A new space race could turn our atmosphere into a ‘crematorium for satellites’

When we look up at the night sky and see a satellite glide past, we might not consider climate change or the ozone layer.

Space may feel separate from the environmental systems that sustain life on Earth. But increasingly, the way we build, launch and dispose of satellites is starting to change that.

Over the past few years, the number of satellite launches has skyrocketed. There are now nearly 15,000 active satellites in orbit around the Earth, most of them part of “mega-constellations” in which each satellite has a service life of only a few years.

New satellites must be quickly launched as replacements. To avoid leaving old, dead satellites in Earth’s already-crowded low orbits, most satellite operators deliberately de-orbit them into Earth’s upper atmosphere.

Here, they burn up or break apart into smaller pieces: a process known as “demisability”. In effect, satellites have become part of throwaway culture.

That approach is now being taken to a vastly larger scale. We are concerned about the implications for Earth’s climate and atmosphere.

A sleeper risk for our climate and ozone layer

Last month, SpaceX applied to the US Federal Communications Commission (FCC) for permission to launch one million more satellites for untested “AI data centres”.

That sheer number isn’t the only issue. SpaceX’s Starlink V2 “mini” satellites happen to weigh about 800 kilograms (kg) – roughly the mass of a small car – with later versions expected to reach around 1,250 kg. The planned V3 satellites are larger still, comparable in scale to a Boeing 737 airliner.

Rocket launches already contribute to climate change and ozone depletion. Scaling them up to deploy a million aircraft-sized satellites would push upper-atmosphere heating and ozone loss far beyond previous estimates, with the steady burn-up of dead satellites compounding the impacts.

This comes as burnt satellite dust is already being found in the atmosphere. In 2023, scientists studying aerosols in the upper atmosphere found metals from re-entering spacecraft. Just recently, lithium has been detected from the uncontrolled re-entry of a Falcon 9 rocket.

This is just a fraction of what is to come if planned megaconstellations go ahead – and SpaceX is far from the only player. Other operators worldwide have already asked for a combined total of over one million satellites.

All the while, the full environmental consequences remain poorly understood because satellite builders rarely disclose what their spacecraft are made of.

Scientists assume a large fraction is aluminium, which burns up into alumina particles, but the exact mix of materials – and the size of the particles produced – remains poorly constrained.

But we know the very smallest particles, finer than a human hair, can stay suspended in the atmosphere for years, contributing to ozone depletion and climate change.

Following similar assumptions to a previous study, we estimate that a million satellites could mean that a teragram (one billion kgs) of alumina accumulates in the upper atmosphere – enough, alongside launch emissions, to significantly alter atmospheric chemistry and heating in dramatic ways we do not yet understand.

There is no public mandate for a single company in one country to make changes on that scale to the planet’s atmosphere.

The consequences are not confined to the atmosphere. Not all re-entering satellites burn up; debris is already hitting the ground and the chance of a casualty from megaconstellation re-entries is now about 40% per five-year cycle – rising for both people and aircraft as more satellites are added to orbit.

In space, the picture is no less stark: the Outer Space Institute’s CRASH Clock suggests a collision would occur within 3.8 days if satellites stopped avoiding each other.

Many experts agree we are in the early stages of the Kessler Syndrome: a cascading chain reaction of collisions that multiplies space debris.

Our skies are not a dumping ground

Our night sky, especially cherished in New Zealand, is one of the few things everyone on Earth still shares.

According to simulations built by astronomers, constellations on the scale proposed by SpaceX would fill the sky with many thousands of satellites visible to the naked eye anywhere on Earth. Eventually, there could be more visible satellites than visible stars.

For scientists, observing the deaths of stars and searching for new planets would become much harder. Stargazing, astrotourism and cultural astronomy would similarly be disrupted worldwide.

All of this means the FCC’s ruling on the SpaceX proposal, now open to public submissions, could affect everyone – whether through changes to the atmosphere, growing collision risks in orbit or the loss of an unspoilt night sky.

One solution being discussed is to dispose of dead satellites in orbits away from Earth. But this would require much more fuel per satellite to escape Earth’s gravity, increasing both payload and the environmental impact of rocket launches. Some debris would still return to Earth.

With SpaceX and others planning rapid expansion, global regulation is needed: in an uncapped system, regulating one firm just shifts the problem elsewhere. As the largest operator, SpaceX is best placed to lead on an environmentally sustainable solution, just as Du Pont did with phasing out CFCs in the 1980s.

A first step is to define a safe atmospheric carrying capacity for satellite launches and re-entries. Environmental assessments should cover the full lifecycle, including atmospheric effects, and address both orbital safety and impacts on cultural and research astronomy.

Whatever the regulatory outcome, using the atmosphere as a crematorium for satellites at this scale cannot be a solution.

Laura Revell receives funding from the Marsden Fund and Rutherford Discovery Fellowships, administered from New Zealand Government funding by the Royal Society Te Aparangi. She is a member of the International Ozone Commission, UN Environmental Effects Assessment Panel, UN Nuclear War Effects Panel, and a lead author on the IPCC's 7th Assessment Report.

Michele Bannister receives funding from the Rutherford Discovery Fellowships, administered from New Zealand Government funding by the Royal Society Te Aparangi. She is a member of the International Astronomical Union's Centre for Dark and Quiet Skies.

Samantha Lawler receives funding from the Natural Sciences and Engineering Research Council of Canada. She is a fellow of the Outer Space Institute, and a Visiting Erskine Fellow at the University of Canterbury.