[Paper Review] A Report to ESO Council on the Impact of Satellite Constellations

Andrew Williams, O. Hainaut+5 more|arXiv (Cornell University)|Aug 9, 2021

Stellar, planetary, and galactic studies7 references4 citations

TL;DR

This report assesses the impact of planned satellite constellations—particularly up to 80,000 satellites in Low Earth Orbit—on ESO's ground-based astronomical facilities, focusing on Paranal Observatory. It quantifies satellite visibility, especially near the horizon, and proposes mitigation strategies and community-wide actions to reduce interference with astronomical observations.

ABSTRACT

Up to 100,000 satellites could be launched into Low Earth Orbit (LEO) in the coming decade. Assuming the two most advanced companies' plans are realised, close to 80,000 satellites will be present at a variety of altitudes between 328 - 1,325 km. At Paranal, more than 5,000 satellites will be over the horizon at any given time. Of these, depending on the hour of night and season, a few hundred to several thousand will be illuminated by the sun and potentially detectable. Satellites show a very strong concentration towards the local horizon, with over 50% of the satellites below 20 degrees elevation. This report informs ESO's Council of the impacts on ESO facilities, mitigation measures that ESO could adopt in the future, and the various community efforts in which ESO is involved.

Motivation & Objective

• To evaluate the growing threat posed by mega-constellations of satellites in Low Earth Orbit to ground-based astronomical observations.
• To quantify the number and visibility of satellites over ESO's Paranal Observatory, particularly during nighttime observing windows.
• To assess the concentration of satellites near the local horizon, where they pose the greatest risk to optical and near-infrared astronomy.
• To propose actionable mitigation measures for ESO and the broader astronomical community to reduce satellite interference.
• To inform ESO Council on the urgency of coordinated responses to preserve the integrity of ground-based astronomical data.

Proposed method

• Modeling satellite distributions based on the most advanced plans from two major companies, projecting up to 80,000 satellites across altitudes from 328 to 1,325 km.
• Using orbital mechanics and ephemeris data to simulate satellite passes over Paranal Observatory, calculating elevation and illumination conditions.
• Analyzing visibility windows by time of night and season to determine peak satellite exposure during astronomical observations.
• Assessing the fraction of satellites below 20 degrees elevation, where they are most likely to interfere with telescopes.
• Evaluating potential mitigation techniques such as satellite deorbiting, sunshades, and operational adjustments to minimize brightness.
• Collaborating with international astronomy and space agencies to promote policy and technical standards for sustainable space use.

Experimental results

Research questions

• RQ1 How many satellites will be visible over Paranal Observatory at any given time, and how does this vary by time of night and season?
• RQ2 What proportion of these satellites will be below 20 degrees elevation, where they are most likely to interfere with astronomical observations?
• RQ3 What fraction of the satellite population will be illuminated by the sun and thus detectable during nighttime observations?
• RQ4 What technical and operational mitigation strategies can be implemented to reduce satellite brightness and interference?
• RQ5 What coordinated actions can the astronomical community and space agencies take to minimize long-term impacts on ground-based astronomy?

Key findings

• Over 5,000 satellites are expected to be above the horizon at any given time over Paranal Observatory due to the projected deployment of mega-constellations.
• Between a few hundred and several thousand of these satellites will be illuminated by the sun and potentially visible during nighttime observations.
• More than 50% of the visible satellites will be below 20 degrees elevation, significantly increasing their potential to interfere with astronomical imaging.
• The number of visible satellites varies substantially by time of night and season, with peak visibility occurring during twilight and winter months.
• The current trajectory of satellite deployment poses a substantial threat to the photometric and spectroscopic integrity of ground-based astronomical data.
• Proactive mitigation measures, including satellite design modifications and operational coordination, are essential to preserve the quality of future astronomical observations.