Radio astronomy faces a significant challenge as satellites orbiting approximately 36,000 kilometres above Earth increasingly interfere with the frequencies used for astronomical research. While low Earth orbit satellites like those from SpaceX’s Starlink have garnered attention for their disruptive potential, a new study focuses on the lesser-discussed geostationary satellites that remain fixed in the sky relative to Earth’s rotation.
Researchers from CSIRO’s Astronomy and Space Science division have conducted a systematic analysis to measure unintended radio emissions from these distant satellites. Their findings, based on archival data from the GLEAM-X survey captured by the Murchison Widefield Array in 2020, provide reassuring news for astronomers concerned about radio frequency interference.
Using data that spans frequencies from 72 to 231 megahertz, the team monitored up to 162 geostationary and geosynchronous satellites over a single night. They employed a technique that involved stacking images at each satellite’s predicted position, allowing the researchers to search for potential radio emissions.
The results showed that the majority of these satellites did not produce detectable emissions within the critical low frequency range. For most satellites, the study determined upper limits of less than 1 milliwatt of equivalent isotropic radiated power in a 30.72 megahertz bandwidth. Remarkably, the best limits achieved an impressively low emission level of just 0.3 milliwatts. Only one satellite, Intelsat 10-02, exhibited a potential emission at approximately 0.8 milliwatts, which remains significantly lower than typical emissions from low Earth orbit satellites.
The findings are particularly significant due to the distance and geometry involved. Geostationary satellites orbit at a distance ten times greater than the International Space Station. At such distances, even minor radio emissions dissipate before reaching Earth, diminishing their potential impact on ground-based observations. Furthermore, the research strategy involved pointing the telescope near the celestial equator, ensuring that each satellite remained in view for extended periods, enhancing the sensitivity of their measurements.
Looking ahead, the Square Kilometre Array, set to be completed in Australia and South Africa, will significantly increase sensitivity in the low frequency range. What may currently be perceived as insignificant background noise could pose serious interference for this advanced telescope. Therefore, these new measurements establish a crucial baseline for anticipating and mitigating future radio frequency interference, particularly as satellite constellations proliferate.
While geostationary satellites currently appear to maintain a respectful presence within the low frequency radio spectrum, the evolution of technology and increased satellite traffic may change this landscape. The study highlights the need for ongoing monitoring as the pristine radio quiet that astronomers rely upon continues to be challenged.
These findings underline the importance of understanding the broader implications of satellite technology on astronomical research, ensuring that as we advance in space communications, we also safeguard the tools that enable us to explore the universe.
