US 4,537,375 AGranted

Method and apparatus for thruster transient control

AssigneeFord Aerospace & Communications Corporation

InventorFred N. Chan

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Abstract

Transients and steady state error induced in maneuvering a satellite due to a disturbance torque caused by thrust mismatch or differential in the alignment of thrusters with respect to the center of mass are minimized by introducing a torque balancing bias at the input of a thrust modulator of the thrusters prior to sensing position or attitude error. The bias may instantly off-modulate the thruster control signal to cancel the effects of attitude transients before errors develop. Other axes thrusters may be on-modulated instantaneously to compensate for cross-axis torque. The bias may be introduced into the satellite control scheme by manual ground control or in automatic on-board compensation based on stored parameters obtained for example from calibration measurements. Specifically, the torque balancing bias may be developed by reference to thrust mismatch detected and stored during previous maneuvers, thus anticipating expected attitude error without actual detection thereof.

Claims13

Dependent claims

For use in a spacecraft during a change in velocity maneuver, the spacecraft employing a plurality of thrusters, at least a first thruster and a second thruster being disposed to develop mutually counteractive moment arms of thrust relative to at least one axis through a center of mass of the spacecraft, said first thruster and said second thruster being capable of developing unequal moment arms of force, a method for counteracting disturbance transients comprising the steps of:

storing prior to said manuever a value representative of an estimated disturbance torque;
thereafter
modulating in response to said stored value one of said first and second thrusters during said maneuver to counteract an actual disturbance torque a sufficient amount to compensate for said actual disturbance torque in order to minimize a net position error without initially detecting said net position error;
thereafter
detecting said net position error, said net position error being indicative of a difference between said estimated disturbance torque and said actual disturbance torque with respect to said axis;
and thereafter
modulating in response to a sum of said stored value and said net position error one of said first and second thrusters during said manuever to counteract said actual disturbance torque to further minimize said net position error.

4 more elements

For use in a spacecraft during a change in velocity maneuver, the spacecraft comprising a plurality of thrusters, at least a first thruster and a second thruster being disposed to develop mutually counteractive moment arms of thrust relative to at least one axis through a center of mass of said spacecraft, said first thruster and said second thruster being capable of developing unequal thrust, an apparatus for independently modulating thruster discharge for counteracting disturbance transients comprising:

means for generating a value representative of an estimated net disturbance torque for storage prior to said manuever;
means for modulating one of said first and second thrusters in response to said estimated disturbance torque value obtained following storae during said maneuver to counteract an actual disturbance torque a sufficient amount to compensate for said actual disturbance torque in order to minimize a net position error without initially detecting said net position error;
means for combining said net position error and said estimated disturbance torque value to produce a control value for controlling said modulating means during said maneuver;
and
means for detecting said net position error, said net position error being indicative of a difference between said estimated disturbance and said actual disturbance torque with respect to said one axis.

2 more elements

Dependencies are inferred from the claim text.