[Paper Review] Concerns about ground based astronomical observations: a step to safeguard the astronomical sky

S. Gallozzi, M. Scardia+1 more|arXiv (Cornell University)|Jan 29, 2020

Space Satellite Systems and Control3 references19 citations

TL;DR

This paper calls for urgent international action to protect ground-based astronomical observations from the growing threat of mega-constellations of low-Earth orbit satellites, which cause sky brightness increases, image trail contamination, and radio frequency interference. It proposes binding legal and technical safeguards—such as launch moratoria, orbital debris mitigation, and veto powers for astronomical facilities—to preserve the scientific and cultural value of the night sky for future generations.

ABSTRACT

This article aims to highlight the impact for ground based astronomical observations in different windows of the electromagnetic spectrum coming from the deployment of fleets of telecommunications satellites. A particular attention is given to the problem of crowding of circumterrestrial space by medium/small size orbiting objects. Depending on their altitude and surface reflectivity, their contribution to the sky brightness is not negligible for professional ground based observations. With the huge amount of about 50,000 new artificial satellites for telecommunications planned to be launched in Medium and Low Earth Orbit, the mean density of artificial objects will be of >1 satellite for square sky degree; this will inevitably harm professional astronomical images leaving trails on them. Only one of these project, Starlink@SpaceX's, authorized by US Federal Communication Commission, plans to deploy about 42,000 not geostationary satellites, which will shine in sky after sunset and before sun dawn. Satellites will be observed in deep field images and particularly negative for scientific large area images used to search for Near Earth Objects, predicting and, eventually, avoiding possible impact events. Serious concerns are also common to other wavelengths eligible for ground based investigation, in particular for radio-astronomy, whose detectors are already saturated by the ubiquitous irradiation of satellites communication from Space stations as well as from the ground. The risk of running into the "Kessler syndrome" is also noteworthy. Understanding the risk for astronomical community, a set of actions are proposed in this paper to mitigate and contain the most dangerous effects arising from such changes in the population of small satellites. A dedicate strategy for urgent intervention to safeguard and protect each astronomical band observable from the ground is outlined.

Motivation & Objective

• Address the growing threat posed by mega-constellations of small satellites to ground-based astronomical observations across optical, radio, and other electromagnetic windows.
• Highlight the scientific and economic risks of unregulated satellite deployment, including image degradation, loss of survey sensitivity, and increased risk of Kessler syndrome.
• Advocate for immediate policy intervention to prevent irreversible damage to astronomical research and the night sky.
• Call for international legal frameworks to protect astronomical facilities and ensure compliance with space sustainability treaties.
• Propose a coordinated, science-led regulatory approach to balance space-based communications with the preservation of astronomical observation capabilities.

Proposed method

• Analyze the impact of satellite constellations on sky brightness and image quality using orbital parameters, reflectivity, and density estimates (e.g., >1 satellite per square degree).
• Assess radio frequency interference from satellite downlinks, which already saturate sensitive radio astronomy receivers.
• Model the cumulative effect of 50,000+ planned satellites, particularly Starlink’s 42,000 satellites, on optical and radio observations.
• Propose a moratorium on further non-geostationary satellite launches pending scientific and environmental impact assessments.
• Advocate for national and international regulatory mechanisms, including the right of veto for astronomical observatories over satellite deployments.
• Align proposed actions with existing international law, such as the Outer Space Treaty (Article IX) and UN Guidelines for Long-term Space Sustainability (2018).

Experimental results

Research questions

• RQ1 To what extent do mega-constellations of small satellites degrade the quality of ground-based optical astronomical images through brightness and trail contamination?
• RQ2 How does the increasing number of satellite transmissions affect the sensitivity and integrity of ground-based radio astronomy observations?
• RQ3 What are the cumulative risks of deploying tens of thousands of satellites in low Earth orbit, particularly regarding the potential for Kessler syndrome and orbital debris cascades?
• RQ4 What legal and regulatory mechanisms can be implemented to protect ground-based astronomical facilities from harmful satellite interference?
• RQ5 How can international cooperation ensure that space-based communication projects do not undermine the scientific value of ground-based astronomical research?

Key findings

• The deployment of ~50,000 new small satellites in Medium and Low Earth Orbits will result in a mean satellite density exceeding one per square degree of sky, significantly degrading sky quality.
• Starlink’s planned 42,000 non-geostationary satellites will shine at 3rd to 7th magnitude, creating bright, persistent trails in astronomical exposures, especially during twilight hours.
• Radio astronomy is already experiencing saturation due to satellite uplink and downlink transmissions, threatening the integrity of sensitive observations.
• The risk of Kessler syndrome—where orbital debris triggers a chain reaction of collisions—is substantially increased by the uncontrolled deployment of large constellations.
• The scientific and economic value of ground-based telescopes, including those in the 1–10 billion euro range, is at risk of being irreversibly damaged by unregulated satellite operations.
• Without immediate regulatory intervention, the damage to astronomical research and the night sky will be irreversible, violating the principles of sustainable space use and international law.