Radio astronomers face a growing challenge as satellites orbiting the Earth increasingly interfere with the frequencies necessary for studying the cosmos. A new study led by the CSIRO Astronomy and Space Science division has provided essential insights into the radio emissions from geostationary satellites located at approximately 36,000 kilometres above the Earth. These findings reveal that, for the most part, these satellites do not significantly impact astronomical research.
Significant Findings on Satellite Emissions
The research team utilized archival data from the GLEAM-X survey, gathered by the Murchison Widefield Array in March 2020. They focused on frequencies between 72 and 231 megahertz, which are crucial for the upcoming Square Kilometre Array, a project expected to revolutionize low-frequency radio astronomy.
Over the course of a single night, the researchers tracked up to 162 geostationary and geosynchronous satellites. By stacking images at predicted satellite positions, they searched for unintended radio emissions. The results were encouraging, as the majority of these distant satellites remained undetectable in the examined frequency range. For most satellites, the team established upper limits of less than 1 milliwatt of equivalent isotropic radiated power within a 30.72 megahertz bandwidth. Notably, the most impressive limit reached just 0.3 milliwatts.
Only one satellite, Intelsat 10-02, exhibited possible unintended emissions, detected at around 0.8 milliwatts. Even this reading is significantly lower than typical emissions from low Earth orbit satellites, which can emit hundreds of times more power.
The Impact of Distance and Geometry
The study’s findings underscore the importance of distance when assessing satellite emissions. Geostationary satellites are located ten times further from the Earth than the International Space Station, meaning that even strong radio emissions diminish considerably by the time they reach ground-based telescopes.
Moreover, the observation strategy employed by the research team, which involved pointing near the celestial equator, allowed each satellite to remain in the telescope’s wide field of view for extended periods. This technique enabled the use of sensitive stacking methods that could reveal even sporadic emissions.
The Square Kilometre Array, once completed, will be far more sensitive than current radio instruments operating in the low-frequency spectrum. What may appear as harmless background noise to today’s telescopes could pose significant interference for the SKA in the future. These new measurements provide vital baseline data for forecasting and mitigating potential radio frequency interference.
As the number of satellite constellations increases and radio telescope technology advances, the pristine radio quiet that astronomers have long depended on is gradually diminishing. Even satellites designed to avoid certain protected frequencies can inadvertently leak emissions through their electrical systems, solar panels, and onboard computers.
For the time being, geostationary satellites appear to be considerate neighbours in the low-frequency radio spectrum. Whether this remains true in the face of evolving technology and increasing satellite traffic remains to be seen. The findings from this study are critical in understanding how to navigate the complexities of radio astronomy in an increasingly crowded space environment.
