Radio astronomy faces a significant challenge as satellites operating at high altitudes increasingly interfere with the frequencies crucial for studying the universe. Research led by the CSIRO‘s Astronomy and Space Science division has provided important insights into the radio emissions from geostationary satellites, which orbit approximately 36,000 kilometres above Earth.
Traditionally, much focus has been placed on low Earth orbit satellites, such as those deployed by SpaceX‘s Starlink project. However, this new study highlights the importance of understanding emissions from the geostationary satellites that remain fixed above a specific point on the Earth’s surface. These satellites play a vital role in various communications, including television broadcasts and military operations, and can stay within a telescope’s field of view for extended periods.
The research team utilized archival data from the GLEAM-X survey, gathered by Australia’s Murchison Widefield Array in March 2020. They examined observations within the frequency range of 72 to 231 megahertz, which is critical for the upcoming Square Kilometre Array project. This extensive analysis tracked up to 162 geostationary and geosynchronous satellites during a single night, employing a stacking technique to pinpoint any radio emissions.
Results revealed that most geostationary satellites did not emit detectable radio frequencies within the studied range. The team established upper limits of 1 milliwatt of equivalent isotropic radiated power in a 30.72 megahertz bandwidth for the majority of satellites. Remarkably, one satellite, Intelsat 10-02, displayed a possible detection of unintended emissions at approximately 0.8 milliwatts. Even this level is significantly lower than the emissions typically observed from low Earth orbit satellites, which can radiate hundreds of times more power.
The implications of these findings are noteworthy. Geostationary satellites orbit at a distance ten times greater than the International Space Station. This distance means that even considerable radio emissions diminish significantly before reaching ground-based telescopes. The study’s methodology, which involved observing near the celestial equator, allowed for reliable detection of emissions over longer periods, enhancing the sensitivity of the results.
As the Square Kilometre Array progresses towards completion, it is expected to be far more sensitive than current instruments in the low-frequency range. What may be regarded as minor background noise today could pose serious interference challenges for future observations. The data gathered in this study serves as essential baseline information for addressing potential future radio frequency interference.
The increasing presence of satellite constellations raises concerns about the preservation of the radio quiet that astronomers heavily depend upon for their studies. Even satellites designed to avoid certain frequencies can unintentionally leak emissions through various components. For the moment, geostationary satellites appear to be largely compliant with the low-frequency radio spectrum. However, as technology advances and satellite traffic increases, the future of this situation remains uncertain.
This pioneering research underscores the importance of monitoring emissions from high-altitude satellites to safeguard the integrity of astronomical observations and to ensure the continued advancement of radio astronomy.
