Satellite attitude determination and control system with agile beam sensing

A method of attitude control for a spacecraft orbiting a celestial body comprising the steps of:

• orienting the spacecraft such that it spins about a spin axis oriented substantially in the orbit plane and pointing substantially at nadir;
• and
• precessing the spin axis at a rate equal to the rotational orbit rate such that the spin axis of the spacecraft will remain substantially fixed relative to a celestial body centered coordinate frame rotating at the rotational orbit rate throughout an entire orbit for the spacecraft about the celestial body, said precessing step including the steps of:
• predicting values of preselected directional parameters relative to the spacecraft of coherent energy signals radiating from a plurality of known remote sources;
• observing the energy signals, determining values of the directional parameters from the observed energy signals, calculating differences between observed and predicted values of the directional parameters, and generating error signals indicative of the differences;
• updating the predicted parameters in accordance with the error signals and generating a spacecraft attitude state estimate from updated parameter values;
• comparing the state estimate to a reference state and generating a plurality of command signals in accordance with the comparison results;
• and
• generating torques upon the spacecraft such that the spin axis will precess about an axis substantially normal to an orbit plane, such as to maintain nadir pointing of the spacecraft.

An on-board control system for a spacecraft orbiting a celestial body comprising:

• means for predicting values of preselected directional parameters of coherent energy signals radiated from a plurality of known remote sources;
• sensing means coupled to the means for predicting and operative to observe the energy signals, to measure differences between observed and predicted values of the directional parameters, and to generate error signals indicative of the difference;
• the means for predicting including means, coupled for receipt of the error signals, for updating the predicted parameters in accordance with the error signals and for generating a spacecraft orbit and attitude state estimate from updated parameter values;
• and
• decision means, coupled for receipt of the state estimate, operative to compare the state estimate with a reference state and to generate at least one command signal in accordance with the comparison results.