Radio astronomy is facing a growing challenge from the increasing number of satellites in orbit. A new study led by researchers at CSIRO (Commonwealth Scientific and Industrial Research Organisation) has taken a closer look at satellites located in geostationary orbit, approximately 36,000 kilometers above Earth. These satellites are crucial for various communications but may also be contributing to radio frequency pollution that can interfere with astronomical observations.
Until this study, there had been little systematic measurement of radio emissions from these distant satellites. The research team utilized archival data from the GLEAM-X survey, collected in 2020 by Australia’s Murchison Widefield Array. The analysis focused on frequencies between 72 and 231 megahertz, which are important for the upcoming Square Kilometer Array (SKA) project, poised to be one of the most sensitive radio telescopes in the world.
The researchers tracked up to 162 geostationary and geosynchronous satellites over a single night, meticulously stacking images at each satellite’s predicted location to detect any unintended radio emissions. The findings were largely positive; the majority of these satellites did not emit detectable radio signals within the studied frequency range.
Most satellites were shown to have upper limits of emissions below 1 milliwatt of equivalent isotropic radiated power in a bandwidth of 30.72 megahertz. Impressively, some results reached as low as 0.3 milliwatts. Only one satellite, Intelsat 10–02, exhibited potential emissions around 0.8 milliwatts, still significantly less than emissions from low Earth orbit satellites, which can emit hundreds of times more power.
The distance and geometry of geostationary satellites play a crucial role in how emissions are perceived from the ground. Positioned ten times farther than the International Space Station, any emitted radio waves diminish significantly by the time they reach Earth. The study’s methodology allowed for prolonged observation of each satellite, as they remained in the telescope’s field of view for extended periods, enhancing the chances of detecting even sporadic signals.
As the Square Kilometer Array nears completion in Australia and South Africa, it will far surpass existing instruments in sensitivity at low frequencies. While current emissions from geostationary satellites appear minimal, the study highlights the need for vigilance as satellite constellations expand. The pristine radio environment essential for astronomers risks being compromised as more satellites enter orbit and technology continues to evolve.
In light of these findings, the researchers emphasize the importance of establishing baseline data to predict and mitigate future radio frequency interference. Even satellites designed to minimize emissions can inadvertently leak signals through various onboard systems. For now, geostationary satellites seem to be maintaining a respectful presence in the low frequency radio spectrum, but the future remains uncertain as technology advances and satellite traffic increases.
This research, titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range,” is available on the arXiv preprint server. The paper underscores the ongoing dialogue about balancing satellite operations with the needs of astronomical research.
