Radio astronomy faces a significant challenge as satellites in high orbits increasingly interfere with the frequencies used for cosmic observation. A team of researchers from the CSIRO Astronomy and Space Science division has undertaken a comprehensive study to measure unintended radio emissions from geostationary satellites located at an altitude of 36,000 kilometers. Their findings, published on December 15, 2025, reveal mostly positive results for astronomers.
Geostationary satellites, which orbit at the same rotational speed as the Earth, are crucial for various applications, including television broadcasts and military communications. Unlike low Earth orbit satellites, which traverse the sky quickly, these satellites remain in the same position for extended periods, making them potential sources of interference for radio telescopes. Until now, there has been no systematic measurement of their radio emissions, particularly in the low frequency range critical for upcoming astronomical projects such as the Square Kilometer Array.
Study Findings and Methodology
The research utilized archival data from the GLEAM-X survey, captured by Australia’s Murchison Widefield Array in 2020. The team analyzed radio emissions from 162 geostationary and geosynchronous satellites across a frequency range of 72 to 231 megahertz. This range is integral to the operations of the Square Kilometer Array, which is projected to be significantly more sensitive than existing instruments.
Through a unique observational strategy, the researchers stacked images at the predicted positions of each satellite over a single night, allowing them to effectively detect radio emissions. The results indicated that the majority of these satellites did not emit detectable signals, with upper limits established at less than 1 milliwatt of equivalent isotropic radiated power in a 30.72 megahertz bandwidth. Impressively, some satellites demonstrated even lower limits, reaching approximately 0.3 milliwatts.
Only one satellite, Intelsat 10–02, displayed potential radio emissions, measuring around 0.8 milliwatts. Even this detection was significantly lower than emissions from low Earth orbit satellites, which can radiate hundreds of times more powerfully.
Implications for Future Astronomy
The distance of geostationary satellites—ten times farther from Earth than the International Space Station—greatly diminishes the impact of any emissions that do occur. By the time radio waves travel to ground-based telescopes, they become faint and less disruptive. Additionally, the study’s methodology, which involved observing near the celestial equator, allowed for prolonged monitoring of each satellite, enhancing the likelihood of revealing any intermittent emissions.
As satellite technology advances and the number of satellites in orbit increases, the pristine radio environment that astronomers depend on is slowly diminishing. The new measurements provide essential baseline data that can help predict and mitigate future radio frequency interference. Even satellites designed to avoid certain protected frequencies can inadvertently emit signals due to their electrical systems, solar panels, and onboard computers.
At present, geostationary satellites appear to be largely non-intrusive in the low frequency spectrum. However, as technology evolves and satellite traffic grows, the long-term impact on radio astronomy remains uncertain.
This study not only enhances our understanding of the current state of radio emissions from geostationary satellites but also sets the stage for ongoing monitoring and management of radio frequencies crucial for astronomical research.
