HCMM (AEM 1, Explorer 58)

HCMM [GDK]

The HCMM (Heat Capacity Mapping Mission) spacecraft was the first of a series of Applications Explorer Missions (AEM). The objective of the HCMM was to provide comprehensive, accurate, high-spatial-resolution thermal surveys of the surface of the earth. The HCMM spacecraft was made of two distinct modules:

• an instrument module, containing the heat capacity mapping radiometer and its supporting gear, and
• a base module, containing the data handling, power, communications, command, and attitude control subsystems required to support the instrument module.

The spacecraft was spin stabilized at a rate of 14 rpm. The HCMM circular sun-synchronous orbit allowed the spacecraft to sense surface temperatures near the maximum and minimum of the diurnal cycle. The orbit had a daylight ascending node with nominal equatorial crossing time of 2:00 p.m. Since there was no inclination adjustment capacity, the spacecraft drifted from this crossing time by about 1 hour earlier per year. There was no on-board data storage capability, so only real-time data were transmitted when the satellite came within reception range of seven ground stations. The repeat cycle of the spacecraft was 16 days. Day/night coverage over a given area between the latitudes of 85 deg N and 85 deg S occurred at intervals ranging from 12 to 36 h (once every 16 days). During February 21-23, 1980, the HCMM orbital altitude was lowered from 620 km to 540 km to stop the drift of the orbit plane to unfavorable sun angles which in turn reduced the power collection capability of the solar panels. The operations of the spacecraft were terminated on 30 September 1980.