The Upper Atmosphere Research Satellite (UARS) is an orbital observatory whose mission is to study the Earth’s atmosphere, particularly the protective ozone layer.

The 5900 kg (13,000 lb) satellite was launched during Space Shuttle mission STS-48 in 1991. The original mission life was to be three years. As of June 2005, six of the ten instruments were still operational. UARS orbits at an altitude of 375 miles with an orbital inclination of 57 degrees.

A final orbit lowering burn, followed by the "passivation" of the Satellite's systems was performed in early December, 2005.