Unintended radio emissions from Starlink satellites are entering spectrum reserved for radio astronomy and are already corrupting telescope data, astronomers say. The signals come from electronics aboard the satellites rather than their main communications transmissions, creating a form of interference that observatories and regulators have struggled to address.
Over the past three years, telescope measurements have recorded thousands of satellite-signal detections, including emissions in protected radio astronomy bands. Researchers at Curtin University reported in 2023 that 1,806 individual Starlink satellites, roughly 28% of the active constellation at the time, were emitting unintended radio signals into those bands.
The issue concerns unintended electromagnetic radiation, or UEMR, which can be produced by equipment that is not a transmitter. Potential sources include switch-mode power supplies, clocks and oscillators, digital backplanes, motor controllers, and inverters that condition power from solar panels.
Observations by LOFAR found broad- and narrow-band signals from second-generation Starlink satellites across 110 to 188 megahertz (MHz). The emissions were weaker than would be expected from deliberate transmissions. Researchers said they were still strong enough to potentially disrupt radio astronomy service operations in primary bands.
Measured EPFD distributions exceeded the interference limits in Recommendation ITU-R RA.769-2 in approximately 50–70% of samples, depending on polarization and observing subset. Based on the conventional 2% compatibility margin, the signals would require uniform attenuation of 16.3–18.6 dB.
Scientists say the problem marks a change in the character of radio interference. Observatories previously dealt mainly with a limited number of identifiable transmitters whose positions could be forecast and avoided. They now face dense and changing groups of emitters across the visible sky. Out-of-band and spurious emissions have consequently become a direct constraint on observatory performance.
The signals can exceed RA.769 thresholds by many orders of magnitude even where the transmitters responsible are operating in nominal compliance with their assigned spectrum masks. Maintaining observatories in the face of such emissions requires significant investment, according to astronomers.
The effects have been recorded at facilities in several regions. Australia loses Square Kilometre Array Low-frequency, or SKA-Low, data because of megaconstellation emissions. Botswana has experienced reduced Global Navigation Satellite System (GNSS) accuracy from such emissions. The Square Kilometre Array, which is being built partly in South Africa and partly in Western Australia, has formally raised concerns over broadband satellite signals entering protected radio astronomy bands.
In the United States, the National Radio Astronomy Observatory filed detailed technical objections with the Federal Communications Commission concerning SpaceX's shell 2 deployment. The observatory cited measurements that it said exceeded the International Telecommunication Union's recommended limits by orders of magnitude.
Interference can also arise through bistatic reflection geometry involving satellite uplinks and observatory receivers. Calculations by the Commonwealth Scientific and Industrial Research Organisation found that this could create detrimental interference for the Australia Telescope Compact Array and the Mopra Radio Telescope, both in New South Wales, Australia.
Current rules leave a gap in responsibility. UEMR falls entirely outside existing International Telecommunication Union regulations. There is presently no clear binding requirement requiring a satellite operator to prevent unintended radiation from causing interference. That leaves unclear how operators could be compelled to reduce emissions from onboard equipment, or how quickly new international or national rules could be introduced.
It is also unknown whether existing satellites can be technically modified to reduce the leakage, which components are responsible for the most damaging emissions, and how far future designs could reduce them at source. The longer-term effect on astronomy remains uncertain, though researchers say the interference is already affecting observations at radio facilities across multiple continents.
Comments (0)