This concept uses an optical interferometric method to determine the density and/or pressure of the gas state contained with tank ullage. The system is similar to compression tank volume methods. By using an optical interferometric technique to determine gas density and/or pressure, a much smaller compression volume or higher-fidelity measurement is possible.
Future space mission concepts are severely limited by the inability to determine the amount of fluid (especially a cryogen) in a tank without some form of stratification (gravity, thermal, etc.). The nature of the fluid in a low- or zero-gravity environment makes metering concepts difficult. The physics governing the flow of liquids under these conditions are dominated by surface tension and viscosity forces.
Various mass gauging schemes have been tried (or proposed) that require complex modifications or inside surface polishing of tanks. Others rely on complex pumping devices. However, this design is far simpler and effective.
In this innovation, the tank (volume to be measured) is coupled to the measurement system, which is a simple optical cell (chamber connected to the tank with optical windows). A laser is passed through the optical cell in a Michelson-type interferometer arrangement. This will couple the optical beam to the physical state of the gas in the tank. A small compression is put on the tank, which compresses the gas phase in the tank and changes its density. This density change is “seen” through a shift in the generated optical fringes. Well-established and proven theory is used to quantify the fringe shift into physical units. The novel feature here involves using the optical method to measure the density change in the gas rather than a standard pressure transducer. The sensitivity of this approach can lead to a 1,000× improvement over the traditional approach, or can lead to a piston 1,000 times smaller for the same performance, which is more of an interest to space applications.
This work was done by William Witherow and Kevin Pedersen of Marshall Space Flight Center, and Valentin Korman of Madison Research Corporation. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at
