A satellite designed to study chemistry, dynamics, and energetics of the stratosphere, mesosphere, and lower thermosphere. UARS was launched in September 1991. UARS instruments include the cryogenic limb spectrometer of etalon array, an improved stratospheric and mesospheric sounder, a microwave limb sounder, a halogen hide experiment, a high-resolution Doppler imager, a wind imaging interferometer, a solar–stellar irradiance experiment of comparison, a solar ultraviolet spectral irradiance monitor, a particle environment monitor, and the active cavity radiometer monitor of irradiance.