Nimbus Power Systems (1960-1969)

The Nimbus program is a major research effort in the development of satellite technology for meteorological purposes. Global cloudcover information is provided by sensors mounted on a 3-axis stabilized, earthoriented spacecraft. Electrical power for the spacecraft and sensors is provided by a solar-conversion energy-storage subsystem. This paper describes the evolution of the power supply subsystems designed for use on the Nimbus spacecraft. The original design, generated during the period 1961-1963, used dissipative regulation techniques and simple battery protection circuits. Battery overcharge protection was provided by ground control of special spacecraft loads. This type of system was successfully flown on Nimbus 1 in August 1964 and on Nimbus 2 in May 1966. The second generation design, currently being fabricated for test and evaluation, is intended for operational flight use in late 1967. The system concept, based on research and development effort in the period 1962-65, incorporates nondissipative regulation techniques and automatic battery overcharge control. A new concept, intended for use in a third generation Nimbus power system, is presently being explored. Recent advances in power conditioning technology will allow substantial gains in terms of extended spacecraft life or increased load capability. The new technology, called maximum power point tracking, assures more optimum source-to-load energy transfer. Thus, the increase in available solar cell energy caused by periodic, large, low-temperature excursions of the Nimbus solar array can be fully utilized.