Evaluation of Earth observing system AM-1 battery cell bypass protection

The Earth Observing System (EOS) AM-1 spacecraft, one in a series of Mission To Planet Earth (MTPE) low Earth orbit (LEO) spacecraft, is designed for a lifetime of 5 years. The spacecraft bus design incorporates cell bypass circuitry, similar to that tested in the two onboard batteries. After initial measurements of the resistance in the bypass circuit design for the batteries, a concern regarding the effects of an inadvertent bypass switch closing was identified. Investigation of the magnitude of damage that would result from a bypass switch closing across a fully charged Ni-H₂ cell was initiated after the short circuit current values were calculated based on measured resistance data. The calculated short circuit current was identified as being higher than specification values for the bypass switch. In order to evaluate the cell bypass circuitry design, a 50 amp-hr Ni-H₂ cell was outfitted with an EOS AM-I bypass harness, fully charged, and then subjected to a simulated inadvertent switch closing. Results of the first test indicate that the bypass circuit harness design permits short circuit discharge currents in excess of 600 amperes peak and 400 amps continuously for over 2 minutes. Other observations included the loss of the bypass harness as well as a temperature rise on the battery cell dome to almost 100°C. The post performance evaluation of the test cell together with recommendations for possible modification of the bypass circuit design for EOS AM-1 spacecraft batteries to increase the probability of post failure survival are presented in this paper