How do thousands of satellites, orbiting around the Earth, communicate between each other and with the planet? Which algorithms and protocols allow these networks to transmit terabytes of data every second? In this essay I explore the innovative software architecture that drives satellite constellations and their role in transforming global connectivity.
The first artificial satellite, Sputnik 1, was launched on October 4, 1957. It was very simple: a small aluminum sphere with four antennas. Its launch marked the beginning of the space age and let us comprehend the huge scientific, military, and civil capabilities offered by artificial satellites.
According to UNOOSA records, there were 8,261 satellites orbiting the Earth in January 2022, of which only 4,852 were active (as of the end of December 2021). This was confirmed by the Union of Concerned Scientists (UCS), which maintains the record of operational satellites.
| Number of satellites | Purpose |
|---|---|
| 3,135 | Communication |
| 1,030 | Earth observation |
| 385 | Technology development |
| 154 | Navigation |
| 22 | Earth science |
| 18 | Other purposes |
The adoption of satellite constellations for internet data transmission represents a major technological innovation that could help overcome the limitations of terrestrial infrastructures. Thanks to their position in orbit, satellites can ensure global coverage, reaching geographical areas that would otherwise be inaccessible. This approach uses advanced software communication systems to improve network resilience and to manage data traffic on a planetary scale, making it a scientifically valid solution for reliable and scalable connectivity.
But how does it actually work?
The satellites of constellations for low-latency global broadband internet access are positioned in low Earth orbit (LEO), working in harmony with terrestrial transceivers.
Low Earth orbit, as the name suggests, is relatively close to the Earth, usually at less than 1,000 km of altitude but potentially lower. LEO satellites don't always have to follow a specific path around the Earth, and their plane can be tilted, which means there are more viable routes for them.
However, individual LEO satellites are less useful for tasks like communication because they move too fast to be tracked from ground stations. For this reason, LEO satellites often work as part of a large constellation, covering large areas of the Earth simultaneously by working together.
Starlink by SpaceX is the most well-known constellation for internet communication. As of November 2024, SpaceX had launched almost 6,770 satellites; it had permission to launch 12,000 and currently has 42,000 planned for the future.
Satellite positioning is crucial to ensure global coverage and maximize network efficiency:
Satellite constellation architecture isn't just a matter of placement, but a balance between physics, engineering, and software working together to ensure reliable, low-propagation-time, and scalable connectivity.
Internet satellite constellations represent an extraordinary evolution of communication infrastructures, made possible by a perfect integration between advanced hardware and new software.
The main component of these constellations' software is network management through dynamic routing and direct connections, called Inter-Satellite Links (ISLs), which reduce latency by implementing error-recovery algorithms. Communication protocols, optimized for satellite networks, also play a fundamental role. Overall, the management of continuous development and cybersecurity are of great importance too.
Routing is the main function of the network layer in a computer network. Satellite networks can be very complex because of the distance between nodes, their movement in orbit, and the varying conditions of the communication links — delay, bandwidth, and potential signal interference. It is therefore important to find the best path for data. Dynamic routing is a process where a router can forward data through a different route for a given destination, based on the current conditions of the communication circuits within a system.
Static vs. dynamic routing:
Dynamic routing in satellite constellations is essential to ensure efficient and reliable communication in networks with highly dynamic topologies. Unlike terrestrial networks, where nodes are generally stationary, LEO satellites move rapidly relative to the Earth's surface, requiring advanced data-path management. Modern constellations use ISLs to create a mesh network in space. These links allow satellites to communicate directly with each other, reducing dependency on ground stations and improving network delay and resilience. Dynamic routing uses these ISLs to route data through optimal paths, adapting in real time to changes in network topology due to satellite movement.
The routing algorithms of these networks need to consider various factors, including latency, available bandwidth, and link stability. Some approaches include:
LEO systems require specialized routing protocols to manage the dynamic and quickly changing network topology. Many satellite constellations have their own dynamic routing protocols, but they are proprietary and little information is available about them.
One example of a dynamic routing algorithm is distance vector: each router has a table containing the outgoing line to reach the destination and an estimated distance. Periodically, each router sends each neighbor a list of its estimated delays. Based on the neighbors' estimates, the router updates its routing table.
At the transport layer, transport protocols play a significant role in satellite constellations. The Transmission Control Protocol (TCP) is one of the most used protocols in terrestrial networks; however, in satellite networks it runs into some difficulties. The main critical points are:
To solve these problems, different versions of the traditional protocols have been developed over time, designed for this specific type of connection.
TCP-Peach — Designed for high-delay networks. It uses test packages called dummy packets to estimate the capacity of the network without penalizing transmission speed.
Split-TCP — Divides the connection into two sections: the first between the sender and an Earth station, the second between the Earth station and the receiver through the satellites. This reduces perceived latency and improves transmission efficiency.
INTCP (Information-centric TCP for Satellite Networks) — A truly innovative proposal: a transport-layer protocol specifically designed to address the unique challenges of satellite networks. It introduces a novel hop-by-hop transport layer design with several key features:
Performance evaluations using a simulated Starlink constellation over distances exceeding 1,000 km have demonstrated that INTCP significantly outperforms traditional TCP. In unicast scenarios, INTCP reduced one-way delay by 42%, decreased delay jitter by 53%, and increased throughput by 60%. In multicast scenarios, INTCP achieved more than six times the throughput of TCP.
How it works:
Communication between the Earth and satellites is fundamental for modern telecommunication networks, including the internet communication systems based on satellite constellations. This interaction involves different technological and operational aspects, such as the use of ground stations, radio or laser frequencies, beam-forming, and traffic management between terrestrial and satellite users.
Ground stations are essential infrastructures that establish and maintain satellite links. Equipped with satellite dishes, receivers, and transmitters, they are responsible for critical operations such as satellite tracking, communications management, and data processing.
Satellite constellations represent one of the most promising innovations for the future of global communications. The expansion of LEO constellations and the progressive evolution of technologies are opening new possibilities to provide high-speed internet connectivity in remote and developing areas, reducing the digital divide and improving network resilience. With these advancements, the ability to ensure efficient, reliable, and scalable communication across vast distances becomes increasingly achievable.
Looking to the future, the expansion of satellite constellations could radically transform global communications. Space communications could become an essential part of the internet's global infrastructure, driven by an increasing density of orbiting satellites, the introduction of new technologies such as AI for dynamic network management, and improvements in routing techniques.
Furthermore, the adoption of hybrid networks — combining satellites with other communication technologies such as 5G — could facilitate the transition to a truly global connectivity system, capable of supporting an increasing number of IoT devices and data-intensive applications.
In this context, the progressive innovation and improvement of transport protocols and other technologies, together with the increasing processing capacity on satellites, will pave the way for a future where the internet is accessible and reliable everywhere, accelerating economic and social development on a global scale.