What are the DMSP spacecraft?
The Defense Meteorological Satellite Program (DMSP) is a series of polar orbiting weather satellites at an altitude of about 840 km operated by the United States Department of Defense. The spacecraft are in 96 degree inclination orbits which means the orbit precesses through 360 degrees per year, which means the orbit stays locked to a local time throughout the year. The first DMSP spacecraft was launched January 19, 1965 and the DOD keeps at least two in operation at any one time. (Sometimes as many as four have been operating simultaneously.) More information on the DMSP spacecraft can be found here. There is a parallel civilian weather spacecraft called TIROS-POES (Polar Orbiting Earth Satellite), but those do not carry any thermal plasma instruments.
