Thermal Gauging and Rebalancing of Propellant in Multiple Tank Satellites

Abstract

An unbalanced propellant load in a geosynchronous communications satellite with multiple tanks can reduce satellite life. Depending on the details of the propellant plumbing system, significant fuel may become unusable in the more full tanks when the least full tank empties. If undetected and uncorrected, such an imbalance will reduce revenue and may even cause a premature loss of service. An improved thermal propellant gauging system is applied to detect imbalances in a pair of satellites and to design and implement new technology: the thermal pumping procedures to correct the imbalances. Thermal pumping is achieved through ground-based control algorithms to create the necessary differences in the heating rates of the four propellant tanks. The ground-based algorithm uses temperature telemetry and heater status telemetry to send heater commands to the satellites. This differential heating approach was employed successfully on two satellites, which were neither designed nor built with these thermal gauging and pumping operations in mind, enabling a considerable extension of profitable operational lifetime for both satellites.

Lessons Learned in the Decommissioning of the Stardust Spacecraft

“…Thus, the primary thruster string had accumulated over twice the number of firing cycles than had been demonstrated in life tests. Although the 1 Manager, Small Bodies Program and EPOXI Project, MS 264-379, 4800 Oak Grove Dr., Pasadena, CA 91109 2 thrusters showed no measurable degradation, a risk assessment led to the decision to switch to the back-up thruster string, providing ample thruster life to complete the extended mission and preserving the original string as a back-up in case of unexpected failure. This was easily accomplished since the thrusters were fully cross-strapped in the system.…”

Study of the thermal characteristics of propellant tanks in microgravity and its application to propellant gauging

“…Yendler and Narita [21] tested the feasibility of the thermal capacitance method on a satellite BSS601 without a dedicated heater, and the results showed that the thermal capacitance method is more accurate than the BK at the end of the satellite's life, but it is necessary to build a higher fidelity thermal model of the satellite. Yendler et al [22] also applied the TPG to a multi-component satellite propellant system, where the residual amount in each tank could be detected individually, and a heat pump could be formed by applying different amounts of heat between the connected tanks to balance the propellant content of different tanks and prolong the lifetime of the satellite. Later on, with Yendler's participation, the TPG was applied on several satellite platforms such as the satellites Telstar 11 [23], SpaceBus 3000A(ArabSat 2B) [24], SpaceBus 2000 (Turksat 1 C) [25], etc., and gained some benefits.…”

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.…”