Is Earth Being Poisoned From Above by a Spacecraft Fallout Crisis?

The Unseen Fallout

The modern space age is defined by a visible, dramatic increase in launch activity. Driven by the rapid deployment of large satellite constellations, thousands of new objects are placed into low Earth orbit every year. But for every satellite launched, an inevitable question arises: what happens when it dies?

When spacecraft and rocket stages reach their end of life, many reenter Earth’s atmosphere at high speed. While this is often seen as a solution to the in-orbit space debris problem, it creates another, less visible one. As these objects burn up, they don’t simply vanish. They ablate, or vaporize, injecting a stream of fine metallic particles and chemicals into the high-altitude mesosphere.

This phenomenon is now referred to as “space waste,” to distinguish it from the problem of debris in orbit. For a long time, this atmospheric injection was considered negligible, a tiny drop in the ocean compared to the natural influx of material from ablating meteoroids.

A new scientific study reveals this assumption is no longer valid. An updated analysis, published as a 2025 preprint titled “Space waste: An update of the anthropogenic matter injection into Earth atmosphere” by Leonard Schulz and a team of international researchers, indicates that the atmospheric pollution from reentering space waste is increasing at an accelerated rate. This man-made fallout is already measurable, fundamentally altering the chemical makeup of the upper atmosphere and posing substantial, long-term environmental risks.

A Growing Problem Driven by Mega-Constellations

The challenge of space sustainability is often discussed as two distinct problems. The first is space debris, the defunct, non-functional material still orbiting Earth that poses a collision risk to active satellites. The second is ground impact risk, which involves parts of a reentering object surviving the fiery descent and hitting the ground, potentially causing damage or injury.

This new research highlights the third, interconnected problem: space waste. It’s the atmospheric consequence of reentry. Ironically, efforts to solve the ground impact problem – by designing satellites that “demise” or burn up more completely – directly amplify the space waste problem. A more complete burn-up means a greater mass of material is released as vapor and particulates into the atmosphere.

This problem is growing because the amount of mass reentering the atmosphere is growing. The study quantified this “mass influx” using publicly available reentry databases.

For the years 2015 to 2020, the total mass of reentering objects was relatively constant, fluctuating just below 1,000 tonnes per year. Since 2020, that number has risen sharply. This increase is attributed almost entirely to the deployment of large satellite constellations, most notably Starlink by SpaceX. The trend is driven by two factors: the reentry of the rocket upper stages used to deploy these satellites, and the reentry of the first batches of satellites themselves as they reach their 5-year end-of-life.

By 2024, the annual mass influx had climbed to 1,600 tonnes. The extrapolation for 2025 projects a total influx of 2,350 tonnes. This reentry mass is composed of satellites and debris, rocket upper stages, and suborbital core stages (boosters that don’t reach orbit but reenter at high speed). The analysis specifically tracks the growing contribution of Falcon 9 upper stages and the test flights of the massive Starship, which at 120 tonnes of dry mass, represents a new class of large-scale reentry object.

From Influx to Injection: Measuring What Burns Up

Not all mass that reenters the atmosphere ablates. Some survives to impact the ground. The “mass injection” is the portion of the mass that actually vaporizes and is deposited in the atmosphere. To estimate this, the researchers used ablation fractions based on previous work:

• Satellites and debris: 80% is assumed to ablate.
• Rocket upper stages: 65% is assumed to ablate.
• Core stages: 30% is assumed to ablate.

Applying these fractions to the rising mass influx reveals a stark trend. From 2015 to 2020, the total mass injected into the atmosphere was steady at around 340 to 380 tonnes per year. By 2024, that injected mass had more than doubled to 887 tonnes.

The projection for 2025 is even more significant: an expected injection of 1,400 tonnes. This 2025 figure is particularly noteworthy because it already matches the “probable” future scenario (Scenario 1) from a 2021 study. What was once considered a future possibility for 2030, based on 19,400 active constellation satellites, is essentially being realized today. This suggests the atmospheric impact of the space industry is accelerating faster than many models had predicted.

On its own, 1,400 tonnes may not sound like much. The study notes that in 2024, the total injected mass from space waste was only about 7% of the total mass injected by natural meteoroids. But this comparison is misleading. The composition of space waste is what matters, and it’s drastically different from the natural background.

An Unnatural Elemental Footprint

Meteoroids are mostly rock and ice, composed primarily of silicates (oxygen, silicon, magnesium) and organic elements. Space waste, in contrast, is made of highly refined metals, alloys, plastics, and complex chemicals.

When the researchers compared the metal injection alone, they found that space waste in 2024 accounted for 14% of the natural metallic injection. This is a much more significant figure, and it doesn’t even tell the whole story. The real issue is found when looking at specific elements.

The study’s most significant finding is that a large and growing number of elements injected by humans now dominate their natural atmospheric influx.

• In 2015, 18 different elements from space waste were being injected in greater quantities than from all natural meteoroids combined.
• By 2024, that number had grown to 24 elements.
• In a future scenario with 75,000 active constellation satellites (Scenario 2), this number could rise to 30 elements.

Aluminum is the most abundant element injected from space waste by mass, but many other elements that are extremely rare in meteoroids are now becoming common in the upper atmosphere. These include lithium, copper, lead, niobium, tin, hafnium, and tungsten.

The following table provides the estimated mass injected into the atmosphere for 43 different elements. It compares the average from 2015-2020 to the years 2021-2024, as well as two future scenarios. It also provides the estimated natural injection from meteoroids for comparison.

Values are marked to show the scale of anthropogenic dominance:

• Yellow: 100-200% of the natural meteoric input (up to 2 times).
• Orange: 200-500% of the natural meteoric input (2 to 5 times).
• Red: Over 500% of the natural meteoric input (at least 5 times).

Deconstructing Space Waste: What Are We Sending into the Atmosphere?

To create these estimates, the researchers had to first determine what spacecraft are made of. This is a major challenge, as the exact composition of satellites and rockets is often proprietary information. The team built an “average” composition for different object types by combining information from space material databases, anonymized manufacturer data provided by a large European satellite builder, industry reports, and scientific literature.

The “Average” Satellite

The model for a typical LEO satellite (under 1000 kg) reveals a complex mix of materials, far beyond the simple aluminum shell one might imagine.

• Structure: The two largest components by mass are aluminum alloys (36.7%) and carbon fibre-reinforced polymer (CFRP) (15.1%). The aluminum alloys are the primary reason Al is the single largest anthropogenic element injected into the atmosphere. The CFRP is typically carbon fibers held in an epoxy or cyanate ester resin. The study notes that some epoxy resins contain small but significant trace amounts of chlorine from their manufacturing process.
• Batteries: Modern satellites almost exclusively use Lithium-ion batteries, which make up about 6.4% of the average satellite’s mass. Two common types are used: LCO (using Lithium Cobalt Oxide) and NCA (using Lithium Nickel Cobalt Aluminum Oxide). These batteries are a primary source for injected lithium, cobalt, and nickel. Their electrolyte, lithium hexafluorophosphate (LiPF6), is also a major contributor of atmospheric fluorine.
• Electronics (PCBs): Printed circuit boards (PCBs) and electronics account for about 5% of the mass. These boards are a cocktail of elements. While copper is a major component, a key contributor is solder. Despite efforts to move to lead-free alternatives, traditional tin-lead solder is still widely used in the space industry. This makes PCBs the dominant source of both injected tin and lead. The boards also contain bromine as part of their flame-retardant laminate material (like FR4).
• Solar Panels: Solar arrays contribute about 1% of the mass. While older silicon-only cells exist, modern satellites predominantly use high-efficiency triple-junction solar cells (InGaP/GaAs/Ge). These cells are built on a germanium substrate, making them the main source of injected germanium. The study also updated previous estimates for arsenic, finding that it’s used in much smaller amounts than once thought, and its injection levels do not dominate the natural influx. The protective cover glass on these panels is often borosilicate glass doped with cerium dioxide to shield from UV radiation, making it the source of injected cerium.
• Wires and Cables: Making up over 7% of the mass, these are mostly copper but are often coated with trace amounts of silver for better conductivity. The insulation is typically a plastic like PTFE (Teflon) or polyimide (Kapton), which themselves contain fluorine and carbon.
• Other Materials: The remainder is a mix of specialized materials:
  • Optical Materials: Glasses like BK7 and ZERODUR, which contain silica, boron, and oxides of zincand sodium.
  • Paints and Coatings: White thermal-control paints commonly use zinc oxide (ZnO) as a pigment, while black paints use carbon.
  • Ceramics: Components like insulators use alumina (aluminum oxide), silicon nitride, and silicon carbide.
  • Multi-Layer Insulation (MLI): The shiny thermal blankets seen on spacecraft are typically plastic (like Kapton) coated with a very thin layer of aluminum.

Rocket Stages: Tanks, Engines, and Superalloys

Rocket stages have a different composition than satellites, with mass dominated by tanks and engines.

• Tanks and Structures: The largest mass fraction by far comes from propellant tanks and structural elements. In most core stages and upper stages (like the Delta II or Vega), these are made from high-performance aluminum alloys, including aluminum-lithium alloys, which are favored for their low weight. This adds to the atmospheric load of both aluminum and lithium.
• The Starship Exception: The study models the Starship upper stage separately due to its enormous 120-tonne mass and unique design. Instead of aluminum, its body is constructed from stainless steel (likely 304L), which is primarily iron, chromium, and nickel. It also features a thermal protection system of silica tiles. This means a single Starship reentry injects a vastly different – and larger – profile of elements than other stages, dominated by iron and chromium.
• Rocket Engines: Engines are a primary source of the most exotic metals. They are complex machines built from superalloys and materials that can withstand extreme temperatures and pressures.
  • Thrust Chambers: The inner liner of the engine, where combustion occurs, is often made of specialized copper alloys like Narloy-Z or nickel-cobalt alloys.
  • Nozzles: Engine nozzles, particularly vacuum-optimized versions, are frequently made from C-103, an alloy that is 89% niobium. The Falcon 9 upper stage engine and Starship’s vacuum engines are reported to use niobium nozzles. This is the single biggest reason why injected niobium from space waste is thousands of times higher than the natural meteoric input.
  • Turbopumps: These rotating components are built from some of the most durable materials, including silicon nitride, cobalt-based alloys like Haynes 188, and various stainless steels.
• Other Rocket Systems:
  • Pressurization Tanks: Often use titanium (Ti6Al4V) or are composite-overwrapped pressure vessels (COPVs), which consist of a titanium liner wrapped in carbon fibre-reinforced polymer.
  • Reaction Control System (RCS): Thruster propellant tanks are often titanium, and the small thruster nozzles themselves can use alloys of cobalt (Haynes 25), niobium, hafnium, molybdenum, and tungsten.

This detailed breakdown explains the source of the anomalous elements. The atmospheric injection is a direct fingerprint of the industrial alloys, batteries, and electronics we use to build spacecraft.

Finding the Evidence: Space Waste in the Stratosphere

These findings are not just theoretical calculations. The study’s estimates were validated by comparing them to real-world atmospheric data.

Atmospheric circulation naturally transports material from the mesosphere (where ablation occurs) down to the stratosphere, where it can be collected. A 2023 study by Murphy et al. did just that, analyzing the chemical composition of individual aerosol particles sampled from the stratosphere.

The Schulz et al. study found that its new injection estimates for 2022 show “excellent agreement” with the elemental ratios discovered in those stratospheric particles. This provides powerful, independent confirmation that space waste is present, measurable, and accumulating in the atmosphere.

The comparison was striking:

• The 2023 measurements found that over 70% of the aluminum in the sampled particles came from space waste. The new study’s model calculated a 67% anthropogenic fraction for 2022.
• The measurements found that over 90% of the lithium, copper, and lead was from space waste. The new study’s model calculated fractions of 98% for lithium, 94% for copper, and 99% for lead.
• The measured ratios of other rare metals like niobium, hafnium, and tantalum relative to aluminum also matched the study’s injection estimates.

This strong correlation implies two things. First, the models of what spacecraft are made of are largely correct. Second, it suggests that a high percentage of the reentering material is vaporized into very small particles (10-100 nanometers). These tiny particles are small enough to be transported by atmospheric circulation and can reside in the stratosphere for several years, allowing them to accumulate. If the material ablated primarily as large molten droplets, it would fall to Earth too quickly to be measured in this way.

Potential Environmental Risks

This confirmation that the upper atmosphere is being systematically altered raises serious questions about the potential environmental consequences. The injected materials are not inert; they are chemically active, and their presence in large quantities could have long-term adverse effects.

• Ozone Depletion: This is a primary concern. Many of the injected metals can act as catalysts, participating in chemical reactions that destroy stratospheric ozone. Aluminum, for example, could form solid alumina particles that provide a surface for ozone-destroying reactions. The new study also notes that aluminum may form other chemical species, like aluminum hydroxides, which could have different but equally potent effects on ozone chemistry.
• Changes in Cloud Formation: The atmosphere needs “seeds,” or condensation nuclei, for clouds to form. These new man-made nanoparticles could serve as abundant seeds, potentially altering the formation, frequency, and properties of high-altitude clouds. This includes polar mesospheric clouds (night-shining clouds) and polar stratospheric clouds. Because polar stratospheric clouds play a direct role in the chemical destruction of ozone, any change to them is a serious concern.
• Radiative Effects (Climate): Creating a new, persistent layer of aerosol particles in the stratosphere could change Earth’s energy balance. These particles can scatter or absorb incoming sunlight, creating a “radiative forcing” effect. This could have unforeseen consequences for the global climate.
• Unknown Chemistry: Perhaps the most significant risk is the unknown. The study highlights that many of the dominant injected materials are transition metals (titanium, copper, niobium, cobalt, etc.), which are famous for their catalytic activity. We are injecting these active materials into a sensitive, high-altitude environment in quantities that dwarf the natural background. This creates the potential for entirely new and unstudied chemical pathways, with consequences for the atmosphere that are not yet understood.

Uncertainties and the Need for More Data

The authors of the study are careful to note that these figures are estimates, and significant uncertainties remain.

The largest single source of uncertainty is “differential ablation.” The model assumes that when a satellite burns up, all its materials are released in the same proportion that they exist in the satellite. In reality, this isn’t true.

Different materials have different melting and vaporization points. Volatile materials like lead in solder will vaporize much more easily and at higher altitudes than refractory metals like niobium or tungsten in an engine nozzle. It’s possible the niobium nozzle survives reentry completely, meaning its atmospheric injection is zero, or that the lead ablates far more efficiently than the 80% average.

This differential ablation is known to strongly influence the natural injection of elements from meteoroids, but there is not enough data to model it for complex, multi-material objects like satellites.

To improve these estimates, the researchers call for more data. This includes more transparency from manufacturers about the materials they use, more ground-based experiments to simulate reentry ablation, and more dedicated searches for and analysis of space waste that has survived reentry to better understand what burns up and what does not.

Summary

This article, based on the findings of Schulz et al. (2025), presents an updated and concerning picture of the atmospheric impact of the space industry. The injection of “space waste” from reentering satellites and rocket stages is no longer a negligible side effect. It is a rapidly growing phenomenon, more than doubling between 2020 and 2024, and it is happening faster than many models had predicted.

This increase is driven by the launch and disposal of large satellite constellations. The 2025 projected injection rate of 1,400 tonnes already matches what was, just a few years ago, considered a “probable” future scenario for 2030.

While the total mass of this waste is still less than that from natural meteoroids, its chemical composition is vastly different. The study finds that in 2024, 24 different elements injected by space waste – mostly metals – dominate their natural atmospheric influx. This number is rising.

This isn’t just a forecast. These materials have been measured and confirmed in stratospheric aerosol particles, with elemental ratios that perfectly match the study’s injection estimates. We are measurably changing the chemistry of the upper atmosphere.

This influx of new, chemically active materials, especially transition metals, indicates a substantial risk of long-term adverse effects. These include the catalytic destruction of the ozone layer, alterations to high-altitude cloud formation, and radiative effects on the global climate. The research highlights the urgent need to understand the new and unknown chemical pathways being opened by this unprecedented atmospheric pollution.