# What is satellite communication? GEO, LEO and IRIS² Satellite communication (SatCom) carries voice, data, internet and broadcast signals via satellites that relay them between user terminals and ground stations connected to terrestrial networks. It reaches places that cable and mobile networks do not cover, serves ships and aircraft, and can keep organisations connected when terrestrial networks fail, for example after a natural disaster. Satellite communication connects ships, aircraft, remote sites, sensors and emergency teams where terrestrial networks end. This page explains how a satellite link works, how the orbits differ, when satellite connectivity makes sense for a business, which European programmes exist and where the limits are. **Definition: Satellite communication (SatCom).** Satellite communication is the transmission of voice, data, internet and broadcast signals between terminals and ground stations via satellites in orbit. ## How satellite communication works ESA counts satellite communication among the oldest space applications, starting with the launches of Telstar in 1962 and Syncom in 1963 [1]. A link has three parts: - **The user terminal:** an antenna and a modem on a building, vehicle, ship, aircraft or sensor. - **The satellite:** it receives the signal from the ground (uplink) and sends it back down (downlink). - **The ground station:** it connects the satellite to terrestrial networks and the internet. Internet service providers, for example, link their servers to the core of the internet by satellite [1]. Mobile standards now include satellites. Release 17 of the 3GPP standards is the first with normative requirements for non-terrestrial networks, in which handheld or IoT devices communicate with a platform in the air or in space. Releases 18 and 19 extend this work [3]. Satellites use different radio frequency bands. Higher bands typically offer wider bandwidth but suffer more from rain fade, the absorption of signals by rain, snow or ice. The L-band gives reliable links at low data rates, used for satellite phones and maritime communication; the Ka-band carries high-throughput satellite internet [4]. The spectrum and orbit resources are coordinated internationally under the ITU Radio Regulations, while licences are issued by national administrations [2]. ## GEO, MEO and LEO satellites The orbit determines how many satellites a service needs and how long a signal travels. **Orbits used for satellite communication** | Altitude | How it looks from the ground | Typical use | | ------------------------- | ---------------------------- | ---------------------------------------------------------------------------------------------------- | | GEO (geostationary orbit) | 35,786 km above the equator | Appears fixed, so antennas can stay pointed at it; three satellites can cover almost the whole Earth | | MEO (medium Earth orbit) | Between LEO and GEO | Moves across the sky | | LEO (low Earth orbit) | Below 2,000 km | Circles the Earth in about 90 minutes, so continuous service needs many satellites | Altitudes and orbit periods as stated by ESA. Sources: ESA for the orbits [5], ITU for constellations of smaller satellites alongside geostationary systems [2], the European Commission for IRIS² [12] and Regulation (EU) 2023/588 for low-latency constellations [6]. Distance affects delay. A signal relayed by a geostationary satellite travels at least 71,500 km up and down, which at the speed of light takes about 0.24 seconds. A request and its reply cross that path twice, so they take almost half a second. Constellations in lower orbits can offer high-speed, low-latency connectivity [6]. The orbit is only one factor: the terminal, the capacity available in the area, the ground stations and the network behind them also affect the quality of a service. **Figure:** Altitudes as stated by ESA. The delay is computed from the GEO altitude at the speed of light. ## When satellite connectivity makes sense for a business Satellite connectivity for business pays off in a few clear situations. The ITU names the main ones [2]: - **No terrestrial network:** sites where cable or mobile networks are difficult, costly or impractical to deploy, such as remote facilities, rural areas and offshore operations. - **Mobility:** ships and aircraft, which connect via Earth stations in motion (ESIM). - **Resilience:** a second path when terrestrial networks fail. In large emergencies, when ground infrastructure collapses, secure satellite communication becomes essential [8]. - **Remote assets:** sensors and machines that report from the field. ESA names asset monitoring, machine-to-machine links and SCADA in energy, water, infrastructure and agriculture [7]. Where fibre or a mobile network is available, a terrestrial connection usually performs better. EU law states that satellite services cannot currently replace the performance of ground-based networks, but can help bridge the digital divide [6]. The use cases in our library that rely on satellite communication: ## Telecommunications For telecom operators, satellites complement terrestrial networks. Ka-band satellites can provide backhaul for 5G networks [4], and satellites extend broadband to remote and underserved communities [2]. With non-terrestrial networks in the 3GPP standards, IoT devices on NB-IoT and LTE-M can connect through a satellite as well [3]. Telecom networks also depend on satellite navigation. GNSS provides the common time and frequency that mobile base stations need, and satellite control stations and telecommunications gateways use it mainly for frequency control [9]. How GNSS timing works, and why its signals need protection, is explained on our page about [satellite navigation](https://leto.space/knowledge/gnss/). ## GOVSATCOM and IRIS² explained The EU has two programmes for secure satellite communication. **GOVSATCOM** is a component of the EU Space Programme: a satellite communication service under civil and governmental control that provides capacity and services to EU and Member State authorities managing security-critical missions and infrastructure [10]. EUSPA runs the GOVSATCOM Hub, a one-stop shop that operates 24/7 and connects governmental users with satellite communication resources [11]. Initial operations of the Hub started in January 2026, with governmental satellite services pooled by France, Greece, Italy, Luxembourg and Spain and available to all Member States [14]. How authorities use it in a crisis is described in our use case on [disaster management](https://leto.space/use-cases/disaster-rapid-mapping/). **IRIS²**, the Union Secure Connectivity Programme, was established by Regulation (EU) 2023/588. It builds a multi-orbital, secure connectivity system under civil control for governmental services, integrates GOVSATCOM and enables commercial services by the private sector [6]. According to the European Commission, IRIS² will use 348 satellites in low and medium Earth orbit, support sectors such as transport, energy and banking, and expand high-speed internet access in rural and underserved areas [12]. Under the implementation agreement signed in August 2026, 330 of these satellites will fly in low Earth orbit and 18 in medium Earth orbit, and the first launches are planned for 2029 [13]. EUSPA expects IRIS² services to become available from 2029 onwards [14]. ## Limits **Limits** - **Weather affects high frequencies:** The higher frequency bands that carry the most data are more susceptible to rain fade \[4]. A link that needs high availability must account for it. - **Capacity is finite:** EU law describes satellite communication as a finite resource, limited by capacity, frequency and geographical coverage \[6]. The data rate a terminal achieves can therefore depend on how many users share the capacity in its area. - **Coverage is not permission:** A satellite that covers an area does not mean a service may operate there. Licensing is the responsibility of national administrations \[2], so check that a service is licensed in each country where you use it. - **Distance adds delay:** Via a geostationary satellite, a signal needs about 0.24 seconds up and down, and a request with its reply almost half a second. Interactive applications notice this; constellations in lower orbits reduce it \[6]. ## Key terms - **Uplink and downlink:** the transmission from the ground to the satellite, and from the satellite to the ground. - **User terminal:** the antenna and modem on the user's side. - **Ground station (gateway):** the station that connects satellites to terrestrial networks. - **GEO, MEO, LEO:** geostationary, medium Earth and low Earth orbit. - **Constellation:** a group of satellites that together provide a service. - **Rain fade:** the weakening of radio signals by rain, snow or ice, stronger at higher frequencies. - **VSAT:** very small aperture terminal, a small dish used for data networks of companies and sites. - **High-throughput satellite (HTS):** a satellite designed for high data rates, used for satellite internet. - **Non-terrestrial network (NTN):** a mobile network in which devices connect via a platform in the air or in space. - **GOVSATCOM:** the EU Space Programme's satellite communication service for authorities with security-critical tasks. ## How we help We help organisations decide whether satellite connectivity fits a task, which availability, data rate and security it needs, and how to compare and procure services against those requirements. If you are new to the field, start with the definition of [space-enabled solutions](https://leto.space/knowledge/space-enabled-solutions/), which places satellite communication next to Earth observation, satellite navigation and AI. **Next steps** - [Our consulting](https://leto.space/consulting/): From the use case to requirements, provider selection and introduction. - [Satellite navigation](https://leto.space/knowledge/gnss/): How GNSS delivers position and time, and how accurate it is. - [Satellite IoT](https://leto.space/use-cases/satellite-iot/): How remote sensors send their readings via satellite. ## Frequently asked questions ### When is satellite connectivity worth it? When a site, vehicle or sensor is where terrestrial networks are difficult, costly or impractical to deploy, when ships and aircraft need a link, or when operations must continue if terrestrial networks fail [2]. Where fibre or mobile networks are available, they usually perform better: EU law notes that satellite services cannot currently replace the performance of ground-based networks [6]. ### What is the difference between GEO and LEO satellites? A geostationary (GEO) satellite orbits at 35,786 km above the equator and appears fixed in the sky, so a few satellites cover large parts of the Earth. Low Earth orbit (LEO) lies below 2,000 km; a satellite there circles the Earth in about 90 minutes [5], so continuous service needs a constellation of many satellites. Constellations closer to the Earth offer lower latency [6]. ### Is satellite communication secure? That depends on the service, not on the use of a satellite as such. For governmental users, the EU is building IRIS² for secure, encrypted communication [12], with protection against cyber and electromagnetic threats among its objectives [6]. For a commercial service, ask how the provider protects links and ground stations, and make it a requirement in the contract. ### What is IRIS²? IRIS² is the EU's secure connectivity programme, established by Regulation (EU) 2023/588. It builds a multi-orbital satellite system under civil control for governmental services and enables commercial services by the private sector [6]. According to the European Commission it will use 348 satellites in low and medium Earth orbit [12], with the first launches planned for 2029 [13]. ## Sources 1. [Satellite communications, European Space Agency (ESA), accessed 2026-10-08](https://www.esa.int/Applications/Connectivity_and_Secure_Communications/Satellite_communications) 2. [Satellite regulation and coordination (backgrounder), International Telecommunication Union (ITU), accessed 2026-10-06](https://www.itu.int/en/mediacentre/backgrounders/Pages/Regulation-of-Satellite-Systems.aspx) 3. [Non-Terrestrial Networks (NTN), 3rd Generation Partnership Project (3GPP), accessed 2026-10-06](https://www.3gpp.org/technologies/ntn-overview) 4. [Satellite frequency bands, European Space Agency (ESA), accessed 2026-10-06](https://www.esa.int/Applications/Connectivity_and_Secure_Communications/Satellite_frequency_bands) 5. [Types of orbits, European Space Agency (ESA), accessed 2026-10-06](https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits) 6. [Regulation (EU) 2023/588 of 15 March 2023 establishing the Union Secure Connectivity Programme for the period 2023-2027, European Union, EUR-Lex, 2023-03-15](https://eur-lex.europa.eu/eli/reg/2023/588/oj/eng) 7. [Satcoms for the Internet of Things, European Space Agency (ESA), Connectivity and Secure Communications, 2016-05-26](https://resilience.esa.int/archives/news/satcoms-internet-things) 8. [Using Space to Save Lives on Earth, EU Agency for the Space Programme (EUSPA), 2025-12-01](https://www.euspa.europa.eu/newsroom-events/news/using-space-save-lives-earth) 9. [EU Space Market Report 2026, Issue 1, EU Agency for the Space Programme (EUSPA), 2026-05-26](https://www.euspa.europa.eu/sites/default/files/documents/EU_Space_Market_Report_2026.pdf) 10. [Regulation (EU) 2021/696 of 28 April 2021 establishing the Union Space Programme and the European Union Agency for the Space Programme, European Union, EUR-Lex, 2021-05-12](https://eur-lex.europa.eu/eli/reg/2021/696/oj/eng) 11. [GOVSATCOM Hub, EU Agency for the Space Programme (EUSPA), accessed 2026-10-06](https://www.euspa.europa.eu/govsatcom-hub) 12. [IRIS²: secure connectivity, European Commission, DG DEFIS, accessed 2026-10-06](https://defence-industry-space.ec.europa.eu/eu-space/iris2-secure-connectivity_en) 13. [European Union is accelerating and reinforcing IRIS², European Commission, DG DEFIS, 2026-08-07](https://defence-industry-space.ec.europa.eu/european-union-accelerating-and-reinforcing-iris2-2026-08-07_en) 14. [Cyprus Completes First Operational Use of EU GOVSATCOM HUB Services, Marking a Milestone in European Secure Connectivity, EU Agency for the Space Programme (EUSPA), 2026-03-10](https://www.euspa.europa.eu/pressroom/press-releases/cyprus-completes-first-operational-use-eu-govsatcom-hub-services-marking) Page: