Precise spacecraft camera image navigation and registration

• US 5,963,166 A
• Filed: 07/23/1998
• Issued: 10/05/1999
• Est. Priority Date: 07/23/1998
• Status: Expired due to Term

• Current Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Original Assignee: Space Systems/Loral Incorporated (Loral Space and Communications Incorporated)
• Inventors: Kamel, Ahmed
• Primary Examiner(s): Tarcza, Thomas
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/121,507
• Time in Patent Office: 439 Days
• Field of Search: 342/352, 342/357.06, 342/357.01, 342/355, 342/462, 701/222, 701/226, 250/203.6, 250/206.1
• US Class Current: 342/357.31
• CPC Class Codes: B64G 1/244 Spacecraft control systems
• CPC Class Codes: B64G 1/26 using jets
• CPC Class Codes: B64G 1/28 using inertia or gyro effect
• CPC Class Codes: B64G 1/285 using momentum wheels
• CPC Class Codes: B64G 1/36 using sensors, e.g. sun-sensors, horizon sensors
• CPC Class Codes: B64G 1/361 using star sensors
• CPC Class Codes: B64G 1/365 using horizon or Earth sensors
• CPC Class Codes: B64G 1/369 using gyroscopes as attitude sensors
• CPC Class Codes: B64G 1/66 Arrangements or adaptations of apparatus or instruments, not otherwise provided for
• CPC Class Codes: B64G 3/00 Observing or tracking cosmonautic vehicles
• CPC Class Codes: G01S 5/0247 Determining attitude

Abstract

A precise, spacecraft camera image navigation and registration system and method wherein a computer 36 on-board the spacecraft and a ground system comprising at least two ground stations precisely compute image navigation and registration data from precise data measurements. The computer on-board the spacecraft (spacecraft control system) uses precise star tracker, gyro, and earth sensor attitude data to precisely point the spacecraft and the camera. The ground system utilizes precise star measurement data from the camera and range data from the ground stations time tagged with GPS precise clock data. The ground system uses these precise measurements to determine precise orbit and attitude coefficients and uploads these coefficient to the spacecraft. The computer on-board the spacecraft uses these precise coefficients to generate and apply precise signals to compensate for slow orbit and attitude variations and register camera images in real time. The computer on-board the spacecraft is also used to generate camera commands to eliminate the need to upload a large number of daily ground commands, which therefore simplifies ground operations.

Claims

1. A precise spacecraft camera image navigation and registration method for use with a spacecraft orbiting about a central body, comprising the steps of:

launching a spacecraft into an orbit about the central body, which spacecraft comprises a camera, and one or more sensors selected from the group including;

a star tracker, a central body sensor, and a gyro; and

selectively processing attitude data derived from (1) the camera, and the star tracker, (2) the camera, the star tracker and the gyro, (3) the camera, the central body sensor and the gyro, or (4) the camera, the star tracker, the central body sensor and the gyro, to point the spacecraft and point the camera.

2. The method recited in claim 1 further comprising the step of:

generating camera orbit and attitude coefficients for pointing the camera using (1) landmark measurements made using the camera, and range measurements from at least two ground stations located on the central body, (2) star measurements made using the camera, and range measurements from at least two ground stations located on the central body, or (3) landmark measurements made using the camera, star measurements made using the camera, and range measurements from at least two ground stations located on the central body.

3. The method recited in claim 2 wherein the orbit and attitude coefficients are processed by one of the ground stations to provide for image navigation of images generated by the camera.

4. The method recited in claim 2 wherein the orbit and attitude coefficients are uploaded to the spacecraft and processed on-board the spacecraft to generate and apply image motion compensation signals to autonomously register camera images in real time.

5. The method recited in claim 2 wherein the orbit coefficients are generated using a precise orbit model that includes significant frequencies produced by perturbing bodies to extend the validity of the orbit model over an extended period of time to simplify operations on the central body.

6. The method recited in claim 5 wherein the perturbing bodies include the earth, the moon, and the sun.

7. The method recited in claim 2 wherein the attitude coefficients are generated using a precise attitude model representing attitude variations over an extended period of time to simplify operations on the central body.

8. The method recited in claim 7 wherein the extended period of time is about one week.

9. The method recited in claim 1 wherein:

the step of launching a spacecraft further comprises the step of launching a spacecraft comprising an on-board computer; and

wherein the method further comprises the step of generating camera commands using the on-board computer to reduce uploading of daily ground commands from the central body.

10. A spacecraft-based imaging system having improved image navigation and registration, comprising:

a spacecraft comprising a camera, camera pointing apparatus that adjusts the pointing direction of the camera, an on-board computer coupled to the camera and camera pointing apparatus for controlling the pointing direction of the camera, and one or more sensors selected from the group including;

a star tracker, a central body sensor, and a gyro; and

the on-board computer selectively processing attitude data derived from (1) the camera and the star tracker, (2) the camera, the star tracker and the gyro, (3) the camera, the central body sensor and the gyro, or (4) the camera, the star tracker, the central body sensor and the gyro, to generate pointing signals that are used to point the spacecraft and point the camera.

11. The system recited in claim 10 further comprising

at least two ground stations located on a central body;

and

wherein the camera orbit and attitude coefficients for pointing the camera are generated using (1) landmark measurements made using the camera and range measurements from the at least two ground stations, (2) star measurements made using the camera and range measurements from the ground stations, or (3) landmark measurements made using the camera, star measurements made using the camera, and range measurements from the ground stations.

12. The system recited in claim 11 wherein the orbit and attitude coefficients are processed by the computer onboard the spacecraft to provide for image navigation, and registration.

13. The system recited in claim 11 wherein the orbit and attitude coefficients are uploaded to the spacecraft and processed by the computer 36 onboard the spacecraft to generate and apply image motion compensation signals to autonomously register camera images in real time.

14. The system recited in claim 11 wherein the orbit coefficients are generated using a precise orbit model that includes significant frequencies produced by perturbing bodies to extend the validity of the orbit model over an extended period of time to simplify operations on the central body.

15. The system recited in claim 11 wherein the attitude coefficients are generated using a precise attitude model representing attitude variations over an extended period of time to simplify operations on the central body.

16. The system recited in claim 10 wherein the extended period of time is about one week.

17. The system recited in claim 10 wherein the on-board computer generates camera commands to reduce uploading of daily ground commands from the central body.