Modeling to Evaluate a Spacecraft Propellant Gauging System

Abstract

INTRODUCTION Prediction of remaining propellant is critical to the phasing of orbital replacements in the telecommunications industry. Increases in demand for data flow capacity have led to the development of larger and more powerful satellites. When such systems are utilized to full capacity, the net annual revenues per vehicle may be in the billions of dollars. Thus it is highly desirable to have very accurate predictions of the end of useful life for each vehicle to best manage the procurement and launch of orbital spares and replacements. The liquid hydrazine propellant used for both orbit insertion and orbit station-keeping is stored in one or more large tanks with an internal passive capillary Propellant Management Device (PMD). The PMD controls liquid mass center and orients the liquid such that it can be extracted at the tank outlet. Typical PMDs are multiple thin vanes to orient the ullage bubble and a finer capillary structure near the tank outlet or sump. As the tank is emptied, a gas bubble grows in volume and is located away from the tank outlet by the PMD. The liquid collects in large fillet regions subtended by the vanes and tank walls. The liquid free surface forms a complex three-dimensional geometry not easily approximated by closed-form equations.