Highlights:
- Proposes methods for designing satellite constellations ensuring continuous global or regional coverage.
- Introduces Walker-Delta and Common Ground-Track constellations to optimize satellite configurations.
- Utilizes bounded Voronoi diagrams and Binary Integer Linear Programming (BILP) to achieve optimal satellite placement.
- Provides a framework for analyzing inter-satellite link (ISL) continuity across constellations.
TLDR:
This paper presents innovative methods for designing communication satellite constellations that ensure continuous coverage and robust inter-satellite link (ISL) connectivity. By utilizing approaches like the Walker-Delta constellation and common ground-track methods, the study optimizes satellite positioning to minimize the number of satellites while maintaining global coverage. Analytical tools like bounded Voronoi diagrams and BILP are used to enhance performance. Simulations show how different constellation designs fare in terms of coverage and ISL continuity, offering a clear path forward for future satellite networks.
Introduction:
The rapid development of Low Earth Orbit (LEO) communication systems, driven by projects like SpaceX’s Starlink and Amazon’s Kuiper, has sparked interest in optimizing satellite constellations. Traditional satellite systems have limitations, particularly when it comes to maintaining continuous coverage and ensuring seamless communication between satellites. This paper explores two key challenges: designing constellations that provide continuous communication coverage and ensuring uninterrupted inter-satellite links (ISLs), especially as satellites move relative to one another in their orbits.
Constellation Design Methods:
One of the most widely discussed configurations for satellite constellations is the Walker-Delta constellation. This method geometrically arranges satellites symmetrically in circular orbits, optimizing coverage over mid-latitude and equatorial regions. Each satellite follows parameters including semi-major axis, inclination, and argument of perigee, which define their positions and orbits. Walker-Delta constellations ensure uniform angular spacing between satellites, enhancing coverage continuity.
For global or regional communications, the Common Ground-Track (CGT) Constellation is another prominent design method. Satellites in this configuration follow repeat ground-track orbits, retracing the same ground path after a specific number of revolutions. The paper introduces two approaches for arranging these satellites: the quasi-symmetric method and the Binary Integer Linear Programming (BILP) method. The BILP method optimizes satellite positioning to minimize the total number of satellites while maintaining the required coverage.
Coverage Analysis:
Ensuring continuous coverage across a region or the entire globe is a core requirement for communication constellations. This paper uses Voronoi tessellation, a geometric method that divides regions into polygons to analyze coverage by calculating the maximum distance between adjacent satellites. These polygons represent regions of satellite coverage, ensuring that every point in the area of interest remains covered.
In cases where fewer satellites are used, the bounded Voronoi diagram focuses on regional coverage by limiting the diagram to the area of interest. For example, simulations designed to cover specific regions like Seoul (with a radius of 100 km) show how bounded diagrams can guide satellite placement to achieve continuous coverage without redundancy.
Inter-Satellite Link Continuity:
Besides coverage, the paper also delves into the continuity of inter-satellite links (ISL), which ensure that communication between satellites remains stable despite orbital motion and the Earth’s rotation. By analyzing relative motion between satellites in adjacent orbital planes, the authors calculate minimum and maximum distances to ensure that ISLs remain connected.
Simulations of Walker-Delta and CGT constellations reveal key insights. While the Walker-Delta design uses more satellites, it offers more consistent ISL performance due to shorter and more predictable relative motion ranges. In contrast, the BILP-optimized CGT constellation requires fewer satellites, but the ISL distances vary more, presenting challenges for maintaining consistent links.
Simulation Results:
Simulations conducted in this study explore the performance of Walker-Delta and CGT constellations across various parameters. For instance, the Walker-Delta constellation, with an inclination of 42 degrees, requires 40 satellites to maintain continuous coverage over the Seoul area. The BILP-optimized CGT constellation, on the other hand, achieves similar coverage with just 31 satellites, albeit with more variation in ISL continuity.
By comparing the relative motion and link continuity between these designs, the study concludes that Walker-Delta constellations, although requiring more satellites, provide superior ISL stability, making them ideal for applications that prioritize link reliability. The BILP method, however, offers a more cost-effective solution by minimizing the number of satellites, though it comes with trade-offs in ISL continuity.
Conclusion:
The study presents a comprehensive framework for designing satellite constellations that balance continuous coverage and ISL continuity. The Walker-Delta constellation is shown to be a robust solution for ensuring continuous communication, particularly when ISL stability is critical. On the other hand, the BILP-optimized CGT constellation demonstrates that fewer satellites can still provide effective coverage, though ISL variability must be managed. These findings offer valuable insights for future communication networks, such as those underpinning global broadband services.
Source:
Jeon, S., & Park, S.-Y. (2024). Communication Constellation Design of Minimum Number of Satellites with Continuous Coverage and Inter-Satellite Link. Preprint arXiv:2410.03354.