How bad is rocket pollution? Depends what part of the atmosphere you look at
It isn’t just about how much rockets pollute, but where they pollute.Troposphere
A rocket blasting off is an explosive spectacle, and launch mishaps have hurled debris into nearby wetlands and habitats.
Relative to other polluting activities, rocket launches don’t release much carbon dioxide (CO2) into the air we breathe.
Larry Walters, a.k.a. Lawnchair Larry, rode a lawn chair attached to 42 helium-filled weather balloons in 1982, soaring up to about 4.9 km.
Spaceflight pollution doesn’t have much of an impact on the climate — yet.
For a better idea, let's compare pollution from jet planes.
Mount Everest’s peak is 8.8 km above sea level.
Wispy cirrus clouds form high in the troposphere.
There are millions more commercial flights than rocket launches. In just hours, the aviation industry burns enough fossil fuels to equal about a year’s worth of rocket launches.
Most commercial jets cruise under 12 km, but some private jets reach up to 15.5 km.
Jets, unlike rockets, add to climate change by releasing CO2 into this lower part of the atmosphere.
Stratosphere
But there’s a lot more to rocket pollution than CO2.
Depending on the type of model and fuel used, rockets can produce soot (black carbon), nitrogen oxides, alumina particles, chlorine, hydrochloric acid and water vapour.
Rocket launches used to be rare enough that pollution wasn’t much of a concern.
But launch rates have more than tripled in recent decades, with a record-setting 180 launches to orbit in 2022.
Stratospheric balloons are used to test technology for space missions.
Spaceflight is the only direct human cause of pollution above about 20 km altitude. Scientists recently found the stratosphere is peppered with particles containing metals vaporized from the re-entry of satellites and rocket boosters.
Beautiful but destructive, colourful polar stratospheric clouds can encourage ozone-depleting chemical reactions.
Some rocket pollution — like water vapour — can act as a greenhouse gas when it’s released here, in the stratosphere.
Other emissions — like nitrogen oxides, alumina particles and chlorine — deplete ozone, which protects us from the sun’s ultraviolet radiation.
The stratosphere is home to the ozone layer.
If rocket launches keep increasing, scientists worry that spaceflight pollution could undermine the progress made on ozone recovery since the late 1980s.
Scientists are also concerned about the soot that rockets spew out.
Up here, black soot particles released by rockets can linger for years. Jets release soot, too, but lower in the atmosphere, where it breaks up within weeks.
Most rocket soot comes from kerosene-fuelled models like SpaceX’s Falcon 9 (the most active rocket in the U.S.), SpaceX’s Falcon Heavy, Rocket Lab’s Electron and Russia’s Soyuz rocket (the most-launched rocket in history).
Right now, rockets produce a relatively small amount of soot (an estimated 900 tonnes yearly).
But when rocket soot is released here, directly into the stratosphere, it can act like an umbrella, absorbing solar radiation.
In 2019, for example, rocket soot equalled only about 0.01 per cent of all the soot spewed out by traditional sources like ships, diesel trucks and coal plants, according to U.K. atmospheric chemist Eloise Marais.
Scientists are trying to get a better handle on how rocket emissions up here will figure into complex climate dynamics.
But according to Marais, even that small amount of rocket soot contributed an estimated three per cent of global warming caused by soot emissions.
In other words, the rocket industry could impact our climate even if it doesn’t grow as big as other polluting industries.
Mesosphere
Some companies are experimenting with new types of fuel that may burn cleaner.
The methane-based fuel used by SpaceX’s Starship leaves less soot residue and makes it easier to reuse engines.
SpaceX’s Starship burns liquid natural gas, which is almost pure methane. It’s not yet clear whether the rocket fuel will reduce environmental impacts — or cause different ones.
Blue Origin’s BE-4 rocket also runs on liquified natural gas. Plumes of methane, a known and potent greenhouse gas, were reported by Carbon Mapper, near Blue Origin’s Texas facilities in 2023.
Companies like Blue Origin charge millions of dollars to take tourists to the edge of space.
Even though methane-fuelled rockets produce a lot less soot than kerosene-fuelled ones, Marais says they still release some.
There’s no guarantee that methane-fuelled rockets will be more environmentally friendly, especially if they burn more propellant and launch more often.
There’s still a lot to understand about how space travel will affect our climate and ozone layer.
Sprites are a type of upper-atmospheric lightning.
If the space industry stopped growing, American research scientist Martin Ross says the scientific world could probably stop worrying about it.
But since the rate of rocket launches is increasing, Ross says “we need to know the answers.”
Many rockets nowadays are what’s called multistage. When the first stage runs out of fuel, it separates. The engine for the next stage kicks in, propelling the cargo onwards and upwards.
“We haven't really had to care about emissions from rockets for many years, because the amount was so small,” says U.S. atmospheric scientist Christopher Maloney.
Now, the scientific community is starting to pay closer attention.
Rocket launches aren’t the only part of the space industry that pollutes.
Discarded satellites and even bathroom waste from the International Space Station burn up when they re-enter Earth’s atmosphere.
Remnants of old space stations are being ditched in the Pacific Ocean, and rocket debris is being left to burn up in the atmosphere. “Is that an OK thing to do? We don't know the answer to that,” Ross says.
Space junk and old rocket stages that don’t re-enter the atmosphere pose a threat, too. Too much debris in Earth’s orbit could set off a chain reaction of collisions, interfering with the satellites that monitor weather and provide early disaster warnings.
Uncrewed sounding rockets are used to study meteorology in the upper atmosphere.
Rocket emissions pollute at such high altitudes, all the way up to 80 km, that it makes it challenging to keep track of the impacts.
Rare noctilucent clouds, the highest clouds in Earth’s atmosphere, sometimes appear at twilight in summer months in the Northern Hemisphere.
“There's this sense that the industry is getting ahead of the research,” Ross says.
Most meteors, or shooting stars, burn up in the mesosphere.
Thermosphere
We know so little about this remote part of the atmosphere that scientists have dubbed it the “ignorosphere."
To make sure we understand the impacts of this new space race, scientists will have to keep up with an industry that is accelerating and changing.
Christopher Maloney has studied how emissions could increase as space travel grows. “We definitely see from these projected launch amounts that there's a potential for an impact,” he says.
But it’s difficult to study the impacts of space travel up here, where the atmosphere is thin and remote and can’t be sampled directly.
Rockets can even create temporary holes in the atmosphere between 100 and 300 km altitude. If launches increase enough, Ross says it’s possible that could affect space weather in low Earth orbit.
Scientists have their work cut out for them. “The big thing right now is research, research, research. We have to get ahead of this,” Ross says.
Elves are a type of upper-atmospheric lightning.
There’s no hard and fast boundary that marks the beginning of space, but 100 km altitude, known as the Kármán line, is sometimes called the edge of space.
Space
Northern lights (aurora borealis) occur between 100 and 600 km altitude when electrons and protons collide with gases.
Troposphere
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