The Solar and Heliospheric Observatory (SOHO)is a spacecraft built by a European industrial consortium led byMatra Marconi Space (now Astrium) that was launched on a LockheedMartin Atlas IIAS launch vehicle on December 2, 1995 to study theSun, and has discovered over 2700 comets.[1] It began normaloperations in May 1996. It is a joint project of internationalcooperation between the European Space Agency (ESA) and NASA.Originally planned as a two-year mission, SOHO continues to operateafter over 18 years in space. In June 2013, a mission extensionlasting until December 2016 was approved.[2]

In addition to its scientific mission, it is the main source ofnear-real-time solar data for space weather prediction. Along withthe GGS Wind and Advanced Composition Explorer (ACE), SOHO is oneof three spacecraft in the vicinity of the Earth–Sun L1 point, apoint of gravitational balance located approximately 0.99astronomical unit (AU)s from the Sun and 0.01 AU from the Earth. Inaddition to its scientific contributions, SOHO is distinguished bybeing the first three-axis-stabilized spacecraft to use itsreaction wheels as a kind of virtual gyroscope; the technique wasadopted after an on-board emergency in 1998 that nearly resulted inthe loss of the spacecraft.