Low rate trickle charging of nickel-hydrogen batteries

Nickel-hydrogen battery management, during spacecraft prelaunch activities, traditionally includes active cooling if high state of charge is required at launch. The NASA AXAF-I Program has been investigating techniques for managing nickel-hydrogen battery state of charge, during prelaunch and launch operations, in the absence of active cooling. These investigations demonstrate that high states of charge can be achieved and maintained, in the absence of active cooling, utilizing adiabatic charging and low rate trickle charging techniques. This paper describes the experimental determination of steady state battery capacity and temperature, during low rate trickle charging, in a simulated prelaunch ambient environment. Initial parametric data was obtained with individual cells. Subsequently a six-cell battery module, simulating the 22-cell flight battery thermal characteristics, was designed and fabricated. The module was mounted in a structure simulating the thermal environment the battery would experience in the spacecraft, during prelaunch operations. The test set up was fully instrumented. The six-cell module was trickle charged at rates in the range C/100 to C/1000. Steady state capacities and temperatures were determined. Test results indicate that trickle charge rates less than or equal to the self discharge rate (~C/750) do not significantly increase dissipation beyond that due to the self discharge. Accordingly, significant trickle charge rates (~C/500) result in battery temperatures only a few degrees (F) higher than observed during periods of open circuit stand