Spacecraft Position Determination via Rolling Shutter Distortion Correction
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Solution Overview
Problem
Current methods for determining the position of spacecraft, particularly in highly dynamic conditions, are limited by the usage limitations of star cameras with rolling shutters, which result in image distortions and unreliable rotation rate measurements beyond low rotation rates, making it difficult to completely replace gyroscopic sensors.
Innovation Solution
The method involves correcting image distortions caused by rolling shutters to enable real-time star identification and position calculation using star groups, allowing for independent position measurements and rotation rate determination in each cycle, even at high rotation rates, without additional hardware interventions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If star cameras with rolling shutters are used for position determination, then real-time measurements are possible, but image distortions occur at high rotation rates making measurements unreliable
Solution Approach 1:
The patent changes the parameter of star group selection by using multiple different star groups depending on the rotation rate. At low rotation rates, one set of star groups is used, while at high rotation rates, a different set of star groups is selected. This adaptation allows the system to maintain measurement accuracy across varying rotation rates by compensating for rolling shutter distortions through appropriate star group selection.
Solution Approach 2:
The system dynamically adapts its measurement approach based on the current rotation rate. The method continuously monitors the rotation rate and switches between different measurement modes and star group configurations accordingly. This dynamic adaptation enables reliable position determination whether the spacecraft is rotating slowly or rapidly.
2Reliability
If conventional star sensors are used, then position measurements can be made, but they cannot work at high rotation rates above a few angular degrees per second
Solution Approach 1:
The patent makes the star sensor system dynamic by adapting its operation to the current rotation rate. The system transitions from conventional operation at low rates to a specialized high-rate mode using multiple star groups. This dynamic capability extends the usable rotation rate range from a few degrees per second to significantly higher rates while maintaining reliability.
Solution Approach 2:
The system changes operational parameters based on rotation rate. At high rotation rates, it employs different star groups with specific geometric configurations that are better suited for capturing stars despite the rapid motion and rolling shutter distortions. This parameter change enables the sensor to remain usable at rotation rates far exceeding conventional limits.
3Device complexity
If gyroscopic sensors are completely replaced by star sensors, then device complexity is reduced, but measurement accuracy deteriorates at high rotation rates
Solution Approach 1:
The patent implements a dynamic measurement system that adapts to rotation rates without requiring gyroscopic sensors. By continuously adjusting which star groups are used for measurement based on the current rotation rate, the system maintains high measurement precision across the full operating range, eliminating the need for gyroscopes while preserving accuracy.
Solution Approach 2:
The system achieves gyro-less operation by changing measurement parameters adaptively. Instead of using a fixed star group configuration that would fail at high rates, the system selects from multiple star group configurations optimized for different rotation rates. This parameter adaptation enables complete replacement of gyroscopic sensors while maintaining measurement precision throughout the operational envelope.
Data Source
AI summary
A method for determining the position of a spacecraft in space, includes cyclically÷ repeating steps of capturing distorted star images; processing the distorted star images to form distorted star group data; storing the distorted star group data; determining a current rotation rate by comparing the distorted star group data of two consecutive cycles; transmitting the current rotation rate to a position control system; and/or the following steps are carried out: processing the distorted star images of a current cycle to form rectified star group data; determining position information by matching the rectified star group data with star group catalog data which is carried along; transmitting the position information to the position control system. A method for determining the position of a spacecraft in space, taking into account known system parameters of an optical system, includes: coding star group catalog data with n = 3...4 stars [xn, yn, zn], which are visible in an image field, into representative focal-plane coordinates; forming a scaling-, translation-, and rotation-invariant star group code on the basis of [xPiX,yPiX]n; or coding star group catalog data with n = 3...4 stars [xn,yn, zn], which are visible in an image field, into representative tangent and/or angular coordinates [tan(a),tan(β)]n. The invention further relates to a device for carrying out such methods and to a computer program product for carrying out such methods.