Satellite Shadow Detection for Daylight Navigation

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Solution Overview

Problem

Traditional celestial navigation systems, such as SkyMark, face challenges in accurately determining position during daylight hours and when satellites are in the shadow of a planet, as they rely on direct observation of satellites against a star-field background, which is difficult or impossible in these conditions.

Innovation Solution

A navigation system that uses a telescope and pixelated image sensor to detect the shadow of transiting satellites against a bright celestial object like the sun or a sunlit planet/moon, employing edge detection, temporal filtering, and adaptive thresholding to estimate the satellite's angle and position, allowing for position determination even in challenging conditions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional celestial navigation systems observe satellites against a star-field background, then position determination can be achieved, but observations become difficult or impossible during daylight hours or when satellites are in planetary shadow

Engineering Contradiction:

Improveposition determination capabilityVSAvoidoperational conditions

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

Instead of observing the satellite directly against the star field, the system inverts the approach by observing the satellite's shadow against the bright celestial object (sun or sunlit planet/moon). This inversion allows observations to be made during daylight hours and when satellites would otherwise be in shadow, significantly expanding operational conditions while maintaining position determination capability

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The satellite shadow serves as an intermediary object that enables observation under conditions where the satellite itself cannot be directly observed. By detecting the shadow cast by the satellite onto the bright celestial background, the system can determine position during daylight and shadow conditions that would otherwise prevent navigation observations

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If specialized optics are used to observe satellites in daylight at low elevations, then observations become possible, but device complexity increases

Engineering Contradiction:

Improvedaylight observation capabilityVSAvoidoptics complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The system captures an image of the bright celestial object with the satellite's shadow projected onto it, then processes this image copy to detect shadow pixels, determine satellite position, and calculate navigation data. This copying approach with subsequent digital processing avoids the need for complex specialized optics while enabling daylight and low-elevation observations

Inventive Principle:

Principle #26Copying

3Adaptability or versatility

If inertial instruments are used to maintain vertical reference when horizon is obscured, then navigation can continue, but inherent drift limits accuracy

Engineering Contradiction:

Improveoperation in obscured conditionsVSAvoidvertical measurement accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The system replaces the mechanical inertial instruments that maintain vertical reference with an optical imaging system that directly observes the satellite shadow against a bright celestial object. This substitution eliminates the drift problem inherent in inertial sensors while maintaining the ability to operate when the horizon is obscured, thereby preserving measurement precision without sacrificing adaptability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 accurate position determination in two and three-dimensional space by observing satellite shadows during daylight or when satellites are in a planet's shadow, overcoming limitations of traditional systems.

Implementation Method 1

detect a shadow cast on the image sensor by a satellite transiting the bright celestial object

Methodology Applied

Scientific EffectShadow detection: Shadow

Data Source

PatentUS10234533B2Position determination by observing a celestial object transit the sun or moon

Publication Date: 2019.03.19 THE CHARLES STARK DRAPER LABORATORY INC

AI summary

A navigation system determines a position by referring to artificial or natural satellites or other space objects during daylight or when the objects are in a planet's shadow. A telescope and image sensor observe and image shadows of the objects as the objects transit the sun or a sunlit surface of a planet or moon, thereby solving problems related to the two key times during which traditional SkyMark navigation is difficult or impossible.