LEO Satellite Antenna Phase Center Prediction Using Attitude Data
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for predicting and fitting the antenna phase center (APC) of low Earth orbit (LEO) satellites are inadequate, particularly due to the rapid variation of corrections and their high dependence on the satellite's attitude, leading to significant APC orbit errors and affecting positioning results.
Innovation Solution
A method is provided to predict and fit the APC of LEO satellites by transforming spacecraft body-fixed and orbital coordinate systems, obtaining rotation angles, calculating correction vectors from the center of mass to the phase center, and performing ephemeris parameter fitting based on these predictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If CoM orbit determination is used for LEO satellites, then orbit prediction precision is improved, but the convenience for ground users is reduced due to the need for additional correction processes
Solution Approach 1:
The patent extracts the attitude-dependent correction process from the user-side operations and integrates it into the satellite's broadcast ephemeris data. By embedding the correction information directly in the broadcast ephemeris, the system eliminates the need for users to perform separate correction calculations, thus maintaining high precision while improving ease of operation.
Solution Approach 2:
The patent introduces an intermediary correction model that transforms the relationship between CoM orbit and APC orbit. This correction model acts as a mediator that accounts for attitude variations, allowing the system to broadcast precise APC orbit information directly without requiring users to implement complex real-time correction algorithms.
2Measurement precision
If real-time attitude data is required for APC correction, then positioning accuracy is improved, but system reliability deteriorates due to potential data loss from unstable attitude control
Solution Approach 1:
The patent applies preliminary action by pre-calculating and embedding attitude compensation parameters into the broadcast ephemeris data before transmission. Instead of requiring real-time attitude data during user positioning operations, the necessary correction information is prepared in advance and included in the standard ephemeris broadcast, ensuring reliability even when real-time attitude data is unavailable.
Solution Approach 2:
The patent provides beforehand cushioning by incorporating attitude variation compensation mechanisms into the ephemeris model itself. This creates a buffer that compensates for potential attitude instability or data loss, allowing the system to maintain positioning accuracy without relying on continuous real-time attitude data streams.
3Ease of operation
If GNSS broadcast ephemeris is used for LEO satellites, then ease of operation is improved, but orbit precision deteriorates to decimeter to meter range errors
Solution Approach 1:
The patent applies parameter changes by modifying the ephemeris model parameters to include attitude-dependent correction terms. By changing the mathematical parameters of the ephemeris system to account for APC variations, the patent maintains the simplicity of broadcast ephemeris usage while achieving precision comparable to or better than CoM-based determination methods.
Data Source
AI summary
A method to predict and fit an APC of a LEO satellite considering attitude information is provided, which includes: transforming a spacecraft body-fixed coordinate system, obtaining a transformation matrix from orbital coordinate system to transformed spacecraft body-fixed coordinate system, obtaining rotation angles during a rotation process, obtaining rotation angles in orbit determination time period to predict rotation angles in orbit prediction time period, obtaining a transformation matrix from spacecraft body-fixed coordinate system to Earth-fixed coordinate system of each prediction moment, obtaining a correction vector from a CoM to a phase center of a downlink signal antenna in the Earth-fixed coordinate system at each prediction moment, and obtaining an orbit of the phase center of the downlink signal antenna of a LEO satellite, and performing an ephemeris parameter fitting on the orbit of the phase center of the downlink signal antenna of the LEO satellite in a fitting time period.