How environmentally friendly is SpaceX's Starship?

a silver spacecraft glows red with the heat of reentry, with earth's ocean in the background
SpaceX's Flight 3 Starship rocket glows red as it heats up during reentry during a test flight on March 14, 2024. (Image credit: SpaceX)

When the 165-foot-tall (50 meters) SpaceX Starship upper stage crashed into the Indian Ocean last week during its third test flight, environmentally conscious observers wondered whether the stainless-steel vehicle, perhaps containing hundreds of kilograms of residual fuel, could endanger marine life. The good news is — not really. Starship uses one of the most environmentally friendly fuel combinations available. Still, sustainability experts warn that the rocket is not without its problems. 

"Debris and fuel [from the latest Starship launch] are a drop in the ocean," Tommaso Sgobba, executive director of the International Association for the Advancement of Space Safety, told 

Starship's Raptor engines burn liquid oxygen and liquid methane, neither of which, fortunately, is toxic to the environment.

Related: Relive SpaceX Starship's 3rd flight test in breathtaking photos

Still, dumping garbage into the ocean is not the most respectable behavior, although the world's space agencies and launch operators have been doing that for decades. 

"The stuff actually dumped is similar to other industrial materials contributed by shipping and fishing," space sustainability researcher Vitali Braun told "Theoretically, the United Nations Convention on the Law of the Sea binds all states 'to protect and preserve the marine environment in all zones of the sea.' So, effectively, states dumping their trash into the ocean is a violation of this treaty."

What concerns Braun most are Elon Musk's plans to ramp up the frequency of Starship launches to perhaps hundreds per year. Each of those flights could loft more than 100 tons' worth of satellites into space. These satellites will not only be going up, but at some point, they will be also falling back down.

"Those numbers are insane," Braun said. "We have already seen an exponential increase in reentering satellites and rocket stages in the past years. With that perspective, I am quite concerned about the consequences."

Satellites and old rockets burn up when they spiral back to Earth, leaving behind metallic ash, the composition of which raises concerns. Some researchers think that these remnants of satellite incineration could damage Earth's protective ozone layer or even affect the planet's magnetic field. Most of the reentering material vaporizes some 75 to 50 miles (120 to 80 kilometers) above Earth's surface. At these altitudes, the ash particles may remain essentially forever, which means their concentrations will only continue to rise. 

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Green or not green?

But there are other concerns about frequent Starship launches. Methane, although not toxic, is a gas commonly found in nature and is used to power everything from city heating through electricity generation to transport. When burned, it converts into carbon dioxide and water vapor. Although the overall greenhouse gas emissions of methane combustion are lower than those of burning oil or coal, the gas still contributes to the warming greenhouse effect that humankind is currently working hard to thwart.

According to Andrew Wilson, assistant professor in environmental management at Glasgow Caledonian University in Scotland, one Starship launch produces 76,000 metric tons of carbon dioxide equivalent (a measure combining different types of greenhouse gases in one unit). That's 2.72 times more emissions than those produced by a single SpaceX Falcon 9 launch but only 0.96 of the emissions produced by a Falcon Heavy liftoff. Both the Falcon 9 and the Falcon Heavy combust the much dirtier oil-based rocket fuel RP-1, so their carbon footprint per ton launched is much higher. The Falcon 9, for example, has less than one-sixth the payload capacity of Starship. 

Carbon emissions are not Starship's only contribution to global warming. Water vapor too is a potent greenhouse gas. The higher layers of Earth's atmosphere naturally contain very little of it, and scientists don't know what water vapor produced by rocket exhaust at high altitudes can do to the planet. On top of that, Starship emissions contain soot, which spreads throughout the upper atmosphere and absorbs incoming heat. This effect, known as radiative forcing, can contribute to additional warming. And let's not forget that methane itself is a greenhouse gas up to 90 times more potent in trapping heat in the atmosphere than carbon dioxide. Methane leaks from processing and storage facilities and gas pipelines are known to be a major contribution to global greenhouse gas emissions. 

A full accounting of the atmospheric impact would also include the greenhouse gases generated by the manufacture of Starship vehicles, which occurs at SpaceX's Starbase facility in South Texas. But that's an even tougher number to pin down. 

Related: Climate change: Causes and effects

Carbon footprint

Wilson cautions that the sheer size of Starship and the frequency at which SpaceX plans to launch it mean that the giant rocket's environmental footprint in the long term is unlikely to remain just a drop in the ocean.

"Historically, the space sector has been granted a lot of exemptions from different legislations, and, as a result, they have essentially been able to get away with doing what they want," Wilson said. "And Starship, because it's the biggest rocket ever built, is also one of the dirtiest."

Right now, the overall amount of greenhouse gas emissions from spaceflight is negligible, equivalent to 1% or 2% of the carbon footprint of aviation, which by itself makes up about 2.5% of overall global greenhouse gas emissions. But the number of rocket launches has been rising steeply in recent years. 2023 saw a record-breaking 223 attempted spaceflights worldwide, according to astronomer and space age historian Jonathan McDowell. That's more than double the 85 attempts made in 2016. SpaceX alone launched a record 96 orbital rockets last year and aims for nearly 150 in 2024. SpaceX's bold ambitions are what worry scientists like Wilson.

"If it scales up and SpaceX launches Starship more and more and more, as they say they will, then there will be an accumulation of those effects on our environment," said Wilson. 

Apart from enabling humankind to colonize Mars, as Elon Musk envisions, Starship has also been proposed as a next-generation means of intercontinental travel that could shorten the duration of the longest journeys here on Earth to a mere hour. 

"The amount of pollution that would cause in comparison to aircraft is orders of magnitude of a difference," said Wilson.

While engineers in most industries are scratching their heads, pondering how to decarbonize by the middle of this century as required by international climate protection pledges, Musk and his company are developing a carbon-intensive business with uncertain impacts on the environment, Wilson suggests. 

The Paris Agreement, signed at the 2015 United Nations Climate Change Conference in the French capital, binds nations to limit global warming to 2.7 degrees Fahrenheit (1.5 degrees Celsius) compared to preindustrial times. So far, that goal appears to be slipping through our fingers. In 2023, in fact, global temperatures breached the 2.7 degrees F threshold on 50% of days, according to the European Copernicus Climate Change Service.

"We are in a climate crisis — we already saw warming that is close to the targets of the Paris Agreement — and here we go, creating a massive launcher which is going to just add more carbon dioxide into the atmosphere," Wilson concluded. 

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Tereza Pultarova
Senior Writer

Tereza is a London-based science and technology journalist, aspiring fiction writer and amateur gymnast. Originally from Prague, the Czech Republic, she spent the first seven years of her career working as a reporter, script-writer and presenter for various TV programmes of the Czech Public Service Television. She later took a career break to pursue further education and added a Master's in Science from the International Space University, France, to her Bachelor's in Journalism and Master's in Cultural Anthropology from Prague's Charles University. She worked as a reporter at the Engineering and Technology magazine, freelanced for a range of publications including Live Science,, Professional Engineering, Via Satellite and Space News and served as a maternity cover science editor at the European Space Agency.

  • Mike from CT
    Does anyone really care about Starships environmental footprint? Im more interested in success and exploration, Starship is a game changer for space exploration.

    Also curious why reusability isn’t discussed.

    Overall a very poor article.
  • 24launch
    I was holding off on commenting.

    Unfortunately Ms Pultarova has what appears to me to be an extreme dislike for Musk, SpaceX and Starlink based on her previous articles with similar critical viewpoints, especially of Starlink.

    I have yet to see an article of hers with genuine concern about Amazon's planned constellation of thousands of satellites launched by initially all 100% throwaway rockets (hopefully eventually reusable with BO's New Glenn). Nor acknowledgement that Starlink, unlike Amazon, have been actively working with astronomers and the Int'l Dark Sky association to try to mitigate not only the reflectivity but the radio frequency impact of the Starlink satellites on astronomy. Amazon has thus far declined any such dialog.

    And then there's China who are planning their own network of thousands of satellites.

    I do agree there needs to be open dialog about such things, but pure opinion and hyperbole like, "environmentally conscious observers wondered whether the stainless-steel vehicle, perhaps containing hundreds of kilograms of residual fuel, could endanger marine life."

    and even just subtitling the article as:

    "Starship, because it's the biggest rocket ever built, is also one of the dirtiest."
    really belong over on a doomsayer site like The Conversation and not here on a Space & Astronomy enthusiast site.

    My US$0.02 for what it's worth.
  • Unclear Engineer
    Seems like a lot of speculation on the potential for negative effects, without any speculation on the potential for positive effects. So, the article comes across as overtly biased.

    For instance, the manufacture of reusable launch vehicles have a reduced carbon emission effect compared to throw-away vehicles. And refueling in space with affordable launches might be used to refuel and even update the satellites that the article decries for being deorbited and burning up in the upper atmosphere. And, about those particulates that will remain in the upper atmosphere "essentially forever", how does that compare to the proposals to intentionally put particulates into our upper atmosphere to cool the planet? Similarly, the water vapor that the article calls a "green house gas" may be a solid in the cold up there, providing reflective clouds that could also cool the Earth.

    Those are speculations, too. But, why don't they get similar amounts of "ink" from this author?
  • bleibold
    These environmental terrorists just won't give up.
  • Cdr. Shepard
    Ms. Pultarova spends most of her time, writing not for LiveScience, Nature, Ars Technica, etc., but for, explaining why SpaceX shouldn't go into space, build things that might go into space, or, if already in space, reenter the atmosphere from it.

    Does she have a counterproposal, other than Elon disbanding all of his ventures and retiring from the public eye?

    The lecturing from certain overtly political and activist corners of journoworld (and from an incorrectly perceived position upon the moral high ground) is growing tiresome.
  • JAS
    A few points for your consideration:
    1) For those interested, Everyday Astronaut does a good more in-depth review of rocket pollution issues at the following link: C4VHfmiwuv4View:
    2) I believe Musk plans to develop a non-fossil-fuel Methane source using the Sabatier Process for Star Ship. This would in essence make the fuel cycle a closed loop, sourcing CO2 from the atmosphere.
    3) The dropping of metals into the ocean is just a short term effect with Star Ship development. Shortly, the prototypes will start making it home intact since the goal for Star Ship is 100% reuse.
    4) While the number of satellites going to orbit is rising significantly, the size of them is dropping on average due to technology, and the fact that so many of them are being used in low (short duration) orbits.
    5) The composition of satellites is changing also, with reductions in toxins, and with materials more compatible with safer destruction in the atmosphere. Lots of room for improvement still.
    6) Satellites living in high orbits such as geo-stationary orbits are typically not brought down into the atmosphere, but instead are parked in a graveyard orbit. I imagine at a future date some smart cookie will build an orbital reclamation factory to reclaim all that valuable material sitting out there waiting to be 'picked up'.
  • Helio
    Per the article...."According to Andrew Wilson, assistant professor in environmental management at Glasgow Caledonian University in Scotland, one Starship launch produces 76,000 metric tons of carbon dioxide equivalent (a measure combining different types of greenhouse gases in one unit). "

    Is it possible that 4,600 metric tonnes of propellant can produce 76,000 metric tonnes of CO2? Call me dubious.
  • Ken Fabian
    It will be important to continue to study and monitor atmospheric and ocean impacts of space launches, failures, returns, end of life burn up in atmosphere, especially if there are going to be a lot more of them.

    Like every other industry rocket manufacturers/operators need to become zero emissions. Mostly it should come from a massive build of low/zero emissions energy, ie manufacturing and fuel production will draw on low emissions energy because that is what grids and energy supply companies are providing. I still expect industries doing things specifically based on combustion, like rocketry to face additional challenges but manufactured fuels made using electricity from a zero emissions grid seems reasonable, or possibly biofuels.

    Being small isn't good enough reason to make an exception; every other "small" industry wants to be exempted too, lots of them, too many of them. But those too are going to reduce in emissions energy as more primary energy is low emissions.

    Being important might exempt rocket launches if some overriding need can be demonstrated but I think ultimately should still be balanced with some kind of genuine negative emissions. Military need will rate important enough like it or not, but ISS, Moon and Mars aren't that kind of important. But there is no technical barrier to becoming a zero emissions industry.
  • Unclear Engineer
    Helio said:
    Is it possible that 4,600 metric tonnes of propellant can produce 76,000 metric tonnes of CO2? Call me dubious.
    Helio, I am not going to try to verify or falsify the assertion. I am just offering a few relevant thoughts.

    First, a ton of carbon composed of atoms with isotopic mass 12, each combined with 2 atoms of oxygen with atomic mass 16, means that ton of carbon makes (12 + 2 x 16)/12 = 3.7 tons of carbon dioxide.

    Similarly, a ton of hydrogen oxidized to water produces ( 2 x 1 + 16)/ (2 x 1) = 9 tons of water, and the activists are probably including the water as a "greenhouse gas".

    Finally, there is some methane leakage, and that is probably simply given a multiplier of 20 for its ratio of effects compared to carbon dioxide.

    So, a ton of methane can make a lot of tons of "greenhouse gases". The ratio of "greenhouse gases" to fuel in the statement is 16.5. So that does seem like it might be a "stretch."
  • Helio

    Lunar fuel production is looking a little better. 😀