Description: NASA Stennis Space Center (SSC) is one of the largest consumers of gaseous helium in the world through its engine testing operations. Because helium is a nonrenewable resource, it is desirable to conserve the gas when possible. For safety purposes, helium is used to purge an engine following a test that utilizes cryogenic liquid hydrogen fuel (e.g. a Space Shuttle Main Engine test). This proposal is another important step toward enabling helium conservation through real-time measurement of the H2 concentration in the purge gas. The STTR will continue the characterization of a commercial H2 detector for use as a real-time sensor for determining the concentration of H2 in the helium purge gas. The H2 concentration can be used as an indicator that the liquid hydrogen has been purged from the engine, allowing the helium purge to be of shorter duration, thereby conserving this resource. Significant analysis of sensor capabilities as well as experimental characterization of the sensor performance in a simulated test-stand environment will be performed. A sensor configuration will be recommended with the goal of identifying the best installation option that avoids pumps, mechanical actuators, or the need to vent or pipe a sample if possible.

Benefits: Liquid hydrogen is a common liquid rocket fuel. Thus, the purging of liquid hydrogen will have the same cost, inherent safety, and conservation of energy benefits in commercial settings as in NASA applications. It will be applicable in the liquid hydrogen piping and storage facilities. There is a place for the technology in concept hydrogen vehicles and many research applications where the storage and flow of liquid hydrogen presents safety and costs issues. Additionally, other vehicle like the T212 and the T214 submarines use liquid hydrogen and may be able to use the technology.

The implementation of configurations that will reduce the purge time of liquid hydrogen will save value quantities of Helium. Accurately determining when the liquid hydrogen has been purged from the engine will save money while conserving the precious He resource. Additionally shorter H2 purge times will reduce operations time and increase safety. The installation option that avoids pumps, mechanical actuators, or the need to vent or pipe a sample will reduce the time and costs needed to approve the utilization of the new sensor. Complicated safety analyses will not be required due to the noninvasiveness of the new sensor.