ABSTRACT
When we speak of designing the spacecraft electrical power system, we really mean designing the electrical energy system. The satellite has a limited time in orbit to generate power, but the loads need to be powered all the time. The battery stores the required energy during sunlight and delivers to the loads during eclipse. The energy balance between the battery charge and discharge over one orbit period must be, on average, positive with some margin. In a simple case of constant load shown in Figure 13.1, the lightly dotted area must exceed the dark area with an acceptable margin. Otherwise, the battery would become totally depleted after some time. The power to and from various components must therefore be managed in order to maintain the energy balance in both the transfer orbit and the operational orbit.
