Problems in the selection and testing of nickel-cadmium batteries for satellites

The electric system of a satellite is usually designed around a storage battery. Operating in a low-temperature environment, the battery is maintained by a constant low-level energy source, yet it must deliver intermittent high loads, its life must be long and trouble-free, and its bulk and weight must be at a minimum. Current literature offers little quantitative information on which the selection of such a battery can be based. Consequently, when a battery was to be applied to a certain satellite in 1958, a special study was carried out to determine what electrical capacity would be needed, and how battery efficiency and life would be affected by a low-voltage nuclear-thermal-electric generator stepped up to about 30 volts by a d-c to d-c converter. At the time, the efficiency at very low charge currents was estimated as anywhere from zero to, at the best, 10%. This paper reports on the investigation which sought answers to these questions.