Protecting the quiet: How astronomers and satellite operators can share the sky

By Balthasar Indermuehle, Principal Scientist and Spectrum Manager, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia, and Chair, ITU-R Working Party 7D, and Ashley VanderLey, Senior Advisor, U.S. National Science Foundation (NSF), Office of International Science and Engineering, United States, and Vice-Chair, ITU-R Working Party 7D

Radio astronomy reveals a universe whose brightest sources are dimmer than a mobile phone on the Moon. Signals from distant galaxies, exploding stars, and the cold gas between them reach our telescopes quadrillions of times weaker than the emissions from other sources, including satellites passing overhead.

For most of the last century, the use of remote observatory sites and protected radio quiet zones gave astronomers the silence they needed to hear those whispers. Today, what is happening overhead is changing fast.

Over 15,000 active satellites now orbit the Earth, and filings for millions of new satellites at the International Telecommunication Union (ITU) suggest the figure could grow significantly over the coming decades.

A new challenge

The challenge is not simply that satellites are louder than the whispers astronomers want to hear. It is that with the growth of non-geosynchronous, non-geostationary orbit (NGSO) satellites in low Earth orbit, they are everywhere.

Placing radio astronomy stations in remote locations or establishing national quiet zones with coordination requirements for ground-based transmitters, may not alone provide sufficient protection against signals beaming down from above.

The new NGSO satellites include direct-to-cell transmissions designed to reach commercial mobile phones and provide complementary Internet connections from satellites. Additionally, electromagnetic radiation emanating from onboard electronics may present challenges to radio astronomy operations as the number of satellites in orbit grow.

The post-2030 radio environment may be fundamentally different from anything astronomers have previously experienced. However, there is reason for optimism as astronomers and satellite operators have been working together, developing mitigation techniques that leverage the use of technologies and measures such as phased arrays, steerable beams and real-time coordination.

Information sharing is fundamental to coexistence and can lead to technical solutions not yet imagined.

The Australian response: Prevention, monitoring, mitigation

At Australia’s national science agency, CSIRO, our response rests on three pillars:

Prevention begins with regulation. We work with the Australian Communications and Media Authority, and internationally through ITU, to develop emission limits and coordination procedures that recognize the needs of passive science. Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory, hosts the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and the low-frequency component of the Square Kilometre Array Observatory (SKAO) inside the world’s largest radio quiet zone. That zone, however, was designed before the satellite era and offers no protection from above.

Monitoring means measuring. Through the SNIFFLES project, with our first paper published in June 2026, we completed the first systematic measurement of satellite emissions spanning 1 to 26 gigahertz, using our Mopra telescope and Australia Telescope Compact Array facilities. Unintended emissions from satellite platforms appear in essentially every band we have looked at, including in some that are allocated to the radio astronomy service.

Mitigation is a multi-layered task involving telescope processing, satellite beam control, and operator coordination. Our Observational Data Sharing system, developed in partnership with the U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO), tells participating operators in near real time where each of our telescopes is pointing, so that satellite beams can be steered away from sensitive observations. Four satellite operators are currently using our ODS system to help protect our observatories.

None of these provides a complete solution, but together they produce measurable benefits today. The next generation of telescopes will need interference handling baked into receivers, antennas, and data pipelines from day one to coexist in this new interference regime that needs to take unprecedented aggregation effects into account.

The U.S. response: Catalysing research in spectrum science

The U.S. National Science Foundation (NSF) supports both basic and use-inspired research in science and engineering fields with the purpose of promoting the progress of science and advancing societal health, prosperity and welfare.

In the area of spectrum management, NSF has been focused on funding research that enables more efficient use of the radio frequency spectrum. In 2020, NSF launched the Spectrum Innovation Initiative (SII) because fundamental research both requires wireless spectrum access for communications and scientific data transfer and can lead to more efficient use of the spectrum.

The SII programme is implemented in partnership with the U.S. spectrum regulators, the National Telecommunications Information Administration and the Federal Communications Commission. NSF has funded more than USD 100 million in the field of “spectrum science” to push the boundaries of dynamic spectrum sharing and satellite-terrestrial coexistence.

While demonstrating compatibility via modelling is a good first step, in practice, systems perform differently in the field than they do in models. Therefore, NSF has been promoting field tests and trials to experimentally verify compatibility.

NSF NRAO has developed Operational Data Sharing (ODS) whereby radio astronomy telescope frequency and pointing information can be shared in near real time with satellite operators, enabling improved compatibility and spectrum access for both radio astronomers and satellite operators.

Prevention of interference begins with technical coordination. NSF serves as the coordinator among U.S. radio astronomy facilities and satellite operators, leading to agreements covering required spectrum limits and voluntary coordination.

Bringing smart engineers and scientists together with a challenge can result in beneficial outcomes for all parties involved, such as provision of broadband to over 99.5% of residents within the U.S. National Radio Quiet Zone while still protecting the mission of the largest fully steerable radio astronomy telescope, the NSF Green Bank Telescope.

The use of ODS has applicability beyond the fixed satellite service to supplemental coverage from space and may also improve astronomy-terrestrial coordination in the future.

International efforts

National efforts should seek to be matched internationally where applicable. Within the ITU Radiocommunication Sector (ITU-R), the expert group for international radio astronomy spectrum protection, Working Party 7D, brings administrations, operators, and scientists together to develop the technical recommendations that underpin sound regulation.

Information exchange and collaboration enable innovative solutions and coexistence.

Working Party 7D recently updated a report on radio quiet zones (ITU-R RA.2259) and a database at the ITU-R was established after the last Radiocommunication Assembly (RA‑23) for the purpose of sharing data about radio astronomy sites of particular national importance to operators of global satellite systems, in addition to the information that can be found in the Master International Frequency Register (MIFR).

Continuing to work together to enable astronomical discoveries into the future requires international effort. The next Radiocommunication Assembly and the World Radiocommunication Conference (WRC-27) to be hosted by China in Shanghai in 2027 both include important topics seeking actions related to space and science services.

Active, evidence-based participation and cooperation from the radio astronomy and satellite communities are critical for ensuring astronomical discoveries continue as the space economy grows.

A shared sky is possible

The growth of satellite services brings real benefits, from connectivity in remote communities to disaster resilience. Radio astronomy delivers benefits of its own, from the precision timing behind global navigation, including space navigation and orbit determination, to discoveries that reshape our understanding of the universe.

The two need not be in conflict, but coexistence demands rigorous measurement, transparent operational sharing, technical innovation in both telescopes and satellites, and patient dialogue at the regulatory level.

CSIRO and NSF are committed to that work, and to ensuring future generations of scientists can continue to explore the cosmos and help humanity find its place in the universe.

Header image credit: CSIRO/Alex Cherney (ATCA by moonlight)