Scientists are using the LOFAR telescope for the first time to observe low-frequency radio waves from satellites in major constellations. Scientists used the Low Frequency Array (LOFAR) telescope to observe unwanted electromagnetic radiation from SpaceX satellites. This radiation, which is different from normal communication signals, can disrupt astronomical research. The study calls for regulation to protect radio astronomy from such unwanted emissions, and thanks SpaceX for its cooperation in mitigation efforts.

Scientists from a number of leading research institutions, including the Max Planck Institute for Radio Astronomy in Bonn, Germany, used the Low Frequency Array (LOFAR) telescope to observe SpaceX’s 68 satellites. The authors conclude that they have detected “undesirable electromagnetic radiation” emitted from onboard electronics. This differs from communications broadcasts, which have hitherto been the primary focus of radio astronomers. Unintentional radiation can affect astronomical research. They encourage satellite operators and regulators to consider this impact on radio astronomy in spacecraft design and regulatory processes.

The results were published on July 5 in the journal Astronomy and Astrophysics.

A new phenomenon in low Earth orbit

Listening to very faint signals from the universe, astronomers have always had to manage man-made radio signals that can obscure astrophysical sources. Therefore, most radio telescopes are built in special radio-protected places from terrestrial interference. Some are even located in silent radio zones sponsored by the relevant national regulators. Recent advances in technology have made it possible to create large arrays of satellites for broadband Internet access or Earth observation. They represent a whole new complexity.

With thousands of satellites in low Earth orbit, any radio telescope will have many satellites emitting signals in its field of view at any given time. A major concern for the satellite groups was expected to be scheduled communications transmissions to and from Earth. The discovery of additional non-communication sources is new and deserves further investigation.

Detection of unwanted electromagnetic radiation from the Starlink satellite using the LOFAR radio telescope. The yellow-green circles show the pixels of the synthetic radio camera forming a hexagonal grid across the sky. The red arrow shows the estimated motion of the Starlink satellite in the telescope’s field of view. Indeed, the satellite caused a signal in pixels along the way. In the background is a preview of an ongoing sky survey currently being carried out with the LOFAR telescope (LOFAR Two Meter Sky Survey, Shimwell et al., in preparation). Blue dots and objects are galaxies that are clearly visible in the radio mode (false color image) of the electromagnetic spectrum. Credit: IAU/CPS

“This work represents the latest attempt to better understand the influence of satellite constellations on radio astronomy,” said lead author Federico Di Vruno. “A theory about this radiation has been suggested in previous seminars on ‘dark and quiet skies’, our observations confirm that it can be measured.” Di Vruno is co-director of the International Astronomical Union’s Center for the Protection of the Dark and Quiet Sky from Constellation Satellite Interference (IAU CPS) and the Spectrum Manager of the SKA Observatory (SKAO). All other authors are active members of the CPSU.

Current and planned constellations

Di Vruno and his co-authors initially focused on SpaceX satellites because SpaceX had the largest number of satellites (over 2,000) in orbit at the time of observations. However, they acknowledge that SpaceX is not the only operator of major satellite arrays. The authors hope to detect similar unintentional emissions from other low-Earth orbiting satellites, and more measurement studies are currently planned that will focus on other satellite constellations.

Detection of unwanted electromagnetic radiation from Starlink satellites using the LOFAR radio telescope. Blue and yellow circles show synthetic radio camera pixels forming a hexagonal grid across the sky. Blue circles mean a weak signal, yellow circles mean a strong signal. The satellite triggered a signal in pixels along the trace. The position of the satellite in the sky perfectly coincided with the pixels. Credit: IAU/CPS

“We detected emissions between 110 and 188 MHz from 47 of the 68 satellites observed with LOFAR. Co-author Sees Bassa of the Netherlands Radio Astronomy Institute ASTRON said, “This frequency range is 150.05 MHz, which is specifically allocated for radio astronomy by the International Telecommunication Union (ITU). “At the same time, SpaceX does not break any rules as such radiation to satellites is not subject to any international regulation. In contrast, terrestrial equipment has strict requirements to ensure that a device does not interfere with another device located nearby.” subject to regulations.

The authors also simulated this effect from several satellite constellations. “Our simulations show that the larger the constellation, the more significant this effect becomes due to increased radiation from all satellites. This causes us to worry even more about not only existing constellations, but those planned. Max Planck Institute for Radio Astronomy in Germany “Also, it’s about the lack of clear regulation that protects radio astronomy bands from unwanted emissions,” says co-author Benjamin Winkel from MPIfR.

Expanding cooperation with satellite operators is crucial

The authors are in close contact with SpaceX, and the company offered to continue discussing possible ways to mitigate any negative consequences for astronomy in good faith. As part of its design iteration, SpaceX has made changes to the next generation of satellites that could reduce the impact of these unwanted emissions on important astronomical projects.

Co-author Jula Jozha (also MPIFR and Rhodes University in South Africa) emphasizes: “We believe that early recognition of this situation gives astronomy and operators of major constellations the opportunity to actively work together on technical mitigations in parallel with the necessary discussions to develop relevant regulations”.

Professor Michael Kramer, Director of MPIFR and President of the Astronomical Society in Germany, said: “This study highlights an example of the different channels in which technological advances can have undesirable side effects for astronomy.” He openly welcomes SpaceX’s collaborative approach. “By leading SpaceX, we hope to gain broad support from the entire satellite industry and regulators.”

About CPS

The International Astronomical Union Center for Dark and Quiet Sky Obstruction Satellites (IAU CPS) is a global organization jointly organized by NSF’s NOIRLab in the US and the IAU’s auspices SKA Observatory (SKAO). CPS encourages the global coordination of the efforts of the astronomical community, with observatories, space agencies, industry, regulatory authorities and other sectors to help mitigate the negative effects of satellite constellations on astronomy. Source