Radio astronomy faces a significant challenge as satellites operating at high altitudes increasingly interfere with the frequencies used to study the universe. While much attention has been given to low Earth orbit satellites like those from SpaceX’s Starlink, researchers have now focused on the effects of geostationary satellites, positioned approximately 36,000 kilometres above Earth.
A team from the CSIRO Astronomy and Space Science division has conducted a comprehensive study to assess whether these distant satellites emit unintended radio signals that could disrupt astronomical observations. Using data from the GLEAM-X survey, captured by Australia’s Murchison Widefield Array in March 2020, the researchers examined signals within the 72 to 231 megahertz frequency range, which is critical for the upcoming Square Kilometre Array.
Over the course of one night, the team tracked up to 162 geostationary and geosynchronous satellites, stacking images at each satellite’s predicted position to search for radio emissions. The findings indicate that most of these satellites remain undetectable in the low frequency range. The team established upper limits of emission for most satellites at less than 1 milliwatt of equivalent isotropic radiated power across a 30.72 megahertz bandwidth, with the best measurements reaching as low as 0.3 milliwatts.
Only one satellite, Intelsat 10-02, demonstrated a potential detection of unintended emissions at approximately 0.8 milliwatts. This level is still significantly lower than typical emissions from low Earth orbit satellites, which can emit hundreds of times more power.
Understanding the Impact of Distance
The importance of these results hinges on the distance at which geostationary satellites operate. Positioned ten times farther from Earth than the International Space Station, any radio emissions from these satellites weaken considerably by the time they reach ground-based telescopes. The study employed a strategic observation method, focusing on areas near the celestial equator, allowing each satellite to remain in the telescope’s wide field of view for extended periods. This technique enabled the team to detect even sporadic emissions that may occur.
The Square Kilometre Array, once completed, will vastly surpass the sensitivity of current instruments in the low frequency range. Consequently, signals considered harmless background noise today could pose significant interference risks for this advanced telescope. The new measurements provide essential baseline data to anticipate and mitigate future radio frequency interference as satellite constellations continue to expand.
Future Considerations for Radio Astronomy
As the number of satellites in orbit increases, the pristine radio environment that astronomers have relied upon is gradually diminishing. Even satellites that aim to avoid certain protected frequencies often leak unintended emissions through their electrical systems, solar panels, and onboard computers.
Currently, geostationary satellites appear to be “respectful neighbours” in the low frequency radio spectrum. However, as technology evolves and satellite traffic grows, the future of radio astronomy may face new challenges. The findings from this research underscore the need for ongoing monitoring and regulation of radio emissions from all satellite systems to preserve the integrity of astronomical observations.
This study, titled “Limits on Unintended Radio Emission from Geostationary and Geosynchronous Satellites in the SKA-Low Frequency Range,” marks a crucial step in understanding the impact of satellite emissions on astronomical research and highlights the delicate balance between technological advancement and scientific exploration.
