About Constellations of Communication Satellites

Constellations refer to a network of multiple satellites working together to provide global coverage and enhance the capabilities of communication systems. Rather than relying on a single satellite, constellations distribute the workload among several satellites on different orbits. This arrangement offers several advantages, including improved coverage, reduced latency, increased capacity, and enhanced system reliability. At the same time, it is highly complex and therefore expensive. New technologies need to be developed to establish constellations for satellite communication (SATCOM).

Existing and upcoming non-geostationary orbits (NGSO) such as OneWeb, Starlink, Telesat Lightspeed, Amazon Kuiper, EU IRIS² constellations will likely increase substantially existing SATCOM supply over the next decades. Thus, it can be expected that NGSO systems will significantly impact the SATCOM environment through a wider variety in terminal types, additional types of SATCOM services, more sophisticated terminals (combining electronic and mechanical antenna/beam steering), and perhaps cheaper terminals when produced in larger quantities.

What are Purpose and Objectives of a Constellation?

Constellations aim to achieve global coverage by strategically distributing satellites in different orbits to ensure that signals can be transmitted and received from anywhere on Earth. By deploying multiple satellites, constellations increase the capacity and available bandwidth for communication services, allowing for higher data rates and supporting a larger number of simultaneous connections. With satellites positioned in closer proximity to Earth’s surface, constellations can significantly reduce signal latency compared to geostationary satellites, improving real-time communication and interactive applications. Constellations provide redundancy in case of satellite failures or disruptions. If one satellite experiences an issue, others in the constellation can compensate and maintain service continuity.

Besides the technical advancements through a communication constellation, a constellation increases the political power of the controlling nation or bloc by providing the infrastructure for information exchange. By owning the infrastructure and controlling the access to it through the regulation and provision of terminals, the access of user groups or countries can be allowed or denied, and the communication can be intercepted and eavesdropped by the controlling power.

Types of Constellations

Low Earth Orbit (LEO): LEO constellations are placed at altitudes ranging from a few hundred kilometers to around 2000 kilometers. They offer low latency and high data rates but require a larger number of satellites to achieve global coverage.

Medium Earth Orbit (MEO): MEO constellations operate at altitudes between 2000 and 36 000 kilometers. They strike a balance between coverage and latency, with a smaller number of satellites compared to LEO constellations.

Geostationary Orbit (GEO): GEO is the classical communication satellite orbit. Also in GEO, constellations can be positioned. GEO constellations consist of satellites positioned at an altitude of approximately 36 000 kilometers, directly above the equator. They provide continuous coverage over a specific region but exhibit higher latency due to the distance between the satellite and Earth.

Advantages and Disadvantages of Constellations

Satellite communication (SATCOM) constellations offer several advantages, but come also with some disadvantages.

Advantages of SATCOM Constellations:

Global Coverage: Constellations provide global coverage, ensuring that communication services are accessible from anywhere on the planet. This is especially beneficial for remote and underserved regions that lack traditional terrestrial infrastructure.

Redundancy and Reliability: With multiple satellites in a constellation, if one satellite experiences a malfunction or failure, others can quickly take over its functions. This redundancy enhances the overall reliability of the system and minimizes service disruptions.

Increased Capacity: Constellations distribute the communication load across multiple satellites, allowing for a higher number of users and increased capacity. This helps meet the growing demand for data-intensive applications such as video streaming and broadband internet services.

Reduced Latency: In particular, Low Earth Orbit (LEO) constellations offer lower latency compared to traditional geostationary satellites. The shorter distance between the satellites and ground stations reduces signal travel time, making real-time applications, such as video conferencing or telemedicine, more responsive.

Flexibility and Scalability: Constellations offer flexibility and scalability, allowing for the addition of more satellites to accommodate increasing user demands or to expand coverage to new areas. This adaptability ensures that the system can evolve and grow with technological advancements and changing user requirements.

Disadvantages of SATCOM Constellations:

Complexity and Cost: Establishing and maintaining a constellation of satellites is complex and expensive. It requires significant investments in satellite development, deployment, ground infrastructure, and ongoing maintenance. The cost of manufacturing and launching numerous satellites can be substantial.

Signal Handover: In LEO constellations, as satellites move rapidly across the sky, there is a need for seamless handover of signals from one satellite to another as users move across coverage footprints. Ensuring uninterrupted connectivity during these handovers can be technically challenging.

Ground Infrastructure: Satcom constellations require a robust ground infrastructure to support the communication network. This includes the construction and maintenance of ground stations, user terminals, and network management systems. Developing this infrastructure adds to the overall cost and complexity.

Regulatory and Spectrum Challenges: The deployment of SATCOM constellations requires regulatory approvals and coordination to ensure that spectrum resources are allocated appropriately. Securing the necessary frequencies and obtaining licenses can be a complex process, involving coordination with national and international regulatory bodies, such as the International Telecommunication Union (ITU).

Orbital Debris: With the increase in the number of satellites deployed in constellations, there is a concern regarding space debris. Satellites reaching their end-of-life or experiencing malfunctions must be properly deorbited or removed from operational orbits to avoid contributing to the growing issue of space debris.

Which new technologies are necessary?

Standardisation and mass production of spacecraft: Due to the high number of necessary satellites, they cannot be produced anymore as unique and handmade complex machines, but need to be as simple, cost-efficient, and standardised as possible to produce them in masses.

Cost-efficient mass launch systems: To enable the launch of huge numbers of satellites, the launchers need to be cheap and able to carry several satellites at once. Reusability of the launcher is one approach to decrease the launch costs.

Inter-Satellite Links (ISLs): ISLs enable communication between satellites within a constellation. Satellites equipped with inter-satellite links can relay data between each other, forming a network that allows for seamless communication across different satellites and orbits. To enable high data throughput, higher frequencies can be utilised with less degradation than for the space to earth link. The components for high frequencies such as Q/V/W-band or optical communication need to be further developed to enable their application for ISL.

Electronically steered Antennas: The satellites of a constellation ae moving from the SATCOM user’s perspective. Therefore, the antennas of the user terminal and the ground station need to track the satellite in line of sight and be able to seamlessly switch to the next satellite once in sight.  

Constellation management and Space Traffic management: Implementing the regulatory and licensing aspects of a communication constellation, the spacecrafts need to be managed in their positioning, spectrum utilisation and interaction throughout their lifetime, with the goal to avoid the creation of space debris and collision with other spacecrafts.

Notable Constellations

Iridium: The Iridium constellation, operational since 1998, consists of 66 cross-linked LEO satellites that provide satellite phone and data services globally.

Starlink: Operated by SpaceX, Starlink is a mega-constellation of LEO satellites designed to provide global broadband internet services. It aims to offer high-speed internet access to underserved and remote regions worldwide.

OneWeb: OneWeb is another LEO constellation aimed at providing global internet connectivity, developed by OneWeb Satellites, a joint venture between OneWeb and Airbus.

O3b mPOWER is SES’s 2nd generation of its O3b constellation. It aims to enhance drastically the capacity of the system, be “Cloud-Ready” and be compatible with 4G and 5G backhauling demand. It is to be integrated into SES’s large multi-orbital network of already more than 50 GEO satellites in orbit.

Kuiper of Amazon signed a launch contract with ULA (United Launch Alliance) for five launches onboard Atlas 5 vehicles for its constellation named Kuiper, to be operational by 2026.

Telesat Lightspeed plans a global network composed of 188 Low Earth Orbit (LEO) satellites, seamlessly integrated with ground data networks.

A set of additional constellations have been announced and appear to be at different developmental stages in, for example, the U.S. (AST SpaceMobile, Boeing, Viasat LEO, Curvanet, Mangata Networks), UK (Laserlight), China (CASIC (China Aerospace Science and Industry Corporation) Hongyun & Hongyan) and Korea (Hanwha).