A satellite of the US Ballistic Missile Defense Organization launched in 1996 April to test technology for identifying and tracking ballistic missiles while in flight. As part of its work it studied celestial background sources at wavelengths from mid-infrared to far-ultraviolet with the Spatial Infrared Imaging Telescope (SPIRIT), a 0.33-m infrared telescope; the SBV (Space-Based Visible) Instrument, a 150-mm visible-band telescope; and a set of Ultraviolet and Visible Imagers and Spectrographic Imagers (UVISI). It performed astronomical observations until 1997 October, and was then used to monitor other orbiting spacecraft until 2008 June.

http://sd-www.jhuapl.edu/MSX/ Official mission website.