Sliced lens star tracker

Patent metadata

Field	Value
Publication number	US-10641859-B2
Application number	US-201715661881-A
Country	US
Kind code	B2
Filing date	Jul 27, 2017
Priority date	Jul 27, 2017
Publication date	May 5, 2020
Grant date	May 5, 2020

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.

First claim

What is claimed is:

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 dat

Assignees

• Charles Stark Draper Laboratory Inc

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

Classifications

• G01C21/025

  with the use of startrackers · CPC title

• H04N7/181

  for receiving images from a plurality of remote sources · CPC title

• G01S3/7867 Primary

  Star trackers (navigation using star trackers G01C21/025) · CPC title

• G01S3/781

  Details · CPC title

• G02B13/0015

  characterised by the lens design · CPC title