Look up on a clear night above the Mühlviertel or high in the Tauern mountains and you will now regularly see something that simply did not exist ten years ago: a string of bright pearls gliding silently across the sky from west to east. They are not stars but satellites — most of them from the Starlink fleet operated by the American company SpaceX. At the end of May 2026, the giant Starship rocket system lifted off in Texas for the twelfth time, for the first time in its new V3 version; a few days later, the US aviation authority, the FAA, ordered an investigation before the next launch could be approved. Above our heads, a technical infrastructure of historic proportions is taking shape at breakneck speed. And a question long relegated to the background is now pushing its way to the front: what does this boom actually mean for the environment?
A sky filling up fast
The numbers are hard to grasp. By early June 2026, around 10,400 Starlink satellites were already circling the Earth — more than all of humanity had launched in the first fifty years of spaceflight combined. SpaceX is aiming for a fleet of up to 42,000 satellites, and in early 2026 the company even filed an application to operate up to a million more in the long term. It is not alone: Amazon is building its own network under the name "Kuiper", and several Chinese consortia are planning constellations on a similar scale. Experts long ago stopped talking about individual satellites and now speak of "megaconstellations".
This is precisely where Starship comes in. The reusable heavy-lift system is designed to carry satellites into orbit in bulk and at falling cost. The test flight in mid-2026 deployed a dummy satellite for the first time and brought the upper stage down in a controlled splashdown in the Indian Ocean — a technical advance likely to accelerate the pace of expansion even further. The cheaper the transport, the more mass migrates into orbit. What is a triumph from an engineering perspective becomes a problem from an environmental one: for the first time, spaceflight is intervening in the upper layers of the atmosphere not occasionally, but permanently and on a grand scale.
Why the launch is only the beginning
On its way up, a rocket burns thousands of tonnes of propellant and leaves its exhaust not on the ground but spread across the entire height of the atmosphere. Alongside carbon dioxide and water vapour, two critical substances are produced above all: soot — "black carbon" in the technical jargon — and, depending on the fuel, chlorine compounds and metal particles. The insidious part is the location. While soot from cars or power stations is washed out within days, the soot from a rocket goes straight into the stratosphere, where it lingers for years and absorbs sunlight.
Researchers estimate that soot at this altitude has many times the climate impact it would have near the ground — some calculations put the effect at several hundred times stronger. For now, the absolute quantity remains small compared with aviation. But what matters is not today's level; it is the growth curve. If the number of launches rises as planned from a few hundred to several thousand a year, the result is a cumulative input that so far appears in no climate accounting at all.
Space was long the only part of our environment that nobody really felt responsible for — neither for what we shoot up, nor for what falls back down.
The invisible trail in the stratosphere
The effect on the ozone layer is by now particularly well studied. A study published in 2025 in the journal npj Climate and Atmospheric Science modelled two scenarios. In the more cautious case — around 880 launches per year — the global ozone layer would thin by about 0.17 per cent by 2030. In the ambitious scenario, with a good 2,000 launches annually, the figure would be 0.29 per cent, and over the Antarctic in spring almost four per cent. The culprits are the chlorine from solid rocket propellants and, once again, the soot.
That may sound like little, but it carries an uncomfortable twist. Since the Montreal Protocol of 1987, the ozone layer has been slowly recovering from the damage done by CFCs — one of the greatest successes in the history of international environmental policy. It is precisely this recovery that could now be slowed by a new and so far unregulated source. The study's authors therefore warn against leaving the choice of propellants to the companies alone.
What re-entry leaves behind
A second, long overlooked effect concerns the end of a satellite's life. Most Starlinks are designed for an operating life of only around five years and are meant to burn up completely on re-entry — a clean solution, or so it seemed. But "burning up" means that metals vaporise and remain behind as ultra-fine particles at altitudes of 60 to 90 kilometres, above all aluminium oxide. While a growing repair movement on the ground is pushing back against throwaway culture, in orbit it remains firmly built into the design.
In 2024, the US weather agency NOAA arrived at a startling finding: for the first time, the share of human-made aluminium in the upper atmosphere exceeded that from natural sources such as meteorite dust. If the approved megaconstellations are built out in full, annual aluminium oxide emissions could rise to around 360 tonnes — many times the natural background. Modelling suggests these particles could alter the temperature of the mesosphere and influence wind patterns all the way up to the polar vortex. In early 2026, researchers managed for the first time to measure the chemical plume of a re-entering rocket stage in real time; at the Leibniz Institute of Atmospheric Physics in northern Germany, a dedicated measurement system is currently being developed to systematically monitor copper, aluminium oxide and fluorine compounds from space debris. Several scientists speak openly of an "uncontrolled experiment" with the upper atmosphere.
The lost night sky
While these chemical effects escape our gaze, another is visible to anyone with the naked eye. Satellites do not shine by themselves; they reflect sunlight — and taken together, they brighten the night sky. Studies suggest the sky worldwide is already around ten per cent brighter than it would be on a natural, satellite-free night. In rural parts of Austria, where the starry sky is still comparatively dark, the bright "Starlink trains" are especially conspicuous; Austrian media, too, have reported on the chains of light in the evening sky.
For astronomy, this is more than an aesthetic nuisance. Bright streaks cut across long-exposure images, and radio signals interfere with radio astronomy. The International Astronomical Union has been warning about the consequences for research for years. SpaceX has responded by fitting some of its satellites with dark coatings and sunshades, roughly halving their brightness — but with tens of thousands of objects planned, the effect remains limited. The dark night sky — in many parts of Austria still a good worth protecting, up to and including certified dark-sky parks — is at once a habitat for nocturnal animals and a piece of cultural history. Neither can be restored after the fact.
The paradox: satellites as a tool of climate protection
Anyone who sees only the dark side here, however, is making things too easy for themselves. Without satellites there would be no modern climate protection. Earth observation programmes such as Europe's Copernicus system measure sea-level rise, melting glaciers, the extent of forests and even individual methane leaks from orbit. Early-warning systems for floods and heatwaves, which overheating cities like Vienna also rely on, precise weather forecasts, internet for remote valleys — all of it hangs on the infrastructure above us.
Austria is more closely involved in this than many people realise. The republic has been a member of the European Space Agency (ESA) since 1987. The Space Research Institute in Graz, part of the Austrian Academy of Sciences, is contributing to a whole series of active and future missions, supplying hardware for the ESA mission SMILE, for instance, which in 2026 is studying the interplay between the solar wind and Earth's magnetic field. Austrian companies deliver components ranging from thermal insulation to payload fairings. The message, then, is not "spaceflight is bad" but rather: what matters is operating it responsibly.
What needs regulating now
And that is exactly where things fall short. Frequencies and orbital slots are allocated internationally, but for the cumulative impact of launches on the atmosphere and climate, for the particles left by re-entry, or for the brightness of the satellites, no single body has so far felt responsible. It is a regulatory gap in the middle of a high-risk technology. The possible levers are obvious: cleaner propellants without chlorine, binding rules for orderly re-entry, caps on reflectivity — and above all an honest environmental audit covering the full life cycle of a satellite — the kind of transparency consumers have long demanded for locally sourced food.
Austria would even hold a particular lever here. Vienna is home to the United Nations Office for Outer Space Affairs (UNOOSA), the central body for international space law. A country with this diplomatic tradition, with ESA membership and a strong environmental movement, could credibly champion treating the upper atmosphere as a common good — just as the community of nations once managed to do with the ozone hole.
What remains
In the end, looking up leads to a very earthly insight. The stratosphere knows no borders; it belongs to everyone and to no one at once. Whether we treat it as a shared resource or as a free dumping ground will be decided over the coming ten years — precisely the period in which the number of objects in orbit is set to multiply. For science, the matter is clear: we need measurements, transparency and rules before the effects become irreversible. The next Starlink train drifting across Austria on a clear evening is, in that sense, both things at once — a piece of the future, and an open question.