Utilization of Small Commercial Grade Nickel Cadmium (NiCd) Cells in Low Earth Orbit (LEO) Applications

The Defense Advanced Research Projects Agency (DARPA) has sponsored the Advanced Space Technology Program (ASTP) to enhance the cost-effectiveness and responsiveness of military space systems. One of the major themes of this program is the development of highly capable small satellites, generally referred to as ''LightSats," which can perform selected defense missions at relatively low cost. A key element of the programmatic approach is the utilization of commercial grade parts and practices where practical, as opposed to the much more conservative aerospace grade parts. ASTP has incorporated commercial grade batteries into its first generation LightSats; however, an attempt has been made to study the trade-offs and design considerations to optimally employ these batteries on small satellites. For certain applications, particularly for small relatively inexpensive satellites, commercial grade cells may be a viable alternative to aerospace cells. Differences between aerospace and commercial grade cells range from physical construction and technology incorporated, to the level of quality control in manufacturing. These differences are reflected in both greater cost and increased lead time for the aerospace cells. Our research and experience suggest that certain manufacturing technologies are preferable when considering commercial cells for space applications. Once the cell type is chosen, candidate cells must be thoroughly screened to insure survival and acceptable performance in the space environment. To insure optimal performance, cells should be rigorously matched in electrical characteristics when forming batteries. Test procedures should be tailored to fit the application in order to yield the best performance in a specific physical, electrical, and operational environment. An acceptance test plan for screening and matching cells is discussed. The present paper is the first in a series of reports which will document the approach, results, and lessons learned from ASTP's commercial battery studies.