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

• US 6,463,366 B2
• Filed: 03/12/2001
• Issued: 10/08/2002
• Est. Priority Date: 03/10/2000
• Status: Expired due to Fees

• Current Assignee: Schafer Corporation (Mantech International Corporation)
• Original Assignee: Schafer Corporation (Mantech International Corporation)
• Inventors: Kinashi, Yasuhiro, Salazar, David
• Primary Examiner(s): NGUYEN, TAN QUANG
• Application Number:
  US09/803,620
• Publication Number:
  US 20020004691A1
• Time in Patent Office: 575 Days
• Field of Search: 701/13, 701/4, 701/213, 701/214, 701/215, 701/216, 701/220, 342/357.01, 342/357.06, 342/357.08, 342/357.11, 342/357.14
• US Class Current: 701/13
• 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 aircraft. An on-board inertial navigation system uses global navigation satellite system equipment and an attitude determination system uses an electro-optical sensor. The electro-optical sensor view the navigation satellites as 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 GPS/GNSS-INS is used to perform required attitude determination system functions.

Claims

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

receiving radio-frequency signals from a plurality of navigation satellites;

applying a filter to determine an expected position and motion of the vehicle from the received radio-frequency signals;

determining an expected angular position and motion of one or more satellites relative to the vehicle;

measuring an actual angular position and motion of said one or more satellites about two axes relative to the vehicle using an electro-optical sensor;

computing a difference, along the two axes, between the expected angular position and motion of said one or more satellites and the measured, actual angular position and motion of said one or more satellites; and

calculating the attitude information for the vehicle using the computed difference and the expected attitude, attitude rate, position and velocity 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 utilized in said applying operation is a Kalman filter.

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

5. The method according to claim 1, wherein the filter utilized in said applying operation 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 spacecraft or 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 GPS/GNSS signals, the GPS/GNSS signals are received with a GPS/GNSS antenna/receiver unit, and the received GPS/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 to 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 information extracted from GPS/GNSS to determine vehicle attitude from the comparison, wherein the processor includes a GPS/GNSS satellite scheduler to provide feedback control to position the optical sensor towards a selected satellite.

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/GNSS antenna to receive radio signals from one or more GPS/GNSS satellites; and

a GPS/GNSS receiver to convert the received radio signals into the GPS/GNSS information.

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

17. 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.

18. A method for determining refined attitude information for a vehicle, comprising:

receiving radio-frequency signals from a plurality of GPS/GNSS navigation satellites and applying a Kalman filter to determine expected position and motion of the vehicle from the received radio signals;

determining coarse attitude information for the vehicle;

selecting one or more satellites for refining the coarse attitude information of the vehicle;

determining expected angular position and motion of the selected one or more satellites relative to said vehicle, equipped by way of a GPS/GNSS antenna/receiver unit and an inertial navigation system;

measuring actual angular position and motion of the selected one or more 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 motion and the measured angular position and motion of the selected one or more satellites; and

refining the coarse attitude information from the computed difference.

19. The method for determining refined attitude information for a vehicle according to claim 18, wherein the coarse attitude information is derived from the received radio frequency signals.

20. The method for determining refined attitude information for a vehicle according to claim 18, wherein the coarse attitude information is derived from an onboard three axis magnetometer.

21. The method for determining refined attitude information for a vehicle according to claim 18, wherein the refined attitude information is vehicle attitude bias information derived from the computed difference.

22. The method for determining refined attitude information for a vehicle according to claim 21, wherein the attitude information comprises four quaternion parameters.

23. The method for determining refined attitude information for a vehicle according to claim 18, wherein a rate of change in vehicle attitude bias is determined from the computed difference.

24. The method for determining refined attitude information for a vehicle according to claim 23, wherein the rate of change in vehicle attitude bias comprises four quaternion rate parameters.

25. An onboard attitude determination system, comprising:

an optical sensor to 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 information extracted from GPS/GNSS to determine vehicle attitude from the comparison, wherein the processor includes a GPS/GNSS satellite scheduler and extracts sensor data within a region of interest defined by the scheduler.

26. The attitude determination system according to claim 25, wherein the optical sensor is a strap down electro-optical sensor unit having a plurality of electro-optical sensors.