Electrical Power Subsystem (EPS)

The electrical power subsystem (EPS) is responsible for generating, storing, conditioning, and distributing electrical power to all spacecraft systems. It typically consists of solar arrays (primary generation), batteries (eclipse and peak-load storage), a power control unit (PCU) that regulates bus voltage, and a distribution network with fault protection. Power budgets are tightly managed — every watt allocated to the payload comes at the cost of bus mass and solar array area. Deep-space missions beyond Jupiter use radioisotope thermoelectric generators (RTGs) instead of solar arrays. Starlink satellites run on 3 kW; the ISS generates 120 kW.