Sliced lens star tracker

• US 10,641,859 B2
• Filed: 07/27/2017
• Issued: 05/05/2020
• Est. Priority Date: 07/27/2017
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Laine, Juha-Pekka J., Dawson, Robin Mark Adrian, Meiser, Daniel M., Lane, Benjamin F., Hoke, Eric T., Jamula, Matthew T., Smith, Stephen P., Sinclair, Matthew A.
• Primary Examiner(s): Bailey, Frederick D
• Application Number:
  US15/661,881
• Publication Number:
  US 20190033421A1
• Time in Patent Office: 1,013 Days
• Field of Search: None
• CPC Class Codes: G01C 21/025 with the use of startrackers
• CPC Class Codes: G01S 3/781 Details
• CPC Class Codes: G01S 3/7867 Star trackers navigation using star trackers G01C21/025
• CPC Class Codes: G02B 13/0015 characterised by the lens design
• CPC Class Codes: G02B 3/06 with cylindrical or toric faces
• CPC Class Codes: H04N 7/181 for receiving images from a plurality of remote sources

Abstract

A star tracker includes a lens slice, a pixelated image sensor, an ephemeral database and a processor configured to estimate attitude, orientation and/or location of the star tracker based on an image of one or more celestial objects projected by the lens slice onto the pixelated image sensor. The lens slice is smaller and lighter than an optically comparable conventional lens, thereby making the star tracker less voluminous and less massive than conventional star trackers. A lens slice is elongated along one axis. Optical performance along the elongation axis is comparable to that of a conventional circular lens of equal diameter. Although optical performance along a width axis, perpendicular to the elongation axis, of a lens slice can be significantly worse than that of a conventional lens, use of two orthogonal lens slices provides adequate optical performance in both axes, and still saves volume and mass over a conventional lens.

Claims

1. A star tracker having a field of view, the star tracker comprising:

a database storing ephemeral data about a plurality of celestial objects;

a pixelated image sensor;

a lens slice disposed between the field of view and the pixelated image sensor, wherein the lens slice comprises an elongated diametric portion, less than all, of a conceptual conventional lens along an elongation axis perpendicular to an optical axis of the conceptual conventional lens, and encompassing the optical axis of the conceptual conventional lens, such that optical performance of the lens slice along the elongation axis is comparable to optical performance of the conceptual conventional lens and optical performance of the lens slice along a width axis perpendicular to the elongation axis is worse than the optical performance of the conceptual conventional lens; and

a processor coupled to the pixelated image sensor and to the database and configured to automatically estimate one or more of;

(a) attitude of the star tracker, (b) orientation of the star tracker or (c) location of the star tracker, based on;

(a) data from the pixelated image sensor generated as a result of an image of at least one celestial object in the field of view being projected onto the pixelated image sensor by the lens slice and (b) the ephemeral data in the database.

2. A star tracker according to claim 1, wherein the lens slice defines a surface, through which passes light that forms the image of the at least one celestial object in the field of view, the surface being a simple curvature surface.

3. A star tracker according to claim 1, wherein the lens slice defines a surface, through which passes light that forms the image of the at least one celestial object in the field of view, the surface being a compound curvature surface.

4. A star tracker according to claim 3, wherein the lens slice comprises:

a first lens slice having a first optical axis and a first longitudinal axis; and

a second lens slice having a second optical axis and a second longitudinal axis;

wherein the first optical axis is spaced apart from the second optical axis, and the first longitudinal axis is perpendicular to the second longitudinal axis.

5. A star tracker according to claim 4, wherein:

the first lens slice defines a first surface, through which passes at least some light that forms the image of the at least one celestial object in the field of view, the first surface being a first compound curvature surface; and

the second lens slice defines a second surface, through which passes at least some light that forms the image of the at least one celestial object in the field of view passes, the second surface being a second compound curvature surface.

6. A star tracker according to claim 4, wherein:

the first lens slice is elongated along the first longitudinal axis; and

the second lens slice is elongated along the second longitudinal axis.

7. A star tracker according to claim 4, wherein:

the first lens slice has a first focal distance;

the second lens slice has a second focal distance equal to the first focal distance; and

the pixelated image sensor comprises;

a first pixelated image sensor array disposed the first focal distance from a center of the first lens slice; and

a second pixelated image sensor array disposed the second focal distance from a center of the second lens slice.

8. A star tracker according to claim 4, wherein the processor is disposed in a volume bounded:

on a first side by a first imaginary plane that intersects one end of the first lens slice and extends perpendicular to the pixelated image sensor;

on a second side by a second imaginary plane that intersects the other end of the first lens slice and extends perpendicular to the pixelated image sensor;

on a third side by a third imaginary plane that intersects one end of the second lens slice and extends perpendicular to the pixelated image sensor; and

on a fourth side by a fourth imaginary plane that intersects the other end of the second lens slice and extends perpendicular to the pixelated image sensor.

9. A star tracker according to claim 1, wherein the lens slice comprises a cross-shaped spherical lens slice.

10. A star tracker according to claim 1, wherein the lens slice comprises a cross-shaped monocentric lens slice.

11. A star tracker according to claim 10, wherein:

the lens slice has a focal length; and

the pixelated image sensor comprises a plurality of image sensor arrays, each image sensor array of the plurality of image sensor arrays being disposed the focal length from a center of the monocentric lens slice.

12. A star tracker according to claim 2, wherein the lens slice comprises:

a first lens slice having a first optical axis and a first longitudinal axis; and

a second lens slice having a second optical axis and a second longitudinal axis;

wherein the first optical axis is spaced apart from the second optical axis, and the first longitudinal axis is perpendicular to the second longitudinal axis.

13. A star tracker according to claim 12, wherein:

the first lens slice comprises a first cylindrical lens; and

the second lens slice comprises a second cylindrical lens.

14. A star tracker according to claim 12, wherein:

the first lens slice defines a first surface, through which passes at least some light that forms the image of the at least one celestial object in the field of view, the first surface being a first simple curvature surface; and

the second lens slice defines a second surface, through which passes at least some light that forms the image of the at least one celestial object in the field of view passes, the second surface being a second simple curvature surface.

15. A star tracker according to claim 5, wherein the pixelated image sensor comprises a plurality of pixels arranged in a two-dimensional pattern.

16. A navigation system, comprising:

a database storing ephemeral data about a plurality of celestial objects;

first, second and third star cameras, wherein each star camera of the first, second and third star cameras has a respective field of view and comprises;

a respective pixelated image sensor; and

a respective lens slice disposed between the respective field of view and the respective pixelated image sensor, wherein the respective lens slice comprises an elongated diametric portion, less than all, of a conceptual conventional lens along an elongation axis perpendicular to an optical axis of the conceptual conventional lens, and encompassing the optical axis of the conceptual conventional lens, such that optical performance of the respective lens slice along the elongation axis is comparable to optical performance of the conceptual conventional lens and optical performance of the respective lens slice along a width axis perpendicular to the elongation axis is worse than the optical performance of the conceptual conventional lens; and

a processor coupled to the pixelated image sensor of each of the first, second and third star cameras and to the database and configured to automatically estimate one or more of;

(a) attitude of the navigation system, (b) orientation of the navigation system or (c) location of the navigation system, based on;

(a) data from the respective pixelated image sensors of the first, second and third star cameras generated as a result of an image of at least one celestial object in the field of view of one or more of;

the first, second and third star cameras being projected onto the respective pixelated image sensor by the respective lens slice or (b) the ephemeral data in the database.

17. A navigation system according to claim 16, wherein each respective lens slice defines a surface, through which passes light that forms the image of the at least one celestial object in the field of view, the surface being a compound curvature surface.

18. A navigation system according to claim 17, wherein each star camera of the first, second and third star cameras has a respective optical axis, and the optical axes of the first, second and third star cameras are mutually orthogonal.

19. A navigation system according to claim 17, wherein, for each star camera of the first, second and third star cameras, the respective lens slice comprises:

a respective first lens slice having a respective first optical axis and a respective first longitudinal axis; and

a respective second lens slice having a respective second optical axis and a respective second longitudinal axis;

wherein the respective first optical axis is spaced apart from the respective second optical axis, and the respective first longitudinal axis is perpendicular to the respective second longitudinal axis.

20. A navigation system according to claim 19, wherein, for each star camera of the first, second and third star cameras:

the respective first lens slice is elongated along the respective first longitudinal axis; and

the respective second lens slice is elongated along the respective second longitudinal axis.

21. A navigation system according to claim 19, wherein:

the processor is configured to provide separate estimates of the one or more of the;

(a) attitude of the navigation system, (b) orientation of the navigation system or (c) location of the navigation system, for each of the first, second and third star cameras; and

the navigation system further comprises;

a navigation filter configured to estimate, based on the separate estimates of the one or more of the;

(a) attitude of the navigation system, (b) orientation of the navigation system or (c) location of the navigation system, an improved one or more of;

(a) attitude of the navigation system, (b) orientation of the navigation system or (c) location of the navigation system.