Quiet Skies Report: A Primer on Protecting Radio Astronomy in the Age of Satellite Mega-Constellations

TL;DR

The paper analyzes how satellite mega-constellations threaten the ultra-sensitive measurements of radio astronomy, detailing the physics of faint cosmic signals, interference pathways, and the regulatory framework governing spectrum use. It explicates how the radiometer equation governs sensitivity, catalogs interference types including aggregate NGSO effects, and critiques EPFD as insufficient alone for modern wide-field arrays. It surveys ITU/RAS protections, national implementations, and emerging EU policy to illustrate the coexistence landscape, while offering concrete practices for satellite operators—conservative emission margins, boresight-avoidance strategies, and proactive collaboration with observatories. Finally, it articulates future directions involving VLEO deployments, ionospheric calibration challenges, and a shared policy-and-technology ecosystem that integrates environmental stewardship with scientific protection, enabling sustainable, coexisting space activity for decades to come.

Abstract

The rapid expansion of satellite constellations is transforming the radio-frequency environment around the Earth. At the same time, radio astronomy is entering a new era of sensitivity and survey capability, requiring unprecedented control of interference. This primer introduces satellite operators, engineers, spectrum managers and policy makers to the basic concepts of radio astronomy, explains why the discipline is uniquely vulnerable to interference, and outlines the regulatory and practical tools available to manage coexistence.

Figures (5)

• Figure 1: Examples of single-dish radio telescopes. Left: The Green Bank Telescope (GBT) in West Virginia, USA. With a fully steerable 100-meter diameter reflector, it is the world’s largest fully movable radio telescope (credit : NSF/NRAO). Right: The Five-hundred-meter Aperture Spherical Telescope (FAST) in Guizhou, China. FAST has an illuminated aperture of approximately 300 meters within a 500-meter fixed spherical dish. Although the structure itself is stationary, the telescope achieves sky coverage by moving its feed cabin and actively deforming sections of its reflector to form a steerable paraboloid (credit : Xinhua/Ou Dongqu).
• Figure 2: Examples of radio interferometers. Left: The Deep Synoptic Array 110 (DSA-110) at the Owens Valley Radio Observatory (OVRO) in California, USA. The instrument consists of 110 parabolic antennas, each 4.5 m in diameter, operating primarily in the 1.28–1.53 GHz band. Its primary mission is the rapid detection and precise localization of fast radio bursts (FRBs) (credit : G. Hallinan). Right: The Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), composed of 352 dual-polarization dipole antennas with nearly omnidirectional response. The array operates over 20–80 MHz, enabling full-sky imaging at high cadence as well as beamformed observations for transient and space-weather science (credit : G. Wiltsie).
• Figure 3: The United States National Radio Quiet Zone (NRQZ). Left: Map of the designated NRQZ, a federally managed region of approximately 34,000 km² spanning parts of West Virginia, Virginia, and Maryland. Within this zone, fixed terrestrial transmitters are subject to coordination to protect the Green Bank Observatory and the Sugar Grove facility (credit : NSF/NRAO). Right: A roadside sign marking the entrance to the Radio Astronomy Quiet Zone near Green Bank, West Virginia, indicating restrictions on the use of radio‐emitting devices to preserve the electromagnetic environment for scientific observations (credit : NSF/NRAO).
• Figure 4: Example of a raw all-sky image produced with the OVRO–LWA telescope in California, USA (see photo \ref{['fig:lwa']}), in the 59–64 MHz band (not allocated to satellite services) during a 10-second observation on 2025-01-14. Left: Full-sky map in zenith-projection, where the circular boundary corresponds to the horizon and the center to the local zenith. Bright white spots along the edge indicate terrestrial transmitters, while several linear streaks across the sky correspond to satellite passes. Right: The same image, but with satellite streaks overlaid and identified using Two-Line Element (TLE) orbital data for known satellites in red.
• Figure 5: Impact of the increasing angle of boresight avoidance. Distribution of instantaneous powers collected with a DSA-2000 prototype antenna with multiple configuration of boresight avoidance (orange, green, red) compared to the powers collected without boresight avoidance. Up to 25 dB attenuation can be measured with the most conservative boresight avoidance configuration.