Today, the conditions under which radio astronomy is practised have changed more profoundly than at any time since the discipline began. Active services are expanding into nearly every accessible band of the radio-frequency spectrum.
Consequently, when the next World Radiocommunication Conference, WRC-27, convenes in Shanghai, China, from 18 October to 12 November 2027, it will reflect a moment when established frameworks are challenged by new realities.
This is because satellite operators are deploying constellations whose aggregate emissions can no longer be characterized by single-system assumptions.
Key instruments derived from single-system assumptions include the detrimental interference thresholds of Recommendation ITU-R RA.769, the per-system equivalent power flux density (epfd) thresholds and consultation procedure of Resolution 739 (Rev.WRC-19), and the footnotes to the Table of Frequency Allocations in Article 5 of the Radio Regulations that invoke them. WRC-27 agenda item 1.16 is the first to address aggregate interference from multiple non-geostationary orbit (non-GSO) systems explicitly.
Increasingly, these vital frameworks for spectrum and orbital coordination, developed over more than half a century, are being asked to do work for which they were not designed.
About this series of articles
This article and related radio astronomy posts take stock of where we stand, what is at stake at WRC-27, and what the radio astronomy community must contribute to the preparatory process if the science we practise is to remain viable in the decades ahead.
Together, these articles examine radio astronomy, the facilities and instruments that support it, the changing spectrum and space environment in which it operates, and the policy and regulatory challenges increasingly emerging.
The present overview, beyond introducing the series, focuses on the regulatory dimension through the work of the International Telecommunication Union (ITU) and specifically ITU’s Radiocommunication Sector (ITU-R). It examines recent measurement campaigns, ongoing studies in Working Party 7D – the expert group responsible for radio astronomy and related space science services – and related activities across other ITU-R study groups and working parties.
The aim is to give spectrum managers, regulators, satellite operators, fellow astronomers, and interested members of the broader telecommunications community a coherent picture of the regulatory landscape taking shape ahead of WRC-27.
A discipline under pressure
The challenges confronting radio astronomy in 2026 are not new in kind, but they are new in scale and in character.
Active satellites in low Earth orbit have increased roughly tenfold since WRC-19, from about 1,500 to more than 15,000, and two-thirds of them belong to a single constellation. Credible filings before ITU now point to a total exceeding 100,000 spacecraft in orbit within the operational lifetime of those being commissioned today.
The dominant interference paradigm has shifted from sparse, identifiable transmitters whose location can be predicted and avoided, to dense, time-varying ensembles of emitters distributed across the visible sky. Aggregate epfd has displaced single-entry interference as the figure of merit.
Our methodologies – including Recommendation ITU-R M.1583 (Interference calculations between non-geostationary mobile-satellite service or radionavigation-satellite service systems and radio astronomy telescope sites) and the epfd calculation tools that underpin it – must evolve to characterize unwanted emission scenarios that were not contemplated when those texts were drafted.
Growing intrusions on protected spectrum
Out-of-band (OOB) and spurious emissions, once a second-order concern, have become a first-order limit on observatory performance.
Recent multi-band measurement campaigns conducted at Australian facilities have shown that downlink signals expose radio astronomy receivers to unprecedented power levels. Such exposure requires significant investment for observatories to retain their usefulness.
In many instances, signals impinge on spectrum bands meant to be protected for radio astronomy. Often, they exceed RA.769 thresholds by many orders of magnitude, even when the offending transmitters are operating in nominal compliance with assigned spectrum masks.
Formerly exotic and rare incidents are becoming a considerable risk factor now. The radio astronomy service (RAS) allocations between 90 gigahertz (GHz) and 114 GHz are emerging as a particular concern as satellite operators look to higher frequencies for backhaul and feeder links.
Bistatic reflection geometry between satellite uplinks and observatory receivers is producing interference levels that, by calculations at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), would cause detrimental interference for facilities such as the Australia Telescope Compact Array and the Mopra Radio Telescope (both in New South Wales, Australia).
Ground- versus space-based interference
Ground-based radio frequency interference (RFI) remains an issue, but in a sense, it is the easier problem.
National regulators can declare radio-quiet zones or coordination zones, and negotiations with operators can yield good protection levels, taking topographic shielding and terrain clutter loss into account.
Spaceborne emitters answer to different regulators, based on a different set of incentives. The most important forum at which spectrum regulation for space can be reshaped is ITU’s World Radiocommunication Conference.
The scientific need for quiet
Meanwhile, the science itself has become more demanding. Applications such as very long baseline interferometry (VLBI), pulsar timing arrays, and the search for extraterrestrial technosignatures all rely on highly precise integration times, dynamic ranges, and bandwidth requirements that are vulnerable to spectrum contamination.
The science cases driving the Square Kilometre Array (SKA) project, the Next Generation Very Large Array (ngVLA), and the future of the Atacama Large Millimeter/submillimeter Array (ALMA) leave little margin for the levels of contamination now routinely observed.
Cosmological 21-centimetre line surveys, in particular, must follow the redshifted hydrogen line continuously from the 1420-megahertz (MHz) rest frequency down to tens of MHz. The observing band is set by the redshift under study, not by the Table of Frequency Allocations, so most of that range lies outside the bands protected for the radio astronomy service.
The mismatch between spectrum required by the science and the spectrum that the regulations protect has rarely been more acute.
What radio astronomy gives back
Radio astronomy has, almost incidentally, produced a disproportionate share of the foundational physics of the past sixty years. The cosmic microwave background was discovered – a finding that earned a Nobel Prize – with a horn antenna built for a balloon and satellite communications experiment.
Pulsars (rapidly rotating neutron stars) and the first observational evidence for gravitational waves from the binary pulsar PSR B1913+16 – both also Nobel Prize-winning discoveries – came from radio observations. The first direct evidence for planetary systems beyond the solar system came from a series of radio pulsar observations.
Black hole imaging at the Event Horizon Telescope, the cosmological distance ladder, the rotation curves that gave us dark matter, the structure of the interstellar medium, and what we know of the lifecycle of stars – all these rest on the ability to observe, in an interference-free environment, the frequencies nature has chosen to emit.
The technological return on investment has been similarly disproportionate. Wireless local area networking (WLAN) traces a direct genealogy to algorithms developed by a radio astronomy team that was working on a problem of black hole evaporation.
The hydrogen maser, VLBI, low-noise amplifier design, software-defined radio at extreme dynamic range, and the digital signal processing pipelines that underpin modern telecommunications have all been advanced by the operational demands of radio observatories.
Geodetic measurements – and the precise celestial and terrestrial reference frames needed for satellite navigation and orbit determination – are a vital product of VLBI, which combines widely distributed radio telescopes to capture a comprehensive Earth and space map. Radio spectrum also supports atmospheric science and climate monitoring through passive microwave observation.
The detection of fast, millisecond-duration radio bursts may yet illuminate fundamental physics. However, none of this happens without protected access to the spectrum.
These are not arguments for special pleading. They are reminders that the radio-quiet sky is infrastructure: shared, finite, and as essential to scientific civilization as the dark sky at optical wavelengths.
The case made in our work at ITU, and specifically at WRC-27, must be made on technical and regulatory grounds. But the underlying interests are far wider.
Perspectives on radio astronomy
Recent ITU news articles take the reader from the science itself, through the institutions and instruments that produce it, into the spectrum environment in which it operates, and finally to the global picture of how radio astronomy is developing across the world.
For starters, an article by Busang Sethole and Harvey Liszt sets out the historical and intellectual context: how radio astronomy emerged as a discipline, what it has contributed to the modern understanding of the universe, and why it matters as a form of fundamental research.
Radio astronomy: Rethinking spectrum for passive services
Three articles take up specific science cases.
Tiziana Venturi and Michael Lindqvist consider active galactic nuclei, supermassive black holes, and the role of VLBI, including the Event Horizon Telescope and the broader continuum-imaging programme that has reshaped our picture of the most extreme objects in the universe.
The unseen universe: Radio galaxies, black holes and synchronized telescopes
Vincenza Tornatore and Hayo Hase address geodetic VLBI, an applied use of the same technique that underpins the international terrestrial and celestial reference frames (ITRF and ICRF respectively) and, through it, satellite navigation, sea-level monitoring, and Earth-orientation measurement.
Geodetic radio astronomy: Key for monitoring Earth and space
In a third case, Neeraj Gupta and Bärbel Koribalski turn to galaxy evolution and the science of neutral hydrogen, the foundational tracer that has made it possible to map the gas content of the universe across cosmic time.
Galaxy evolution and neutral hydrogen
Further articles explore some of the most challenging and rapidly developing areas of contemporary radio astronomy.
Emma van der Wateren and Jack Burns consider the Epoch of Reionization and the Cosmic Dark Ages, along with proposals now advancing for radio astronomy from the lunar far side, where the absence of an ionosphere and the shielding of the Moon itself open observational windows that are simply unavailable from Earth.
Cosmology from the Moon in a radio-quiet environment
Another article, by Emma van der Wateren and Laura Spitler, examines pulsars and the rapidly expanding field of radio transients, from fast radio bursts to the long-term timing programmes that now constitute a gravitational wave detector in their own right.
Protecting the briefest flashes in the radio sky
A dedicated article from Boris Sorokin considers the search for extraterrestrial intelligence (SETI), whose technical and regulatory requirements overlap substantially with those of the rest of the discipline even as its scientific aims sit somewhat apart.
Are we alone? Listening for neighbours in an ever-noisier sky
Patrick A. Woudt and Anthony J. Beasley focus on observatories, examining the technological and institutional foundations of radio astronomy’s resurgence, from global telescope networks and major new facilities to the advances in computing, data processing and international collaboration that are opening new windows on the radio universe.
The new golden age of radio astronomy
Several articles turn directly to the spectrum environment.
Balthasar Indermuehle and Federico Di Vruno survey the satellite landscape, the emission characteristics of modern constellations, and the specific mechanisms by which they affect radio astronomy observations.
Three kinds of satellite signal, three challenges for radio astronomy
A companion piece from Balthasar Indermuehle and Ashley VanderLey examines how astronomers and satellite operators are developing practical approaches to coexistence, including coordination arrangements and operational data-sharing mechanisms that complement regulatory protections.
Protecting the quiet: How astronomers and satellite operators can share the sky
Further articles place radio astronomy within a broader societal and policy context.
Gyula I. G. Józsa and Boris Sorokin highlight the Dark and Quiet Skies initiative, situating the protection of radio astronomy within broader astronomical advocacy coordinated through the International Astronomical Union (IAU), including the published recommendations now being taken forward at the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS).
Protecting radio astronomy and our shared human heritage
Federico Di Vruno and Piero Benvenuti explore the wider relationship between satellite systems, astronomy and society, and the challenge of ensuring that scientific discovery and global connectivity continue to advance together.
Satellites, astronomy and society: Sharing space and the skies
Finally, two articles step back to consider wider implications for people on the ground.
Boris Sorokin and Masaaki Hiramatsu examine the direct technological spinoffs of radio astronomy, drawing on the IAU’s documented record of contributions from the discipline to society at large.
Radio astronomy’s quiet gifts to everyday life
Busang Sethole, meanwhile, considers the growth and impact of radio astronomy in Africa, including the role that major facilities, capacity-building efforts and infrastructure investment play in advancing both scientific research and broader technological development.
Evolving radio astronomy and its impact on Africa
Collectively, the series underlines the scientific opportunities, technical challenges and wider societal implications of radio astronomy.
The present overview article builds on those themes by more closely examining the regulatory dimension: the work of ITU-R Working Party 7D, the broader ITU-R study-group process, and the preparations under way for WRC-27, where key decisions affecting the future of radio astronomy spectrum access will be debated.
WRC-27 from the space science perspective
Nineteen substantive agenda items were adopted at WRC-23 for the WRC-27 cycle, and Working Party 7D has a direct interest in nearly all of them.
Two items, 1.16 and 1.18 (for its radio astronomy component), are within Working Party 7D’s responsibility. For the remaining items, the group contributes alongside other working parties, principally from ITU-R Study Groups 4, 5, and 7.
The full list of WRC-27 agenda items where Working Party 7D is engaged spans the spectrum from below one through to several hundred gigahertz. Agenda items 1.1 (FSS A-ESIM and M-ESIM operations in the 47.2–51.4 GHz range), 1.3 (FSS gateway operations in 51.4–52.4 GHz), and 1.6 (equitable access conditions in 37.5–51.4 GHz) all touch radio astronomy bands either directly or through adjacency.
Item 1.7 – on International Mobile Telecommunications (IMT) identification studies in 4400–4800 MHz, 7125–8400 MHz, and 14.8–15.35 GHz – is among the most consequential of the cycle for our service. This item brings the radio astronomy community into close engagement with Working Parties 5D (IMT systems) and 5C (fixed wireless systems).
Item 1.8 (radiolocation and other applications in 231.5–275 GHz, with possible identifications up to 700 GHz) carries implications for terahertz astronomy, 1.10 (Article 21 limits in 71–76 and 81–86 GHz) is situated adjacent to RAS bands at 76–81 and 86–92 GHz, and 1.11 (space-to-space links in mobile-satellite service [MSS] bands) concerns the protection of 1610.6–1613.8 MHz and 1660–1670 MHz, critical to spectroscopic observations.
Item 1.19 (Earth exploration-satellite service [EESS] passive allocations in 4200–4400 and 8400–8500 MHz) intersects with our concerns through shared sensitivity to unwanted emissions from active services.
Within this broad portfolio, five items deserve particular attention. They are the ones that will most directly determine the operating environment for radio astronomy before major new facilities come online in the 2030s.
Aggregate interference, radio quiet zones, and the protection of primary RAS allocations
Agenda item 1.16, prepared under Resolution 681 (WRC-23), puts a more explicit focus on radio astronomy than any previous WRC agenda.
Studies under this item follow three strands. The first considers interference from a single non-GSO system into the seven RAS bands listed in Resolution 681, all allocated on a primary basis globally. The second addresses the harder problem of aggregate interference from multiple non-GSO systems in those same bands. The third concerns two specific radio quiet zones.
The second strand requires methodologies that can characterize the cumulative impact of multiple non-GSO systems operating under separate regulatory regimes, often filed at different epochs, with substantially different orbital architectures and emission characteristics. The work calls for evolution of epfd-style metrics into the multi-system case, integration with epoch-of-emission considerations, and operational provisions that can be verified in practice.
Working Party 7D has been engaged on these methodologies for several meeting cycles, and the contribution of measurement efforts will be central to placing the studies on an empirical footing.
The third strand addresses, in parallel, the technical and regulatory provisions necessary to protect radio astronomy stations operating in two specific radio quiet zones from aggregate radio-frequency interference caused by non-GSO systems.
The radio quiet zones contemplated here are the host site for the SKA-Mid telescope in South Africa’s radio astronomy reserve and the site of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. These are sites of generational scientific significance, established at considerable expense to multiple nations, precisely because they offer the radio quietness that no urban or suburban environment ever could.
Recognizing them in the Radio Regulations would mark a significant evolution in how the international community treats spectrum-dependent scientific infrastructure.
Updating safeguards for radio astronomy above 76 GHz
Agenda item 1.18, prepared under Resolution 712 (WRC-23), addresses the protection of EESS (passive) and the radio astronomy service in certain frequency bands above 76 GHz from unwanted emissions of various active space services, including fixed-satellite, mobile-satellite, broadcasting-satellite and the radionavigation services. The agenda item has two principal objectives.
The first objective focuses on space-based sensors, including an update to Resolution 750 (Rev.WRC-19). The second focuses on the radio astronomy service to update Resolution 739 (Rev.WRC-19), which currently only covers bands up to 22 GHz.
Resolution 739 sets the unwanted-emission thresholds that space stations are asked to meet at in certain adjacent and nearby frequency bands of the radio astronomy service, backed by a consultation procedure when they cannot. As satellite operators move into the higher-frequency millimetre regime, it is important to recognize that many radio astronomy facilities around the world have been routinely operating in these bands for several decades. This update to Resolution 739 must be extended and brought up to date and has immediate consequences for the radio astronomy service.
The propagation models in Recommendations ITU-R P.452, P.619, and P.676 also need attention in this regime, and the joint work of Working Parties 7D and 3M on this front is among the more technically intricate parts of the cycle.
The agenda item also speaks to a structural feature of high-frequency astronomy: The bands of greatest scientific interest are determined by molecular spectroscopy, not by regulatory convenience. We cannot move our observations to less congested frequencies; the science is fixed by the laws of physics.
This makes the case for protective regulation in these bands particularly compelling, and the ITU-R studies underway in support of this regulatory update are accordingly substantive.
Coordinated mobile-satellite expansion
Three agenda items in the cycle concern proposed expansions of the mobile-satellite service, and together they represent the most significant new pressure on RAS bands below 3 GHz.
Agenda item 1.12, under Resolution 252 (WRC-23), considers possible new MSS allocations in 1427–1432 MHz (space-to-Earth), 1645.5–1646.5 MHz (bidirectional), 1880–1920 MHz (bidirectional), and 2010–2025 MHz (bidirectional), to support low-data-rate non-GSO mobile-satellite systems.
The first of these bands is immediately adjacent to the protected RAS allocation in 1400–1427 MHz, the most important radio astronomy band in existence by virtue of its protection of the neutral hydrogen 21-centimetre line.
The second is 13.5 MHz below the RAS allocation in 1660–1670 MHz, used for OH (hydroxyl molecule) spectroscopy.
The compatibility studies underway, and the eventual regulatory provisions that emerge from them, will determine whether the integrity of these foundational bands is preserved into the next decade.
Agenda item 1.13, under Resolution 253 (WRC-23), is in some respects the most challenging of the three. It addresses possible new MSS allocations to support direct connectivity between space stations and IMT user equipment, the so-called direct-to-cell (DTC) paradigm, also known as direct-to-device (DTD) in some parts of the world, across a wide range of frequency bands between 694/698 MHz and 2.7 GHz.
The fundamental concern from a radio astronomy perspective is the aggregate behaviour of mass-deployed satellite emitters serving handset-class user equipment in bands that include or border RAS allocations at 1400–1427 MHz, 1610.6–1613.8 MHz, 1660–1670 MHz, and 2655–2690 MHz.
The emission characteristics of such systems, in particular the spurious emissions such as harmonics of space-based transmitters operating at high density, and the cross-band aggregate effects all require careful study.
Agenda item 1.14, under Resolution 254 (WRC-23), considers further new MSS allocations in 2010–2025 MHz (Earth-to-space), 2160–2170 MHz (space-to-Earth) in Regions 1 and 3, and 2120–2160 MHz (space-to-Earth) in all regions.
The ITU Radio Regulations divide the world into three ITU regions for the purposes of managing the global radio spectrum.
While these bands are not adjacent to primary RAS allocations in the same manner as those under 1.12 and 1.13, the cumulative effect of new satellite deployments across the 2 GHz region must be considered alongside the other MSS items, and the impact on EESS (passive) operations in the 1400–1427 MHz band, through receiver saturation in wideband front-ends or terrestrial reflections for EESS, cannot be assumed to be negligible.
The three items must be considered together. Each on its own could suggest compatibility. But coordinated expansion of MSS into all these frequency bands – as can be inferred from the wider view – poses questions about the long-term viability of passive operations in adjacent and nearby bands. This is a challenge that the current studies will need to address explicitly.
The path to Shanghai
The path between now and WRC-27 is short, and the work to be done is considerable. The second session of the Conference Preparatory Meeting (CPM27-2) is upon us, and the regional preparatory groups: APT (Asia-Pacific), ATU (Africa), CEPT (Europe), CITEL (Americas), ASMG (Arab States), and RCC (CIS Region) will be finalizing their positions through the second half of 2026 and into 2027.
The radio astronomy community must engage at every level of this process, with technical contributions of high quality and with consistent representation across the responsible and contributing working parties.
The recent ITU news articles are offered in that spirit: as contributions to a conversation that will shape the conditions under which the science of the next generation will be done.
The decisions taken at WRC-27 will not be the last word. WRC-31 and the agenda items already taking shape for that cycle will return to many of the themes considered here, and to others that are only beginning to come into view. But WRC-27 is the conference at which the framework is set. Getting it right matters.
ITU holds the World Radiocommunication Conference (WRC) every three to four years to review, and, where necessary, revise the Radio Regulations, the international treaty governing the use of the radio-frequency spectrum and the geostationary-satellite and non-geostationary-satellite orbits.
Source: https://www.itu.int/hub/2026/09/radio-astronomy-at-the-regulatory-crossroads-wrc-27-and-beyond/
