Space Debris: What Governments Fear

Imagine a thin layer around the Earth, teeming with activity. This is where the data that powers our modern world transits: weather forecasts, financial transactions, global communications, GPS signals. But this vital artery is becoming increasingly congested, not with traffic jams, but with a silent, invisible threat: space debris. Millions of fragments, ranging from the size of a screw to that of a bus, hurtle along at dizzying speeds of over 28,000 km/h. At this velocity, even a paint chip can inflict catastrophic damage on an operational satellite or the International Space Station.

What governments and space agencies fear most is not a simple collision, but a devastating domino effect known as the "Kessler Syndrome." This chain reaction could render entire sections of Earth's orbit unusable for generations. Faced with this growing peril, a race against time is underway. It's no longer just about launching new technologies, but about developing ingenious methods to prevent our gateway to space from closing for good.

To understand the scale of the problem, we must first understand the enemy. Space debris, or "orbital pollution," is any human-made object orbiting the Earth that no longer serves a useful purpose.

Threats of all sizes

The danger of a piece of debris is not always proportional to its size. Kinetic energy (related to mass and the square of velocity) is the key factor. Debris is generally classified into three categories:

• Over 10 cm: About 36,500 of these are tracked. They are the most dangerous, capable of completely destroying a satellite or spacecraft. They include defunct satellites, upper stages of rockets, and large fragments from collisions. They are actively tracked from the ground.
• Between 1 cm and 10 cm: Estimated at over one million, these objects are too small to be tracked reliably but large enough to cause critical damage, or even the loss of a satellite if they strike a vital component.
• Less than 1 cm: There are more than 130 million of these micro-debris. While they cannot destroy a satellite, they erode surfaces, degrade solar panels, and can damage sensitive instruments. A space shuttle's windshield once had to be replaced due to an impact with a mere paint chip.

Where does all this orbital junk come from?

Space pollution is the legacy of over 60 years of space activity. Its sources are numerous:

1. End-of-life satellites: Thousands of satellites launched since Sputnik in 1957 are now inert "ghosts."
2. Launcher stages: The parts of rockets used to place satellites into orbit are often abandoned once their mission is complete.
3. On-orbit explosions: The most significant cause of new debris. They can be due to leftover fuel or batteries exploding on old spacecraft.
4. Accidental collisions: The most infamous event is the 2009 collision between the active Iridium 33 communications satellite and the defunct Russian military satellite Kosmos-2251. This impact alone generated over 2,300 trackable fragments.
5. Anti-satellite (ASAT) weapon tests: Some countries have tested missiles capable of destroying satellites in orbit, creating immense clouds of extremely dangerous and long-lasting debris.

The real nightmare for space planners was theorized as early as 1978 by NASA scientist Donald J. Kessler. The "Kessler Syndrome" describes a scenario where the density of debris in low Earth orbit reaches a critical threshold.

At this point, a single collision generates a cloud of new debris. Each of these fragments increases the probability of further collisions, which in turn create even more debris. This self-sustaining chain reaction accelerates exponentially, eventually creating an impassable belt of debris around the Earth.

The consequences would be catastrophic for our space-dependent civilization:

• Loss of essential services: The end of GPS, accurate weather forecasting, satellite telecommunications, and direct-to-home television.
• Risks for astronauts: The International Space Station, which already has to perform avoidance maneuvers several times a year, would become untenable.
• End of access to space: Launching new rockets would become extremely risky. Future space exploration, missions to Mars or the Moon—everything would be compromised for decades, if not centuries.

Aware of the danger, space agencies around the world have established guidelines to limit the creation of new debris. These measures are known as "mitigation," meaning prevention.

The 25-Year Rule

This is the cornerstone of mitigation. International guidelines recommend that any satellite launched into low Earth orbit (below 2000 km) be removed from orbit within 25 years of the end of its mission. There are two options for this:

• Controlled atmospheric reentry: The satellite uses its last fuel reserves to brake and lower its orbit. It then plunges into the atmosphere where friction causes it to burn up and largely disintegrate.
• Graveyard orbit: For satellites in geostationary orbit (at 36,000 km), atmospheric reentry would be too fuel-intensive. They are instead sent to a "graveyard orbit," a few hundred kilometers higher, where they will not interfere with active satellites.

Systematic Passivation

To prevent on-orbit explosions, a procedure called "passivation" is now standard. At the end of its life, a satellite or rocket stage must be drained of all stored energy: fuel tanks are vented and batteries are disconnected to avoid any risk of short-circuits or late explosions.

Design for Demise (D4D)

Engineers are now working on designing satellites that disintegrate more easily and completely during reentry into the atmosphere. This involves using materials with lower melting points and avoiding highly resistant alloys like titanium for large components, which might survive reentry and crash to the ground.

Surveillance and Avoidance

The U.S. Space Command (USSPACECOM) maintains a public catalog of over 27,000 trackable objects. Using a global network of radars and telescopes, it can predict trajectories and alert satellite operators in case of a collision risk. They can then perform an avoidance maneuver to move to safety.

Mitigation is essential, but it doesn't solve the problem of debris that is already there. For that, we need "active debris removal," a booming technological field where solutions worthy of science fiction are being developed.

Harpoons and Nets

The European mission RemoveDEBRIS successfully tested several techniques. One involves firing a harpoon at a target debris to securely attach to it before dragging it into the atmosphere. Another approach involved deploying a large net to capture a tumbling object.

Space Tugs with Robotic Arms or Magnets

The Japanese startup Astroscale launched its ELSA-d mission to demonstrate a magnetic capture technology. A "chaser" satellite approaches a "client" satellite (pre-equipped with a docking plate) and docks with it magnetically to then de-orbit it. Other projects, notably led by the European Space Agency (ESA), are focusing on using robotic arms to grab non-cooperative debris. Some experts are even considering the role that future heavy-lift launchers, at the heart of Starship missions, could play in capturing and de-orbiting massive debris.

Ground-Based Lasers

A more futuristic approach involves using powerful ground-based lasers. The idea is not to destroy the debris, which would create even more fragments, but to "nudge" it slightly. By heating one of its sides, a small amount of thrust is created through laser ablation. Repeated regularly, this impulse can alter the debris's trajectory enough to accelerate its decay into the atmosphere.

The orbital pollution equation is becoming more complicated with the arrival of satellite mega-constellations, such as SpaceX's Starlink or OneWeb. These projects plan to deploy tens of thousands of satellites in low Earth orbit to provide global internet access. The frenzied pace of launches, illustrated by the SpaceX 2026 schedule and other players, drastically increases the density of objects in orbit.

This new space era imposes increased responsibilities. The operators of these constellations are aware of this and are integrating advanced technologies:

• Autonomous avoidance systems: Their satellites are capable of detecting collision risks and altering their trajectory autonomously, without human intervention.
• 100% successful de-orbiting: They are designed to de-orbit automatically at the end of their life using their electric propulsion, with a targeted reliability rate of 100%.
• Low orbit: They operate at relatively low altitudes (around 550 km), where residual atmospheric drag ensures that a failed satellite will fall back and burn up naturally within just a few years, instead of the centuries or millennia it would take in higher orbits.

However, these private initiatives are not enough. The international community agrees on the urgent need to move from simple "guidelines" to truly binding regulations for Space Traffic Management, similar to air traffic control, to ensure a sustainable future for space activities.