For a study published in the Astronomy and Astrophysics journal, scientists from a number of leading research institutions  used the Low Frequency Array (LOFAR) telescope centred in the Netherlands to observe 68 Starlink satellites made by SpaceX. The authors conclude that they detected "unintended electromagnetic radiation" emanating from onboard electronics. This is different from communications transmissions, which had been the primary focus for radio astronomers so far.
Further scientific evaluation including other satellite systems is underway, as this unintended radiation could impact astronomical research. The authors encourage satellite operators and regulators to consider this impact on radio astronomy in spacecraft development and regulatory processes alike.
A new phenomenon in Low Earth Orbit
Astronomers listening for very faint signals from the Universe have always had to manage human-made radio signals that can outshine astrophysical sources. Hence, most radio telescopes are built in locations with special radio protections from terrestrial interference. Some are even located in radio-quiet zones supported by the respective national regulators. The recent advance of technology-enabled large satellite constellations that are being deployed for broadband internet access or Earth observation introduces an entirely new complexity.
With many thousands of satellites in low Earth orbit, any radio telescope will have many satellites radiating signals in its view at any given time. The expectation has been that the primary source of concern from satellite constellations will be their planned communications transmissions to and from Earth. The discovery of additional non-communication sources is novel and merits further investigation.
"This study represents the latest effort to better understand satellite constellations' impact on radio astronomy," said lead author Federico Di Vruno. "Previous workshops on Dark and Quiet Skies theorised about this radiation, and our observations confirm it is measurable." Di Vruno is the co-director of the International Astronomical Union's Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) and also spectrum manager for the SKA Observatory (SKAO). The other authors are all active members of the CPS.
Existing and planned constellations
Di Vruno and his co-authors initially focused on SpaceX satellites because SpaceX had the largest number of satellites - more than 2000 - in orbit at the time of the observations. However, they recognise that SpaceX is not the only operator of large satellite constellations. The authors expect to detect similar unintended emissions from other low-Earth-orbiting satellites, and further measurement work is already planned focusing on other satellite constellations.
"With LOFAR, we detected radiation between 110 and 188 MHz from 47 out of the 68 satellites that were observed. This frequency range includes a protected band between 150.05 and 153 MHz specifically allocated to radio astronomy by the International Telecommunications Union (ITU)", says co-author Cees Bassa from ASTRON, the Netherlands Institute for Radio Astronomy.
SpaceX is nevertheless not violating any rules, as for satellites this kind of radiation is not covered by any international regulation. In contrast, terrestrial equipment is regulated by strict rules to ensure that one device does not interfere with another one nearby.
The authors also performed simulations of this effect from several satellite constellations. "Our simulations show that the larger the constellation, the more important this effect becomes as the radiation from all the satellites adds up. This makes us worried not only about the existing constellations but even more about the planned ones - and also about the absence of clear regulation that protects the radio astronomy bands from unintended radiation," said co-author Benjamin Winkel from the Max Planck Institute for Radio Astronomy (MPIfR) in Germany.
Increased collaboration with satellite operators is key
The authors are in close contact with SpaceX, and the company has offered to continue to discuss possible ways to mitigate any adverse effects on astronomy in good faith. As part of its design iteration, SpaceX has already introduced changes to its next generation of satellites which could mitigate the impact of these unintended emissions on important astronomical projects.
SpaceX's approach to collaborating with astronomers is setting an example, but the participation from other satellite operators is also critical. Astronomers are hoping to intensify collaboration and engagement with the space industry and regulators to prevent the consequences of this unintended effect on astronomical observations.
Co-author Gyula Jozsa (also MPIfR and Rhodes University in South Africa) highlighted: "We believe that the early recognition of this situation gives astronomy and large constellation operators an opportunity to work together on technical mitigations pro-actively, in parallel to the necessary discussions to develop suitable regulations".
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