A NASA orbiting observatory used to investigate the upper atmosphere's structure and behaviour. It was launched in September 1991 aboard the space shuttle Discovery. UARS was the first satellite to provide systematic and comprehensive data on the stratosphere, mesosphere, and lower thermosphere. The information increased our understanding of the ways in which human activities and natural events affect these areas. After 14 years of service, it ceased operations on 15 December 2005.

Among the accomplishments of the spacecraft's ten science instruments have been the infrared mapping of the effects of aerosols, the first global maps of chlorofluorocarbons (CFCs) from space, and the first direct measurement of winds from space.