[Source: Nationa Space Science Data Center, http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1979-050A
DMSP 5D-1/F4 was one of a series of meteorological satellites developed and operated by ... the Air Force under the Defense Meteorological Satellite Program (DMSP). This program, previously known as DAAP (Data Acquisition and Processing Program), was classified until March 1973. The objectives of this program are to provide global visual and infrared cloud-cover data and specialized environmental data to support Department of Defense requirements. Operationally, the program consisted of two satellites in planned 830-km sun-synchronous polar orbits, with the ascending node of one satellite in early morning and the other at local noon. The 5.4-m long spacecraft was separated into four sections: (1) a precision mounting platform (PMP) for sensors and equipment requiring precise alignment, (2) an equipment support module (ESM) containing the electronics, reaction wheels, and some meteorological sensors, (3) a reaction control equipment (RCE) support structure (including the third-stage motor, hydrazine reaction control system) that supported (4) a 9.29 sq m solar cell panel. The spacecraft stabilization was controlled by a combination flywheel and magnetic control coil system, so that sensors were maintained in the desired 'earth-looking' mode. One feature was the precision-pointing accuracy of the primary imager to 0.01 deg provided by a star sensor and an updated ephemeris navigation system. This allowed automatic geographical mapping of the digital imagery to the nearest picture element. The operational line scan system (OLS) built by Westinghouse, was the primary data acquisition system that provided real-time or stored, multi-orbit, day-and-night visual and infrared imagery at 1/3 nautical mile resolution for all major land masses, 1-1/2 nautical mile resolution for complete global coverage, and provided with this data calibration, timing, and other auxiliary signals to the spacecraft for digital transmission to the ground. A supplementary sensor package, the special sensor H (SSH), a step-scanning radiometer, was the infrared temperature-humidity-ozone sounder. The data processing system, which included three high-density tape recorders, was capable of storing a total of 400 min of data, each allowing full global coverage twice daily. Either recorded or real-time data were transmitted to ground-receiving sites by two redundant S-band transmitters. Recorded data were read out to tracking sites located at Fairchild AFB, WA, and Loring AFB, ME, and relayed by SATCOM to Air Fource Global Weather Central, Offutt AFB, NE. Real-time data were read out at mobile tactical sites located around the world. A more complete description of the satellite can be found in the report `The Defense Meteorological Satellite Program,' D.A. Nichols, Optical Engineering, 14, 4, July - August 1975.