Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
2001-10-15
2003-06-24
Jordan, Charles T. (Department: 3641)
Aeronautics and astronautics
Spacecraft
Attitude control
C244S172200
Reexamination Certificate
active
06581880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present disclosure is directed to new and improved methods and systems for managing the orbits of satellites and the like that employ electrical propulsion (“EP”) systems for stationkeeping.
2. Background of Related Developments
EP systems provide a substantial mass advantage over chemical propulsion systems. EP systems operate by converting electrical energy into momentum, typically by heating or ionizing a gas and accelerating it. The propellant mass efficiency of an electric propulsion device is characterized by its specific impulse (“Isp”). An EP device with a higher Isp requires less propellant mass to provide a given total impulse. However, a device with a higher Isp also requires more energy to provide a given total impulse. This means that the device will require more power and/or more time to complete a given mission.
Because of the need to balance propellant mass and power capability, there is an optimum Isp (and therefore optimum power level) for every electric propulsion mission. In general, the optimum Isp depends on the amount of power available for use by the EP device. The more power that is available to the EP device the higher the optimum specific impulse.
SUMMARY OF THE INVENTION
New and improved methods and systems are disclosed for managing an EP system of a satellite requiring stationkeeping. The methods and systems maintain a prescribed Earth orbit employing the following referenced steps and device elements to be considered in combination with one another.
(a) Orbit analysis is used for calculating the burn time of an EP device and the storage battery recharge time required for tracking a predetermined stationkeeping orbit. (b) Power analysis is used for calculating solar eclipse power draw and battery recharge power input.
EP device thruster voltage, current and maximum allowed thruster battery power draw are [c] set and the EP device is (d) ignited to start an EP device burn simultaneously with starting a satellite clock. The (e) satellite clock time is compared to the EP device burn time and the EP device burn is (f) ended if clock time is greater than burn time.
(g) Determining that power draw is greater than or lesser than maximum power draw when clock time is less than burn time. When (h) power draw is greater than maximum power draw, EP thruster current is increased and thruster voltage is decreased. When power draw is less than maximum power draw, (i) decrease thruster current and increase thruster voltage and repeat steps or elements (e) through (i) until step or device (f) when clock time is greater than burn time.
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Guenter Fischer
Oh David
Randolph Thomas
Holzen Stephen A.
Jordan Charles T.
Perman & Green LLP
Space Systems Loral, Inc.
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