The Future of Rocket Propulsion, What To Do About Emissions

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Astronuc
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The Kazakh Steppe is a vast area of grassland that stretches from northern Kazakhstan into Russia. It is home to the world's oldest spaceport, the Baikonur Cosmodrome. From its launchpads, both the world's first artificial satellite and the first human spaceflight, Sputnik 1 and Vostok 1, were launched.

The fuel used by many of the rockets that blasted off from Baikonur was UDMH (unsymmetrical dimethylhydrazine), a very useful propellant for the pioneering Soviet scientists. UDMH didn't need a source of ignition. It could be stored at room temperature, and it released a lot of energy. Yet it came to be dubbed "devil's venom" by the scientists who used it.

Devil's venom was highly carcinogenic to humans and it's blamed for turning a large area of the steppe into an ecological disaster zone. It's reported that UDMH rained down on the grasslands when it spilled out of the used first and second stages of Proton rockets and poisoned the soil for decades to come.
https://www.bbc.com/future/article/20220713-how-to-make-rocket-launches-less-polluting

"Last year's number of missions was 144 worldwide," says William Pomerantz, vice president of special projects at Virgin Orbit, which launches small satellites horizontally from under the wing of a Boeing 747. Their rocket uses about 1/20th of the fuel of typical ground-launched, heavy-lift rockets, and recent launches include satellites now playing a key role in the collection of climate data. "Given this volume, the space launch industry remains a relatively small driver of atmospheric emissions compared with say, commercial aviation with more than 20 million flights worldwide, and other industries."

Eloise Marais, an associate professor in physical geography at University College London, and co-author of one of the recent research papers, thinks this comparison is "erroneous".

"When we compare the amount emitted from rocket launches to aircraft, it doesn't sound like a lot," she says. "But this comparison was always erroneous because aircraft released their pollutants within the troposphere and the lower stratosphere, whereas rockets are releasing their pollutants all the way from the surface of the Earth to the mesophere, and when pollution is released into those upper layers it lasts for a longer time than earthbound sources."
 

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256bits
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How many aircraft fly 12 km up into the stratosphere?
Not many I would take a guess.
Of course the troposphere with mixing and the washout from rainfall is self cleaning of particulates.
But those particulates then pollute the land and water system on the surface.
Not sure what she is getting at.
 
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Pairing the UDMH-focused preface with the otherwise global warming focused main body is a bit ambiguous, at the very least.
 
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Their rocket uses about 1/20th of the fuel of typical ground-launched, heavy-lift rockets
It uses 1/20th of the fuel for 1/40th of the payload mass (approximate ratios for Atlas V, Ariane 5 and Falcon 9, the last one with booster reuse). These heavier ground-launched rockets burn less fuel per payload mass by a factor 2, and that's not including the fuel of the Boeing 747 used to fly the rocket to its release altitude.

Here are the assumptions the study authors used to get significant a impact from space tourism:
We also calculate emissions for a speculative scenario of annual space tourism offerings by Virgin Galactic, Blue Origin and SpaceX. Only Virgin Galactic has announced plans to offer 400 flights each year (Sheetz, 2020). Given this, we determine emissions for daily suborbital launches by Virgin Galactic and Blue Origin and weekly orbital launches by SpaceX.
Virgin Galactic has made one touristic flight and their typical flight rate has been 1-2 per year (not counting tests at aircraft altitude).
Blue Origin has made six tourist flights in a bit over a year, with no sign of increasing flight rate. Their rocket is using hydrogen and oxygen, so there is no carbon in the exhaust anyway.
SpaceX has launched one tourist flight and plans about one or two per year in the following years. They do fly Falcon 9 once per week, but not for tourism. They don't have nearly enough Dragon capsules for weekly crew flights.

We might get to a tourism industry that large at some point, but it won't be in the next years and likely not with the existing vehicles. Starship could lead to that, but that's using methane and oxygen so it needs a new analysis. The publication doesn't mention Starship or methane as fuel at all.
 

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