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.

Example Impact of Nonuniform Acceleration Fields on Liquids in Spacecraft

“…Even in uniform zero gravity, asymmetric propellant positions can exist as the low-energy static equilibrium condition [6] and if unanticipated can introduce large errors into tank thermal models. This error can even impair propellant gauging efforts [7]. The inclusion of the gravity-gradient physics alters the symmetry of the problem, and this is found to be an important effect not indicated by the relative magnitudes shown in Fig.…”

Magnetic retention of LO2 in an accelerating environment

“…The ability of the Surface Evolver [20] to accurately simulate cryogenic propellant positioning induced by surface tension in spacecraft propellant tanks is also well established [21][22][23][24][25][26]. The simulation is capable of modeling any physical phenomenon that can be formulated analytically in Cartesian space and expressed as an energy integral.…”

Thermal Propellant Gauging at EOL, Telstar 11 Implementation

“…These are bookkeeping, Pressure-Volume-Temperature (PVT), and thermal Propellant Gauging System (PGS/TPGS). Basics of the modern PGS method can be found elsewhere 1,2 . The PGS method has distinct advantages over the bookkeeping and PVT methods, in particular, near end of life (EOL).…”

“…A Thermal Propellant Gauging method is based on a concept of measuring the thermal capacitance of a tank containing liquid fuel and pressurant gas by measuring the thermal response of the propellant tank to heating and comparing the observed temperature rise to simulation results obtained from a tank thermal model [1][2][3] . Described in Ref.…”