WRS-22: Regulation of satellites in Earth’s orbit

By ITU News

The vast networks that enable so much of modern life depend on an ever-expanding constellation of space services. These rely on radio-frequency spectrum and satellite orbits – limited natural resources which are increasingly in demand as radiocommunication services expand worldwide.

The Radio Regulations treaty maintained by the International Telecommunication Union (ITU) ensures reliable satellite operation and, hence, space services in two key ways: firstly, by allocating radio frequencies to those services; and secondly, by coordinating the orbital positioning of different satellites. Article 5 of the treaty distributes radiofrequencies to space services.

“We also indicate the transmission direction of the allocated service – if it’s space-to-Earth or Earth-to-space, or even sometimes space-to-space,” adds Alexandre Vallet, Chief of the Space Services Department in ITU’s Radiocommunication Bureau.

“A satellite is a repeater in orbit, and it cannot repeat on the same frequency band that it receives on from Earth. Otherwise, the satellite will interfere with itself.”

Both radio spectrum and orbits around the Earth amount to finite resources, necessitating international cooperation among governments, globally recognized regulation, and structured coordination among radio and satellite operators worldwide.

As the number and size of satellite constellations keep growing to meet mushrooming demand, the “space in space” -needs to be well managed to ensure sustainability. 

Satellites are classified into four broad types, based on their orbital characteristics:

• Low Earth orbit (LEO), between 200 and 2,000 kilometres above the Earth’s surface
• Medium Earth orbit (MEO), located mainly between 8,000 and 20,000 kilometres above the Earth’s surface
• Geostationary Earth (or geosynchronous equatorial) orbit (GEO), also known as the Clarke Orbit, fixed at 35,786 kilometres above the equator
• Highly elliptical orbit (HEO), which might reach 40,000 kilometres from Earth in apogee, or at the farthest point of the orbit

To guarantee  operability without harmful interference, ITU allocates frequencies, and positions (for GEO satellites) or orbital characteristics (for non-geostationary satellites) for every radio transmitting and/or receiving satellite in each orbital category, recording all these allocations in the Master International Frequency Register (MIFR).

Coordination, when required, amongst satellite operators and centralized global registration helps optimize spectrum and orbital resource use by all nations and discourages the “warehousing” of frequencies that might be needed for other uses, Vallet added.

Coordination and notification to avoid interference

Mitsuhiro Sakamoto, Head of ITU’s Space Systems Coordination Division, describes the procedure for putting a satellite into orbit as “similar to joining a club – with four steps to get in.”

The four steps are:

• Publish planned use of satellite networks
• Guarantee alignment with Radio Regulations articles 5, 21, and 22
• Negotiate and reach coordination agreements, when required, with concerned administrations
• Record frequency assignments in MIFR

The first step, in which a national administration publishes the planned characteristics of a satellite project, is essential for coordination with others, if required. This is then checked against key Radio Regulations articles. If coordination is required, the concerned administrations – the one submitting the project and any others whose existing space services might be affected – then negotiate over the proposed spectrum use. Agreement must be reached before the new usage can be entered into the MIFR.

Another key regulatory procedure is notification, particularly for satellites not subject to coordination.

“The basic difference is that for satellites that don’t require coordination, you just submit advance publication information, or an API,” explained Chuen Chern Loo, Head of ITU’s Space Publication and Registration Division.

Article 5 of the Radio Regulations – the Table of Frequency Allocations – will indicate whether a frequency band is subject to coordination or can be claimed via API. Once the API is submitted, other administrations can comment formally on the intended band usage.

The proposed satellite system must be in orbit and put to its designated use within seven years of API issuance.

An orbit unto itself

The geostationary Earth orbit, or GEO, is exactly 35,786 kilometres above the equator. Satellites positioned in this orbit travel around the globe at the same speed that the Earth rotates – approximately 1,669.8 kilometres per hour.

Worldwide communication via a satellite in a fixed, geostationary orbit was first envisioned by science-fiction author Arthur C. Clarke – giving rise to GEO’s “Clarke Orbit” or “Clarke Belt” nickname. 

Each GEO satellite always stays in the same position – fixed in the sky – when viewed from Earth. This means you can connect to one of these satellites by pointing an antenna at it, without any need for additional infrastructure to stay connected to it.

For the everyday users around the world, GEO satellites provide the least costly and most accessible services.

The Radio Regulations sometimes prioritize GEO over non-GEO satellites. Limits placed on equivalent-power flux density (EPFD) for non-GEO satellites, for example, protect GEO satellites from harmful interference, explained Alexandre Vallet.

Plans for future resource management

As demand for frequency and orbital resources keeps growing, international coordination must keep pace and streamline its services/processes. To facilitate the necessary discussion, ITU has outlined expected needs, and possible allocations, for broadcasting satellite service (BSS) and fixed satellite service (FSS) uses.

Space plans reserve certain capacity for future uses to each ITU Member State, ensuring that the global regulatory framework for managing radio spectrum and associated orbits continues to guarantee equitable access.

These so-called space plans define frequency and orbital resource usage, along with other parameters, how newcomers should request entry, and provisions for primary use, modification, and additional uses.

Jian Wang, Head of ITU’s Space Notification and Plans Division, suggests we should “think of space plans like a parking plan for an apartment complex, with assigned spaces and rules.”

Mapping out those spaces in space helps to anticipate and mitigate future challenges, such as competing demands for band usage by Earth stations on aircraft and other moving vessels. Future sustainability calls for space plans to be envisaged and discussed sooner rather than later.

When interference occurs

Despite the mechanisms in place to ensure compatibility between various radio systems, cases of harmful interference sometimes occur.

To better monitor them, the 2022 ITU Plenipotentiary Conference revised Resolution 186 which establishes an enhanced framework for international monitoring between the Radiocommunication Bureau, national administrations, and designated satellite monitoring facilities.

Read the Provisional Final Acts of the 2022 Plenipotentiary Conference (PP-22).

This special ITU News blog series features content from the 30th World Radiocommunication Seminar, including a closer look at the latest trends in broadcasting, international mobile technologies, maritime communications, space and terrestrial services, and more.

The series will conclude with a preview of the World Radiocommunication Conference (WRC-23), set to take place in Dubai from 20 November to 15 December 2023.

Image credit: ITU/D. Woldu