The LOFAR radio telescope has shown that satellites can unintentionally emit radio waves that interfere with the observations of radio telescopes. Satellites circle the globe in ever increasing numbers. Their radio emission could, if not addressed, close unique and scientifically valuable windows into the Universe. It is of crucial importance for the astronomy sector and industry to collaborate to overcome these issues and for the International Telecommunications Union to establish regulation to control this emission.

The study, accepted for publication in the scientific journal Astronomy & Astrophysics, used the LOFAR radio telescope, the largest low-frequency radio telescope on Earth developed by ASTRON (Netherlands Institute for Radio Astronomy) and scientifically exploited jointly with nine other European countries in the International LOFAR Telescope (ILT), to observe satellites from SpaceX's Starlink constellation in April 2022. While being licensed to operate within the 10.7 to 12.7 GHz radio frequency band, primarily designated for internet connectivity, these satellites were found to emit electromagnetic signals at significantly lower frequencies, as detected by LOFAR.

In a press release issued by the Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS), the authors report that radio signals were detected with LOFAR between 110 and 188 MHz for 47 out of the 68 satellites that were observed. This frequency range includes a protected band between 150.05 and 153 MHz, which is specifically allocated to radio astronomy by the International Telecommunications Union (ITU). The authors conclude that the detected emission is emanating from onboard electronics, and hence distinct from intended communications transmissions.

SpaceX is currently not violating rules, as for satellites, these kinds of signals are not covered by any international regulation. This absence of regulation may jeopardize radio astronomy, as several large constellations of satellites in low-Earth orbit are currently under construction or planned to be launched in the future. In the press release the authors encourage satellite operators and regulators to consider this impact on radio astronomy in spacecraft development and regulatory processes alike.

Radio frequency interference (RFI) has always been a challenge for astronomers, who continuously strive to refine strategies to account for human-made radio signals. Jessica Dempsey, Director General of ASTRON: “We have a track record of working closely with industry stakeholders to safeguard the future of scientific discoveries. ASTRON is renowned for its commitment to maintaining an interference-free or manageable environment. By joining forces, we can ensure the continuation of groundbreaking research and exploration of the Universe.”

René Vermeulen, director of the International LOFAR Telescope (ILT), warns: "The cumulative effect of unintended emissions from thousands of low-Earth orbit satellites could have a profound impact on radio astronomy, not only on LOFAR observations but other radio telescopes as well. It would introduce disruptive noise across multiple wavelengths, including those reserved for the exploration of deep space. Regulation of this noise is crucial for science."

Published by the editorial team, 5 July 2023

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