Power and energy budgets

Power and energy, like other resources in a design, are tracked and managed through budgets. In the simplest probes, this may simply be a case of adding up the power used by each subsystem and determining how long the probe can

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Figure 9.1. Regime diagram showing the typical applicability of various energy sources as a function of power and duration.

10 10 10 10 10 10 10 Duration (s) Hour Day Month Year

Figure 9.1. Regime diagram showing the typical applicability of various energy sources as a function of power and duration.

operate with a given energy supply. More generally, various margins and factors need to be tracked - degradation of batteries in flight, for example - which make resource tracking somewhat more involved.

Often the power requirements vary through a mission - for example if a relay satellite is used, energy-consuming downlinks may occur several times a day, while electrical power from solar arrays will only be available for some of these opportunities. To determine the required array and battery size needs a detailed study. Such operational considerations may also run into thermal constraints -e.g. under summer conditions the Mars Exploration Rovers had enough power to conduct additional operations during the day, but thermal dissipation would have caused overheating.

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