Solar Mesosphere Explorer

The Solar Mesosphere Explorer (also known as Explorer 64) was a NASA spacecraft to investigate the processes that create and destroy ozone in Earth's upper of the atmosphere of Earth. The mesosphere is a layer of the atmosphere extending from the top of the stratosphere to an altitude of about 80 km. The spacecraft carried five instruments to measure ozone, water vapor, and incoming solar radiation.

Mission
Explorer 64 studied the processes that create and destroy ozone in the Earth's mesosphere. Over its 7.5 years mission, SME measured ultraviolet solar flux, ozone density, and the density of other molecules important to the understanding of ozone chemistry. During the mission over one hundred undergraduate and graduate students were involved in nearly every aspect of SME operations, including planning and scheduling spacecraft and science activities, controlling the spacecraft and its ground support system, and analyzing spacecraft subsystem performance.

Spacecraft
Managed for NASA by the Jet Propulsion Laboratory, the Solar Mesosphere Explorer was built by Ball Space Systems and operated by the Laboratory for Atmospheric and Space Physics of the University of Colorado Boulder.

Characteristics:
 * Mass: 437 kilograms
 * Power: Solar panels and nickel-cadmium batteries
 * Configuration: Cylinder 1.25 meter diameter by 1.7 meter high
 * Science instruments: Ultraviolet ozone spectrometer, Micrometre spectrometer, Nitrogen dioxide spectrometer, Four-channel infrared radiometer, Solar ultraviolet monitor, Solar proton alarm detector

Launch
Launched on 6 October 1981, on a Thor-Delta 2310 from Vandenberg Air Force Base, in California, the satellite returned data until 4 April 1989.

Atmospheric entry
The spacecraft reentered Earth's atmosphere on 5 March 1991.