Toward Microgravity Mass Gauging with Electrical Capacitance Volume Sensing: Sensor Design and Experiment

The use of capacitance sensors for fuel mass gauging has been in consideration since the early days of manned space flight. However, certain difficulties arise when considering tanks in microgravity environments. Surface tension effects lead to fluid wetting of the interior surface of the tank, leaving large interior voids, while thrust/settling effects can lead to dispersed two-phase mixtures. With the exception of capacitance-based sensing, few sensing technologies are well suited for measuring annular, stratified, and dispersed fluid configurations. Two modalities of capacitance measurement are compared: Electrical Capacitance Volume Tomography (ECVT) and Electrical Capacitance Volume Sensing (ECVS). ECVT is a non-invasive imaging modality first introduced in 2006. ECVS is a measurement modality introduced in this paper that is derived from ECVT technology but does not reconstruct an image as part of the mass measurement. To optimize the design of future capacitance-based spherical tank mass gauging sensors, different electrode plate layouts are evaluated in a mass gauging context. Prototype sensors are constructed, and experiments are conducted with fluid fills in various orientations. The plate layouts and their effect on the performance of the sensor as a fuel mass gauge are analyzed through the use of imaging and averaging techniques.