Star tracker-aided airborne or spacecraft terrestrial landmark navigation system

Patent metadata

Field	Value
Publication number	US-10048084-B2
Application number	US-201615267918-A
Country	US
Kind code	B2
Filing date	Sep 16, 2016
Priority date	Sep 16, 2016
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

Methods and apparatus automatically determine a location, such as of an aircraft or spacecraft, by matching images of terrain below the craft, as captured by a camera, radar, etc. in the craft, with known or predicted terrain landmark data stored in an electronic data store. A star tracker measures attitude of the camera. Optionally, a rangefinder measures altitude of the camera above the terrain. A navigation filter uses the attitude, and optionally the altitude, to resolve attitude, and optionally altitude, ambiguities and thereby avoid location solution errors common in prior art terrain matching navigation systems.

First claim

What is claimed is:

1. A location determining system, comprising:
a database storing terrain landmark data in association with geographic location information about the terrain landmark data;
an imager configured to aim downward toward terrain below the imager and generate terrain data representing a surface aspect of the terrain;
a matching engine that compares the terrain data to the terrain landmark data and determines an estimated location of the imager, based on: (a) a match between the terrain data and the terrain landmark data and (b) the geographic location information associated with the terrain landmark data;
a star tracker configured to measure attitude of the imager; and
a navigation filter that calculates a corrected location of the imager from: (a) the estimated location of the imager and (b) the attitude of the imager.

2. A location determining system according to claim 1 , wherein the imager comprises a radar.

3. A location determining system according to claim 2 , wherein the terrain data comprises terrain topographical data.

4. A location determining system according to claim 1 , wherein the imager comprises an optical camera and the terrain data comprises terrain image data.

5. A location determining system according to claim 4 , wherein the imager and the star tracker share a common image sensor.

6. A location determining system according to claim 5 , wherein the imager further comprises an objective lens and the star tracker comprises a telescope, the location determining system further comprising a beam splitter disposed to combine light from the objective lens and light from the telescope into an output signal directed toward the common image sensor.

7. A location determining system according to claim 5 , wherein the imager further comprises an objective lens and the star tracker comprises a telescope, the location determining system further comprising:
a first mirror disposed between the objective lens and the common image sensor and oriented to reflect light from the objective lens toward the common image sensor; and
a second mirror disposed between the telescope and the common image sensor and oriented to reflect light from the telescope toward the common image sensor.

8. A location determining system according to claim 1 , wherein the imager and the star tracker comprise a single objective lens having a field of view sufficiently large to simultaneously include the terrain and at least one bright celestial object.

9. A location determining system according to claim 1 , wherein the imager and the star tracker comprise a single objective lens configured to simultaneously capture light from the terrain and from at least one bright celestial object.

10. A location determining system according to claim 9 , wherein the imager and the star tracker share a common image sensor onto which light from the single objective lens impinges.

11. A location determining system according to claim 1 , further comprising an altimeter configured to provide an altitude of the imager above the terrain, wherein the navigation filter calculates the corrected location of the imager from: the estimated location of the imager, the attitude of the imager and the altitude of the imager above the terrain.

12. A location determining system according to claim 11 , wherein the altimeter is configured to determine the altitude of the imager based on the terrain data from the imager.

13. A location determining system according to claim 12 , wherein the imager comprises an optical camera and the terrain data comprises terrain image data.

14. A location determining system according to claim 12 , wherein the imager comprises a radar.

15. A location determining system according to claim 14 , wherein the terrain data comprises terrain topographical data.

16. A method for automatically determining a location, the method comprising:
storing, in an electronic database, terrain landmark data in association with geographic location information about the terrain landmark data;
generating, by an imager, terrain data representing a surface aspect of terrain below the imager by imaging the terrain from above;
automatically comparing the terrain data to the terrain landmark data and outputting an estimated location of the imager, based on: (a) a match between the terrain data and the terrain landmark data and (b) the geographic location information associated with the terrain landmark data;
automatically measuring attitude of the imager with a star tracker; and
automatically calculating a corrected location of the imager from: the estimated location of the imager and the attitude of the imager.

17. A method according to claim 16 , wherein generating the terrain data comprises generating the terrain data with a radar and the terrain data comprises terrain topographical data.

18. A method according to claim 16 , wherein generating the terrain data comprises generating the terrain data with an optical camera and the terrain data comprises terrain image data.

19. A method according to claim 18 , wherein generating the terrain data and automatically measuring the attitude of the imager with the star tracker comprises using a common image sensor to image the terrain and to image a bright celestial object.

20. A method according to claim 19 , further comprising combining light from an objective lens of the imager and light from a telescope of the star tracker into an output signal directed toward the common image sensor.

21. A method according to claim 19 , further comprising:
reflecting light, with a first mirror, from an objective lens of the imager toward the common image sensor; and
reflecting light, with a second mirror, from a telescope of the star tracker toward the common image sensor.

22. A method according to claim 16 , further comprising:
providing a single objective lens having a field of view sufficiently large to simultaneously include the terrain and at least one bright celestial object; wherein:
generating the terrain data and automatically measuring the attitude of the imager with the star tracker comprises using the single objective lens to simultaneously image the terrain and the at least one bright celestial object.

23. A method according to claim 16 , further comprising:
providing a single objective lens configured to simultaneously capture light from the terrain and from at least one bright celestial object; wherein:
generating the terrain data and automatically measuring the attitude of the imager with the star tracker comprises using the single objective lens to simultaneously direct light from the terrain and from the at least one bright celestial object onto a common image sensor.

24. A method according to claim 16 , further comprising:
automatically measuring an altitude of the imager above the terrain; wherein:
automatically calculating the corrected location of the imager comprises automatically calculating the corrected location of the imager from: the estimated location of the imager, the attitude of the imager and the altitude of the imager above the terrain.

25. A method according to claim 24 , wherein automatically measuring the altitude of the imager above the terrain comprises automatically determining the altitude based on the terrain data from the imager.

26. A method according to claim 25 , wherein generating the terrain data comprises generating the terrain data with

Assignees

• Charles Stark Draper Laboratory Inc

Inventors

• Laine Juha-Pekka J
• Blasche Gregory P
• Jamula Matthew T
• Bohn Paul A
• Dawson Robin Mark Adrian
• Lane Benjamin F
• Hoke Eric T
• Meiser Daniel M
• Kinast Joseph M
• Smith Stephen P

Classifications

• G06V20/17

  taken from planes or by drones · CPC title

• G06V20/13

  Satellite images · CPC title

• G06F16/583

  using metadata automatically derived from the content · CPC title

• G01C21/3602 Primary

  Input other than that of destination using image analysis, e.g. detection of road signs, lanes, buildings, real preceding vehicles using a camera · CPC title

• G01C21/30

  Map- or contour-matching · CPC title