A Radio-Frequency-Based Propellant Slosh Sensor for Spacecraft Tanks

Fuel sloshing is a problem that has threatened the success of many satellites and has been widely studied in the field of controls. Currently, leading research in this topic has focused on Computational Fluid Dynamics (CFD) simulations to devise methods of predictively controlling the location of fuel within a spacecraft's tank. In this paper, a Radio Frequency (RF)-based mechanism to measure the location and quantity of fuel in spacecraft tanks is presented. By treating the tank as a resonating cavity, movement of the fuel inside produces a shift in resonant frequency and a change in the quality factor for the different cavity resonating modes. This results from the differing dielectric properties for the volume of air, gas, or vacuum, compared to the volume of liquid propellant. It is shown that as a sphere of distilled water is moved linearly across the resonating cavity, and the S-parameters response of the cavity is strongly correlated with the position of the sphere. Exploiting this can attain the capability to measure both location and quantity of propellant contained within a tank in microgravity environments in real time while in flight.