Star Tracker Attitude Estimation Using Inter-Star Distance Calibration
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Solution Overview
Problem
Current methods for estimating the attitude of a spacecraft equipped with a star sensor are complex and require heavy calculations, and existing star trackers fail to effectively reject point errors such as proton disturbances and calibrate spatial errors in flight, while also being prone to temporal single-star noise.
Innovation Solution
A method that involves onboard star catalog-based attitude estimation using inter-star distances, partitioning the field of view into elementary zones to model and calibrate spatial errors, and employing an estimation filter to readjust spatial error amplitudes, which simplifies the process and improves accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex methods like Kalman filter based on temporal and spatial noise modeling are used, then measurement error correction is improved, but device complexity and calculation burden increase
Solution Approach 1:
The patent segments the field of view into multiple elementary zones and processes stars in different zones separately. By dividing the star tracker's field of view into distinct zones and applying zone-specific calibration parameters, the system achieves comprehensive error correction without requiring complex global models, thus reducing overall computational complexity while maintaining measurement precision.
Solution Approach 2:
The patent applies local quality by using spatial error calibration specific to each elementary zone. Each zone has its own calibration parameters that account for local spatial errors, allowing precise correction tailored to each region's characteristics rather than using a uniform correction approach, thereby achieving high measurement precision with manageable complexity.
2Reliability
If traditional star tracker methods are used, then basic attitude estimation is achieved, but the ability to reject point errors and calibrate spatial errors in flight is insufficient
Solution Approach 1:
The patent implements preliminary action by performing spatial error calibration during ground testing before flight operations. The star tracker is calibrated on the ground to establish baseline spatial error characteristics, which then enables the system to reject point errors and perform in-flight calibration more effectively, as the preliminary ground calibration provides a reference framework for ongoing error correction.
Solution Approach 2:
The patent employs feedback mechanisms by continuously monitoring measurement residuals and using them to detect and reject point errors in real-time. The system compares observed star positions with catalog positions, uses the residuals to identify outliers through statistical tests, and adjusts processing accordingly, creating a closed-loop feedback system that enhances reliability and enables adaptive in-flight calibration.
3Measurement precision
If heavy calculation methods are employed, then error correction performance is improved, but processing time and computational resources increase
Solution Approach 1:
The patent reduces processing time by segmenting the field of view into elementary zones and processing stars independently within each zone. This segmentation allows parallel processing of different zones and reduces the computational burden compared to processing all stars globally, achieving efficient error correction performance with reduced processing time and computational resource requirements.
Data Source
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AI summary
The invention relates to a method for estimating the attitude of a spacecraft equipped with a stellar sensor and an onboard star catalog, comprising measuring inter-star angular distances in axes relative to the stellar sensor, calculating said distances from information in the onboard star catalog, characterized in that the measured inter-star angular distances are compared with the calculated inter-star angular distances in order to deduce information on the accuracy of the attitude measurements of the sensor, in that the spatial errors of the stellar sensor are calibrated, and in that point-like star errors due, for example, to false stars, planets, protons or other energetic particles disturbing the star measurement are eliminated.