Power Supplies for Space Vehicles

Abstract

It is becoming more apparent as space vehicles are developed for a variety of missions that a major limitation will be the availability of long life electric power sources. This dissertation discusses many of the problems associated with the development of such power sources and they are utilized in two different purposes. One is power for propulsion, and the other is electric power for devices which are used in communications packages, probes, navigation, weather surveillance, space, moon or planet stations, instrumentation, guidance and control, scientific observation packages, and devices for manned vehicles and an assortment of various servo-machinery powered by electricity. An immediate observation concedes that reliability of the power system should be at least as good as the various electrical devices to be operated. A power system which will operate for several years is a goal to be sought. In terms of specific requirements, the power system should be no better, or perhaps a bit better, than the electrical devices to be driven. Throughout this paper an attempt will be made to indicate he role of reliability in space power. The subject of reliability has been dealt with rather extensively in the field of electronics because a vast array of equipment depends on it. If power systems for space are developed with a reliability such that the systems can be operated for a year or two, one may find that the electronics in space vehicles are not quite as reliable. A the present time, solar cells coupled with nickel-cadmium batteries are the only power systems being currently used in U.S. space vehicles. Other types, however, are in development stages. Although there is experimental evidence to indicate that the solar cells with proper protection against radiation will have lifetimes (1 to 5 years), there is some pessimism regarding the reliability of sealed nickel-cadmium batteries. The thousands of cycles that this compact battery must be subject to and the normally slow but sure degradation that generally occurs at the electrodes and in the membranes has resulted in a present estimate of mean life to failure of four months where a low orbit vehicle is involved. However, if a space vehicle is in an orbit containing large amounts of high energy protons (2000 miles altitude), little can be done to protect the solar cell for long periods of time.