Spacecraft disturbance compensation using feedforward control

A spacecraft control system for use with a spacecraft that includes actuator dynamics that are coupled to spacecraft dynamics, said control system comprising:

• a sensor for providing a measurement of the attitude of the spacecraft and for providing an output signal indicative thereof;
• a closed loop control system coupled to the sensor for processing the output signal from the sensor and for providing a timing signal indicative of the time of occurrence of a predictable transient disturbance that affects the spacecraft;
• a summing device coupled between the closed loop control system and the actuator dynamics;
• and
• a feedforward compensation processor coupled between the disturbance sensor/predictor and to the summing device for storing predetermined feedforward compensation signals that are intended to compensate for the predictable transient disturbance and for outputting the predetermined feedforward compensation signals in response to the timing signal provided by the disturbance sensor/predictor that are combined in the summing device with the actuator command signals provided by the actuator control system to reduce the effects of the predictable transient disturbance on the spacecraft,
• wherein the predetermined feedforward compensation signals are comprised of a torque doublet having a first constant torque level modeled for a first period of time corresponding to entry into an eclipse, when the spacecraft passes through the earth's shadow, and a second constant torque level modeled for a second different period of time corresponding to exit from the eclipse.

A spacecraft control system that compensates for a predictable disturbance induced in a spacecraft that includes actuator dynamics that are coupled to spacecraft dynamics, said control system comprising:

• a sensor for providing a measurement of the attitude of the spacecraft;
• a closed loop control system coupled to the sensor for processing the output signal from the sensor and for providing actuator command signals;
• a disturbance sensor/predictor for providing a signal indicative of the occurrence of the disturbance;
• a summing device coupled between the closed loop control system and the actuator dynamics;
• and
• a feedforward compensation processor coupled between the disturbance sensor/predictor and to the summing device for providing predetermined feedforward compensation signals that are combined with the actuator command signals provided by the actuator control system to reduce the effects of the disturbance on the spacecraft, and wherein the predetermined feedforward compensation signals are comprised of a torque doublet having a first constant torque level modeled for a first period of time corresponding to entry into an eclipse, when the spacecraft passes through the earth's shadow, and a second constant torque level modeled for a second different period of time corresponding to exit from the eclipse.

A spacecraft control method that compensates for thermal shock induced in the spacecraft due to an eclipse, said control method comprising the steps of:

• orbiting the spacecraft through the eclipse;
• acquiring data regarding the attitude of the spacecraft prior to, during and after the eclipse;
• analyzing the data to determine the shape of the thermal disturbance caused by the eclipse;
• calculating desired feedforward torque profiles corresponding to entering and exiting eclipse transients for application to the spacecraft upon the occurrence of subsequent eclipses;
• determining times to apply torques comprising the calculated feedforward torque profiles to the spacecraft by sensing when the spacecraft enters and exits the eclipse;
• applying an appropriate feedforward torques to the spacecraft depending upon whether the spacecraft is entering or exiting the eclipse to control the spacecraft in response to the thermal shock.

A spacecraft control method that compensates for thermal shock induced in the spacecraft due to an eclipse, said control method comprising the steps of:

• orbiting the spacecraft through the eclipse;
• acquiring data regarding the attitude of the spacecraft prior to, during and after the eclipse;
• downloading the acquired data to an earth station;
• analyzing the downloaded data to determine the shape of the thermal disturbance caused by the eclipse;
• calculating desired feedforward torque profiles corresponding to entering and exiting eclipse transients;
• uploading the calculated feedforward torque profiles to the spacecraft for application thereto upon the occurrence of subsequent eclipses;
• determining times to apply torques comprising the calculated feedforward torque profiles to the spacecraft by sensing when the spacecraft enters and exits the eclipse;
• applying the appropriate feedforward torque profiles to the spacecraft depending upon whether the spacecraft is entering or exiting the eclipse to control the spacecraft in response to the thermal shock.