Radio Signals Detected due to Starlink Interference
The International Telecommunication Union - Radiocommunication sector (ITU-R) is the global body responsible for radio-frequency spectrum allocations and satellite orbit regulations. Under its purview lies the Radio Astronomy Service (RAS), a service dedicated to the observation of celestial events through radio frequencies. The allocation of the radio spectrum for the RAS has long been a critical aspect of astronomical research.
In a recently published paper by Di Vruno et al, they document their observations of 68 Starlink satellites, of which 47 have been noted to emit unusual signals. Using the LOFAR radio telescope, they detected signals from these satellites in the frequency range of 110 to 188 MHz, identifying both narrow and broadband emissions. These signals are far below the 10.7 to 12.7 GHz frequencies used by typical downlink communication signals. While the study notes that these may be of alternative origin, such as electromagnetic (EM) waves reflecting from these satellites, they conclude that these are most likely intrinsic emissions. For example, some of these signals were periodic in time, suggesting these correspond to some internal oscillator or clock.
While astronomers have grappled with satellite interference for years, attempting to avoid it wherever possible, the increasing number of satellites, especially with the anticipated launch of large satellite constellations like Amazon’s Kuiper Project, is heightening these concerns. The sheer number of satellites in orbit might soon make ground-based astronomical observations at certain bandwidths nearly impossible.
The study discusses the unfortunate scarcity in the allocation of the spectrum to the RAS, especially below 4 GHz. Only 5% of the spectrum is allocated to radio astronomy, with a mere 1.6% enjoying exclusive use. However, modern astrophysics often requires observations to anywhere between 30MHz and 300 GHz. This limited access poses a substantial constraint on modern radio astronomical research and is largely considered insufficient for the needs of most scientists, highlighting an urgent need for a re-evaluation of the spectrum allocation process.
The study employs simulations using the Equivalent Power Flux Density method, recommended by the ITU-R, to assess the potential impact of satellite generated EM radiation on radio astronomical observations. Regulations, such as ITU-R RA.1513-2, typically limit the data loss of astronomical measurements to 2%. The Starlink satellites' unintended emissions were found to exceed this threshold in the simulations. However, it's important to note that the ITU-R’s regulations, which primarily address intentionally emitted signals, might not cover these unintended emissions.
As the conditions for celestial observation become less favourable, the need for collaborative efforts intensifies. The primary aim of this paper is a call to action, underscoring the urgency of re-evaluating spectrum allocation and introducing more stringent regulation in an attempt to safeguard astronomical research. With only a small fraction of the spectrum dedicated to radio astronomy, researchers find themselves in a precarious position. Lead author Di Vruno acknowledges ongoing dialogues with SpaceX and regulatory bodies, aiming for a harmonious coexistence between technological advancements and observational efforts.
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Journal Source: F. Di Vruno et al, Unintended electromagnetic radiation from Starlink satellites detected with LOFAR between 110 and 188 MHz, Astronomy and Astrophysics, Vol. 676, No. A75, 2023, https://doi.org/10.1051/0004-6361/202346374
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