Attitude control system for momentum-biased spacecraft

An attitude and nutation control system for a momentum-biased vehicle having roll, pitch, and yaw axes comprising:

• (a) sensor means for measuring instantaneous roll attitude, roll rate, and yaw rate;
• (b) estimator means coupled to said sensor means for predicting steady-state values for roll attitude, roll rate, and yaw rate, said estimator means including a microprocessor programmed with a set of state equations employing negative feedback of steady-state roll attitude, roll rate, and yaw rate values;
• (c) logic means coupled to said estimator means for generating correction signals when the steady-state values for roll attitude, roll rate, and yaw rate are outside predetermined limits, said logic means including a microprocessor for implementing software logic functions, a first software logic function receiving the steady-state roll attitude and steady-state yaw rate outputs of said estimator means and determining a roll component of the vehicle's angular momentum vector, a second set of software logic functions generating correction signals, and a third set of software logic functions determining the proper phase of correction signals and whether the roll component, steady-state roll rate, and steady-state yaw rate exceed predetermined limits, said logic means also including control circuit means for controlling transmission of the correction signals to the firing means, and comparison means coupled to said microprocessor for generating error signals when the roll component, the steady-state roll rate, and the steady-state yaw rate differ from commanded values, said error signals causing said second set of software logic functions to generate correction signals;
• (d) a plurality of thrusters for producing torque for bringing the steady-state values for roll attitude, roll rate, and yaw rate within predetermined limits;
• and
• (e) firing means coupled between said logic means and said thrusters for activating said thrusters, said firing means including a sampling circuit for sampling correction signals between thruster activations, optimal thruster selection means coupled to said sampling circuit for selectively choosing thrusters for activation, for determining the duration of thruster activation, and for determining torques associated with changes in the correction signals, said firing means also including actuators coupled to said optimal thruster selection means for activating said thrusters.

A method for controlling a momentum-biased vehicle having roll, pitch, and yaw axes comprising:

• (a) measuring instantaneous roll attitude of the vehicle;
• (b) predicting steady-state values for roll attitude, roll rate, and yaw rate;
• (c) generating correction signals when the steady-state values for roll attitude, roll rate, and yaw rate are outside predetermined limits;
• (d) producing torque for bringing the steady-state values for roll attitude, roll rate, and yaw rate within predetermined limits;
• and
• (e) determining torques associated with changes in the correction signals for use in predicting steady-state values for roll attitude, roll rate, and yaw rate.