How much does space tourism pollute?

First Branson, then Bezos: the era of space tourism seems to have really begun. And it's time to start thinking about its environmental impact too

(Image: Virgin Galactic) On July 11, Virgin Galactic patron Sir Richard Branson climbed up to 80 kilometers on board his VSS Unity. And just nine days later Jeff Bezos, with a Blue Origin rocket, responded by reaching an even greater altitude, about 120 kilometers. Only Elon Musk is missing (for now), but he has stated that his SpaceX plans to offer a commercial package of five days of orbital flight aboard the Crew Dragon 2 already by the end of 2021.
br> In short, the era of space tourism has officially begun. And therefore, behind the sequins, it is legitimate (and only right) to start thinking about the environmental impact that these launches will have in the long term. Indeed, the scientific community has already begun to ask itself the problem. "Will space tourism have consequences in terms of pollution and climate change?" , asked for example Eloise Marais, associate professor of physical geography at University College of London, who has been studying the impact of the space industry on the health of the atmosphere for some time. “Probably yes - she added. If international regulators are to keep pace with this nascent industry and adequately control its pollution, scientists need a better and quicker understanding of the effect these "billionaire astronauts" will have on our planet's atmosphere. "

The impact of the launches

The skirmishes, on the other hand, have already begun. According to Bezos, his rocket is more environmentally aware than Branson's. For its part, the owner of Virgin Galactic claims that the carbon dioxide emissions of its flights are equivalent to those of a plane ticket between London and New York, and that "the company has already taken all the necessary steps to eliminate emissions of carbon dioxide from test flights and is examining the possibility of eliminating emissions from future passenger flights and reducing the amount of emissions from the entire supply chain ".

Gavin Schmidt, NASA climate advisor, he does not say worried: "The carbon dioxide emissions from space flights are totally negligible compared to other human activities and compared to commercial aviation". For the moment, perhaps, that's true. But it must be taken into account that the comparison still makes little sense (the take-offs of space rockets are about 100 every year, a trifle compared to the 100 thousand commercial flights that depart every day): what will happen later, when the volume of space tourism increases?

Engines in orbit

Let's look again at the three main actors on the scene. The Blue Engine 3 (Be-3) engine, which carries Blue Origin's rockets into orbit, uses liquid hydrogen and liquid oxygen propellants. The Vss Unity is powered by a solid fuel-based hybrid propellant (polybutiadene with terminal hydroxyl radicals, or Htpb) and a liquid oxidant, nitrogen oxide. Finally, the Falcon rockets work with liquid kerosene and liquid oxygen.

The use of propellants of this type provides the energy necessary to overcome Earth's gravity and launch rockets into space, emitting, at the weather, greenhouse gases and other pollutants in both the lower and upper layers of the atmosphere. The propellant of the Be-3, in particular, releases large quantities of water vapor, while the combustion of the fuel of the Vss Unity and the rockets of the Falcon produces carbon dioxide and soot (as well as water vapor and various other substances).

Again: the oxidant of Vss Unity produces (and emits) nitrogen oxides, compounds known to be polluting. According to a study published in the journal Earth's Future in 2016, two thirds of the exhausted propellant is released into the stratosphere (between 12 and 15 kilometers of altitude) and the mesosphere (between 50 and 85 kilometers of altitude), where they can remain for a period of time. between two and five years. The very high temperatures that are reached during take-off and during re-entry into the atmosphere (due, in this case, to the friction that is generated between the protective shield of the spacecraft and the atmosphere itself) convert the atmospheric nitrogen (which is stable) in nitrogen oxides, which are very reactive.

The effects of pollution

What do all these substances do in the atmosphere? Nothing good, it seems. Nitrogen oxides and molecules that are formed by the "breaking" of the chemical bonds of water vapor in the stratosphere convert ozone into oxygen, thinning the ozone layer that protects our planet from ultraviolet radiation from the Sun. Water vapor, on the other hand. , produces clouds in the stratosphere that represent a "surface" that further accelerates the above chemical reactions. Carbon dioxide and soot then trap heat in the atmosphere, contributing to global warming.

To complicate matters, there are also mechanisms that go in the opposite direction: clouds that form from water vapor reflect the sun's rays back into space, and a thinning ozone layer absorbs less sunlight: both phenomena that make the atmosphere less warm. "It is not easy to estimate the total effect of rocket launches in the atmosphere - says Marais -. Very detailed models would be needed, which take into account all the chemical processes and the persistence of pollutants in the upper layers of the atmosphere. And a deeper and more realistic understanding of how the space tourism industry will develop would also be needed. ”

According to what we know today, Virgin Galactic plans to propose around 400 takeoffs each year, while Blue Origin and SpaceX have yet to go public with their plans. According to a report, carbon dioxide emissions for four tourists aboard a space flight are between 50 and 100 times greater than the estimated 1-3 tons for each passenger on a long-haul flight. And according to another estimate, calculated by French astrophysicist Roland Lehoucq, Virgin Galactic's emissions hover around 4.5 tons per passenger, more than double the individual annual carbon dioxide budget recommended to meet the goals of the Accord. Paris. Not really negligible.


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Topics

Climate pollution Jeff Bezos SpaceX Space Virgin Galactic globalData.fldTopic = "Climate, pollution, Jeff Bezos, SpaceX, Space, Virgin Galactic "

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