“How the billionaire space race could be one giant leap for pollution,” The Guardian wrote. “The cost [...] will be paid in carbon emissions,” read a Popular Science headline. “Who is thinking about the atmosphere?” asked The Hill.
One billionaire that claims to be thinking about the atmosphere is Elon Musk. The CEO claims he is “working on sustainable energy for Earth with Tesla & protecting future of consciousness by making life multiplanetary with SpaceX.”
But does SpaceX’s work to explore the stars undermine Tesla’s work to clean up Earth’s atmosphere? The short answer is that we don’t really know.
Martin Ross, senior project engineer of commercial launch projects at advisory nonprofit The Aerospace Corporation, tells Inverse that more research is needed in this area.
“The current level of data about rocket emissions does not provide researchers with enough information to fully assess the impact of launches on the global environment,” he says.
Current rocket launches have a negligible effect on total carbon emissions — Everyday Astronaut found they accounted for 0.0000059 percent of global carbon emissions in 2018, while the airline industry produced 2.4 percent the same year.
But the long-term effect is less clear, especially as companies like SpaceX move from hosting 26 launches in a year to 1,000 launches per rocket in a year.
“I think we can guess that rockets won't be a huge impact on the environment, and they probably won't stand out as a sole source of new problems,” Darin Toohey, professor at the University of Colorado Boulder’s Atmospheric and Ocean Sciences, tells Inverse. “But they will add to the growing list of activities that have negative impacts on the environment.”
Here is what we know so far.
What is the carbon footprint of space travel?
This depends a lot on the rocket, and which fuel it burns to create thrust.
Eloise Marais, an associate professor of physical geography at University College London, told The Guardian in July that she has simulated the effects of rocket launches for a decade. She found that one rocket launch can produce from 200 to 300 tons of carbon dioxide.
This largely corresponds with Everyday Astronaut’s calculations. The United Launch Alliance’s Delta IV Heavy, which just burns hydrogen, comes out on top with basically no carbon. The SpaceX Falcon 9 and NASA Space Shuttle both produce around 400 tons of carbon dioxide per launch.
USA Today reported that Blue Origin’s New Shepard emitted basically no carbon dioxide. That’s because it uses liquid hydrogen and oxygen as its fuel.
The upcoming SpaceX Starship and Super Heavy produce a staggering 2,683 tons per launch. When adjusted for payload, it produces about the same as the Falcon 9: 27 tons of carbon dioxide per ton to low-Earth orbit.
Marais noted that these figures are small compared to global air travel. But air travel produces one to three tons of carbon dioxide per passenger. As rocket launch emissions increase nearly six percent per year, she warned that it may not take long to outpace air travel.
How much pollution do rockets produce?
Beyond the carbon emissions outlined above, it’s important to remember that rockets can also emit other gases and pollutants.
In a 2020 analysis, Everyday Astronaut explained that each rocket will produce varying amounts of pollution. Take the SpaceX Falcon 9: It burns rocket propellant and liquid oxygen, so it emits carbon dioxide, water vapor, nitrogen oxides, carbon soot, carbon monoxide, and sulfur compounds.
Other rockets produce pollutants like inorganic chlorine and alumina. Some, like the hydrogen-burning Delta IV Heavy, only produce water vapor and nitrogen oxides.
Water vapor has an effect on the atmosphere. In a 2012 paper published in the Journal of Geophysical Research, the authors observed how the final NASA Space Shuttle launch in 2011 emitted around 350 tons of vapor during its ascent. That created polar mesospheric clouds brighter than 99 percent of other such clouds in the area.
Are reusable rockets better for the environment?
In terms of launch emissions per ton sent to space, reusable rockets are actually worse. That’s because the ship can’t send as much weight into space at once, because it needs to save some fuel to return.
Everyday Astronaut notes that the SpaceX Falcon 9 can send 15.5 tons to low-Earth orbit when it’s being reused, but it can launch 22.8 tons if it doesn’t need to return to Earth. That means a reusable Falcon 9 emits 27 tons of carbon dioxide per ton sent to space, while the expendable model emits 19 tons.
Of course, that doesn’t factor in the emissions from producing the rocket itself. Reusable rockets will avoid emissions from the manufacturing process.
What is the most environmentally-friendly rocket fuel?
It’s hard to say, as each fuel comes with its downsides.
In October, a University of Exeter study found that Orbex’s new Prime rocket would have a carbon footprint 96 percent smaller than comparable launch programs. The engine uses biopropane and liquid oxygen.
The study looked at the direct emissions from launch, indirect emissions from production, and radiative forcing effects of non-carbon dioxide emissions in the atmosphere. It found that one Orbex Prime rocket launch would produce the equivalent of 13.8 tons of carbon dioxide.
The rocket is designed to send payloads of up to 150 kg (330 pounds) to low-Earth orbit. It should be noted that it hasn’t flown yet. As of June 2021, the company was targeting a launch date of the end of 2022.
Do space launches damage the ozone layer?
They do tend to, but as with many other areas, it requires greater scrutiny.
Ozone is a gas in the Earth’s stratosphere. The oxygen molecules in the breathable air consist of two oxygen atoms, but ozone molecules consist of three oxygen atoms. The BBC notes that this layer absorbs around 98 percent of the Sun’s harmful ultraviolet rays.
Scientists in the 1970s warned that commonly-used chlorofluorocarbons, or CFCs, were creating a hole in the ozone layer. The Montreal Protocol in 1990 banned such ozone-depleting chemicals, but the CBC notes that the protocol didn’t cover aerospace.
In 2009, research published in the journal Astropolitics claimed that current rocket launches deplete a few hundredths of a percent of the ozone layer per year.
Toohey, who contributed to the study, claimed at the time that “if left unregulated, rocket launches by the year 2050 could result in more ozone destruction than was ever realized by CFCs." Toohey tells Inverse that this statement was made in reference to solid rocket motors that contain ammonium perchlorate.
“There are no limits on their use, as far as I know,” he says.
In January 2020, a new article in the Journal of Cleaner Production warned that rocket launches moving through the ozone layer is a key concern. It explained that rockets do cause ozone loss, but solid rocket motors like those on the NASA space shuttle cause far greater loss.
Newer rockets that use liquid propellant, like SpaceX’s Falcon 9, cause less ozone loss. These rockets have increased in popularity since the 2009 study. The problem is that most studies have focused on solid rocket motors, so more research is needed to understand how they differ.
Can rockets be eco-friendly?
In terms of carbon dioxide, Musk has indicated that he’s thinking about the issue. In September 2019, he wrote that carbon capture would enable net zero carbon flights long-term.
In January, Musk announced a $100 million prize for carbon removal. The four-year XPrize competition, which will conclude by Earth Day 2025, invites teams to demonstrate a cost-effective solution for removing gigatonnes of carbon per year.
Of course, carbon dioxide only covers part of the equation, and doesn’t factor in other pollutants. Even if Musk captures all of the Starship’s carbon dioxide, it will still emit water vapor and nitrogen oxides. It’s an issue with other zero-carbon rockets like Blue Origin’s New Shepard.
The problem is that there’s not enough data or research to understand what rockets are doing to the environment.
“As atmospheric scientists, we would like to be able to assess what those impacts are likely to be so that efforts can be taken to reduce those impacts as launches become more frequent,” Toohey says. “But we lack the observations of emissions from rockets that are necessary to do that.”
It may be a small issue for now, but as rocket launches increase in frequency, that could change soon.