Spacecraft Sun Reacquisition Using Star Tracker Vector Alignment
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Solution Overview
Problem
Current spacecraft attitude control systems require multiple sun sensors and rely on known orbital parameters to efficiently reacquire sun pointing orientation, which can be limiting in terms of autonomy and sensor redundancy.
Innovation Solution
A method utilizing a star tracker to determine a vector aligned with the ecliptic pole, adjusting the spacecraft attitude to align a primary axis with this vector, and rotating until the sun is registered, potentially using a single sun sensor and without knowledge of orbital position, epoch, or angular rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple sun sensors are used for spacecraft attitude control, then the reliability of sun acquisition is improved, but the device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary computational process that uses star tracker data to calculate the sun's position in the spacecraft body frame. This computational intermediary replaces the need for multiple physical sun sensors, as the sun's position is derived mathematically from star tracker observations and orbital parameters, thereby maintaining reliability while reducing sensor complexity
Solution Approach 2:
The patent replaces the mechanical/optical system of multiple sun sensors with a computational system using a single sun sensor combined with star tracker data processing. The sun's position is determined through coordinate transformations and calculations rather than direct physical sensing, substituting mechanical redundancy with computational processing
2Speed
If known orbital parameters are used for sun reacquisition, then the speed of sun acquisition is improved, but the spacecraft autonomy is reduced
Solution Approach 1:
The patent implements self-service by enabling the spacecraft to autonomously determine the sun's position using its own star tracker observations and onboard orbital parameter storage. The spacecraft independently performs coordinate transformations and sun position calculations without requiring real-time ground support or external data, achieving both speed and autonomy
Solution Approach 2:
The patent applies preliminary action by pre-storing orbital parameters (such as orbital element sets) in the spacecraft's memory before deployment. These pre-stored parameters are readily available for immediate use in sun acquisition calculations, enabling fast autonomous operation without requiring real-time parameter updates from ground stations
3Measurement precision
If six to eight sun sensors are required for geosynchronous satellite, then the measurement precision of sun position is improved, but the quantity of sensors and system complexity increase
Solution Approach 1:
The patent applies multi-functionality by using the star tracker for dual purposes: primary attitude determination and secondary sun position determination. The same star tracker hardware that provides attitude data is also used to calculate the sun's position through coordinate transformations, eliminating the need for dedicated multiple sun sensors and achieving precision through computational methods
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 prompt and reliable sun pointing orientation with reduced sensor requirements, enhancing spacecraft autonomy and reducing the time needed for sun reacquisition, even in the absence of initial attitude or rate information.
Implementation Method 1
determining, using a star tracker on board the spacecraft, a first vector aligned between an ecliptic pole of the earth and the spacecraft
Implementation Method 2
the presence of the sun is registered by a sun sensor of the spacecraft
Data Source
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AI summary
Techniques for orienting an earth-orbiting spacecraft include determining, using a star tracker on board the spacecraft, a first vector aligned between an ecliptic pole of the earth and the spacecraft, adjusting attitude of the spacecraft so as to align a first axis of the spacecraft with the first vector, and rotating the spacecraft about the first axis until presence of the sun is registered. Rotation rates may be subsequently reduced, such that the sun remains within a field of view of the sun sensor or of a solar array of the spacecraft.