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MidSTAR-1 uses improved triple junction (ITJ) gallium arsenide (GaAS) photovoltaic cells for primary power. Each solar panel consists of 20 cells wired in series generating 50 V open circuit. Two panels are mounted on each side of the spacecraft for a total of 16. All 16 solar panels are wired in parallel; each comes with an isolation diode factory-installed. Maximum power for an individual panel under direct solar illumination is approximately 11 W at 42 V.
Four batteries, each composed of 28 rechargeable nickel cadmium (NiCd) cells wired in series provide secondary power. The four batteries are diode-isolated and connected in parallel. The solar panels supply power to the spacecraft power bus and to the batteries through direct energy transfer. Refined power is delivered to spacecraft subsystems and payloads on five DC buses: +28 V, +15 V, +12 V, +5 V and -5 V.
External connections provide 39 V input for charging batteries while on the launch pad; thermistors internal to the battery boxes monitor battery temperature during charging. Inhibit switches between the batteries and the distribution bus ensure no payloads activate prior to deployment on-orbit.
Detailed voltage listing: Power Requirements Table