More ““The main problem is elsewhere.” warns aerospace and energy engineer Loïs Miraux, researcher on environmental issues linked to space activities. Indeed, these life cycle calculations do not take into account the launch itself.
Three to five years in the atmosphere
“To place its payload in orbit, a rocket will have to cross all layers of the atmosphere. It is the only human activity to do so. Indeed, all human activities emit in the lowest layer of the atmosphere. the atmosphere (which is the troposphere), including aviationexecutive Loïs Miraux. The problem is that launchers will emit a wide variety of products, given the wide variety of fuels used. We will therefore find different greenhouse gases, particles warming the atmosphere and other molecules which will destroy ozone. The effect of a substance on the climate and on ozone will vary depending on its altitude. Emitted in the highest layers of the atmosphere, each compound produced by rockets will remain in suspension much longer than when this compound is emitted by the rest of human activities on the ground or at the altitudes where planes fly. These compounds will therefore have much more time to exert their warming or ozone-destroying power on the climate. The residence time of these particles emitted in the stratosphere by launchers is of the order of 3 to 5 years whereas when they are emitted by the rest of human activities in the troposphere, it is rather of the order of a few days or a few weeks at most.
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Fine particles like those from cars
Among these particles are soot or black carbon (70%), a subcategory of fine particles, such as those emitted by cars and resulting from fuel combustion. “Soot is the main cause of the impact of launches on the climate. Launchers are particularly emitters of this type of particle. The fuel most used by the launcher industry, kerosene, emits these aggregates of burned hydrocarbons It is the most problematic fuel because it emits a lot of soot. The worst kerosene rocket engine will emit 1000 times more soot than an airplane engine. This is particularly the case with SpaceX’s Falcon 9 rocket, which runs on kerosene.
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This soot is also emitted by methane, a new fuel, which will undoubtedly be used more and more, without however making kerosene disappear. Methane notably powers SpaceX’s famous Starship mega-rocket. If this fuel emits less soot than kerosene, science still does not know to what extent. “This is going to be a big problem if the Starship has to do a lot of launches. These gigantic rockets could dominate all emissions produced, believes Loïs Miraux. Knowing that a study estimated that, emitted into the stratosphere, a kilogram of soot has a warming effect 500 times greater than if it had been emitted by the rest of human activities which also emit soot.
Need for simulations
Generally speaking, continues the researcher, “models estimating the effect of launches on the climate show that emissions in the stratosphere warm it with an effect corresponding to one tenth of that of aviation on the lowest layer, the troposphere. We are therefore very far from this initial 0.01% which concerned ground activities.” However, an important nuance must be made: “Studies on launcher emissions have to date focused on the stratosphere because this is where most of the emissions accumulate, with a multiplication of their effect. The effect on this stratosphere is a warming, a positive radiative forcing on this layer On the other hand, this tells us nothing at this stage about the effect on the troposphere where said “global warming” is taking place, which is what mainly interests us since we live there!” underlines Loïs Miraux.
We would therefore need to carry out simulations to understand what will happen at our level, but this work still needs to be carried out. “This is where scientific studies remain cautious and comment qualitatively: the warming of the stratosphere from launch emissions would lead to complex changes in atmospheric circulation, which could lead to cooling zones and areas on the ground. warming. In short, we do not yet really know what the precise consequences will be on the climate. What we do know is that the magnitude of the quantified effect on the stratosphere is far from negligible, and is cause for concern given the rapid growth (read below) of the sector. And in all cases, it is an intervention on the radiative balance of the atmosphere, which rarely brings good.”
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In any case, research is beginning to be launched by European universities and space agencies to better understand the impact of launches on the atmosphere. But establishing this knowledge will take time: “A fear shared by many specialists in the matter is that industry will move much faster than science. However, regulation can only really be done on the basis of precise scientific data.”
Under-paper: A sector experiencing impressive growth
The space sector is growing impressively. An evocative figure: between the first launch of Sputnik in 1957 and the start of the launch of the Starlink internet constellation in 2019, 9,000 satellites were placed in orbit. And just between 2019 and today… 9,000 too! Between 2019 and 2023, the mass of fuel burned by launchers globally has also tripled. “This is almost mainly due to Starlink, launched by the Falcon 9, which uses kerosene and is therefore a large emitter of soot. Today, 6,000 Starlink satellites are in orbit. The total configuration provides for 42,000, having a lifespan of 5 years and which must therefore be renewed If we add to Starlink the other constellations announced (Amazon, three Chinese constellations with more than 10,000 satellites, etc.), we realize that we could arrive very quickly. with a climate impact equivalent to that of aviation, in 10 or 20 years SpaceX currently completely dominates launches If we look at the orders of magnitude, perhaps SpaceX would become the most polluting company on the planet. .”
Today and for several years, the majority of space activities – and therefore environmental impacts – relate to telecommunications and large constellations of Starlink-type satellites, notes the researcher.. “Scientific observation missions which serve to provide information on the evolution of the climate and the environment (of the Copernicus type, Editor’s note) provide an undeniable environmental benefit at a much more moderate environmental cost. Let’s be discerning. Space missions have an impact, but some have a much more positive impact on society than others. We should question our uses of digital technology and the Internet, because these large constellations of satellites will explode the sector’s footprint.”
Pinned: And the returns?
After the launches, there are also… returns, when the launcher stages and satellites at the end of their life are voluntarily lowered back into the atmosphere to be burned. What could be the environmental consequences? “Launcher stages, in general, break down little in the atmosphere upon re-entry, unlike satellites. Satellites that are launched into orbit end up falling back and almost completely disintegrate. This will emit in the highest layers of the atmosphere of metallic particles which have nothing to do there A study found traces of these metals from satellites in 10% of the aerosol particles measured. However, this can have effects on the layer. ozone is potentially also on the climate and its 42,000 satellites would represent 9,000 tonnes of metal entering the atmosphere every year.
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