Risley Prism Star Tracker Optical Steering
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Solution Overview
Problem
Risley prisms in star tracker and celestial navigation systems are limited by lateral chromatic aberration and require large size, weight, and power (SWaP), with mechanical steering mechanisms adding excessive bulk and optical steering mechanisms introducing chromatic error or distortion.
Innovation Solution
A pair of Risley prisms positioned along an optical axis, with at least one rotatable transverse to the other, and an optical detector array, along with a focusing lens, to eliminate mechanical slewing and reduce mechanical motion, thereby minimizing SWaP and chromatic aberration, and incorporating achromatic prisms and a light shade to enhance signal detection and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical steering mechanisms are used to achieve field of regard, then field of view coverage is improved, but size, weight, and power (SWaP) increase excessively
Solution Approach 1:
The patent replaces mechanical steering mechanisms with an optical steering approach using rotatable Risley prisms. The prisms are rotated transverse to the optical axis to steer the beam across the field of regard, eliminating the need for bulky mechanical slewing mechanisms while achieving the required field coverage.
Solution Approach 2:
The patent employs dynamic rotation of the Risley prisms transverse to the optical axis to achieve continuous beam steering. This dynamic optical adjustment allows the system to scan across a large field of regard without mechanical motion, providing adaptability while minimizing SWaP.
2Device complexity
If optical steering mechanisms are used to reduce SWaP, then size, weight, and power are reduced, but chromatic error or distortion becomes intolerable
Solution Approach 1:
The patent changes the orientation parameter of the Risley prisms by rotating them transverse to the optical axis. This parameter change enables optical steering while the prism pair configuration naturally compensates for chromatic aberration, maintaining image quality without introducing intolerable chromatic error.
Solution Approach 2:
The patent uses a pair of Risley prisms as an intermediary optical element that performs both beam steering and chromatic aberration correction. The prism pair acts as a mediator that achieves the dual function of reducing SWaP through optical steering while maintaining manufacturing precision by compensating for chromatic errors.
3Ease of operation
If Risley prisms are used for beam deflection, then variable beam steering is achieved, but lateral chromatic aberration limits performance
Solution Approach 1:
The patent divides the beam steering function into two separate Risley prisms arranged in a pair. Each prism handles a portion of the beam deflection, and their combined action achieves variable beam steering while the segmented structure allows for better control and compensation of lateral chromatic aberration.
Solution Approach 2:
The patent utilizes parameter changes in the prism rotation angles to achieve variable beam steering. By adjusting the rotation angles of the Risley prism pair, the system achieves flexible beam deflection while the specific parameter relationships between the prisms help minimize lateral chromatic aberration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces the need for mechanical motion, SWaP, and chromatic aberration, enhancing the field of view and signal integrity within a larger field of regard, improving overall system performance and reducing costs.
Implementation Method 1
Risley prisms are wedge-shaped glass prisms that enable variable beam deflection. Typically, Risley prisms are used as prism pairs in which one of the two prisms rotates to move from maximum to minimum beam deflection.
Implementation Method 2
At least one lens is positioned along the optical axis to receive the light beam from the pair of Risley prisms, with the at least one lens configured to focus the light beam.
Data Source
AI summary
An optical system comprises a pair of Risley prisms positioned along an optical axis to receive a light beam from a field of view, wherein at least one of the Risley prisms is rotatable, transverse to the optical axis, with respect to the other of the Risley prisms. At least one lens is positioned along the optical axis to receive the light beam from the pair of Risley prisms, with the at least one lens configured to focus the light beam. An optical detector array is positioned along the optical axis at an image plane, wherein the optical detector array receives the focused light beam on the image plane from the at least one lens. The optical system can be implemented as a light beam steering mechanism in a star tracker or celestial aided inertial navigation unit.