This is a continuing work toward the development of leak detection point sensors for cryogenic propellants in the presence of purge gases including helium and nitrogen. Both commercial sensors and sensors designed in-house were tested in the Gas Detection Sensor Test Station (GDSTS) (figure 1), developed by YA and the Engineering Support Contractor, Dynacs Inc. These sensors will be used for locating leaks in ground support equipment, the Space Shuttle, and future-generation spacecraft. The goals of this work include the following:

• Maintain a state-of-the-art sensor test station and capabilities.
• Test new, promising propellant sensors, designed to operate in air or purged environments, at room or cryogenic temperatures, and at ambient or high-altitude pressures.
• Develop in-house sensors where commercial sensors are lacking.
• Ultimately shorten vehicle processing time.

The GDSTS was validated as a sensor test station using the Detronics combustible gas sensor presently utilized on the Shuttle launch pads for hydrogen leak detection. Test station performance parameters were monitored during the tests that included wide variations of hydrogen concentrations, pressures, and temperatures. After successful validation, the GDSTS was used to simultaneously validate the performance of a group of five Detronics combustible gas sensors from the supply batches currently used at Shuttle launch pads for outdoors and in purged area leak detection. Another test apparatus was constructed to perform quick screening tests of propellant sensors required to operate at very low temperatures (figure 2).

Promising hydrogen sensors to be used in purged areas and in very cold environments are being developed by a partnership between Glenn Research Center, Makel Engineering, and Case Western Reserve University (figure 3). The first generation of these devices, based on palladium alloy deposited on a micro-hotplate, was tested in the GDSTS and its performance was reported to the developers as feedback for the next generation. Ultimately, NASA intends to qualify these sensors for ground support equipment and flight hardware.

A commercial oxygen sensor was recently tested in the GDSTS and found to be of very superior design and performance. Packaging issues are already solved for this zirconia-hydrate-based sensor, which is housed in a standard transistor package (figure 4). By testing in the GDSTS, this sensor was found to operate successfully in an environmental range of temperatures well below the manufacturer’s specifications.

Part of the development process is to search for and partner with research or commercial entities willing to join with NASA and codevelop sensors that meet NASA requirements. A number of these arrangements are being pursued:

• Florida Institute of Technology, Electrical Engineering, fiber-optics hydrogen sensor (in place).
• Florida Solar Energy Center, hydrogen-sensitive optical fibers and devices fabrication using state-of-the-art microdevice equipment.
• SNECMA, a French company that has a hydrogen sensor reported to be qualified for cryogenic temperature operation deployed on the Ariane rocket.
• Advanced Magnet Lab, a Florida research company that has proposed a low-temperature hydrogen sensor based on nuclear magnetic resonance concepts.
• National Institute of Standards and Technology (NIST) Laboratory in Washington, D.C., provided NASA technical support and micro-hotplates that will be coated in-house with palladium alloys sensitive to hydrogen.

Contacts: F.W. Adams (Frederick.Adams-1@ksc.nasa.gov), YA-C3-A, (321) 867-6671; and R.P. Mueller, YA-D1, (321) 867-2557
Participating Organization: Dynacs Inc. (Dr. R.G. Barile, J. Dominguez, M.A. Bertucci, S.J. Stout, D.P. Schmidt, C.B. Mattson, J.G. Gates, and A.J. Eckhoff)