Note, the reactant gasses themselves are somewhat reactive, so an acceptable and safe instrumentation systems are not easy to find.

• JSC is currently developing a breadboard integrated Proton Exchange Membrane (PEM) fuel cell spacecraft power system
• One of the concerns with the design currently being pursued is the level of humidification of inlet reactant (both hydrogen and oxygen) streams to the fuel cell stack. These reactant streams are passively humidified by mixing incoming dry consumption reactants with recycled humid reactant exit streams from the outlet ports of the fuel cell stack. We have analysis capability that can predict the level of humidification based on assumptions associated with the recycle ratio (quantity of recycled, high-humidity reactants ratioed to the quantity of incoming dry consumption reactants), temperatures in the flow streams, and recycled reactant humidity level.
• This Design project will provide added test capability and is relevant to the Development of second generation fuel cells Requirements: Design, and develop a prototype of a humidity sensor instrumentation system that can be configured so that the sensor is:
  1. Inline with the inlet reactant stream (i.e., no tap-offs or bypass lines will be required which can complicate the measurement at hand)
  2. Requires a minimum of low voltage electrical power to operate
  3. The design must operate at acceptable safety so that it can be approved for installation in pressurized (up to 75 psia) hydrogen and oxygen streams at temperatures up to 170F
  4. JSC EP5 personnel can provide hardware like some variable capacitance sensors and suggested circuits, electrical feedthrough components, and some equipment that could be used ultimately to test the device