Radio astronomy is facing a new challenge as satellites operating at significant altitudes threaten to contaminate critical frequencies used for cosmic exploration. Researchers from the CSIRO’s Astronomy and Space Science division have conducted a systematic study to measure potential radio emissions from satellites located in geostationary orbit, approximately 36,000 kilometers above Earth.
The study, published on the arXiv preprint server, utilized archival data from the GLEAM-X survey captured by Australia’s Murchison Widefield Array in 2020. The researchers focused on the frequency range of 72 to 231 megahertz, which is essential for the upcoming Square Kilometer Array (SKA) project. They tracked up to 162 geostationary and geosynchronous satellites over a single night, an approach that allowed them to stack images at each satellite’s predicted position and scrutinize for unintended emissions.
The findings are largely optimistic: the majority of the satellites analyzed were effectively invisible to radio telescopes operating within this frequency range. The researchers established upper limits for emissions, with most satellites emitting less than 1 milliwatt of equivalent isotropic radiated power across a 30.72 megahertz bandwidth. The most sensitive measurements achieved an impressive low of 0.3 milliwatts. Only one satellite, Intelsat 10–02, showed a possible detection of unintended emissions at around 0.8 milliwatts, significantly lower than the emissions typically seen from low Earth orbit satellites.
This distinction is crucial, considering the vast distances involved. Geostationary satellites orbit at a distance ten times greater than the International Space Station, meaning that even relatively strong emissions would diminish considerably by the time they reach Earth-based telescopes. The study’s methodology, which pointed the telescope near the celestial equator, allowed satellites to remain in the field of view for extended periods, enhancing the sensitivity of the emissions detection.
As the Square Kilometer Array nears completion in both Australia and South Africa, it promises to be vastly more sensitive than current instruments in the low frequency range. This enhanced sensitivity raises concerns about potential interference from satellite emissions that may appear negligible today but could disrupt observations in the future.
These new measurements provide a critical baseline for anticipating and mitigating future radio frequency interference. As the number of satellite constellations increases and radio telescopes become more advanced, the once pristine radio quiet that astronomers have relied upon is gradually diminishing.
While current findings indicate that geostationary satellites are largely respectful neighbors in the low frequency spectrum, the future remains uncertain as technological advancements and satellite traffic continue to evolve. The ongoing monitoring of these emissions will be essential to preserving the integrity of radio astronomy.
For further details, refer to the study by S. J. Tingay et al., titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range,” available on the arXiv preprint server.
