Gyroless Three-Axis Sun Acquisition Using Unscented Kalman Filter
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Solution Overview
Problem
Spacecraft attitude control systems face challenges in mission accomplishment due to limited resources or gyroscope failure, requiring alternative methods to re-orient disoriented spacecraft without relying on expensive and prone-to-failure gyroscopes or star trackers.
Innovation Solution
The system employs sun sensors and an unscented Kalman filter to estimate spacecraft attitude using Euler equations, leveraging angular momentum as an additional attitude reference to overcome uncertainties and drift issues, allowing for three-axis attitude determination without gyroscopes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a gyroscope is used to provide attitude information, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent removes the gyroscope from the attitude determination system and extracts only the essential sun sensor measurements. By eliminating the gyroscope and using only sun sensor data processed through Euler equations and unscented Kalman filter, the system achieves three-axis attitude determination without the expensive and failure-prone gyroscope component.
Solution Approach 2:
The patent replaces the mechanical gyroscope system with a computational approach using sun sensor measurements, Euler equations, and unscented Kalman filter algorithms. This substitution eliminates mechanical moving parts and replaces them with mathematical models and signal processing techniques to achieve the same attitude determination function.
2Device complexity
If a sun sensor is used to sense sun direction, then device complexity is reduced, but measurement precision deteriorates because it cannot detect attitude changes about the sun line
Solution Approach 1:
The patent introduces the unscented Kalman filter as an intermediary computational layer that processes sun sensor measurements and infers complete three-axis attitude information. The filter uses Euler equations to relate sun sensor observations to spacecraft attitude, effectively mediating between the limited sun sensor data and the complete attitude state, thereby recovering the missing about-sun-line attitude information.
3Measurement precision
If gyroscope and star tracker are used to provide attitude information, then measurement precision is improved, but reliability deteriorates due to component failure
Solution Approach 1:
The patent replaces expensive, failure-prone gyroscope and star tracker components with a simpler, more reliable sun sensor system. The sun sensor is inherently more reliable as it has no moving parts and cannot fail like mechanical gyroscopes, and the system accepts that the sun sensor alone must provide all attitude information without relying on multiple sophisticated sensors that could fail.
Data Source
AI summary
An attitude estimator that uses sun sensor outputs as the only attitude determination measurements to provide three-axis attitude information. This is accomplished by incorporating the Euler equation into the estimator. An unscented Kalman filter is employed to accommodate various nonlinear characteristics and uncertainties of the spacecraft dynamics and thus improve the robustness and accuracy of the attitude estimate.