Context: 

Recently, approximately 120 SpaceX Starlink satellites burned up upon re-entry into Earth's atmosphere, generating spectacular artificial meteor showers visible to many around the world. 

Satellite Re-Entries and Their Environmental Impact

• During satellite re-entry into the atmosphere, satellites travel at about a speed of 27,000 km per hour. 
• This generates extreme heat through aerodynamic friction, causes the satellite to disintegrate in the atmosphere, with most components vaporising before reaching Earth’s surface.
• During re-entry, the aluminium in satellites oxidizes, creating aluminium oxide particles.
• Starlink satellites are made up of about 40% aluminium.
• A typical Starlink satellite weighs around 250 kg, producing 30 kg of aluminium oxide during re-entry.
• Aluminium oxide particles remain suspended in the mesosphere for extended periods, eventually descending into the stratosphere (where Earth’s Ozone layer is present).
• These particles act as catalysts for chemical reactions involving chlorine, potentially contributing to ozone layer depletion. 

Satellite Constellations and Growing Numbers

• According to the European Space Agency (ESA), over 28,000 objects, including small satellites, are currently in space, with most of them in LEO.
• SpaceX has launched nearly 8,000 Starlink satellites, with plans to deploy 42,000.
• Other companies, like Amazon, are also planning large satellite constellations.
• In 2022 alone, satellite re-entries released an estimated 41.7 metric tons of aluminium oxide, more than natural inputs from micrometeoroids.
• If the current pace continues, annual releases of aluminium oxide could reach 360 metric tons, a 646% increase compared to natural levels.
• These particles remain suspended in the mesosphere before potentially descending to the stratosphere, where the ozone layer exists.

Ozone Depletion Risks

• Although aluminium oxide does not directly consume ozone, it acts as a catalyst for chemical reactions involving chlorine, a process that can lead to ozone depletion similar to the damage caused by chlorofluorocarbons (CFCs) in the past. 
• Research indicates that just one particle of aluminium oxide can contribute to the destruction of thousands of ozone molecules over several decades. 
• This slow process could delay the ozone layer's expected recovery and aggravate environmental challenges.

Challenges 

• Despite the growing concerns, there is currently no comprehensive regulatory framework to address the environmental impacts of satellite re-entries. 
• The US Federal Communications Commission (FCC) provides licenses for satellite constellations, but it does not consider the environmental impact of satellite re-entries in its assessments. 
• Additionally, commercial satellites are excluded from environmental reviews under the National Environmental Policy Act (NEPA). 
• International efforts to address space sustainability are still in their nascent stages, with the UN Committee on the Peaceful Uses of Outer Space (COPUOS) holding discussions but without binding agreements.

Potential Solutions

To mitigate the environmental impact, some experts advocate for developing alternatives to aluminium in satellite design. 

Another potential solution is placing decommissioned satellites in "graveyard orbits"—higher orbits where they are less likely to interfere with operational satellites. 

• However, this would require additional fuel and may only delay the problem.

As part of the ESA's Zero Debris initiative, the agency aims to prevent the generation of new orbital debris by 2030, ensuring that satellite launches and operations are conducted with greater environmental responsibility.