Power subsystem design for the Montana EaRth Orbiting Pico-Explorer (MEROPE) CubeSat-class satellite

Montana State University´s Space Science and Engineering Laboratory (SSEL) under support from the Montana NASA Space Grant Consortium is engaged in an Earth orbiting satellite student project that will carry a reproduction, using current-day technology, of the scientific payload flown on Explorer-1 in 1958 into a 650 km sun-synchronous polar orbit. The off-the-shelf emphasis of the MEROPE component selections has required the power system to adapt to widely different electrical needs across subsystems. The size limitations of the CubeSat-class specifications confine body-mounted solar arrays to approximately 64 cm² per side, restricting overall power production and necessitating the use of an extremely efficient power bus. MEROPE will employ dual junction GaAs solar cells (19% efficiency) to produce the 5 W necessary for satellite operation and battery maintenance. Included in the system will be two Li-ion battery cells chosen for their high energy density, rapid charge characteristics, low mass, and lack of memory effects. The power system is responsible for providing a highly regulated 5 V bus to the microcontroller subsystem and a 6 V bus to the communication subsystem. In addition, the Geiger tube scientific payload aboard MEROPE requires a stable 500 V high voltage power supply (HVPS) to operate the experiment. This will be accomplished using a prototype HVPS requiring +/- 5 V buses.