Satellite attitude determination and control system with agile beam sensing
First Claim
1. An on-board attitude determination system for a spacecraft orbiting a celestial body comprising:
- means for estimating the orbit and attitude of the spacecraft relative to a plurality of remote sources of coherent energy signals;
an agile beam sensor sensing the locations of the remote sources;
means for pointing the agile beam sensor at the estimated relative locations of the remote sources;
means for determining error signals representative of the difference between the estimated locations of the remote sources and actual locations of the remote sources as sensed by the agile beam sensor; and
said estimating means being adapted to receive said error signals and update the predicted orbit and attitude of the spacecraft.
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Accused Products
Abstract
Agile (electronically steerable) beam sensing with associated on-board processing, previously used exclusively for positioning of antennas for beam formation and tracking in communications systems, is now also used for satellite active attitude determination and control. A spinning satellite (100) is nadir oriented and precessed at orbit rate using magnetic torquing determined through use of an on-board stored magnetic field model (520) and attitude and orbit estimates (212). A Kalman filter (211) predicts parameters (202, 203) associated with a received signal (204) impinging on the satellite'"'"'s wide angle beam antenna (201). The antenna system measures the error between the parameter predictions and observed values and sends appropriate error signals (207) to the Kalman filter for updating its estimation procedures. The Kalman filter additionally outputs the spacecraft attitude error signals (215) to an attitude control law (213), which determines commands to attitude-altering magnetic torque elements (220) to close the control loop via the spacecraft dynamics (230).
43 Citations
25 Claims
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1. An on-board attitude determination system for a spacecraft orbiting a celestial body comprising:
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means for estimating the orbit and attitude of the spacecraft relative to a plurality of remote sources of coherent energy signals; an agile beam sensor sensing the locations of the remote sources; means for pointing the agile beam sensor at the estimated relative locations of the remote sources; means for determining error signals representative of the difference between the estimated locations of the remote sources and actual locations of the remote sources as sensed by the agile beam sensor; and said estimating means being adapted to receive said error signals and update the predicted orbit and attitude of the spacecraft. - View Dependent Claims (2, 3, 4, 5)
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6. A method of attitude control for a spacecraft orbiting a celestial body comprising the steps of:
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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. - View Dependent Claims (7)
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8. An on-board control system for a spacecraft orbiting a celestial body comprising:
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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. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification