Star Tracker Positioning Under High Satellite Rotation
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Solution Overview
Problem
Conventional star sensors are limited by their rotation rate tolerance due to optical aperture, restricting the detection of faint stars, which is problematic for Earth observation missions requiring continuous Earth orientation.
Innovation Solution
An optical star sensor is fixed orthogonally to a satellite's axis of rotation, combined with additional sensors like gyroscopes, and uses a boxcar operator for real-time image processing to extend the field of view and improve position determination by linearly distributing light intensity across pixels, allowing faint stars to be detected and processed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical aperture is increased to detect faint stars, then the detection capability improves, but the exposure time increases which causes star images to blur due to satellite rotation
Solution Approach 1:
The patent segments the star sensor's optical system into multiple independent optical channels (e.g., multiple lenses or mirror segments) that simultaneously capture different portions of the star field. Each channel operates with short exposure time, avoiding blur, while the combined data from all channels provides comprehensive coverage and maintains ability to detect faint stars through integrated signal processing.
Solution Approach 2:
The patent transitions from traditional 2D sensor plane imaging to a multi-dimensional approach by adding temporal dimension (multiple exposure instances) and spatial dimension (multiple optical channels). Star positions are determined by tracking their motion trajectories across multiple short-exposure frames rather than relying on a single long-exposure image, thereby detecting faint stars without blur from rotation.
2Measurement precision
If the exposure time is shortened to avoid blur from rotation, then the measurement of star positions improves, but the detection of faint stars deteriorates due to insufficient light intensity
Solution Approach 1:
The patent merges data from multiple optical channels and/or multiple sequential short-exposure measurements to achieve the equivalent detection capability of a long exposure. By combining signals from multiple sources that each captured sufficient photons during their brief exposure windows, the system reconstructs accurate star positions and detects faint stars without the blur that would result from any single long exposure.
Solution Approach 2:
The patent implements continuous or near-continuous short-exposure measurements rather than intermittent long exposures. The star sensor continuously tracks stars across multiple frames, accumulating positional data over time through sequential measurements. This continuous action maintains sharp star images in each frame while building up sufficient signal-to-noise ratio for detecting faint stars through temporal integration of positional information.
3Reliability
If the satellite rotation rate is increased for spin stabilization, then the attitude control improves, but the field of view detectable by the star sensor is restricted to very bright stars only
Solution Approach 1:
The patent employs dynamic image processing that adapts to the satellite's rotation rate. The processing algorithm dynamically compensates for the motion blur pattern created by rotation, using the known rotation characteristics to reconstruct sharp star positions from the blurred images. This dynamic compensation enables detection of faint stars even at high rotation rates where traditional static sensors would fail.
Solution Approach 2:
The patent implements feedback mechanisms where the star sensor continuously measures star positions and feeds this information back to the attitude control system. The system uses this feedback to refine its understanding of the rotation dynamics and improve its image processing algorithms, creating a closed-loop system that maintains accurate star detection and attitude determination even as rotation conditions vary.
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
Enhances the measurement accuracy and extends the detectable field of light objects, enabling precise inertial attitude determination even at high rotation rates, thus improving satellite positioning and attitude control.
Implementation Method 1
a light sensor aligned to a detected light object field with a sensor surface provided with a sensor coordinate system and a row-wise arrangement of light-sensitive pixels
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention relates to a method for determining the position of a satellite (100), which rotates about an axis of rotation (3), at least by means of a star tracker (1), the star tracker being directed at a captured light object field along an optical axis (4), wherein the axis of rotation (3) and the optical axis (4) are at a fixed angle to each other and a light sensor (6) is provided, the light sensor having a sensor surface which is perpendicular to the optical axis (4) and which contains a sensor coordinate system having an arrangement of light-sensitive pixels in rows. In order to achieve improved position control of the satellite (100), image data captured in the individual rows of the light sensor (6) are captured row by row and sequentially, for each row the image data of the row in question are convoluted over a predefined time interval by means of a boxcar operator having a predefined number of pixels, a light maximum is determined by means of the boxcar operator, the light maximum is assigned to a position of a light object on the basis of a position of the row and within the row in the sensor coordinate system, and an object list containing light object coordinates, light maximum and measurement time is determined by means of an image from a plurality of light objects, said image being captured over the entire sensor coordinate system.