International Space Station

The International Space Station (ISS), formally designated International Space Station Alpha, is a habitable orbital facility that has been under construction since 1998 and is scheduled for completion in 2006. When finished, it will contain about four times as much working space as the Russian space station Mir (1986–2001), the former record holder, and will weigh about one million pounds (453,000 kg). The ISS orbits at an average altitude of 240 mi (387 km). A number of science experiments are to be conducted aboard the ISS in such fields as health effects of radiation, molecular and cell biology, earth science, fluid dynamics, astronomy, combustion physics, and crystal growth.