Star Tracker Kalman Filter Navigation Drift Correction
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Solution Overview
Problem
Current navigational systems using celestial object tracking and inertial measurement face limitations in achieving accurate position and attitude determination due to the inherent drift of inertial sensors and the paucity of trackable objects under operational conditions.
Innovation Solution
The method involves optically imaging skymarks of known ephemeris using a sensor coupled to a platform, obtaining attitude measurements from an inertial navigation system, and applying a recursive estimation filter, such as a Kalman filter, to tightly couple and update the platform's navigation state, while employing multi-hypothesis tracking and frame stacking to compensate for motion and remove spurious detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If inertial sensors are used for navigation, then autonomous navigation capability is improved, but measurement accuracy deteriorates due to inherent drift
Solution Approach 1:
The patent introduces celestial objects (stars, satellites) as intermediary reference points to correct inertial sensor drift. The star tracker observes these celestial objects to provide periodic absolute position and orientation updates, acting as a mediator between the autonomous inertial system and external reference frames, thereby eliminating drift accumulation without requiring continuous external signals.
Solution Approach 2:
The patent merges inertial navigation system (INS) with star tracker to create a hybrid navigational system. The INS provides continuous autonomous navigation while the star tracker provides periodic correction updates, combining the advantages of both systems to achieve both autonomy and long-term accuracy.
2Measurement precision
If celestial object tracking is used for navigation, then position and attitude determination accuracy is improved, but the number of trackable objects decreases under operational conditions
Solution Approach 1:
The patent makes the star tracker universally applicable to track multiple types of celestial objects including stars, planets, and artificial satellites. This multi-functionality ensures that sufficient trackable objects are available under various operational conditions, whether in space or atmospheric flight, maintaining navigation capability across different environments.
Solution Approach 2:
The patent implements dynamic selection and tracking of celestial objects based on current operational conditions, platform orientation, and visibility. The system dynamically adjusts which celestial objects to track, ensuring optimal use of available objects under varying conditions such as daytime vs. nighttime, different latitudes, and platform maneuvering.
3Measurement precision
If satellite sightings are used for navigation, then position derivation is improved, but system complexity increases due to data processing requirements
Solution Approach 1:
The patent pre-computes and stores ephemeris data (predicted positions) for celestial objects before navigation operations. This preliminary preparation allows the star tracker to quickly match observed celestial objects with catalogued positions without performing complex real-time orbital calculations, significantly reducing on-board processing complexity while maintaining high position derivation accuracy.
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
This approach enhances the accuracy and robustness of navigational state estimation by integrating celestial tracking and inertial data, improving the ability to determine platform attitude, direction, and position, even under conditions where traditional methods fall short.
Implementation Method 1
optically imaging skymarks of known ephemeris using a sensor coupled to a platform
Data Source
AI summary
Methods and computer products for establishing at least one of attitude, direction and position of a moving platform. At least one skymark of known ephemeris is imaged at each of a first set of discrete instants by means of an optical sensor coupled to the platform. A measurement is also obtained of the attitude of the platform at each of a second set of discrete instants by means of an inertial navigation system. A recursive of estimation filter is then applied to successive skymark position vectors to update an estimate of platform navigation state, with the measurement of attitude of the platform tightly coupled to the estimate of platform navigation state as updated by the recursive estimation filter. Various techniques of frame stacking and multi-hypothesis tracking may be applied to improve the robustness of navigation solutions.