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The International Space Station Alpha Electrical Power System has a thermal control system to remove heat from the batteries and power distribution electronics. A major subsystem of this thermal loop is the Pump and Flow Control Subassembly (PFCS) which functions as an ammonia fluid distribution and control subsystem. This paper will detail the development, construction and operational performances of the PFCS hydraulic elements operating with an ammonia fluid. These elements include flow meter, accumulator, flow control valve, and pumps. The electronics which are utilized to operate these hydraulic elements will also be described. The combination of these hydraulic and electronic elements form a subassembly to safely control a hazardous, low viscosity fluid.

The Extravehicular Mobility Unit (EMU) used by astronauts during space walks is powered by an 11-cell, silver-zinc battery. The present battery is certified for 6 cycles with a minimum discharge requirement of 7 hours above 16.0 volts at a 3.8 Amp load. Its certified wet-life is 170 days. Operational requirements for the International Space Station (ISS) led to a design capable of 32 cycles over a 425 day wet-life. Other battery parameters including capacity, rate capability, weight, volume, safety and the need for continuing compatibility with the EMU and the Space Shuttle charger dictate that the new battery will also be silver-zinc.