Megaconstellations of satellites: an imminent and unavoidable Kessler syndrome? 🛰️

Since 2019, the number of active satellites has more than doubled, reaching nearly 11,700 by May 2025. Satellite constellations, such as SpaceX's Starlink, dominate this space landscape, accounting for over 60% of the total.


Experts estimate that the maximum capacity of low Earth orbit is around 100,000 active satellites. Beyond this, the risk of collisions and the creation of space debris in a chain reaction—the infamous Kessler syndrome—could render this zone unusable. This limit could be reached before 2050 at the current launch rate.

Megaconstellations also have consequences for ground-based astronomy, interfering with optical and radio observations. Electromagnetic leaks from communication satellites mask signals from distant celestial objects, compromising certain astronomical research.

The environmental impact of launches and satellite disintegration in the atmosphere is also raising concerns. Greenhouse gas emissions and metallic pollution could have poorly understood effects on Earth's upper atmosphere.

What is the Kessler syndrome?

The Kessler syndrome describes a scenario where the density of objects in low Earth orbit becomes so high that collisions between them generate additional debris. This debris can, in turn, cause further collisions, creating a chain reaction.

This phenomenon could render certain orbits unusable for satellites and space missions. Scientists fear such a situation could severely limit future generations' access to space.

Measures to mitigate this risk include designing satellites capable of deorbiting at the end of their lifespan and developing technologies to clean up existing debris. However, international cooperation is essential to implement these solutions effectively.

How do satellites affect astronomy?

Satellites, particularly those in megaconstellations, reflect sunlight, creating bright streaks that can interfere with astronomical observations. These disruptions are especially problematic for optical telescopes studying deep space.

Unintentional radio emissions from communication satellites can also obscure signals picked up by radio telescopes. This complicates the study of distant cosmic phenomena, such as fast radio bursts or primordial galaxies.

Astronomers are working with satellite operators to find solutions, such as adjusting solar panel angles to minimize reflection or using radio frequencies that don't interfere with scientific observations. Despite these efforts, the growing impact of satellites on astronomy remains a major concern.