Series of US scientific SATELLITES designed to study the SUN from orbit round the EARTH. The first of the series was OSO 1, launched on 7 March 1962 into a near-circular orbit of altitude 570 km. To date seven successful launchings have taken place and more are anticipated. A considerable success was achieved with OSO 5; launched on 22 January 1969, it continued to function until "closed down" three years later. In July 1974, after more than two years' inactivity, it was reactivated and brought back into service.
Instrumentation carried by these satellites includes a coronagraph, a spectroheliograph, and an ultra-violet spectrometer. One of the principal objectives is to study solar flares.
