WASHINGTON — Large satellite constellations can unintentionally generate electromagnetic noise, creating an additional source of interference for radio astronomers.

Astronomers announced July 5 that they detected radio emissions at relatively low frequencies from dozens of SpaceX Starlink satellites as they passed over a Dutch radio observatory. The emissions, at frequencies between 110 and 188 megahertz, are different from the deliberate transmissions from the satellites used to provide broadband internet access between 10.7 and 12.7 gigahertz.

Using the Low Frequency Array (LOFAR) radio telescope, astronomers detected emissions from 47 of 68 Starlink satellites they monitored. They detected several narrowband emissions at specific frequencies in that range, primarily from Starlink satellites in their operational orbits rather than those still in the process of raising their orbits after launch. They also detected broadband emissions over the entire range as well as one signal at 143.05 megahertz that was likely reflections from the French GRAVES space surveillance radar.

The emissions, researchers said, likely come from electromagnetic interference from subsystems within the spacecraft. There are no international regulations regarding such emissions from spacecraft, in contrast to rules for terrestrial equipment.

“This study represents the latest effort to better understand satellite constellations’ impact on radio astronomy,” said Federico Di Vruno, co-director of the International Astronomical Union’s Center for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference and lead author of the study being published in the journal Astronomy & Astrophysics. Astronomers had theorized that such emissions could be detected, he noted in a statement. “Our observations confirm it is measurable.”

It’s unclear what effect the electromagnetic interference emissions from Starlink satellites would have on radio astronomy, but astronomers noted that it spans one frequency range between 150.05 and 153 megahertz that is protected for radio astronomy by the International Telecommunication Union.

The emissions do not violate any regulations, and astronomers noted that SpaceX has been willing to talk about ways to mitigate any interference. That includes design changes already made to its next generation of Starlink satellites that can reduce those emissions.

However, astronomers said that similar emissions are likely from other satellite constellations, creating additional interference. “Our simulations show that the larger the constellation, the more important this effect becomes as the radiation from all satellites adds up,” said Benjamin Winkel of the Max-Planck-Institute for Radio Astronomy (MPIfR), a co-author on the study, in a statement.

“This makes us not only worried 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,” he said.

Astronomers have raised concerns for several years about the potential deleterious impact of satellite constellations on astronomy. That has included both the deliberate radio transmissions from such satellites as well as reflected sunlight that can interfere with optical observations.

In January, the U.S. National Science Foundation (NSF), which funds several optical and radio astronomy observatories, announced a coordination agreement with SpaceX to mitigate the impacts of Starlink satellites on astronomy. That features efforts to reduce the brightness of Starlink satellites to least magnitude 7 as well as agreeing not to transmit while passing over major radio observatories.

During a town hall session at a meeting of the American Astronomical Society June 5, NSF officials said a similar coordination agreement had been reached with OneWeb, with more details to be released in the near future.

Astronomers involved in this study said they hope the detection of the electromagnetic interference emissions from the Starlink satellites will encourage other operators to take steps to mitigate similar emissions from their satellites.

“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,” said Gyula Józsa of MPIfR and Rhodes University in South Africa.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...