Space Stations in the Earth Orbit

A Space Station is a spacecraft capable of supporting a crew which is designed to remain in space for an extended period of time, and to which other spacecraft can dock. It is also called an orbital station, most space stations remains commonly in low Earth orbit.

As of November 2012 two space stations are in orbit:

• The International Space Station – ISS and 
• China's Tiangong 1 (which successfully launched on September 29, 2011, after failing in its prior August launch attempt).

Among some previous space stations include the Almaz and Salyut series, Skylab and most recently Mir from Russia.

International Space Station - ISS:
The International Space Station (ISS) is a habitable artificial satellite in low Earth orbit. The ISS is a modular structure on the space consists of pressurized modules, external trusses, solar arrays and other components; the first component was launched in 1998. Now, the ISS is the largest artificial body in orbit, it can often be seen at the appropriate time with the naked eye from Earth. The ISS has been continuously occupied for more than 12 years on the space.

ISS components have been launched by American Space Shuttles as well as Russian Proton and Soyuz rockets. Budget constraints led to the merger of three space station projects with the Japanese Kibō module and Canadian robotics. In 1993 the partially built components for a Soviet/Russian space station Mir-2, the proposed American Freedom, and the proposed European Columbus merged into a single multinational program.

The ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology and other fields. The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.

Some images of ISS:

Tiangong-1:
Tiangong-1 is the China's first space station which is an experimental Testbed to demonstrate orbital rendezvous and docking capabilities. It has launched unmanned aboard a Long March 2F/G rocket, on 29 September 2011, it is the first operational component of the Tiangong program, which aims to place a larger, modular station into orbit by 2020. Tiangong-1 will be de-orbited in this year, and replaced over the following decade by the larger Tiangong-2 and Tiangong-3 modules.

The unmanned Shenzhou-8 mission successfully docked with Tiangong-1 on 2 November 2011 GMT, marking China's first orbital docking. Shenzhou-8 undocked from Tiangong-1 on 14 November, before successfully completing a second rendezvous and docking, thus testing the reusability of the docking system. Shenzhou-8 de-orbited on 17 November 2011, and landed intact in Siziwang Banner in Inner Mongolia.

Tiangong-1 is intended as a Testbed for key technologies that will be used in China's large modular space station, which is planned for launch in 2020. Furthermore, modified versions of Tiangong-1 will be used as robotic cargo spacecraft to resupply this station. The launch mass of the Tiangong-1-derived cargo spacecraft is expected to be around 13 metric tons (29,000 lb), with a payload of around 6 metric tons (13,000 lb).

Images of Tiangong-1:

Mir (1986–1998):
Mir was a space station that operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Mir was the first modular space station and had a greater mass than that of any previous spacecraft. Mir served as a micro-gravity research laboratory in which crews conducted experiments in biology, human biology, physics, astronomy, meteorology and spacecraft systems.

Images of Mir:

The Mir programme held the record for the longest uninterrupted human presence in space, at 3,644 days, until 23 October 2010 (when it was surpassed by the ISS), and it currently holds the record for the longest single human spaceflight, of Valeri Polyakov, at 437 days 18 hours.

The first module of the station, known as the core module or base block, was launched in 1986, and was followed by six further modules, all launched by Proton rockets. When complete, the station consisted of seven pressurized modules and several un-pressurized components.


Salyut, Almaz, and Skylab (1971–1986):
The first space station was Salyut 1, launched by the Soviet Union on April 19, 1971. Like all the early space stations, it was "monolithic", intended to be constructed and launched in one piece, and then manned by a crew later. As such, monolithic stations generally contained all their supplies and experimental equipment when launched, and were considered "expended", and then abandoned, when these were used up.

The earlier Soviet stations were all designated "Salyut", but among these there were two distinct types: civilian and military. The military stations, Salyut 2, Salyut 3, and Salyut 5, were also known as Almaz stations. The civilian stations Salyut 6 and Salyut 7 were built with two docking ports, which allowed a second crew to visit, bringing a new spacecraft with them; the Soyuz ferry could spend 90 days in space, after which point it needed to be replaced by a fresh Soyuz spacecraft. This allowed for a crew to man the station continually.

Image of Salyut, Almaz, and Skylab:

Skylab was also equipped with two docking ports, like second-generation stations, but the extra port was never utilized. The presence of a second port on the new stations allowed Progress supply vehicles to be docked to the station, meaning that fresh supplies could be brought to aid long-duration missions.


Early concepts of Space Station:
The Brick Moon, first known depiction of a space station. Space stations have been envisaged since at least 1869 when Everett Hale wrote about a 'brick moon' in Atlantic monthly magazine. Space stations were also later envisaged by Konstantin Tsiolkovsky and Hermann Oberth. In 1929 Herman Potočnik's The Problem of Space Travel was published, and remained popular for over 30 years. In 1951, in Collier's weekly, Wernher von Braun published his design for a wheel-shaped space station.

During the Second World War, German scientists researched an orbital weapon that could utilize the sun's energy. This so-called "sun gun" would be part of a space station orbiting Earth at a height of 5,100 miles (8,200 km). With the Apollo 11 landing on the Moon in July 1969, the United States won the race to the Moon over the world's other superpower of the era, the Soviet Union. This caused the Soviet Union to seek other ways to display their spaceflight capabilities.

Ref: wikipedia

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