Mass Gauging for Sustained Presence in Outer Space: A Technology Review

NASA is entering the era of sustained presence in space, including cis-Lunar space and Lunar surface and possibly Mars. NASA’s ongoing program elements, such as the Artemis program, with the help of sustainable innovation from commercial and international partners, are instrumental in achieving this sustained presence. NASA has identified low gravity mass gauging methods as an enabling technology for deep space exploration. Based on the mission, mass gauging technology must be applied to specific scenarios of usage. The type of propellant, the size, material, and shape of the tank must be considered. In this paper, we review and analyze challenges to mass-gauging of propellant at low gravity from the perspective of basic underlying physics. The main challenge to propellant gauging in a low gravity environment is the uncertainty of propellant configuration in the tank. We examine several low-gravity gauging methods, both classic and modern, and analyze them from the first principle physics and engineering perspectives. Our analysis allows grouping of these technologies into two main-categories: i) (propellant-configuration-) model-based methods and ii) model-free methods. It appears that no single technology can address mass gauging requirements across the range of operations and scenarios. While certain technologies have been developed to a high TRL, they cannot fill in all the gaps. The identified gaps are the lack of high TRL model- free mass gauging methods, which limits the state of the art to mass gauging of settled propellant or, more generally, to propellant configurations constrained by either tank hardware or operational conditions to a particular class of tabulated configurations. With this, it appears that the development of model-free technologies is on the critical path of mass gauging technology development for deep-space NASA missions.