Modal Propellant Gauging: High-resolution and non-invasive gauging of both settled and unsettled liquids in reduced gravity

• Published in: Acta astronautica Vol. 159; pp. 499 - 507
• Main Authors: Crosby, Kevin M., Williams, Nehemiah J., Werlink, Rudolph J., Hurlbert, Eric A.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2019; Elsevier BV
• Subjects: Acoustic excitation; Finite element method; Flight tests; Flow rates; Gaging; Gravitation; High resolution; Liquids; Mass flow rate; Mathematical models; Modal analysis; Modal response; Orion ESM; Parabolic flight; Propellant Mass Gauging; Propellants; Service modules; Stiffening; Technology; Ullage; Propellant Mass Gauging; Modal analysis; 70J10; Orion ESM; 76M22; MSC: 76M22; Orion ESMMSC: 70J10
• ISSN: 0094-5765; 1879-2030
• DOI: 10.1016/j.actaastro.2019.01.050

The modal response of a liquid-filled tank to external acoustic excitation can be used to infer with high resolution the mass of contained liquid, the mass flow rate of liquids into and out of the tank, and changes in tank pressure. Both contained liquid mass and internal ullage pressure affect the modal response of the tank walls through fluid mass-loading of the tank walls and pressure-induced wall stiffening, respectively. Modal Propellant Gauging refers to the technology that exploits these shifts in modal frequencies to infer the mass of propellant in a tank. MPG is a non-invasive gauging technology that has demonstrated gauging resolutions of 1% for settled propellants and 2–3% for unsettled, sloshing propellants. Extensive parabolic flight testing of the MPG system on model tanks has been conducted to validate the technology in reduced gravity. MPG testing on a qualification tank for the Orion Program's European Service Module has also been conducted and is reported here. Finite element modeling of the Orion ESM ″upper” tank is discussed and compared with measurement data. Three computational approaches to mass determination, Peak Tracking, Point Sensor, and Spectral Density methods, are described here. Use cases are defined and analyzed in the context of the Orion ESM Qualification tank data, and an implementation scheme for continuous mass gauging on the Orion ESM is discussed. •Non-invasive, low-gravity propellant gauging achieved through real-time modal analysis.•Three computational approaches to contained propellant mass gauging demonstrated.•Orion Service Module tank testing results in 1–2% resolution for settled liquids.•Parabolic flight testing results in 2–3% resolution for sloshing liquids.