Description: The Modal Propellant Gauging (MPG) experiment is designed to assess the mass gauging resolution of a novel implementation of experimental modal analysis (EMA). The central objectives of the MPG experiment are to (1) record the modal response of a model propellant tank at different fill-levels under unsettled, microgravity conditions, and (2) record the modal response of the propellant tank during simulated propellant transfer. Phase II of the Modal Propellant Gauging (MPG) project will assess the gauging resolution of the MPG technique at low fill fractions for unsettled, sloshing propellant simulant. Phase II will utilize a full-fidelity propellant tank with flight heritage and will extend the gauging analysis to accommodate changes in tank pressure during low-gravity propellant transfer operations. This work is a continuation of previous flight testing under T0123 and T0147. Problem Statement The experimental modal analysis (EMA) technique is an inexpensive, non-invasive and computationally robust method of assessing propellant mass through its effect on structural resonance modes in the propellant tank. EMA is a computational technique that extracts the resonant modes of the structure from real-time vibrational data obtained from sensors affixed to the structure. The natural resonances of a structure depend on the stiffness and the effective mass of the structure, and so the EMA technique can be used to determine the effective mass of the propellant tank. The effective mass of the tank is, in turn, dependent on the mass loading of the structure by its liquid contents. EMA uses the shifts in resonant frequencies of the tank as liquid level changes to calculate the change in effective mass of the tank and thereby the change in liquid mass.

Benefits: The ability to gauge the amount of propellant in fuel tanks in low-gravity is a critical technology, as it is the only way to verify the propellant quantity without having to settle the liquid via a propulsive maneuver. This technology will benefit the commercial industry and future NASA missions.