Artificial satellites come from more than 50 countries and have used the satellite launching capabilities of ten nations. A few hundred satellites are currently working, but thousands of unused satellites and satellite fragments orbit the Earth as space debris. The largest satellite is the International Space Station, which was put together by several different countries (including the organizations of NASA, ESA, JAXA and RKA). It usually has a crew of six astronauts or cosmonauts living on board. It is permanently occupied, but the crew changes. The Hubble Space Telescope has been repaired and updated by astronauts in space several times.