International Space Station (ISS) is a research facility currently being assembled in space. The on-orbit assembly of ISS began in 1998. The space station is in a low Earth orbit and can be seen from Earth with the naked eye: It has an average altitude of 340 km (210 statute miles) above the surface of the Earth, and travels at an average speed of 27,700 km (17,210 statute miles) per hour, completing 15.77 orbits per day. The ISS is a joint project between the space agencies of the United States (NASA), Russia (RKA), Japan (JAXA), Canada (CSA) and several European countries (ESA).

The Brazilian Space Agency (AEB, Brazil) participates through a separate contract with NASA. The Italian Space Agency similarly has separate contracts for various activities not done in the framework of ESA's ISS works (where Italy also fully participates). China has reportedly expressed interest in the project, especially if it is able to work with the RKA. The Chinese are not currently involved, however.

The ISS is a continuation of what began as the U.S. Space Station Freedom, the funding for which was cut back severely. It represents a merger of Freedom with several other previously planned space stations: Russia's Mir 2, the planned European Columbus and Kibo, the Japanese Experiment Module. The projected completion date is 2010, with the station remaining in operation until around 2016. As of 2007, the ISS is already larger than any previous space station.

The source of electrical power for the ISS is the sun: light is converted into electricity through the use of solar panels. Before assembly flight 4A (shuttle mission STS-97, November 30, 2000) the only power source was the Russian solar panels attached to the Zarya and Zvezda modules: the Russian segment of the station uses 28 volts dc (like the Shuttle). In the rest of the station, electricity is provided by the solar cells attached to the truss at a voltage ranging from 130 to 180 volts dc. The power is then stabilized and distributed at 160 volts dc and then converted to the user-required 124 volts dc. Power can be shared between the two segments of the station using converters, and this feature is essential since the cancellation of the Russian Science Power Platform: the Russian segment will depend on the U.S. built solar arrays for power supply. Using a high-voltage (130 to 160 volts) distribution line in the so-called U.S. part of the station led to smaller power lines and thus weight savings.

The solar array normally tracks the sun to maximize the amount of solar power. The array is about an acre in area and 190 feet (58 m) long. In the fully-complete configuration, the solar arrays track the sun in each orbit by rotating the alpha gimbal; while the beta gimbal adjusts for the angle of the sun from the orbital plane. (However, until the main truss structure was brought up, the arrays were in a temporary position perpendicular to the final orientation, and in this configuration, as shown in the image to the right, the beta gimbal was used for the main solar tracking.) Another slightly different tracking option, Night Glider mode, can be used to reduce the drag slightly by orienting the solar arrays edgewise to the velocity vector.

The ISS Environmental Control and Life Support System provides or controls elements such as atmospheric pressure, oxygen levels, water, and fire extinguishing, among other things. The Elektron system generates oxygen aboard the station. The highest priority for the life support system is the ISS atmosphere, but the system also collects, processes, and stores waste and water produced and used by the crew. For example, the system recycles fluid from the sink, shower, urine, and condensation. Activated charcoal filters are the primary method for removing byproducts of human metabolism from the air.

One of the main goals of the ISS is to provide a place to conduct experiments that require one or more of the unusual conditions present on the station. The main fields of research include biology (including biomedical research and biotechnology), physics (including fluid physics, materials science, and quantum physics), astronomy (including cosmology), and meteorology. The 2005 NASA Authorization Act designated the U.S segment of the International Space Station as a national laboratory with a goal to increase the utilization of the ISS by other Federal entities and the private sector. As of 2007, little experimentation other than the study of the long-term effects of microgravity on humans has taken place. With four new research modules set to arrive at the ISS by 2010, however, more specialized research is expected to begin.

The Destiny Laboratory Module is the main research facility currently aboard the ISS. Produced by NASA and launched in February 2001, it is a research facility for general experiments. The Columbus module is another research facility, though it was designed by the ESA for the ISS. Its purpose is to facilitate scientific experiments and is set to be launched into space with the STS-122 shuttle launch in January 2008. It should provide a generic laboratory as well as ones specifically designed for biology, biomedical research, and fluid physics. There are also a number of planned expansions that will be implemented to study quantum physics and cosmology.

The Japanese Experiment Module, also known as Kibō, is scheduled to be in space after the STS-127 launch in or around January, 2009. It is being developed by JAXA in order to function as an observatory and to measure various astronomical data. The ExPRESS Logistics Carrier, developed by NASA, is set to be launched for the ISS with the STS-129 mission, which is expected to take place no earlier than September 11, 2009. It will allow experiments to be deployed and conducted in the vacuum of space and will provide the necessary electricity and computing to locally process data from experiments. The Multipurpose Laboratory Module, created by the RKA, is expected to launch for the ISS in late 2009. It will supply the proper resources for general microgravity experiments.

Version 1.2, November 2002

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