Daytime and nighttime stellar sensor with active polarizer

• US 10,302,433 B2
• Filed: 01/20/2016
• Issued: 05/28/2019
• Est. Priority Date: 01/21/2015
• Status: Active Grant

• Current Assignee: Centre National D'Etudes Spatiales
• Original Assignee: Centre National D'Etudes Spatiales
• Inventors: Montel, Johan
• Primary Examiner(s): Kiswanto, Nicholas
• Application Number:
  US15/542,691
• Publication Number:
  US 20170370725A1
• Time in Patent Office: 1,224 Days
• CPC Class Codes: G01C 17/34 Sun- or astro-compasses
• CPC Class Codes: G01C 21/025 with the use of startrackers
• CPC Class Codes: G01C 21/1656 with passive imaging devices, e.g. cameras
• CPC Class Codes: G01C 21/18 Stabilised platforms, e.g. by gyroscope

Abstract

The invention relates to a daytime and nighttime stellar sensor (1), comprising: at least one video camera (2) suitable for taking images of stars (3) in the sky; and a control unit (4), characterized in that it furthermore comprises: a polarizer (5), the control unit (4) being configured: to obtain an estimation of a direction of polarization of the polarized light received from the sky by the video camera (2); and to control the orientation of the polarizer (5) so that said polarizer (5) filters polarized light from the sky directed toward the video camera (2) and having said polarization direction.

Claims

1. A daytime and nighttime stellar sensor, comprising:

at least one camera adapted for taking images of stars of the sky,

a control unit,

characterized in that it further comprises;

a polarizer,

the control unit being configured for;

obtaining an estimation of a polarization direction of the polarized light from the sky received by the camera, and

controlling the orientation of the polarizer so that said polarizer filters the polarized light from the sky directed towards the camera and having said polarization direction.

2. The stellar sensor according to claim 1, further comprising a light filter, exclusively letting through the light in the infrared band.

3. The stellar sensor according to claim 2, wherein the light filter exclusively lets through the light having a wavelength comprised between 1.5 μ

m and 2 μ

m or between 0.9 μ

m and 1.4 μ

m.

4. The stellar sensor according to claim 1, comprising a device for measuring an angle between a target direction of the stellar sensor and the sun, the control unit being configured for estimating the polarization direction of the polarized light from the sky received by the camera from said angle.

5. The stellar sensor according to claim 1, wherein the control unit comprises a memory storing ephemerides and/or a solar direction model for calculating an angle between a target direction of the sensor and the sun, from which the control unit calculates the polarization direction of the polarized light from the sky received by the camera.

6. The stellar sensor according to claim 1, comprising:

a first optical head, comprising a first camera and a first polarizer, and

a second optical head, comprising a second camera and a second polarizer,

the first optical head and the second optical head being positioned in a diametrically opposite direction in azimuth.

7. A device for measuring the attitude of a vehicle, comprising:

an inertial central unit and/or a gyrometer, for providing an estimation of the attitude of the vehicle,

characterized in that the device further comprises;

a daytime and nighttime stellar sensor according to claim 1,

a memory storing a catalogue of known stars,

the device being configured for resetting the estimation of the attitude of the vehicle provided by the inertial central unit and/or by the gyrometer from images taken by the stellar sensor and from the catalogue of known stars.

8. A vehicle, characterized in that it comprises a device for measuring attitude according to claim 7.

9. A method for taking images of stars in a daytime and nighttime period, applying a daytime and nighttime stellar sensor comprising a camera and a polarizer, characterized in that it comprises steps consisting of:

controlling the orientation of the polarizer so that said polarizer filters the polarized light from the sky directed towards the camera and having said polarization direction,

taking images of stars of the sky with the camera.

10. A method for measuring the attitude of a vehicle, comprising the steps consisting of:

taking images of stars of the sky according to the method of claim 9, exclusively in a wavelength band comprised between 0.9 μ

m and 2 μ

m,

comparing the images of the stars with a catalogue of known stars, for resetting an estimation of the attitude of the vehicle when the latter has an altitude comprised between 0 and 25 km.