Gyroless Three-Axis Sun Acquisition Using Sun Sensor and Unscented Kalman Filter
AssigneeThe Boeing Company
InventorsTung-Ching Tsao, Richard Y. Chiang
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Abstract
An attitude estimator that uses sun sensor outputs as the only attitude determination measurements to provide three-axis attitude information. This is accomplished by incorporating the Euler equation into the estimator. An unscented Kalman filter is employed to accommodate various nonlinear characteristics and uncertainties of the spacecraft dynamics and thus improve the robustness and accuracy of the attitude estimate.
Claims20
A method of estimating a three-axis attitude of a spacecraft, comprising:
- (a) measuring sun unit vectors at successive instants of time using a plurality of sun sensors attached to a spacecraft;
- (b) calculating angular rates and angular accelerations of the spacecraft about first and second axes perpendicular to the sun line based on the sun unit vector measurements;
- (c) calculating an angular acceleration of the spacecraft about the sun line using the sun unit vector measurements, a Euler equation and an unscented Kalman filter;
- and
- (d) calculating a three-axis attitude of a spacecraft based on the calculation results in steps (b) and (c).
A spacecraft comprising a body, at least one solar panel coupled to said body, a plurality of sun sensors arranged on said body, and a computer system programmed to perform the following operations:
- (a) measuring sun unit vectors at successive instants of time using a plurality of sun sensors attached to a spacecraft;
- (b) calculating angular rates and angular accelerations of the spacecraft about first and second axes perpendicular to the sun line based on the sun unit vector measurements;
- (c) calculating an angular acceleration of the spacecraft about the sun line using the sun unit vector measurements, a Euler equation and an unscented Kalman filter;
- and
- (d) calculating a three-axis attitude of a spacecraft based on the calculation results in operations (b) and (c).
A method of commanding a satellite to adjust its attitude to achieve sun acquisition, the method comprising:
- (a) measuring sun unit vectors at successive instants of time using a plurality of sun sensors attached to a spacecraft;
- (b) calculating angular rates and angular accelerations of the spacecraft about first and second axes perpendicular to the sun line based on the sun unit vector measurements;
- (c) calculating an angular acceleration of the spacecraft about the sun line using the sun unit vector measurements, a Euler equation and an unscented Kalman filter;
- (d) calculating a three-axis attitude of a spacecraft based on the calculation results in steps (b) and (c);
- and
- (e) commanding changes in spacecraft attitude based on differences between a target three-axis attitude and said calculated three-axis rates.
A system for controlling the attitude of a spacecraft based on sun sensor measurements and not gyroscope measurements, comprising:
- a spacecraft body;
- at least one solar panel coupled to said body;
- a plurality of sun sensors arranged on said body;
- a control processor that outputs torque commands;
- and
- means for producing torques that change the attitude of the spacecraft in response to torque commands from said attitude control processor,
- wherein said control processor is programmed to perform operations in accordance with software comprising:
- an attitude estimator for calculating a three-axis attitude and rate of said spacecraft body in a spacecraft body frame of reference based on sun unit vector measurements made by said plurality of sun sensors and a Euler equation;
- and
- an attitude controller that outputs a torque command based on a difference between a target three-axis attitude and said calculated three-axis attitude and rate.
Dependencies are inferred from the claim text.