The Power Subsystem

Batteries

OPAL uses 10 commercial high-capacity SANYO 1.2 V NiCd batteries (part number KR5000DELY) wired together in series.  Their capacity, 5 Ah,  was chosen with considerable design margin.  The capacity is large enough to operate OPAL throughout several orbits.  The CPU monitors battery charge levels and regulates the charge by power cycling satellite subsytems.  No other hardware overcharge protection circuitry has been added. 

The batteries are located at the bottom of the satellite on the inside face of the bottom panel.  Direct contact with an external panel allows energy dissipated by the batteries to be conducted to the outside of the spacecraft.  The batteries are placed in an aluminum box, with the batteries surrounded by a potting material. This potting material provides both structural support for the batteries and a thermal path for the dissipation of heat. The combined mass of the batteries, box, and potting makes for a large thermal mass (about 2.5 kg). Due to this large thermal mass, the batteries will not suffer significant temperature variations due to the sunlight/shadow cycles derived from the satellite's attitude. Thermal sensors are placed in contact with the batteries to monitor their temperature periodically.

The picture on the right is one battery mounted on the OPAL's bottom panel.  More pictures can be found in the photo gallery.
 

Solar Panels

The solar arrays will consist of seven body-mounted panels. The current design calls for 17 strings of cells with 21 Ga-As cells in each string. These cells have an efficiency of approximately 18% and will provide a voltage of 14.4V.  The cells have been donated, and the panels will be built by members of the OPAL team at Lockheed-Martin.  The following picture is one from SQUIRT I, Sapphire.  OPAL's panels will closely resemble this one.
 

Regulators

Telemetry

The power subsystem gathers extensive telemetry about its own components. Temperatures of the batteries and  solar panels are monitored. Currents from each solar panel are monitored individually, as well as the current coming in or out of the batteries. Bus and battery voltages are also monitored. The most important telemetry values (battery voltage, temperature and current, as well as bus voltages) are sent directly to the CPU, while the rest is sent through a multiplexer to the CPU.

The picture below is of the flight power box.   It contains the telemetry boards as well as the multiplexer and the 5V and 8V regulators. The box dimensions are 29.2 x 12.7 x 4.45 cm.  Some of the boards are not attached completely since the picture was taken during the middle of testing.