Radio astronomy faces a significant challenge from satellites operating in the upper atmosphere, particularly those in geostationary orbit, which are positioned approximately 36,000 kilometers above the Earth. A team from the CSIRO’s Astronomy and Space Science division has conducted a comprehensive study to assess the potential radio emissions from these satellites, providing valuable insights for future astronomical research.
Geostationary satellites, which maintain a fixed position relative to the Earth’s surface, are crucial for various communications, including television and military transmissions. Unlike their low Earth orbit counterparts, which dart across the sky, these satellites can remain in the view of telescopes for extended periods. Despite their importance, little has been known about their unintended radio emissions, particularly in the low frequency range critical for astronomical observations.
To address this gap, researchers utilized archival data from the GLEAM-X survey conducted by the Murchison Widefield Array in 2020. They analyzed radio frequencies between 72 to 231 megahertz, the range where the upcoming Square Kilometer Array will operate. The team focused on tracking up to 162 satellites during a single night, employing advanced imaging techniques to detect any radio emissions that could interfere with astronomical observations.
The findings were largely reassuring. The researchers established that the majority of geostationary satellites did not emit significant radio signals in the studied frequency range. They set upper limits for emissions at less than 1 milliwatt of equivalent isotropic radiated power across a bandwidth of 30.72 megahertz, with the most sensitive measurements reaching an impressively low 0.3 milliwatts. Only one satellite, Intelsat 10–02, showed potential signs of unintended emission at around 0.8 milliwatts, which remains significantly lower than the emissions from low Earth orbit satellites, known to radiate hundreds of times more power.
The distance of geostationary satellites from Earth plays a crucial role in the impact of their emissions. Situated ten times farther than the International Space Station, any radio signals emitted by these satellites diminish considerably before reaching ground-based telescopes. The study’s method of observing near the celestial equator allowed the team to capture extended views of each satellite, enhancing the sensitivity of their detection techniques.
This research provides critical baseline data necessary for anticipating and mitigating future radio frequency interference, especially as the sensitivity of radio telescopes increases. The Square Kilometer Array, once completed, will far surpass current instruments in terms of sensitivity, making it imperative to understand and address any potential interference from satellite constellations.
As satellite networks continue to expand, the pristine radio quiet essential for astronomical observations faces increasing threats. While geostationary satellites currently appear to respect the low frequency radio spectrum, concerns remain about future technological advancements and the potential for increased traffic in space.
The detailed findings from this study are available in the paper published on the arXiv preprint server, titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range.” This research marks a significant step in understanding the impact of space technology on astronomical research and highlights the need for ongoing monitoring as satellite technology evolves.
