Star Tracker Light Shield for Stray Light Rejection
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Solution Overview
Problem
Conventional star trackers face challenges in preventing unwanted light, such as from the sun or moon, from reaching the sensor due to their fixed sun shields, which can block navigational stars, especially when these bright objects are close to the field of view, and require precise aiming mechanisms.
Innovation Solution
A star camera with a mechanically positionable light blocker that can selectively block a portion of the field of view, allowing light from navigational stars to reach the sensor while minimizing interference from bright objects, using a variable or fixed light blocker with a size that can be adjusted to block between 30° and 45° of the field of view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a fixed sun shield is used to block unwanted light, then sunlight blocking capability is improved, but the shield necessarily becomes large and blocks navigational stars when the orientation changes
Solution Approach 1:
The patent applies the dynamics principle by making the light blocker movable rather than fixed. The light blocker can be repositioned within the optical path to dynamically adjust which portions of the field of view are blocked. This allows a smaller light blocker to effectively block sunlight at different orientations without permanently obstructing navigational stars, resolving the contradiction between blocking capability and shield size.
2Object-affected harmful factors
If a large fixed sun shield is used to prevent unwanted light, then light blocking effectiveness is improved, but navigational stars are blocked when the vehicle rotates or orbits
Solution Approach 1:
The movable light blocker enables the system to adapt to different vehicle orientations and orbital positions. By repositioning the light blocker, the system can maintain effective sunlight blocking while keeping navigational stars visible, thus improving adaptability without sacrificing light blocking effectiveness.
Solution Approach 2:
The patent segments the field of view control by using a light blocker that can be positioned at different locations within the optical path. This segmentation allows selective blocking of specific angular regions while leaving other regions open for star observation, resolving the contradiction between blocking effectiveness and field of view flexibility.
3Productivity
If a mechanically aimable star tracker is used to use more navigational stars, then star detection capability is improved, but precise aiming mechanisms become complex
Solution Approach 1:
Instead of using complex mechanical aiming mechanisms, the patent employs a movable light blocker that can be repositioned to dynamically adjust the field of view. This simpler dynamic approach allows the star tracker to access more navigational stars by blocking sunlight at different positions without requiring precision mechanical aiming systems.
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
Enables effective blocking of unwanted light, allowing for accurate navigation by reducing the impact of stray light and eliminating the need for precise aiming mechanisms, thus improving the ability to detect navigational stars even when they are near bright objects.
Implementation Method 1
A light blocker is disposed within the light path. The light blocker blocks visibility by the sensor of a selectable portion of the field of view
Implementation Method 2
a lens having a focal length and a field of view... such that the lens projects an image of the field of view onto the sensor
Data Source
AI summary
A navigation system includes a star camera having a field of view. The star camera includes a sun shields that selectively block portions of the star camera's field of view, to prevent unwanted light, such as light from the sun or moon, reaching image sensors of the star cameras. Some sun shields include x-y stages or r-θ stages to selectively position a light blocker to block the unwanted light. Some sun shields use positionable partially overlapping orthogonally polarized filters to block the unwanted light. Some sun shields use counter-wound spiral windows that are selectively rotated to block the unwanted light. Some sun shields a curved surface that defines a plurality of apertures fitted with individual mechanical or electronic shutters.