties and agreements that
allow the Russian Federation to retain full ownership of its own
modules, with the remainder of the station allocated between the other
international partners. The station is serviced by Soyuz spacecraft,
Progress spacecraft, space shuttles, the Automated Transfer Vehicle and
the H-II Transfer Vehicle, and has been visited by astronauts and
cosmonauts from 15 different nations. The cost of the station has been
estimated by ESA as €100 billion over 30 years, and, although estimates
range from 35 billion dollars to
160 billion dollars, the ISS is believed to be
the most expensive object ever constructed. The financing, research capabilities and technical design of the ISS programme have been criticised because of the high cost.
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