Abstract
Now more than 12 years in orbit, Mars Express battery telemetry during some of the deepest discharge cycles has been analysed with the help of the ESTEC lithium ion cell model. The best-fitting model parameter sets were then used to predict the energy that is expected to be available before the battery voltage drops below the minimum value that can support the power bus. This allows mission planners to determine what future power profiles could be supported without risk of entering safe mode. It also gives some more insights into the ageing properties of these batteries.
Highlights
After Proba-1, Mars Express, launched in June 2003 for an initial 4-year mission, is the spacecraft with the longest duration in orbit that relies upon lithium ion batteries to provide main-bus energy storage
More than 12 years in orbit, Mars Express battery telemetry during some of the deepest discharge cycles has been analysed with the help of the ESTEC lithium ion cell model
Since the cell model calculates the cell potential under a given imposed current profile, the simplest way of fitting the model parameters to the telemetry data is by imposing the battery telemetry current and temperature profiles on the model of a single cell scaled to the battery configuration, and comparing the resulting voltage prediction to the voltage telemetry
Summary
After Proba-1, Mars Express, launched in June 2003 for an initial 4-year mission, is the spacecraft with the longest duration in orbit that relies upon lithium ion batteries to provide main-bus energy storage. The batteries cannot be discharged individually to determine their useful capacity so the problem is to predict how much energy would be available under a given power and ambient battery temperature profile using telemetry date from discharge-charge cycles with relatively shallow depths of discharge. Comparison of ground test battery performance data with early in-flight eclipse data using the lithium ion battery model developed at ESTEC [2] was reported at the 2006 NASA Aerospace Battery Workshop [3]. 10 years later and after improvements in the model and the availability of ground test data on aged batteries this analysis is revisited and extended to include recent telemetry
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