Astronomers warn that low Earth orbit satellite constellations could exceed 100,000 spacecraft, creating unmanageable data loss for ground-based observatories. A European Southern Observatory study published in Astronomy & Astrophysics finds that proposed mega-constellations threaten night-sky visibility and asteroid tracking.
As thousands of new spacecraft enter orbit, ground-based astronomical research faces a technological squeeze. A study published in the journal Astronomy & Astrophysics by the European Southern Observatory reveals that existing proposals to launch more than 1.7 million satellites would substantially degrade cosmic observation.
The global satellite industry has expanded dramatically since 2019, driven by internet services such as SpaceX’s Starlink and Amazon’s Leo. While roughly 15,000 satellites currently orbit Earth, thirty-three large constellations filed with the International Telecommunication Union propose a total of 1,766,623 spacecraft.
Simulating the Atacama Desert Night Sky
The ESO research team based its findings on simulations carried out at the Paranal Observatory in Chile’s Atacama Desert. One examined model simulated a constellation of up to a million satellites, showing thousands of illuminated objects visible above the observatory’s Very Large Telescope shortly after sunset.
“Each of these satellites, when it crosses a telescope’s field of view, leaves a bright line.”
Olivier Hainaut, ESO astronomer and study author
Olivier Hainaut explained that while a single streak of light acts as a minor nuisance, multiplying numbers wipe away significant portions of a telescope’s view. A simulated two-hour exposure using the Very Large Telescope showed dozens of SpaceX satellite trails, with up to 28% of the observing field calculated as degraded.
The 100,000-Spacecraft Threshold and Reflect Orbital Projections
Researchers identified 100,000 satellites as the critical tolerance ceiling for ground-based astronomy. Exceeding this limit turns manageable technical downtime into permanent data loss.
“100,000 is the red line for keeping data loss from satellite constellations within the level of technical downtime caused by equipment failures. Beyond this number, observational data loss becomes unmanageable.”
Dr. Olivier Hainaut
Among the planned networks, Reflect Orbital secured a Federal Communications Commission approval in July for an initial satellite featuring an 18-metre mirror. The startup aims to deploy 50,000 space mirrors by 2035 to beam sunlight onto the ground at night on demand. These reflectors would appear four times brighter than a full moon when observed from within a reflected light beam, potentially making them the only “stars” visible in light-polluted cities like Munich.
Broader Impacts on Planetary Defense and Institutional Funding
Beyond light pollution from direct streaks, scientists warn of diffuse light and scattered light. Diffuse light forms a faint veil across the night sky from dim satellites, while scattered light from brighter reflectors spreads through Earth’s atmosphere, increasing the overall night-sky brightness by up to three to four times. This atmospheric brightening threatens the Vera C. Rubin Observatory’s 3.2-gigapixel camera and compromises the ability to monitor potentially hazardous asteroids approaching Earth.
The observational crisis coincides with funding pressures across international research institutions. In July, UK Research and Innovation confirmed it will cut funding from e-MERLIN—the radio network anchored by the 76-metre Lovell Telescope at Jodrell Bank—when the current agreement expires in March 2028. The Royal Astronomical Society characterized the decision as devastating for UK astronomy.
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