Insight | A straightforward introduction to satellite communications


A straightforward introduction to satellite communications


With over three thousand communication satellites in multiple orbits today, satellite communications are relied upon by millions of people around the world to deliver cellular, radio, television, broadband and military applications.

Satellite communication is the transfer of information using artificial satellites that have been launched into Earth's orbit, transmitting and relaying information from one place to another on a global scale.

Before we get into how satellite communications work, it is important to understand the role of a satellite company and the applications for satellite communications.

Satellite companies, like Inmarsat, facilitate the infrastructure, technology and solutions for governments, organisations, industries and ultimately individuals to relay information via satellite communication.

Why do we need satellite communications?

Satellite communications have opened access to voice and data communication services across the globe in places where terrestrial cellular and broadband connectivity is not available or network coverage is patchy, thus making terrestrial communications more resilient– such as across the world’s oceans, flying at 35,000 feet or remote places on land. 

Satellite communication services are used every day, for example: 

  • Telecommunications
  • TV and radio broadcasting
  • High speed Wi-Fi and mobile broadband
  • Navigation and GPS (Global Positioning System)

With new advancements in technology, satellite communications are leading the way to a more connected world with endless possibilities, such as UAVs (Uncrewed Aerial Vehicles), autonomous transport, crop monitoring and sustainability efforts.


How do satellite communications work?

Satellite communications use a combination of orbiting satellites above the Earth and ground stations to transmit and relay information using microwaves from one point on Earth to another.

There are three stages in the process:

  • Uplink
  • Transponder
  • Downlink

Take Live Television for example. A broadcaster will send out (or transmit) a signal to a designated satellite via it's user terminal. This is referred to as an “uplink.”

Once received by the orbiting satellite, onboard amplifiers boost the signal strength and change the frequency of the signal before it is relayed back to a designated Earth station(s) on the ground. This is also referred as the “transponder” stage.

Finally, these transmitters send out one or multiple signals to ground station(s) across the globe back on Earth. This is referred as the “downlink.” 


Diagram of a one way communication satellite network consisting of three stages: uplink, transponder and downlink..

Two-way satellite communications

Two way communication satellite network displaying information relayed between the same ground stations via the same satellite.

Two-way communication satellite networks provide point-to-point connectivity, meaning information can be transferred to and from the same ground stations via the same satellite.

The development of two-way satellite communication has opened possibilities of accessing the internet where traditional fibre cables cannot reach, such as inflight Wi-Fi, offshore platforms, and remote areas such as on the summit of Mount Everest or in the middle of the Sahara Desert.


Ground stations back on Earth

To complete the satellite network, all satellite communications are sent and received via satellite access stations (SAS), through either flat panels (electronic steered arrays) or a dishes (circular reflectors). This is where information is processed and delivered to its destination.

Ground stations tend to be in fixed points on the planet, however in recent years, technological innovations for Earth stations have optimised signal strengths and the capacity of data that can be transferred. Making it easier to receive and transmit a signal whilst moving, such as inflight Wi-Fi, 5G networks, satellite news gathering and other mobility applications.

For example, as Inmarsat launches additional satellites of unprecedented power and agility to meet future demand for global mobile connectivity, our ground network of satellite access stations is being expanded to keep pace. Discover more about our ground network programme.

Are there distinct types of satellites?

Yes, there are many types of satellites, serving different purposes for different organisations.

The application or purpose of any given communication satellite will determine several factors; from onboard technology and equipment to orbital paths. And whilst some satellites travel in sync with the Earth’s rotation (geosynchronous orbit), others orbit much faster and closer to Earth.

Based on the orbit, communication satellites fall into one of four categories:

  1. Geostationary Earth orbit (GEO)
  2. Medium Earth orbit (MEO)
  3. Low Earth orbit (LEO)
  4. Highly elliptical orbit (HEO)


The 4 different satellite orbit paths. LEO, MEO, GEO & HEO. All providing coverage to different areas of the earth for various applications.

These different orbits maximise the coverage and signal strength required for the given application. 

Let us look at each type of orbit and the applications that are best suited for each type:


Geostationary Earth orbit (GEO) 

If you ever saw a geostationary satellite, it will appear to be still. This is because they revolve around the Earth at the same speed as Earth's orbit. They are also the furthest away from Earth.

Satellites networks such as Inmarsat’s ORCHESTRA,  ELERA (L-band) and Global Xpress (Ka-band) networks, intend to serve communication markets where big data is needed for advancements in technology.

This is the orbit that Inmarsat currently operates in. To date, we own and operate 16 satellites in geostationary orbit at 35,786 kilometres (22,236 miles) above the Earth.

GEO satellites are extremely efficient due to their large coverage area and their ability to focus capacity where and when needed with no wasted capacity over areas that have no or little demand. Therefore, fewer ground stations are required, compared to LEO satellites, for example. This is ideal for mobile satellite communications services where seamless and reliable connectivity is paramount – such as maritime and aviation safety services or governments. Additional examples of use-cases for GEO satellites include:


Medium Earth orbit (MEO)

MEO satellites orbit somewhere between 2,000 and 35,786 kilometres (1,243 and 22,236 miles) above the Earth's surface with an orbital cycle of two to eight hours. 

Traditionally used for Global Positioning System (GPS) and other navigation applications, MEO constellations deliver low-latency, high-bandwidth connectivity to service providers, government agencies and commercial enterprises, providing new internet options to remote areas were laying fibre is not an option. 

The benefit of MEO satellites compared to GEO and LEO satellites is that you do not need many satellites, unlike LEO, and they offer reduced latency compared to GEO.


Low Earth orbit (LEO)

Compared to GEO satellites, LEO satellites are much smaller and orbit much closer to Earth, ranging from around 160 to 2,000 kilometres (99 to 1,243 miles) with an orbit time of about 90 minutes. Unlike GEO orbit, where you only need three satellites for global coverage, LEO orbit requires a much larger constellation of satellites.

At a much lower altitude compared to other orbit paths, LEO satellites benefit from a smaller field of vision and low latency to accurately relay higher levels of data, with much stronger signal strengths at greater speeds. Because of this, they can be used for several applications such as: 

  • Industrial IoT (Internet of Things)
  • Maritime and tourism
  • Government and tactical networks
  • Emergency response and aid 
  • Telecommunications and mobile 5G broadband

However, this comes at a cost; LEO satellites have a lifespan of approximately  five to seven years compared to GEO satellites that can last 15+ years in orbit. In general, it takes two to three years to deploy a full LEO constellation which in another two to three years, will need to be replaced, exacerbating the growing concerns around space debris and space sustainability.


Highly elliptical orbit (HEO)

A highly elliptical orbit (HEO) satellite orbits the Earth on an elliptical path with an altitude that varies from about 1,000 to 42,000 km above the Earth’s surface.

This enormous range in altitude is due to a highly elliptical orbit path that travels in an oval shape.

A key feature of HEO is that these satellites move much faster when it is close to the Earth than when it is farther away. This is because when the satellite is in perigee (the point of orbit closest to the Earth), the gravitational pull from the Earth is high compared to when the satellite is in apogee (the point farthest from the Earth).  

To provide seamless connectivity, it requires two satellites in HEO orbit. As a result of this, when in the apogee, over the North Pole, satellites in HEO can provide better coverage, as it is visible for a longer period.

Inmarsat has two Global Xpress satellite payloads, GX10A and 10B, scheduled to launch into HEO orbit in 2023. When in service they will be the world’s first and only mobile broadband payloads dedicated to the Arctic region above 60N, and will support industries such as aviation, maritime and government.


Differing altitudes have a profound impact on how satellites operate and the different applications they can unlock. Discover more about orbits in our Space explained: How do satellite orbits work?

Frequency bands, beams, and power

Communication satellites use multiple frequencies bands, just like a radio, to transmit information. Although there are multiple frequency bands, the most common frequencies used in satellite communications are L-band, C-band, S-band,  and Ka-band.

There are considerations between the size of the geographic area in which signals can be transmitted or received and the amount of power that can be used to send or receive the signal. 

Modern satellites support a variety of” beam” types to allow the satellite to focus its power at various levels to locations. 


Chart of the Radio Frequency spectrum (RF) displaying the different frequency bands and relevant applications used within satellite communication networks


L-band frequencies operate at 1-2 GHz range on the electromagnetic spectrum and are used for many radars and GPS services. With a low bandwidth and low frequency range, L-band is not suitable for streaming applications like video, voice, and high-speed broadband connectivity. But is perfect for applications such as fleet management, asset tracking, Internet of Things (IoT) and maritime and aviation safety services.

Inmarsat operates its 99.9% reliable voice and data ELERA network in L-band which provides our critical Global Maritime Distress Safety System (GMDSS) Fleet Safety service and International Civil Aviation Organization (ICAO)-approved Swift Broadband Safety service.


S-band frequencies operate at 2-4 GHz and are used for satellite communication and radar. S-band is of key importance to the shipping, aviation, and space industries. 

Inmarsat launched its S-band satellite, S EAN (European Aviation Network) in June 2017 for the European Aviation Network. It was the first dedicated aviation connectivity solution to combine satellite and terrestrial networks by integrating space-based and ground-based networks to deliver a seamless Wi-Fi experience for airline passengers throughout Europe.


C-band operates in the 4-8 GHz range of the electromagnetic spectrum. 

With antennas reaching 1.8 metres – 2.4 metres long, C-band satellites relay a direct, end-to-end signal, primarily used for satellite communications, full-time satellite TV networks and raw satellite feeds, which are useful in areas impacted by heavy rain to extreme climate related weather.


Ka-band measures at 27-40 GHz on the electromagnetic spectrum and primarily offers satellite internet that requires high data transfers.

This higher power frequency supports applications that need a higher bandwidth, such as video conferencing, live streaming, high-speed internet for services such as inflight Wi-Fi, and multi-media applications. This frequency also makes it easier to offer satellite internet in residential and remote regions on the planet. 

Inmarsat’s operates its award-winning high-speed broadband Global Xpress network in Ka-band.


Communication satellites vary in size depending on their orbit cycle and application.

Some satellites can be 7 metres long with solar panels that extend another 50 metres. For comparison, Inmarsat's I-6 F2 satellite is 7.5m with a wingspan of 47m, compared to the International Space Station which is 108.8 metres - as large as a rugby field.

With its highest point at 375,000 km from Earth's surface, Transiting Exoplanet Survey Satellite (TESS) is the highest orbiting satellite with a full orbit time of roughly 328 hours. 

For comparison, Inmarsat's furthest satellite orbits roughly 35,786km (22,236 miles) above the Earth's surface with a geostationary orbit time of 24 hours.

Based on reliability and speed, satellite internet is slower with average downloads speed of 15-30Mbps compared to fibre connections with 50Mbps-1Gbps.

The advantage of satellite internet is that a connection can be established in areas where fibre cables cannot reach such as inflight Wi-Fi, offshore platforms, and remote areas on the planet.

There are a few disadvantages to satellite communication networks such as cost to manufacture and launch, maintenance, signal delay and signal interference.

In some cases, excessive costs are incurred through investment manufacture and deployment; however, the application and technology onboard can outweigh these costs overall.

Signal latency is rare but can occur where a signal may take a few milliseconds longer to be received.

As with any connection, interference can occur. This is usually caused by sunspots, jamming and unusually high electro-magnetic interference.