Attitude determination and alignment using electro-optical sensors and global navigation satellites

• US 20020004691A1
• Filed: 03/12/2001
• Published: 01/10/2002
• Est. Priority Date: 03/10/2000
• Status: Active Grant

• Current Assignee: Schafer Corporation (Mantech International Corporation)
• Original Assignee: Schafer Corporation (Mantech International Corporation)
• Inventors: Kinashi, Yasuhiro, Salazar, David
• Granted Patent: US 6,463,366 B2
• Time in Patent Office: Days
• US Class Current: 701/4
• CPC Class Codes: G01C 21/24 specially adapted for cosmonautical navigation
• CPC Class Codes: G01S 19/14 specially adapted for specific applications

Abstract

An attitude determination and alignment method and system use electro-optical sensors and global navigation satellites to determine attitude knowledge for a spacecraft, satellite, or a high-altitude airborne. An on-board inertial navigation system uses global navigation satellite system equipment and an electro-optical sensor. The electro-optical sensor view the navigation satellites as a surrogate stellar reference sources. The electro-optical sensor replaces the function of a star sensor or tracker and associated processing required for an onboard attitude determination system. Navigation and timing information generated by the GNSS-INS performs required attitude determination system functions.

Claims

1. a method for determining an attitude information for a vehicle, comprising:

receiving radio-frequency signals from at least two navigation satellites;

applying a filter to determine an expected position of the vehicle and the at least two satellites;

determining an expected angular position and motion of the at least two satellites relative to the vehicle;

measuring an actual angular position and motion of the at least two navigation satellites about two axes relative to the vehicle using an electro-optical sensor; and

computing a difference, along the two axes, between the expected angular position and the rate of the at least two navigation satellites and the measured, actual angular orientation of the vehicle.

2. The method according to claim 1, further comprising:

producing an attitude alignment error to correct for instrument drift rate and accumulated alignment error due to the drift to update attitude knowledge of the vehicle.

3. The method according to claim 1, wherein the filter is a Kalman filter.

4. The method according to claim 1, wherein the filter is a non-linear least squares estimate batch filter.

5. The method according to claim 1, wherein the filter is a Marquardt'"'"'s method for calculating a non-linear least squares estimate in a batch filtering process.

6. The method according to claim 1, wherein the vehicle is a satellite.

7. The method according to claim 1, wherein the vehicle is a high-altitude aircraft.

8. The method according to claim 1, wherein the vehicle is a low earth orbit spacecraft.

9. The method according to claim 1, wherein the expected position determined in said applying operation is within 10 meters of an actual position.

10. The method according to claim 1, wherein the radio signals received in said receiving step are GNSS signals, the GNSS signals are received with a GNSS antenna/receiver unit, and the received GNSS signals are processed with an inertial navigation system onboard the vehicle.

11. The method according to claim 1, wherein said determining operation includes performing angular position and rate estimates for pointing a gimbaled electro-optical sensor on board the vehicle toward a navigation satellite, or establishing sensor detection windows for extracting measurement data of strap-down electro-optical sensors.

12. An onboard attitude determination system, comprising:

an optical sensor receive and focus light energy, including a camera to convert the received light energy into digital electronic data; and

a processor to compare the digital electronic data with received GPS signal data and to determine vehicle attitude from the comparison.

13. The attitude determination system according to claim 12, wherein the camera further comprises

a photo-cathode,

a multi-channel plate,

a phosphor screen, and a fiber optic bundle to provide image gain for improving detection capability and measurement precision.

14. The attitude determination system according to claim 12, wherein the camera is a focal plane array.

15. The attitude determination system according to claim 12, further comprising:

a GPS antenna to receive GPS signals from at least two GPS satellites; and

a GPS receiver to convert the received GPS signals into the GPS signal data.

16. The attitude determination system according to claim 12, wherein the optical sensor is a strap down electro-optical sensor unit having a plurality of electro-optical sensors.

17. The attitude determination system according to claim 12, wherein the optical sensor is a gimbaled optical sensor.

18. The attitude determination system according to claim 12, wherein said processor includes a GPS satellite scheduler to provide feedback control to position said optical sensor toward a selected satellite.

19. The attitude determination system according to claim 12, wherein the camera is a CMOS focal plane array providing optical or UV streak detection of a selected satellite.

20. A method for determining an accurate attitude information for a spacecraft, satellite or high-altitude aircraft comprising:

receiving radio-frequency signals from GPS and other navigation satellites and applying Kalman Filter to determine an expected position of the vehicle;

determining expected angular position and motion of navigation satellites relative to said vehicle equipped by way of a GNSS antenna/receiver unit and an inertial navigation system;

measuring an actual, angular position and motion of the navigation satellites about two axes relative to the vehicle using an onboard electro-optical sensor and an inertial measurement unit;

computing a difference, along two axes, between the expected angular position and the rate of the navigation satellites and the measured, actual angular orientation of the vehicle; and

producing attitude alignment error to the IMU to correct for the instrument drift rate and accumulated alignment error due to drift.