Satellite attitude sensor using thermal imaging

• US 6,066,850 A
• Filed: 10/08/1997
• Issued: 05/23/2000
• Est. Priority Date: 09/17/1996
• Status: Expired due to Term

• Current Assignee: Centre For Research In Earth and Space Technology, Canadian Space Agency (Government of Canada), Thomson-CSF Optronics Canada Inc.
• Original Assignee: Centre For Research In Earth and Space Technology, Canadian Space Agency (Government of Canada), Thomson-Csf Optronique Canada Incorporated
• Inventors: Hollinger, Allan, Thomas, Paul J., Hersom, Charles, Afik, Zvika
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Israel, Andrew
• Application Number:
  US08/946,702
• Time in Patent Office: 958 Days
• Field of Search: 250/342, 250/340, 250/338.4, 250/338.1, 244/158 R
• US Class Current: 250/342
• CPC Class Codes: B64G 1/22 Parts of, or equipment specially adapted for fitting in or to, cosmonautic vehicles
• CPC Class Codes: B64G 1/281 Spin-stabilised spacecraft
• CPC Class Codes: B64G 1/32 using earth's magnetic field
• CPC Class Codes: B64G 1/363 using sun sensors
• CPC Class Codes: B64G 1/365 using horizon or Earth sensors
• CPC Class Codes: B64G 1/366 using magnetometers
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01S 3/7868 using horizon sensors

Abstract

The present invention provides a method for distinguishing a boundary of an object, and the object itself, from its background. In the method electromagnetic radiation is detected from at least one field of view substantially spanning the boundary of the object and background adjacent to the boundary and superimposed or overlaid as images onto a detector. The method includes correlating spatial transitions in intensity of the overlaid images on the detector with a boundary of the object. When used for determining the attitude of a satellite with respect to the earth, the detector is a thermal infrared detector thereby providing a sharp contrast between the thermal emission of the earth and cold space. The invention provides a simple, effective method and device for determining satellite orientation and/or attitude with respect to a thermal infrared-emitting target body. The sensor includes a segmented limb-looking mirror to provide multiple fields-of-view within the field-of-regard and superimposing these fields-of-view as images onto a common detector. The required resolution can be obtained while providing a wide range of operational orbital altitudes. The attitude of the satellite can vary by a large angle from the minimal orientation while still permitting an accurate determination of attitude. Multiple channels in a modular form provide redundancy, improved accuracy, and the opportunity of providing more diverse configurations. The utilization of uncooled microbolometer arrays as imaging detectors removes the requirement for additional cooling equipment thereby providing a low cost, small size and low mass sensor with configurational flexibility and no moving parts.

Claims

1. A method for distinguishing a boundary of a celestial object from background of space using a sensor mounted on a satellite, comprising:

a) focusing electromagnetic radiation from at least one field of view of about 10 degrees, said field of view substantially spanning at least a portion of a boundary of an object and background adjacent to said at least a portion of said boundary as an image onto a detection means, the detection means including a microbolometer having an elongate array of microbolometer elements capable of providing spatial sampling of an image focussed thereon; and

b) determining a boundary of an object from its background from a spatial transition in intensity of an image focussed on said detection means.

2. The method according to claim 1 wherein the step of focusing the image from at least one field of view includes superimposing images from at least two fields of view.

3. The method according to claim 2 wherein the step of focusing said images comprises refractively focusing said images from said at least two fields of view onto said detection means.

4. The method according to claim 1 wherein the sensor means includes at least one mirror, and wherein the step of focussing said image from said at least one field of view onto said detection means includes reflecting the image from the least one mirror onto a focussing mirror that focuses said image onto said detection means.

38. The method according to claim 2 wherein the sensor means includes at least two mirrors, and wherein the step of superimposing said images from said at least two fields of view onto said detection means includes reflecting the images from the at least two mirrors onto a focussing mirror that focuses said images onto said detection means, wherein each mirror is disposed at preselected angles with respect to the other mirrors.

5. A device for distinguishing a boundary of an object from its background, comprising:

a housing;

detection means mounted in said housing for detecting electromagnetic radiation, said detection means including a microbotometer having an elongate array of microbolometer elements for spatial sampling of images focused thereon;

optical focusing means mounted in said housing for focusing electromagnetic radiation from at least one field of view as an image onto said detection means; and

processing means connected to said detection means for correlating a spatial transition in intensity of an image focused on said detection means with a boundary of an object, wherein said processing means includes a semiconductor chip integrated with said detection means for processing of the output of the detection means.

6. The device according to claim 5 wherein said optical focusing means includes a first substantially flat mirror mounted in said housing for collecting electromagnetic radiation from at least one field of view, and a focusing mirror for focusing said image onto said detection means.

7. The device according to claim 6 wherein said optical focusing means comprises a segmented mirror provided with said first substantially flat mirror and at least a second substantially flat mirror segment disposed at a preselected angle with respect to said first substantially flat mirror segment for collecting electromagnetic radiation from at least two fields of view, and wherein said focusing mirror superimposes images from each mirror segment onto said detection means.

8. The device according to claim 7 wherein said segmented mirror and said housing is a module housing, said module housing being releasibly attachable to a sensor housing.

9. The device according to claim 8 including a plurality of module housing releasibly attached to said sensor housing, and wherein said sensor housing is releasibly attached to a satellite.

10. A device for determining satellite orientation and attitude with respect to a celestial body, comprising:

an effective number of optical modules adapted to be attached to a satellite in preselected positions with respect to each other, each optical module including a detection means adapted to spatially sample an image focused thereon, a segmented mirror having at least one mirror segment, and focusing mirror means located with respect to said segmented mirror for receiving images reflected from said at least one mirror segment and focussing said image onto said detection means; and

processing means connected to said detection means, said processing means adapted to correlate spatial transitions in intensity of said image focused on said detection means with a boundary of the celestial body and determining therefrom satellite attitude with respect to the celestial body.

11. The device according to claim 10 wherein said segmented mirror includes n mirror segments disposed at a preselected angle with respect to one another, wherein n is an integer greater than or equal to 2, and wherein said focusing mirror means is adapted to superimpose images from each of said mirror segments onto said pixelated detection means.

12. The device according to claim 11 wherein said effective number of optical modules is at least two optical modules, and wherein said optical modules are releasibly attachable to a satellite structure.

13. The device according to claim 12 wherein said detection means is a pixelated detection means. releasibly attachable to a satellite structure.

14. The device according to claim 13 wherein said pixelated detection means is a pixelated thermal detector.

15. The device according to claim 13 wherein said optical modules are releasibly attachable to a sensor housing, and wherein said sensor housing is adapted to be attached to a satellite housing.

16. The device according to claim 15 wherein said sensor housing defines an axis, and a plurality of said optical modules disposed about said axis in said sensor housing.

17. The device according to claim 16 wherein said plurality of optical modules is six optical modules.

18. The device according to claim 13 wherein said preselected angle between each mirror segment is in the range from about 1 degree to about 15 degrees.

19. The device according to claim 18 wherein n equals 4 mirror segments.

20. The device according to claim 19 wherein said preselected angle between each mirror segment is about 2.5 degrees.

21. The device according to claim 14 wherein said pixelated thermal detector comprises a plurality of microbolometer detector elements forming an array on a detector support member.

22. The device according to claim 21 wherein said processing means comprises a semiconductor chip, and said detector support member in each module being mounted on an associated semiconductor chip.

23. The device according to claim 22 wherein the processing means in each module is connected to the processing means in the other modules, and wherein each processing means is adapted to receive and process data from the detection means in each optical module.

39. The device according to claim 11 wherein said effective number of optical modules is at least three optical modules, and wherein said optical modules are releasibly attachable to a satellite structure.

24. A device for determining orientation and attitude of a satellite with respect to a celestial body, comprising:

an effective number of modules adapted to be attached to a satellite in preselected positions with respect to each other, each optical module including pixelated detection means, optical focusing means mounted in each module for collecting and focusing electromagnetic radiation from at least one field of view onto said pixelated detection means, said optical focusing means including a segmented mirror having n mirror segments each disposed at preselected angles with respect to one another, wherein n is an integer greater than or equal to 2, and a focusing mirror means for superimposing images from each of said mirror segments onto said pixelated detection means; and

processing means connected to said pixelated detection means for correlating a spatial transition in intensity of said image with a boundary of said celestial object and determining therefrom satellite attitude and/or orientation with respect to the celestial body.

25. The device according to claim 24 wherein said preselected angle between each mirror segment is in the range from about 1 degree to about 15 degrees.

26. The device according to claim 24 wherein said optical modules are releasibly attachable to a satellite structure.

27. The device according to claim 24 wherein said optical modules are releasibly attachable to a sensor housing, and wherein said sensor housing is adapted to be attached to a satellite structure.

28. The device according to claim 24 wherein said pixelated detection means is a pixelated thermal detector.

29. The device according to claim 28 wherein said pixelated thermal detector comprises a plurality of microbolometer detector elements forming an array on a detector support member.

30. The device according to claim 29 wherein said processing means comprises a semiconductor chip, and said detector support member in each module being mounted on an associated semiconductor chip.

31. The device according to claim 30 wherein the processing means in each module is connected to the processing means in the other modules, and wherein each processing means is adapted to receive and process data from the detection means in each optical module.

32. A satellite having a satellite structure and an equipment complement, comprising:

an orientation and attitude sensor for determining satellite orientation and attitude of said satellite with respect to a celestial body, said sensor including;

an effective number of optical modules adapted to be attached to said satellite structure in preselected positions with respect to each other, each optical module including pixelated detection means, optical focusing means mounted in said module for collecting and focusing electromagnetic radiation from at least one field of view as an image onto said pixelated detection means, said optical focusing means including a segmented mirror having n mirror segments each disposed at preselected angles with respect to one another, wherein n is an integer greater than or equal to 2, and a focusing mirror means for superimposing images from each of said mirror segments onto said pixelated detection means; and

processing means connected to said pixelated detection means for correlating a spatial transition in intensity of said image with a boundary of said celestial object and determining therefrom satellite attitude and/or orientation with respect to the celestial body.

33. The satellite according to claim 32 wherein said preselected angle between each mirror segment is in the range from about 1 degree to about 15 degrees.

34. The satellite according to claim 32 wherein said optical modules are releasibly attachable to a sensor housing, and wherein said sensor housing is adapted to be attached to said satellite structure.

35. The satellite according to claim 32 wherein said pixelated detection means is a pixelated infrared detector.

36. A satellite sensor device for detecting fires on the earth, comprising:

a sensor housing;

a pixelated infrared detector mounted in said housing for detecting infrared electromagnetic radiation characteristic of fires;

optical focusing means mounted in said sensor housing for superimposing images from at least two fields of view of the earth'"'"'s surface as overlaid images onto said infrared detector; and

means for correlating a spatial transition in intensity of said overlaid images on said infrared detector with a boundary of a region emitting infrared radiation characteristic of fires.

37. The device according to claim 36 wherein said pixelated infrared detector is a short-wave infrared detector sensitive to the spectral range of from about 1.4 microns to about 4 microns.