Battery Failure on the Electric Propulsion Space Experiment (ESEX)

The anomaly experienced on the USAF Electric Propulsion Space Experiment ESEX mission related to the silver-zinc battery is described. The on-orbit observations of the battery behavior in relationship to the thruster firings are summarized, as well as a description of the catastrophic failure which ended the ESEX mission. Although a final cause of the battery failure was not definitized, the data collected on-orbit, from ground tests, and from previous programs suggest a combination of effects that ultimately led to electrolyte leakage, and a subsequent short circuit between the battery cells and the case. The contributing effects likely include degradation of the mechanical interconnections between the cells, inadequate charge current, and excessive discharge current requirements. Lessons learned from the ESEX experience focus on the need for more realistic simulations of the on-orbit operations during ground test including the use of actual flight hardware and the associated timelines as much as possible.