Flight performance of the ERTS-1 spacecraft power system

The initial spacecraft of the Earth Resources Technology Satellite Program, ERTS-1, was launched on July 23, 1972, and has provided broad earth resource data for use by numerous governmental and scientific agencies. This paper reports on the basic design and flight performance to date of the ERTS-1 power system. The design is based on earlier Nimbus spacecraft power system configurations with modifications introduced to provide increases in average and peak power capabilities. Data is presented showing overall design performance in terms of allowable load duty cycles, solar array capability, and battery charge and discharge behavior. Of special interest is the effect of solar flare activity occurring on August 3 to 7, 1972, in abruptly reducing the solar array output. After 10 months in orbit sufficient power remains for another 18 months of ERTS operation.