A satellite constellation for internet – what and why?

The SODaH project is aimed at the development of a key component for satellite constellations providing internet to remote places and citizens. But you might be wondering what a ‘satellite constellation’ is, or why we need it to provide internet when we have done quite well with cables so far. If that is the case, this page is the place for you to start.

What is a satellite constellation?

If you know the word ‘constellation’ in relation to space, you’re probably thinking of Orion or the Big Dipper (Ursa Major). In that sense, constellations are stars that together make up a pattern that we recognize as an animal or person. With satellites, there are some similarities.

A satellite constellation is a group of smaller, cheaper satellites that work together around Earth to provide a larger coverage than traditional bulky and expensive satellites.

What does a satellite constellation look like?

A satellite constellation may consist of a few hundred to a few thousand satellites that are (nearly) identical, and that orbit the earth at a low altitude and in such a way that they are evenly distributed over the planet. Because there are so many, one single satellite is always near a few others that it can communicate

with. And because they are in a low orbit, they allow for quick and cost-effective communication. These two aspects will help to understand why they are a great solution for telecommunications. We explain both of them below, starting with the advantages of many satellites.

A satellite constellation around the earth

As a rough representation, a satellite constellation looks like this (satellites not to scale; the orange lines represent the paths of the satellites and the communication between them)

Why a satellite constellation for internet?

Most people in Europe have fast internet that comes through a cable – copper or fiber. These cables, especially fiber, deliver internet in great quantities. But most of these people also live in cities – places where the costs of laying cable can be spread out over a lot of households. But what about the rural communities? The length of cable necessary to reach them is longer, and the costs have to be divided between a smaller number of houses.This is not feasible.

The European Union wants to provide fast internet to all of its citizens, and it turns out that satellites are a great way to do that.

Satellite constellations are the ideal system to provide internet connectivity in undeserved or under deserved areas, which are often remote places where the cost of fiber deployment is very high, and even oceans.

Satellite constellations are a great addition to cables

Satellites roam the earth, and they don’t care about cities or rural areas: every piece of the earth gets the same coverage. The satellites in a constellation are near enough to each other so they can communicate and send data to one another. When you create them in such a way that they can send data to individual users on the ground as well, you create a ‘fiber in the sky:’ a user can send data to a satellite, the satellites pass it on to each other until it reaches the right place on the planet, and then it gets sent down again to the recipient. To see some examples of how that works, look at the image below.

SODaH satellite constellation

Why not use the large satellites?

Satellite internet services are not new. But traditionally they have been provided by large geostationary satellites: huge satellites the size of a bus, costing hundreds of millions of euros, and sitting at 36.000km altitude directly above the equator. Thanks to their fixed position with respect to Earth, these satellites require only fixed parabolic dishes on end-user homes. Only three satellites are necessary to cover the whole Earth – except the polar regions. One such satellite is able to provide up to 1 TeraBit/s of connectivity. However, due to the long distance (36 000 Km) they come with a quite long latency (0.5 s round trip).

The benefit of many small, low-hanging satellites

A constellation consists of small (max 500kg), cheap (max 1 million euro) satellites that have a relatively small throughput (~10 Gbit/s). But because there are hundreds and because they are at low altitudes (around 1000km instead of 36.000km for traditional big communication satellites) they provide a connectivity of several TeraBit/s while keeping a low latency (30ms).

The emergence of these constellation satellites, that, unlike geostationary ones, are moving very fast with respect to the Earth’s surface (~7 km/s), has also been enabled by the development of electronically manoeuvrable antennas that can compensate for the movement of the satellite over the end user.

Goal of the SODaH project

The SODaH project aims to demonstrate a key component that allows the satellites in a constellation to direct, send and receive all those data signals in an efficient, robust and cost-effective way. This will truly allow future satellite constellations to provide internet to every citizen in Europe, as well as improve the internet connections for ships and planes.

How does SODaH do this?

SODaH prepares next generation of constellation satellites plans to consolidate concepts of LEO broadband constellations using Optical Inter Satellite Links and RadioFrequency Up/Down links enabling an optical space data highway and demonstrate the feasibility of a “Software Defined Optical Highway”.

SODaH aims at developing and making a sufficiently mature concept of Photonic Modulation, Routing and Digitalization Unit that enable a smart and advanced used of an OISL interconnected satellites network.

Read all the SODaH objectives

Implications for the design of constellation satellites

In order to meet their low cost target and high performances needs, the architecture of small satellites in constellations relies on Commercial Off The Shelf (COTS) components. These are components that have not been designed or screened for dedicated space use.

The other side of the coin is that the components, and hence the satellites, degrade quicker due to radiation in space, and thus are less reliable and have limited lifetimes in orbit (typically 5 years). However, given the number of satellites, the failure of some of them does not impact the overall performances thanks to in-orbit spares.

About the development of the P_MRD demonstrator

Examples of constellations

A few satellites constellations are already under development:

  • OneWeb (900+ satellites planned, with 6 in orbit)
  • LEO SAT (108+ satellites planned)
  • SpaceX/Starlink (2 000 + satellites planned, with 60 in orbit)
  • Telesat (360+ Satellites planned, with 1 in orbit)
  • Amazon/Kuiper (3 200+ satellites planned)

For the most part, these satellites will be equipped with laser links in order to connect the satellites to create a network in the sky. Technologies and concepts developed in the frame of SODaH are aimed at supporting the development of future constellations of satellites combining all advantages of current constellation technologies all together.