Radio astronomy faces increasing challenges as satellites orbiting Earth impact the frequencies astronomers rely on for studying the universe. A recent study led by researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has systematically measured potential radio emissions from satellites located at a height of 36,000 kilometers, specifically in the geostationary orbit.
Geostationary satellites maintain a fixed position relative to the Earth’s surface, allowing them to facilitate a variety of services, including television broadcasts and military communications. Unlike low Earth orbit satellites that move rapidly across the sky, these satellites can remain within the field of view of a telescope for extended periods. Until now, there had been no comprehensive analysis of whether these distant satellites emit unintended radio frequencies that could interfere with astronomical observations.
Using archival data from the GLEAM-X survey, captured by Australia’s Murchison Widefield Array in 2020, the research team analyzed frequencies ranging from 72 to 231 megahertz. They tracked up to 162 geostationary and geosynchronous satellites over a single night, stacking images based on each satellite’s predicted position to detect any radio emissions.
The outcomes of this study are largely reassuring. The researchers determined that the majority of these geostationary satellites do not emit significant radio signals in the frequencies crucial for radio astronomy. Most satellites had upper limits of less than 1 milliwatt of equivalent isotropic radiated power over a bandwidth of 30.72 megahertz, with the best results showing a notably low threshold of 0.3 milliwatts. Only one satellite, Intelsat 10–02, indicated a possible emission of about 0.8 milliwatts, which remains significantly lower than the emissions often seen from low Earth orbit satellites.
The distance of geostationary satellites plays an important role in the impact of their emissions. Positioned ten times farther from Earth than the International Space Station, any radio signals emitted from these satellites weaken considerably by the time they reach ground-based telescopes. The study’s observation strategy focused on the celestial equator, allowing each satellite to remain in the telescope’s wide field of view for longer, enhancing the chances of detecting even sporadic emissions.
The Square Kilometer Array (SKA), which is currently under construction in Australia and South Africa, is set to be far more sensitive than existing instruments in the low-frequency range. What may be considered harmless background noise by today’s technology could prove detrimental to the sensitive operations of the SKA. The findings from this research provide essential baseline data that will help predict and mitigate future radio frequency interference as the number of satellites in orbit continues to rise.
Despite the current findings indicating that geostationary satellites are largely respectful of the low-frequency radio spectrum, the evolving landscape of satellite technology poses an ongoing challenge. As new technologies develop and the volume of space traffic increases, the potential for unintended emissions remains an open question.
This significant study, published on the arXiv preprint server, underscores the importance of monitoring satellite emissions to preserve the integrity of radio astronomy. The ongoing dialogue around satellite technologies will be crucial as astronomers work to maintain the pristine radio quiet that has long been vital for their research.
