Research on imaging method of gas-liquid interface in aerospace propellant tanks based on ultrasonic tomography

The distribution of gas and liquid within aerospace liquid propellant tanks exhibits uncertainty under microgravity environments, which reflects the working state of the propellant tank, affecting the timing of pressure relief, overall attitude control, and propellant mass gauging. Current ground-based propellant mass gauging technologies have become relatively mature, with diverse methods, high measurement accuracy, and assured reliability and safety. However, in spacecraft on-orbit measurements, the accuracy of commonly used ground-based methods decreases due to limitations in techniques for determining the gas-liquid interface position. This paper proposes a gas-liquid distribution reconstruction method based on ultrasonic tomography for spacecraft tank measurement scenarios. It investigates the priority back projection method, elliptical reflection method, and local curvature reconstruction method for gas-liquid interface based on transmitted signals, elliptical reflection signals, and echo signals, respectively. The image is processed based on the prior characteristics of the gas-liquid distribution material field, with the introduction of morphological image processing methods. Both intrusive and non-intrusive measurement experiments were conducted for validation. For intrusive experiments, the mean area estimation error in the gas domain is approximately 8.52%, with a positioning error of approximately 1.88 mm; and for non-intrusive experiments, the mean area estimation error is approximately 6.51%, with a positioning error of approximately 3.87 mm.