spase://SMWG/Observatory/DMSP_5D-2/F13

DMSP 5D-2/F13, also known as USA 109, is 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 DAPP (Data Acquisition and Processing Program), was classified
until March 1973. The objective of this program is to provide global visual and infrared cloudcover
data and specialized environmental data to support Department of Defense operational weather analysis
and forecasting requirements. Operationally, the program consists of two satellites in sun-synchronous
polar orbits, with the ascending node of one satellite in early morning
and the other at local noon. The local time nodes for DMSP F13 are 17:30 and 05:30.

        The 6.4-m-long spacecraft is separated into four sections: (1) a precision mounting platform for

sensors and equipment requiring precise alignment; (2) an equipment support module containing the
electronics, reaction wheels, and some meteorological sensors; (3) a reaction control equipment
support structure containing the third-stage rocket motor and supporting the ascent phase reaction
control equipment; and (4) a 9.29-sq-m solar cell panel. The spacecraft stabilization is controlled
by a combination flywheel and magnetic control coil system so that sensors are maintained in the
desired earth-looking mode. One feature is the precision-pointing accuracy of the primary imager to
0.01 deg provided by a star sensor and an updated ephemeris navigation system. This allows automatic
geographical mapping of the digital imagery to the nearest picture element.

        The operational linescan system is the primary data acquisition system and provides real-time or

stored, multi-orbit, day-and-night, visual and infrared imagery of clouds. A supplementary sensor
package contains: (1) a microwave imager; (2) a microwave temperature sounder; (3) a microwave
water vapor profiler; (4) an ion and electron scintillation monitor; (5) a precipitating electron/ion
spectrometer; (6) a gamma/X-ray detector; (7) a magnetometer; and (8) a static earth-viewing sensor
monitoring electromagnetic radiation.