Researchers have made significant strides in understanding the impact of distant satellites on radio astronomy. A team from the CSIRO’s Astronomy and Space Science division has conducted a systematic measurement of radio emissions from geostationary satellites located at an altitude of 36,000 kilometers. Their findings, published on December 15, 2025, indicate that these satellites are largely respectful of the low frequency bands essential for astronomical observations.
Radio Emissions and Their Impact on Astronomy
In recent years, the proliferation of satellite constellations, particularly those in low Earth orbit like SpaceX’s Starlink, has raised concerns about radio frequency interference. While these lower satellites have received considerable attention for their potential to disrupt astronomical observations, less focus has been placed on satellites in geostationary orbits. These satellites, which remain fixed over a specific point on Earth, are crucial for various communications, including television broadcasts and military operations.
To assess the extent of any unintended radio emissions from these distant satellites, the CSIRO team utilized archival data from the GLEAM-X survey, conducted using the Murchison Widefield Array in Australia. The researchers analyzed a frequency range from 72 to 231 megahertz, which is significant for the upcoming Square Kilometer Array (SKA), an initiative expected to be much more sensitive than existing instruments.
Key Findings from the Study
The researchers tracked up to 162 geostationary and geosynchronous satellites over a single night. By stacking images at the predicted locations of each satellite, they searched for radio emissions. The results were promising: most satellites did not emit detectable levels of radio interference. For the majority, the team established upper limits of less than 1 milliwatt of equivalent isotropic radiated power over a bandwidth of 30.72 megahertz. One satellite, Intelsat 10–02, showed a possible emission around 0.8 milliwatts, but even this was significantly lower than the emissions noted from low Earth orbit satellites, which can emit hundreds of times more power.
The study indicates that geostationary satellites are currently minimal contributors to radio emissions relevant to astronomers. Given their distance—ten times farther from Earth than the International Space Station—even minor emissions diminish considerably by the time they reach Earth-based telescopes.
Importantly, the study’s methodology allowed for extended observation of each satellite, as they remained within the telescope’s wide field of view for prolonged periods. This approach enabled the detection of even intermittent emissions, underscoring the thoroughness of the investigation.
As astronomical instruments like the SKA become operational, they will require a pristine radio environment to function effectively. The findings provide a critical baseline for predicting and mitigating future radio frequency interference, which is increasingly relevant as satellite technology evolves and traffic in space intensifies.
For now, the results indicate that geostationary satellites are maintaining a low profile in the low frequency spectrum. Nonetheless, as technological advancements continue, the ongoing monitoring of these emissions remains essential to ensure that the integrity of astronomical observations is preserved.
For further details, refer to the full study published on the arXiv preprint server by S. J. Tingay et al., titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range.”
