Radio astronomy faces challenges as satellites in high orbits increasingly interfere with the frequencies used by astronomers. A new study conducted by researchers from CSIRO’s Astronomy and Space Science division has provided insights into whether geostationary satellites, located approximately 36,000 kilometers above Earth, emit unintended radio signals that could disrupt astronomical observations.
Historically, much focus has been placed on low Earth orbit satellites, such as those from SpaceX’s Starlink program, which are known for their rapid movement across the sky. In contrast, geostationary satellites maintain a fixed position relative to the Earth’s rotation, making them ideal for communications and broadcasting. These satellites can remain within a telescope’s field of view for extended periods, raising concerns about potential radio interference.
The research team utilized archived data from the GLEAM-X survey, captured by the Murchison Widefield Array in 2020. They analyzed signals in the 72 to 231 megahertz frequency range, which is crucial for the upcoming Square Kilometer Array, a project expected to revolutionize low-frequency radio astronomy.
Over a single night, the researchers monitored up to 162 geostationary and geosynchronous satellites, employing advanced techniques to detect any radio emissions. Their findings revealed that the majority of these satellites did not produce significant emissions detectable by current radio telescopes. Specifically, they established upper limits for emissions at less than 1 milliwatt of isotropic radiated power in a 30.72 megahertz bandwidth, with the most impressive limit reaching just 0.3 milliwatts.
Only one satellite, Intelsat 10–02, showed possible emissions at around 0.8 milliwatts, which still falls significantly below the levels observed from low Earth orbit satellites, which can emit hundreds of times more power. The distance of geostationary satellites—ten times farther from Earth than the International Space Station—means that any emissions would be considerably weakened by the time they reach ground-based telescopes.
The study’s methodology involved observing near the celestial equator, allowing each satellite to remain in the telescope’s wide field of view for extended durations. This strategy enhanced the sensitivity of their measurements, making it possible to detect even brief emissions.
As the Square Kilometer Array nears completion, it will offer much greater sensitivity than current instruments in the low-frequency range. What may currently be considered background noise could become detrimental interference for this next-generation facility. The new measurements provide a crucial baseline for understanding and mitigating future radio frequency interference, particularly as satellite constellations continue to grow and radio telescopes become more advanced.
Despite the current findings suggesting that geostationary satellites are largely respectful of the low-frequency radio spectrum, concerns linger. Satellites designed to avoid certain frequencies can still unintentionally leak emissions through their electrical systems and onboard computers. The ongoing evolution of technology and increasing satellite traffic pose challenges to maintaining the radio quiet that astronomers rely on.
As this research progresses, astronomers will need to remain vigilant about the potential impacts of satellite emissions on their observations. The study, titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range,” is published on the arXiv preprint server, providing a valuable reference for future investigations into radio frequency interference.
