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If we are using lots of toxic fuels like hydrazine for rockets, wouldn't this cause pollution due to the burnt leftovers ? I mean, just consider the amount of rockets and missiles launched in world so far and all the jet fuel that's being burnt by jet engines everyday. And then comes the huge debate about wood burning by people in poor countries when even the most developed countries pollute the air everyday as mentioned above.

I always have this doubt within me whenever I read about various scientific experiments like rockets, missiles, jet engines, etc. Why don't someone study and emphasize these effects just like ozone depletion or deforestation....

called2voyage
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user132257
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    This question should probably be narrowed to remove the mention of weapon systems and aircraft unrelated to space. There's no point in asking about jet fighter pollution on Space Exploration SE. – Nathan Tuggy Jun 23 '17 at 02:16
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    You're incorrect in assuming it isn't studied: https://ntrs.nasa.gov/?N=0&Ntk=All&Ntt=rocket%20exhaust%20environmental%20impact&Ntx=mode%20matchallpartial – Hobbes Jun 23 '17 at 07:21
  • Can be related to this question: https://space.stackexchange.com/questions/2903/what-is-a-typical-energy-demand-and-carbon-footprint-of-a-space-launch – Gp2mv3 Jun 23 '17 at 07:49
  • It wouldn't surprise me if the most polluting exhaust element of most rocket is NOx, also widely emitted by vehicles. The aluminium compounds from some solid-fuel rockets wouldn't be good to breathe in but shouldn't hang around in the atmosphere for long. Some of the early experiments, particularly military, used fluoride oxidisers. These produce HF, which is nasty, and have been discussed before. Which pollutants are you most concerned about? – Chris H Jun 23 '17 at 09:26

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Hydrazine burns very nicely to water and ammonia. It is the unburnt stuff that is dangerous.

LH/LOX engines burn products are water.

RP1/LOX engines burn much the same as car engines, just hotter so some weird nitrogen compounds form.

The SRB's are really quite polluting. But consider that in 30 years 135 pairs were launched. (Not sure if that should be 136 and include Challenger or not, or 137 and include Ares-1X). Over something as large as a planet that is a negligble amount.

The number of rocket and missile launches, again, over the scale of a planet is surprisingly low.

geoffc
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  • Hydrazine monoprops go to ammonia; the usual hypergolic biprop suspects go to a variety of stuff, mostly N2 and water. http://yarchive.net/space/rocket/fuels/hydrazine.html – Russell Borogove Jun 23 '17 at 02:39
  • (Plus a little ammonia if run fuel-rich, which I guess is generally done.) – Russell Borogove Jun 23 '17 at 02:48
  • I think you can include Challenger, because as they were ignited they probably burn entirely. – le_daim Jun 23 '17 at 07:24
  • What should be also taken into account is the energy needed to produce and store LH, LOX, RP1,... Because those aren't negligible. – Gp2mv3 Jun 23 '17 at 07:43
  • @Gp2mv3 nor is the energy needed to make the aluminum and other components, build and light the buildings and get the people to and from the launch site every day. Some launches have in fact had major net beneficial impact on pollution by putting the satellites up there that are busy measuring and reporting both polutant levels and their effects. I think taken all together, the effect of launches and spaceflight is a huge pollution reducer. – uhoh Jun 23 '17 at 07:59
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    @uhoh I agree, and I'm totally convinced that spacial activities are highly profitable for humanity. But speaking about the pollution of the propellants, it's also interesting to thing about their production. – Gp2mv3 Jun 23 '17 at 08:47
  • It's not just RP1 burning which produces those nasty NOx components. Any open flame in the atmosphere will break N2 and O2 bonds, and the resulting radicals may recombine as NOx compounds. That includes LH/LOX rockets. – MSalters Jun 23 '17 at 10:31
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    If RP1 is burned with LOX, no nitrogen is present in the combustion chamber, so no NOx is produced there. If the hot gases after the nozzle mix with air, some nitrogen of the air might react with the oxygen of the air to build NOx. But this is possible for LH2 and LOX too. But are the gases after the nozzle and after mixing with some air still hot enough to produce NOx? – Uwe Jun 24 '17 at 18:28
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About 150 thousand kg of kerosene (RP-1) is used in a single Falcon 9 launch.

About 500 billion kg of gasoline is used in the US per year.

Thus, launching 80 rockets a day would increase pollution in the US by about 1%.

Russell Borogove
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    How 16 ships create as much pollution as all the cars in the world. (not space ships) Not much sulphur in RP-1! – uhoh Jun 23 '17 at 08:09
  • @uhoh: That's assuming the only pollution source is sulphur. In fact, sulphur isn't even the most lethal, that's soot. – MSalters Jun 23 '17 at 10:33
  • @MSalters Sulphur hurts the atmosphere & environment even if you don't breathe it yourslef. Pollution is a multi-faceted issue for sure. – uhoh Jun 23 '17 at 11:58
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    @uhoh: Actually, it doesn't hurt "the atmosphere". It's a global problem in the higher atmosphere, but ship exhausts don't rise that high. In the lower atmosphere, it's a problem above land, but not above the sea. And in many seas, marine life (plankton) benefits from a bit of sulfate fertilization. Locally high concentrations can cause algae blooms, but that's associated with waste water streams. Exhaust gases are too rarefied to cause such blooms. – MSalters Jun 23 '17 at 13:23
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    @MSalters that's a really helpful breakdown. Consider posting as an answer? – uhoh Jun 23 '17 at 14:32
  • @uhoh: It's rather unrelated to rockets. Sulphur pollution is caused by fossil fuels. It's an essential element for proteins, so it's present in crude oil. It can be removed in refining, but what are you going to do with the result? Build a pyramid ? For marine diesel, the sulphur is left in, but in RP-1 it's aggressively removed. – MSalters Jun 23 '17 at 17:05
  • FWIW, although sulfur dioxide (& trioxide) contribute to acid rain, they're actually anti-greenhouse gases. – PM 2Ring May 15 '21 at 17:58
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For launching rockets and now with the newest high bypass turbofan engines, the engines are tuned and controlled to the point that the chemical reaction is stoichiometric. For the most part, the chemical reactions in the engines operating in the atmospheric layers produce byproducts of either just water (for a liquid hydrogen/liquid oxygen engine) or water and carbon dioxide (Jet Fuel/Liquid Oxygen). The efficiency of these engines is so vitally important that companies and governments cannot afford to have reactions less than perfect. Neither of those sets of byproducts shall alter the homeostasis of our atmosphere. What does make a difference is the example of a wood fire. That is a burn that is incredibly dirty with incomplete reactions and many large particulate molecules coming from the combustion reaction. The incentive to change habits for someone using a wood stove just do not exist.

Lilibete
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    You may be right for turbofans, but rocket engines are usually run just a bit off the stoichiometric ratio. – Hobbes Jun 26 '17 at 07:28
  • Hobbes, is it that they run slightly off of stoichiometric or is it that they use a little extra for cryogenic cooling of the nozzle. There really is no room for extra weight to be lifted, and everything must serve a purpose. From what I have seen of the newer designs, they are using either liquid helium, liquid nitrogen or both for cryogenic cooling as well as fire suppression if needed. No matter what though, all of those elements make up our atmosphere, and they do not disrupt atmospheric homeostasis. – Lilibete Jun 26 '17 at 07:36
  • @aviatrix Any examples of rocket engines that are cryogenic cooled with liquid nitrogen, liquid helium or both? – Uwe Jun 26 '17 at 07:55
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    Even unburned exhaust products contribute to thrust. Discussion of mixture ratio in rockets: http://yarchive.net/space/rocket/fuels/fuel_ratio.html and https://space.stackexchange.com/questions/5642/are-oxidizer-to-fuel-mixture-ratios-based-on-mass-or-volume – Hobbes Jun 26 '17 at 08:43
  • @Hobbes Every gas molecule leaving the nozzle with high velocity contributes to thrust. But injecting pure water into the combustion chamber to get more thrust might be inefficient. Increasing the mass flow and decreasing combustion temperature in the chamber may lower the thrust when the gas velocity at the end of the nozzles decreases. – Uwe Jul 01 '17 at 15:26
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    I was incorrect, the mixture ratio is not "just a bit" off the stoichiometric ratio, but a large amount, see this answer: https://space.stackexchange.com/questions/22148/liquid-fuel-oxygen-proportions – Hobbes Jul 01 '17 at 16:59
  • The link to the space question 22148 was incorrect. The stoichiometric ratio is [2 hydrogen atoms to 1 oxygen atom] (https://blogs.nasa.gov/Rocketology/tag/liquid-hydrogen/) for a 2:1 ratio, hence, H2O aka water. To run fuel rich with a ratio greater than 2:1, greater chilling is required as well as efforts to prevent hydrogen embrittlement as well as having to seal the system. It is a pain in the a&* to seal hydrogen systems. – Lilibete Jul 02 '17 at 07:07
  • @Uwe Here are a couple of links to technology of cryogenic cooling using liquid nitrogen or helium: https://blogs.nasa.gov/Rocketology/tag/liquid-hydrogen/ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660022898.pdf The primary area of cryogenic cooling is the nozzle, and then the warmed super heated liquid of either liquid is pumped up through heat exchangers to either heat the fuel or keep the fuel pumps from freezing. This is especially important on the first stage that operates in the atmosphere where there is still water. – Lilibete Jul 02 '17 at 07:10
  • @Lilibete Nice link, but I miss the words nitrogen or helium in that blog text. The PDF is about a test engine using gaseous hydrogen and oxygen for combustion and liquid hydrogen as coolant. Liquid nitrogen is used only as a coolant bath for liquid hydrogen and oxygen but not as coolant for the engine. So where is the information about cryogenic cooling of a rocket engine using liquid nitrogen or helium? – Uwe Jul 02 '17 at 16:04