Dual-Head Star Sensor for Satellite Line of Sight Stability
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Solution Overview
Problem
Current satellite systems rely on expensive and complex gyroscopes and multiple sensors to measure and control the stability of the line of sight, which increases mass, consumption, and complexity, while also requiring periodic readjustments and failing to effectively manage high-frequency mechanical vibrations.
Innovation Solution
A method utilizing a star tracker with two heads, one capturing images at a low frequency for direction measurement and another at a higher frequency to deduce angular displacement and velocity, allowing for in-flight measurement and control of microvibrations, reducing the need for gyroscopes and simplifying the processing architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gyroscopes are used to measure angular velocity and line of sight stability, then measurement capability is improved, but cost, mass, and complexity increase significantly
Solution Approach 1:
The patent combines the functions of gyroscopes and star sensors into a single integrated system. The star tracker's image processing unit performs both attitude determination (traditionally star sensor function) and line of sight stability measurement (traditionally gyroscope function) by analyzing star image sequences at different frequencies, eliminating the need for separate gyroscope hardware.
Solution Approach 2:
The star tracker is designed to perform multiple functions: it determines satellite attitude by comparing star positions with a catalog, measures line of sight stability through high-frequency image analysis, and characterizes mechanical vibrations. This multi-functional approach replaces dedicated gyroscope hardware with a versatile imaging system.
2Measurement precision
If multiple sensors (gyroscope, star sensor) are used to control satellite attitude and line of sight stability, then measurement accuracy is improved, but mass and power consumption increase
Solution Approach 1:
The patent merges multiple sensing functions into a single star tracker assembly. By using the same optical path and detector for both attitude determination and vibration measurement, the system eliminates redundant hardware mass while maintaining measurement capabilities through software-based signal processing of the captured star images.
3Speed
If gyroscopes are used for measuring angular velocity, then high-frequency vibration measurement is improved, but periodic readjustment is required due to drift
Solution Approach 1:
The system uses continuous feedback from star position measurements to maintain accuracy. By constantly comparing observed star positions with catalog data and adjusting the line of sight direction accordingly, the system compensates for any drift without requiring periodic manual readjustment, ensuring long-term measurement reliability.
Solution Approach 2:
The star tracker performs self-calibration and self-correction by using the star field itself as a reference. The system automatically detects and corrects for drift by repeatedly measuring star positions against the known catalog, making the system self-sufficient without external intervention or separate calibration mechanisms.
4Measurement precision
If star images are processed at high frequency to measure microvibrations, then vibration measurement capability is improved, but processing complexity increases
Solution Approach 1:
The patent extracts only the essential information needed for vibration measurement from the full star images. By focusing on the displacement of star centroids rather than processing entire high-resolution images, the system reduces computational complexity while maintaining the ability to detect microvibrations through angular displacement calculations.
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 reduces satellite mass and consumption, simplifies processing, and enables higher frequency attitude control, eliminating the need for gyroscopes and multiple sensors, while effectively managing microvibrations and improving image quality.
Implementation Method 1
a first head suitable for taking image of stars at a first frequency, for measuring a direction of the line of sight by comparison with a catalog of stars
Implementation Method 2
a second head adapted for taking an image of stars at a second frequency higher than the first frequency... deducing information relating to the angular displacement of the line of sight from the relative displacement of at least one star
Data Source
Figure 1~2
Figure 3~4
AI summary
The method involves capturing a first set of star images (14) using a capturing head (6) of a star sensor (4) at frequency in a successive manner, where the sensor comprises another capturing head (5) for capturing a second set of star images (10) at another frequency that is lower than the former frequency. Information relative to angular displacement of a line of sight is deducted from relative displacement of a star in the two sets of the images, where the former frequency is higher than 30 Hertz. : Independent claims are also included for the following: (1) a method for measuring mechanical vibrations of a device (2) a method for processing images (3) a method for controlling an attitude of a satellite (4) a satellite. USE : Method for measuring stability of a line of sight of a device such as radar or remote-sensing laser type deduction device and imaging device used for imaging Earth, in a satellite (all claimed) i.e. observation satellite. ADVANTAGE : The method enables measuring stability of the line of sight in an accurate and inexpensive manner. The method enables reducing mass and consumption of the satellite. The method enables simplifying an image processing architecture embarked at the satellite. The method enables reducing the number of different sensors in the satellite, and avoiding disturbances related to microvibrations. The method enables measurements at higher frequencies to increase the bandwidth of satellite attitude control. DESCRIPTION OF DRAWINGS : The drawing shows a schematic view of a star sensor. 4 : Star sensor 5, 6 : Capturing heads 10, 14 : Star images 11 : Star catalog 20 : Image processing unit.