Satellite Crosslink Timing Synchronization via Ranging Signals
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Solution Overview
Problem
Current satellite constellations face challenges in achieving precise timing and frequency synchronization, especially for non-timing satellites without access to accurate time sources like GPS, which can lead to inaccuracies in positioning and navigation.
Innovation Solution
The method involves using crosslink ranging signals between satellites, where timing satellites equipped with accurate time sources like GPS transmit signals to non-timing satellites, allowing for the calculation of ranging measurements to synchronize time and frequency across the constellation, leveraging a network of satellites with varying orbits and constellations like Iridium LEO, MEO, and GEO satellites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If crosslink ranging signals are transmitted between satellites to enable time synchronization, then timing accuracy for non-timing satellites is improved, but system complexity increases due to additional signal transmission and calculation requirements
Solution Approach 1:
The patent uses timing satellites as intermediaries that receive accurate time from GPS and relay this time information to non-timing satellites through crosslink ranging signals. This mediator approach allows non-timing satellites to achieve synchronization without directly accessing GPS, resolving the contradiction by adding a functional layer rather than requiring complex modifications to each satellite
Solution Approach 2:
The satellite constellation is segmented into timing satellites (with GPS receivers) and non-timing satellites (without GPS receivers). This segmentation allows the system to distribute timing functionality selectively, improving overall timing accuracy while managing complexity by having only subset of satellites perform the computationally intensive GPS processing
2Reliability
If all satellites are equipped with GPS receivers to achieve accurate time synchronization, then timing reliability is improved, but cost and device complexity increase significantly
Solution Approach 1:
Timing satellites perform multiple functions: they act as navigation satellites providing positioning data, as time sources with GPS receivers, and as relay nodes distributing time information to non-timing satellites. This multi-functionality improves timing reliability across the constellation while avoiding the need to equip every satellite with GPS capability
Solution Approach 2:
Instead of each satellite having its own GPS receiver, the patent creates virtual copies of GPS time information through crosslink signals. Non-timing satellites receive copied time data from timing satellites, achieving the same synchronization effect without duplicating the expensive GPS hardware on every satellite
3Device complexity
If crosslink ranging measurements are used for time synchronization, then ground infrastructure requirements are reduced, but measurement precision challenges arise in determining accurate time and frequency offsets
Solution Approach 1:
The patent implements feedback mechanisms where satellites transmit their estimated time and frequency offsets back to the network, allowing for continuous refinement of synchronization. Timing satellites use GPS time as a reference feedback source to correct their own and other satellites' timing drift, improving measurement precision without requiring extensive ground-based timing infrastructure
Solution Approach 2:
The patent replaces mechanical/physical ground-based timing infrastructure with space-based atomic clocks and GPS time references. By using atomic clocks on satellites and GPS time as references, the system achieves high precision time and frequency estimation without relying on ground laboratories or physical time distribution networks
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 enables accurate time and frequency synchronization across the satellite network, reducing the need for extensive ground-based infrastructure and providing precise timing information for satellite operations and user receivers, with accuracy improvements in TOA and Doppler measurements for orbit determination.
Implementation Method 1
transmitting, by at least one first satellite, at least one crosslink ranging signal to at least one second satellite
Data Source
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AI summary
A system, method, and apparatus for advanced timing and time transfer for satellite constellations using crosslink ranging and an accurate time source are disclosed herein. In particular, the present disclosure relates generally to systems for providing improved positioning, navigation, and/or timing information for oscillator calibration and more specifically, to use at least one satellite with accessibility to an accurate time source to calibrate the local oscillator on a crosslink paired satellite. In at least, one embodiment, time synchronization on a subset of satellites with crosslinking capabilities is used to distribute time through a network of crosslinked satellites.