SOLAR was an ESA science observatory on the Columbus Laboratory, which is part of the International Space Station. SOLAR was launched with Columbus on February 2008 aboard STS-122. It was externally mounted to Columbus with the European Technology Exposure Facility (EuTEF). SOLAR has three main space science instruments: SOVIM, SOLSPEC and SOL-ACES. Together they provide detailed measurements of the Sun's spectral irradiance. The SOLAR platform and its instruments are controlled from the Belgian User Support and Operations Centre (B.USOC), located at the Belgian Institute for Space Aeronomy (BISA) in Uccle, Belgium.
The mission was originally planned for a 2003 launch, but was delayed following the Space Shuttle Columbia disaster. Some other components are also planned to be mounted externally on Columbus on future missions, including the Atomic Clock Ensemble in Space (ACES). Another name for SOLAR may be Solar Monitoring Observatory or SMO.
In 2012, the entire 450-tonne station was rotated so SOLAR could observe a full rotation of the Sun continuously. A Solar rotation takes about 24–28 days depending on the latitude.
SOLAR's mission ended in 2017 with the failure of all but one of its instruments. On the morning of January 28, 2020 SOLAR was removed from FRAM 1 where it rested since is was delivered on STS 122 and strapped to the side of Cygnus NG-12 with the SDS placed on the other side. SOLAR was released from the station on February 3, 2020 and burnt up in the atmosphere over the Pacific Ocean on March 13, 2020 ending the mission which spent a decade photographing the sun.