Antenna autotrack control system for precision spot beam pointing control

• US 7,663,542 B1
• Filed: 11/04/2004
• Issued: 02/16/2010
• Est. Priority Date: 11/04/2004
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Weigl, Harald J., Goodzeit, Neil E.
• Primary Examiner(s): Black; Thomas G
• Assistant Examiner(s): Chen; Shelley
• Application Number:
  US10/980,305
• Time in Patent Office: 1,930 Days
• Field of Search: 342 73- 77, 342/350, 342/352, 342/354, 342/359, 342385-386, 342/417, 342/420
• US Class Current: 342/359
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 3/08 for varying two co-ordinates of the orientation

Abstract

The present invention provides a system and a method for improving spacecraft antenna pointing accuracy utilizing feedforward estimation. The present invention takes advantage of the fact that spacecraft antenna pointing error has periodic behavior with a period of 24 hours. Thus, unlike the prior art feedback systems which blindly correct antenna pointing error continuously reacting only to presently sensed error, the present invention takes an intelligent approach and learns the periodic behavior of spacecraft antenna pointing error. Then, an estimate of antenna pointing error at a particular time going forward is predicted based on the learned model of the periodic behavior of the antenna pointing error. The predicted estimate is then used to correct or cancel out the antenna pointing error at a particular time in the future. The result is more accurate correction of spacecraft antenna pointing error by more than a factor of two.

Claims

1. A closed-loop system for improving spacecraft antenna pointing accuracy, comprising:

an antenna pointing error detection module for detecting and measuring spacecraft antenna pointing error;

an adaptive feedforward estimator module for learning spacecraft antenna pointing error behavior from currently measured spacecraft antenna pointing error, and for concurrently generating predictive output of estimated future spacecraft antenna pointing error, the feedforward estimator module utilizing an autoregressive model given by φ

_d[k]=a₁φ

_d[k−

1]+a₂φ

_d[k−

2]+ . . . +a_pφ

_d[k−

p], where φ

_d[k] is current distortion angle, and φ

_d[k−

1], φ

_d[k−

2], and φ

_d[k−

p] are previously measured distortion angles, the autoregressive model being a discrete-time non-Fourier model; and

an antenna pointing error correction module for prospectively correcting spacecraft antenna pointing error based on the predictive output from the feedforward estimator module.

2. The system of claim 1, wherein the antenna pointing error detection module is an autotrack sensor that measures error between an antenna boresight pointing direction and a line of sight vector to an uplinked beacon signal source.

3. The system of claim 1, wherein processing for the feedforward estimator module is performed onboard the spacecraft.

4. The system of claim 1, wherein processing for the feedforward estimator module is performed at a ground station.

5. The system of claim 1, wherein the antenna pointing error correction module prospectively corrects the spacecraft antenna pointing error by outputting a gimbal step command to step at least one antenna gimbal based on the predictive output from the feedforward estimator module.

6. A method for improving spacecraft antenna pointing accuracy, comprising the steps of:

detecting and measuring spacecraft antenna pointing error;

providing the measured spacecraft antenna pointing error as input to an adaptive feedforward estimator module;

the feedforward estimator module learning spacecraft antenna pointing error behavior from currently measured spacecraft antenna pointing error input, the feedforward estimator module utilizing an autoregressive model given by φ

_d[k]=a₁φ

_d[k−

1]+a₂φ

_d[k−

2]+ . . . +a_pφ

_d[k−

p], where φ

_d[k] is current distortion angle, and φ

_d[k−

1], φ

_d[k−

2], and φ

_d[k−

p] are previously measured distortion angles, the autoregressive model being a discrete-time non-Fourier model;

the feedforward estimator module generating predictive output of estimated future spacecraft antenna pointing error based on the measured spacecraft antenna pointing error input and concurrently with the feedforward estimator module learning spacecraft antenna pointing error behavior; and

prospectively correcting spacecraft antenna pointing error based on the predictive output from the feedforward estimator module.

7. The method of claim 6, wherein the antenna pointing error detection module is an autotrack sensor that measures error between an antenna boresight pointing direction and a line of sight vector to an uplinked beacon signal source.

8. The method of claim 6, wherein processing for the feedforward estimator module is performed onboard the spacecraft.

9. The method of claim 6, wherein processing for the feedforward estimator module is performed at a ground station.

10. The method of claim 6, wherein:

in the step of detecting and measuring spacecraft antenna pointing error, the measured spacecraft antenna pointing error is total distortion angle, φ

_d(t) which is given by;

φ

_d(t)=φ

_a(t)+φ

_g(t), where φ

_a(t) is autotrack error angle and φ

_g(t) is gimbal angle; and

in the step of the feedforward estimator module generating predictive output of estimated future spacecraft antenna pointing error, the predictive output is estimated future distortion angle given by;

φ

_d[k+1]=a₁φ

_d[k]+a₂φ

_d[k−

1]+ . . . a_pφ

_d[k−

p+1], where φ

_d[k+1] is the estimated future distortion angle, and φ

_d[k], φ

_d[k−

1], and φ

_d[k−

p+1] are previously measured distortion angles.

11. The method of claim 6, wherein the spacecraft antenna pointing error is prospectively corrected by outputting a gimbal step command to step at least one antenna gimbal based on the predictive output from the feedforward estimator module.

12. A closed-loop system for improving spacecraft antenna pointing accuracy, comprising:

means for detecting and measuring spacecraft antenna pointing error;

means for providing the measured spacecraft antenna pointing error as input to an adaptive feedforward estimator module;

means for the feedforward estimator module learning spacecraft antenna pointing error behavior from currently measured spacecraft antenna pointing error input, the feedforward estimator module utilizing an autoregressive model given by φ

_d[k]=a₁φ

_d[k−

1]+a₂φ

_d[k−

2]+ . . . +a_pφ

_d[k−

p], where φ

_d[k] is current distortion angle, and φ

_d[k−

1], φ

_d[k−

2], and φ

_d[k−

p] are previously measured distortion angles, the autoregressive model being a discrete-time non-Fourier model;

means for the feedforward estimator module generating predictive output of estimated future spacecraft antenna pointing error based on the measured spacecraft antenna pointing error input and concurrently with the feedforward estimator module learning spacecraft antenna pointing error behavior; and

means for prospectively correcting spacecraft antenna pointing error based on the predictive output from the feedforward estimator module.