General Electric Company

Keith Davies

Joseph A Pulkowski

William H Meise

Susan M Hubert

Daniel A Lichtin

Laura E Brauer

Siu H Chun

Marc B Young

A spacecraft includes bipropellant and monopropellant engines or thrusters. The oxidizer-fuel mixture ratio of the bipropellant engine is not known exactly. The spacecraft is loaded with only sufficient oxidizer to achieve the velocity for transfer from an intermediate orbit to geosynchronous orbit if the mixture ratio is nominal. Therefore, more fuel can be loaded. If the bipropellant engine burn is nominal, there is no excess oxidizer when on-orbit and more fuel is available for stationkeeping. If the burn is oxidizer-rich, there is a velocity shortfall, which is made up by firing monopropellant engines. If the burn is oxidizer-lean, the geosynchronous orbit is achieved with a load of excess oxidizer, which must be moved during each stationkeeping maneuver. A net gain of stationkeeping time results in any of the three mixture ratio cases by comparison with loading of sufficient oxidizer for a full bipropellant burn under worst-case mixture conditions.

Spacecraft with increased stationkeeping fuel load

A spacecraft includes a pair of pressurized propellant tanks. The pressure may be provided from a common pressurant tank. Each propellant tank has a propellant output port. A manifold includes a first branch coupled between a common juncture and the output port of the first tank, and a second branch between the juncture and the output port of the second tank. At least the second tank is associated with a heater. A controllable valve, such as a normally open pyrovalve, is coupled in the second branch. In order to fully utilize the propellant in the tanks, the second tank is differentially heated relative to the first when the tanks are nearly empty, to create a tendency toward a pressure difference, which drives propellant from the second tank to the first. When all or most of the propellant is transferred, the valve is operated to close off the second branch of the manifold, to isolate the now-empty tank. The thruster continues to be operated from time to time, drawing the remaining propellant from the first tank. The heating may be performed at times of day and/or seasons of the year when the appropriate tank receives solar radiation. The fuel remaining can be directly measured, or the spacecraft is launched with a known amount of propellant in the tanks. The thrusters are operated from time to time for attitude control and/or stationkeeping, and records are kept of the cumulative fuel use.

Thermal fuel transfer and tank isolation to reduce unusable fuel

The unknown amount or mass of liquid contained in a storage tank is measured by calibrating the tank in an empty and partially full condition. The calibration includes measuring the mass of the empty tank, and is accomplished by applying a measured amount of heater power or energy to the tank and its contents, and measuring the temperature response to determine the product of total mass multiplied by specific heat. The specific heat depends upon the mass or amount of liquid in the tank, but a linear relationship is established between total mass and the product of total mass times specific heat. The unknown mass of liquid is then determined by applying a known amount of heater power or energy to the tank and its contents, and measuring the temperature rise or rate of rise in response thereto. The mass of the system multiplied by specific heat is determined from the temperature rise or rate of rise, and is interpolated or extrapolated relative to the calibration to determine the mass of the system with its unknown amount of liquid. The mass of the tank is subtracted from the unknown system mass to determine the mass of the liquid. In a spacecraft fuel tank application, the tank-empty calibration is performed in an evacuated test chamber, and the partially-full calibration is performed on-orbit after one thruster burn has consumed an amount of fuel which is determined from a schedule based upon knowledge of the consumption of the particular thrusters or types of thrusters being used.

Method for measuring the mass of liquid in a storage tank

A fuel or fluid level measurement arrangement for a spacecraft includes one or more electromagnetic transmission lines extending into the reservoir. The presence of fuel adjacent the transmission line changes the dielectric constant or loss characteristics of the transmission line(s) in a measurable manner. In one embodiment, strip transmission lines extend parallel to the fluid surface at various degrees of ullage, and the fuel level can be established to within the spacing between the transmission lines.

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Robbinsville, NJ, United States of America

Keith Davies