NASA battery testbed: lessons learned applications to orbiting spacecraft

A spacecraft battery testbed has been operational for the last two years. The objective of the testbed is the verification (on the ground) of proposed operational battery management techniques on spacecraft. The testbed consists of a computer controlled system which has the capability to simulate power/orbit profiles with varying occultation periods and charge control methodologies (V/T levels, CC. etc.). Currently the testbed is deployed to simulate the NASA Modular Power System (MPS). This system consists of three NASA standard 50 Ah 22 cell nickel-cadmium batteries. Several orbital profiles have been implemented on the testbed. Since spacecraft telemetry channels are at a premium, battery data from spacecraft is usually very sparse. On the testbed, data on the performance of each of the cells within the batteries can be obtained, and hence a very accurate assessment of the battery performance is available. This data can subsequently be compared with telemetered data for analysis. A 'Taguchi' orthogonal array was utilized to determine the effect of five factors (at four levels) on battery characteristics. These factors are inrush-current, depth-of-discharge, temperature, orbit duration, and VT level. Sixteen independent experiments consisting of 60 orbits each were performed. Based on the results of this experiment, verification experiments were proposed. To date the verification experiments confirm the optimization of parameters yield better performance. Details of the experiment and recommendations based on the data are presented.