Satellites, astronomy and society: Sharing space and the skies

By Federico Di Vruno, Spectrum Manager, SKA Observatory; Vice-Chair, ITU-R Working Party 7D; Associate Director, IAU Centre for the Protection of the Dark and Quiet Sky, and Piero Benvenuti, Professor Emeritus of Astrophysics, University of Padua; Director, IAU Centre for the Protection of the Dark and Quiet Sky

For millennia, humanity has looked to the night sky for inspiration, to wonder and to seek understanding. The stars have guided us, shaped calendars, inspired art, literature, philosophy and connected cultures through shared stories.

Beyond this cultural significance, astronomy has profoundly influenced humanity by advancing science and technology, from fundamental physics to medical imaging and communications techniques.

But perhaps the most importantly, astronomy provides a unique perspective of our place in the Universe. Engagement by enthusiasts – not only professionals – fosters curiosity, international collaboration, and a sense of shared human heritage.

The night sky remains one of the few global commons experienced by all people, regardless of geography or background. Our ability to observe and connect with the cosmos is therefore not only important for scientific discovery, but also for education, culture, and maintaining an enduring source of wonder that has accompanied civilization throughout history.

Satellite growth and its effect on radio astronomy

Technological advances such as reusable rockets, combined with the growing need to expand connectivity to underserved and remote regions, have propelled space activity to unprecedented levels.

Private companies have started launching thousands of low Earth orbit satellites as part of so-called large satellite constellations. While these systems bring important societal benefits, including improved global connectivity and resilience, they also introduce new challenges for astronomy and humanity’s experience of the night sky.

The rapid increase in satellite numbers has transformed astronomy’s view of the night sky from a low satellite-density scenario to one with hundreds of satellites visible at any given time in almost any part of the world.

Increased density comes with several associated challenges. Satellites, for example, when illuminated by the Sun, reflect sunlight towards Earth, contaminating astronomical images as visible streaks that can be visible even to casual stargazers.

Radio astronomy is also increasingly affected by both intentional transmissions and unintended electromagnetic radiation (UEMR), the latter arising from electrical noise generated by onboard satellite electronics.

Radio astronomy and satellites on the WRC-27 agenda

After the first launch of Starlink satellites back in 2019, the astronomical community came together and responded to the situation with different actions.

Radio astronomers, in particular, stepped up efforts through the ITU Radiocommunication Sector (ITU-R – a key sector of the International Telecommunication Union) ahead of the last World Radiocommunication Conference (WRC-23). This has resulted in two new agenda items for the upcoming WRC-27:

• 1.16 – on protecting of radio astronomy from aggregate interference caused by non-geostationary (NGSO) satellite constellations.
• 1.18 – on protecting radio astronomy and passive Earth-observation sensors above 76 gigahertz (GHz) from unwanted emissions.

Several astronomical organizations started participating as permanent observers in the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) to raise wider awareness of the situation and seek an international, coordinated response. This resulted in the establishment of an agenda item on dark and quiet skies in the COPUOS Scientific and Technical Sub Committee.

In parallel, the International Astronomical Union (IAU) –, together with the joint Australian-South African SKA Observatory and the U.S. National Science Foundation’s National Optical and Infrared Laboratory –, established the IAU Centre for the Protection of the Dark and Quiet Skies, recently joined by European Southern Observatory (ESO). The IAU Centre aims to generate a space where all stakeholders can meet to discuss possible solutions on both the astronomy and satellite sides.

Collaboration with the space industry

Collaboration with industry has been the selected approach of the IAU and other international astronomical organizations, recognizing that the use and observation of space is to be shared among all humanity. This has resulted in some technical mitigation measures for optical interference, such as using dielectric mirrors to divert reflected sunlight away from Earth and tilting satellites and solar panels to minimize their brightness.

On the radio side, operators have tested new techniques such as boresight avoidance, where the spot beams of satellite downlinks are controlled to avoid illumination of telescope sites and the effect of satellite transits through telescope beams can be minimized. There is still much ground to cover on the effects of UEMR, which are still being studied by telescopes and satellite manufacturers. Discussions are ongoing at regulatory forums and standardization bodies alike.

Mitigation efforts on the telescope side are also ongoing, with many observatories first conducting theoretical studies and now moving into implementation of software routines to improve scheduling and data collection. Upgrades, for example, now enable online radio frequency interference (RFI) flagging and post-processing for RFI identification and removal.

However, all these measures involve significant resources, and most result in some data being discarded, reducing the overall efficiency of astronomical instruments.

New threats to dark and quiet skies

The rapid commercialization of space does not stop there; astronomy and the night sky constantly face new threats.

The prospect of direct-to-device (D2D) communications, entailing signals several orders of magnitude stronger than any typical communication signals up to now, could severely constrain observations in some frequency ranges and could even contribute to harmful interference in bands specifically allocated for radio astronomy.

Novel solutions to terrestrial power needs – like satellites equipped with mirrors reflecting sunlight to illuminate nighttime areas, or space-based solar power plants proposed to beam radio frequency energy towards Earth – are another great concern.

Meanwhile, space use keeps increasing in sheer volume, with companies now planning on moving datacentres from Earth to space. Their technical arguments are reasonable, but such plans raise serious concerns about effects on the environment and our dark and quiet skies.

Space sustainability discussions

The effects of space activities on science and the night sky have come to be recognized at the highest levels of international policy. They are well understood by the scientific community and, no doubt, by most space actors.

Dark and quiet skies are part of the wider discussion on space sustainability, from the United Nations forums like COPUOS to the Zero Debris Charter and Technical Booklet from the European Space Agency (ESA) and the S7 Joint Statement on Sustainable Space from the Science Academies of the G7 nations.

Nevertheless, the pace of space activities continues to accelerate, and enforceable regulation is not keeping up. A serious discussion needs to happen on the potential of space activities to fundamentally alter humanity’s ability to experience and study the night sky.

We need this if we intend to preserve our skies – skies to which the future generations may also turn, whether to wonder about our existence or to devise the technologies of their future.

The night sky is one of humanity’s oldest shared cultural experiences. The challenge today is not whether space should be used, but how humanity can continue expanding into space while preserving scientific discovery.

Radio astronomy is a topic under discussion at next year’s World Radiocommunication Conference (WRC-27)

Header image: One hour of satellites over the northern Atacama Desert in Chile (October 2025). Credit: F. Kamphues, ESO/M. Kornmesser