The NASA Glenn Research Center used modern simulation tools to model a mass-gauging technique based on the electromagnetic radiofrequency (RF) resonance spectrum of closed cavities. Changing the quality or quantity of a dielectric, such as a propellant, from a cavity will shift the resonant frequencies of that cavity. The measurement of those frequency shifts can be incorporated into an algorithm to determine the weight of the propellant inside a cryogenic tank.
RF mass gauging is a promising technique that was investigated by a number of NASA contracts from 1964 to 1988. Most notable was the 1988 NASA contract with Ball Aerospace. Using a solid wax to emulate low-gravity fluid configurations, Ball Aerospace demonstrated up to 1 percent of full-scale accuracy. In comparison to other methods, RF mass gauging showed the following advantages: fast measurement time; simple, rugged, low-weight, low-power electronics; and technology that is applicable to any dielectric liquid (e.g., hydrogen, oxygen, or methane). In previous attempts, analytical or numerical methods could only be used to predict the response of tanks with very simple structures and basic Earth gravity (1g) liquid configurations. Today, the combination of powerful, yet relatively inexpensive, computers and highly advanced three-dimensional electromagnetic analysis software allows the simulation of arbitrary liquid configurations in cryogenic tanks containing baffles, struts, and many other internal devices and structures.
12- by 22-in. cryogenic tank being filled with liquid oxygen.
Glenn researchers validated the three-dimensional electromagnetic software by comparing simulated data with experimental data gathered on a 12-in.-diameter, 24-in.-high tank (shown in the photograph), which was incrementally filled with liquid oxygen. The following graph shows excellent agreement between the experimental and simulated data. The excellent results assure us that we can use the software to predict the resonance spectrum of complex cryogenic tanks, create electromagnetic field plots to identify specific resonance modes, and determine the optimum shape and location(s) of antenna to couple to specific resonance modes.
Comparison of experimental and eigenmode simulated RF tank resonances for a tank incrementally filled with liquid oxygen.
Ongoing work at Glenn includes performing extensive numerical simulations to predict resonance modes in various tanks that contain internal hardware, determining of the optimum shape and location of antenna for those tanks, simulating low-gravity fluid configurations, and developing a mass-gauging algorithm. We also plan to perform an in-flight validation of the algorithm.
This work is part of a larger RF mass-gauging effort being performed in-house that is funded by Exploration Systems Research and Technology, and Propulsion and Cryogenics Advanced Development.
Glenn contacts:
Karl R. Vaden: 216-433-8131, Karl.R.Vaden@nasa.gov
Dr. Gregory A. Zimmerli, 216-433-6577, Greg.Zimmerli@nasa.gov
Author:
Karl R. Vaden
Headquarters program office:
Exploration Systems Mission Directorate
Programs/projects:
Exploration Systems Research and Technology, Propulsion and Cryogenics Advanced Development, Highly Reliable/Autonomous Deep-Space Cryogenic Propellant Refueling Systems Technology Theme; High Energy Space Systems Element Technology Maturation Program
Last updated: September 10, 2007
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