Star Tracker Row-Scan Positioning for Spin-Stabilized Satellites
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Solution Overview
Problem
Conventional star trackers have limitations in rotation rate tolerance due to optical opening and light availability, restricting their ability to process dim stars, especially in spin-stabilized satellites used for Earth observation missions.
Innovation Solution
Utilizing a method that fixes an optical star tracker at a predefined angle relative to the satellite's axis of rotation, combined with additional sensors like gyro sensors, to enhance measurement accuracy and position determination, and employing row-by-row image processing with a boxcar operator to process dim stars and expand the effective light object field.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional star trackers use short exposure times to capture point-shaped star images, then the star images remain sharp and resolution is maintained, but only very bright stars can be processed and the light object field is considerably restricted
Solution Approach 1:
The patent applies dynamics by making the integration time variable rather than fixed. The control unit dynamically adjusts the integration time based on the detected rotation rate of the satellite. When rotation rate is low, longer integration times are used to capture dim stars; when rotation rate is high, shorter integration times prevent star trails from exceeding the field of view. This dynamic adaptation resolves the contradiction between maintaining sharp star images and detecting more stars.
Solution Approach 2:
The patent changes the parameter of integration time based on the rotation rate condition. By monitoring the rotation rate and adjusting the integration time parameter accordingly, the system optimizes star detection capability. The control unit modifies this parameter in real-time to balance between capturing enough light from dim stars and preventing excessive blurring from satellite rotation.
2Quantity of substance
If the integration time is increased to capture more light from dim stars, then more stars become detectable, but star trails extend beyond the field of view at high rotation rates
Solution Approach 1:
The system dynamically adjusts integration time based on real-time rotation rate measurements. When the satellite rotates slowly, the system uses longer integration times to accumulate light from dim stars. When rotation rate increases, the system automatically reduces integration time to keep star trails within the field of view. This dynamic control resolves the contradiction between detecting more stars and maintaining field of view coverage.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the rotation rate and using this information to adjust the integration time. The control unit receives rotation rate data and feeds it back to modify the integration time parameter, creating a closed-loop system that adapts to changing conditions and maintains optimal performance across varying rotation rates.
3Measurement precision
If additional star trackers and non-optical sensors are added to improve position determination accuracy, then measurement accuracy increases, but the mass of the satellite increases
Solution Approach 1:
The patent makes the star tracker system multi-functional by enabling it to operate effectively across a wide range of rotation rates through dynamic integration time adjustment. This allows a single star tracker to perform both high-precision position determination and adapt to spin-stabilized satellite operations, reducing the need for additional specialized sensors and minimizing mass increase.
Solution Approach 2:
By changing the integration time parameter dynamically, the existing star tracker hardware can adapt to different operational conditions and achieve high measurement accuracy without requiring additional sensors. This parameter-based adaptation allows the system to maintain precision across varying rotation rates, avoiding the need for mass-increasing hardware additions.
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
Improves the resolution and accuracy of inertial position determination in spin-stabilized satellites, enabling the processing of dim stars and maintaining high availability even at high rotation rates.
Implementation Method 1
at least an optical star tracker having a light sensor which is aligned, relative to the axis of rotation at a predefined angle fixed optical axis, with a recorded light object field and has a sensor surface, which is provided with a sensor coordinate system and has an arrangement of light-sensitive pixels in rows
Data Source
AI summary
A method for determining the position of a satellite rotating about an axis of rotation using at least a star tracker which is aligned along an optical axis with a recorded light object field, the axis of rotation and the optical axis being at a fixed angle relative to one another and a light sensor having a sensor surface which is perpendicular to the optical axis and contains a sensor coordinate system having an arrangement of light-sensitive pixels in rows being provided. To achieve improved position control of the satellite, image data recorded in the individual rows of the light sensor are recorded row by row and sequentially, the image data for each row are convoluted with a predefined number of pixels over a predefined time interval using a boxcar operator, a light maximum is identified using the boxcar operator, the light maximum is assigned to a location 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, the light maximum and a measurement time is identified from a plurality of light objects using an over the entire sensor coordinate system.