International Space Station Russian space station called OPSEK. The ISS is the ninth space station to be inhabited by crews, following the Soviet and later Russian "Salyut", "Almaz", and "Mir" stations as well as "Skylab" from the US. The station has been continuously occupied for since the arrival of Expedition 1 on 2 November 2000. This is the longest continuous human presence in low Earth orbit, having surpassed the previous record of held by "Mir". It has been visited by astronauts, cosmonauts and space tourists from 17 different nations. After the American Space Shuttle programme ended in 2011, Soyuz rockets became the only
Halo orbit each Lagrange point. Because halo orbits tend to be unstable, stationkeeping is required to keep a satellite on the orbit. Most satellites in halo orbit serve scientific purposes, for example as space telescopes. Robert W. Farquhar first used the name "halo" for these orbits in his 1968 Ph.D. thesis. Farquhar advocated using spacecraft in a halo orbit on the far side of the Moon (Earth–Moon ) as a communications relay station for an Apollo mission to the far side of the Moon. A spacecraft in such a halo orbit would be in continuous view of both the Earth and the