Star tracker with steerable field-of-view baffle coupled to wide field-of-view camera

Patent metadata

Field	Value
Publication number	US-9544488-B2
Application number	US-201313893987-A
Country	US
Kind code	B2
Filing date	May 14, 2013
Priority date	May 14, 2013
Publication date	Jan 10, 2017
Grant date	Jan 10, 2017

Abstract

A star tracker has an electronically steerable point of view, without requiring a precision aiming mechanism. The star tracker can be strapped down, thereby avoiding problems associated with precision aiming of mechanical devices. The star tracker images selectable narrow portions of a scene, such as the sky. Each stellar sighting can image a different portion of the sky, depending on which navigational star or group of navigational stars is of interest. The selectability of the portion of the sky imaged enables the star tracker to avoid unwanted light, such as from the sun.

First claim

What is claimed is:

1. A star tracker, comprising:
a camera having a field of view; and
an electronically adjustable baffle assembly disposed relative to the camera and configured to expose a selectable portion, less than all, of the camera field of view to a scene, wherein direction of the selectable portion of the field of view, relative to the star tracker, is electronically selectable in both azimuth and elevation, and wherein the baffle assembly comprises at least a portion of a dome, the dome defining an aperture configured to expose the selectable portion of the camera field of view to the scene, the baffle assembly being rotatable about an optical axis of the camera.

2. A star tracker according to claim 1 , wherein the selectable portion of the camera field of view is circular.

3. A star tracker according to claim 1 , wherein the camera field of view is greater than 10°.

4. A star tracker according to claim 1 , wherein the selectable portion of the camera field of view comprises less than 30% of the camera field of view.

5. A star tracker according to claim 1 , wherein the dome defines an aperture configured to define the selectable portion of the camera field of view exposed to the scene.

6. A star tracker according to claim 1 , wherein the aperture is positionable along an arc that intersects, and is coplanar with, the optical axis of the camera.

7. A star tracker according to claim 1 , wherein the aperture is positionable within the camera field of view.

8. A star tracker according to claim 6 , wherein the baffle assembly comprises a baffle having an axis that coincides with an optical axis of the selectable portion of the camera field of view.

9. A star tracker according to claim 1 , wherein the selectable portion of the field of view of the camera comprises at least two discontiguous regions of the field of view of the camera.

10. A star tracker according to claim 1 , wherein size of the selectable portion of the field of view of the camera is electronically adjustable.

11. A star tracker according to claim 1 , wherein the camera comprises a monocentric objective lens.

12. A star tracker according to claim 11 , wherein the camera comprises a plurality of pixelated image sensor arrays and a plurality of optical fibers optically coupling each pixelated image sensor array of the plurality of pixelated image sensor arrays to the monocentric objective lens.

13. A star tracker according to claim 1 , further comprising:
a first rate sensor having a first sensory axis and being mechanically coupled to the camera;
a second rate sensor having a second sensory axis perpendicular to the first sensory axis and being mechanically coupled to the camera; and
a controller coupled to the camera, the baffle, the first rate sensor and the second rate sensor and configured to:
measure vibration of the camera, based on input signals from the first rate sensor and the second rate sensor; and
process an image captured by the camera, based on the vibration.

14. A star tracker according to claim 1 , further comprising a controller coupled to the camera and the baffle assembly and configured to:
cause the camera to capture a first image; then
adjust the baffle assembly, such that a different portion of the camera field of view is exposed to the scene; and then
cause the camera to capture a second image.

15. A star tracker according to claim 14 , wherein the controller is configured to determine a location of the camera, based at least in part on an analysis of at least a portion of the first image and at least a portion of the second image.

16. A star tracker according to claim 1 , further comprising a controller coupled to the camera and the baffle assembly and configured to:
adjust the baffle assembly, such that the selectable portion of the camera field of view includes a portion of the scene expected to include a space object having a predictable location;
cause the camera to capture an image; and
determine a location of the camera, based at least in part on information about the space object and an analysis of at least a portion of the image.

17. A star tracker according to claim 16 , wherein the space object comprises an astronomical object.

18. A star tracker according to claim 16 , wherein the space object comprises an artificial satellite.

19. A star tracker according to claim 16 , wherein the controller is configured to determine the location of the camera based at least in part on dispersion of light from the space object through earth's atmospheric limb.

20. A star tracker according to claim 16 , wherein the controller is configured to determine the location of the camera based at least in part on refraction of light from the space object through earth's atmospheric limb.

21. A star tracker according to claim 1 , further comprising a controller coupled to the camera and the baffle assembly and configured to:
cause the camera to capture an image; and
analyze a portion, less than all, of the image, the portion of the image corresponding to the portion of the camera field of view exposed to the scene.

22. A star tracker according to claim 1 , wherein:
the camera comprises a plurality of image sensor arrays, each image sensor array of the plurality of image sensor arrays comprising a plurality of pixels; and further comprising:
a controller coupled to the camera and the baffle assembly and configured to read a subset, less than all, of the pixels of the plurality of image sensor arrays, the subset corresponding to the selectable portion of the camera field of view exposed to the scene.

23. A method for exposing a selectable portion, less than all, of a field of view of a camera in a star tracker to a scene, the method comprising:
disposing a baffle assembly adjacent the camera, such that the camera is aimed toward an interior of the baffle assembly, the baffle assembly being configured to define an aperture whose position on the baffle assembly is electronically adjustable, in both azimuth and elevation, and such that the aperture defines the selectable portion, less than all, of the field of view of the camera exposed to the scene, and wherein the baffle assembly comprises at least a portion of a dome, the dome defining an aperture configured to expose the selectable portion of the camera field of view to the scene, the baffle assembly being rotatable about an optical axis of the camera; and
under control of a processor, adjusting the position of the aperture on the baffle assembly, such that the aperture is oriented toward the scene.

24. A method according to claim 23 , wherein:
the baffle assembly comprises a dome that defines an elongated opening extending along a longitude of the dome; the method further comprising:
disposing a curtain within the opening, the curtain being movable along the longitude of the dome, the curtain obscuring the opening from the camera field of view, except the curtain defining the aperture;

wherein adjusting the position of the aperture comprises:
under control of a processor, rotating the dome about an axis of symmetry of the dome, such that the opening in the dome is oriented toward the scene; and
under control of a processor, moving the curtain along the longitude of the dome, such that the aperture is oriented toward the scene.

25. A method according to claim 23 , further comprising:
under control of a processor, measuring vibration of the camera,

Assignees

• Charles Stark Draper Laboratory Inc

Inventors

• Dawson Robin Mark Adrian
• Laine Juha Pekka
• Chaparala Murali

Classifications

• H04N23/58 Primary

  Means for changing the camera field of view without moving the camera body, e.g. nutating or panning of optics or image sensors · CPC title

• B64G1/361

  using star sensors · CPC title

• H04N5/2259 Primary

  Electricity · mapped topic