I am interested in if the exhaust from a rocket would lead to space pollution like space junk does. Particularly, I am talking about the exhaust that stays in interplanetary orbit and does not return to our atmosphere. When a rocket ejects its propellent, wouldn't some of it stay in interplanetary space? And, if so, why would or wouldn't this exhaust be harmful over time, especially with the increase in spacecraft launches every year. This gas would be traveling at high speeds, and I would think that gravity would clump some types of exhaust together to form pellets that could damage satellites and rockets. If this truly is an issue, is there anything we can do about it?
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$\begingroup$ Presumably most of the fuel combustion products exhaust in the atmosphere which is more problematic to living systems and atmospheric chemistry, the orbital exhausts must be a tiny fraction of the fuels that put the vehicle as it were up there. And as stated solar wind fluxes must also dwarf attitude and positional adjustment thrusting. $\endgroup$– civitasCommented 19 hours ago
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5$\begingroup$ The sun emits ~1.5 million tons per second of solar wind. Rocket exhaust is a drop in the bucket - we've launched ~20 thousand tons into space total. $\endgroup$– TLWCommented 15 hours ago
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$\begingroup$ The answers that say that space is big and rocket fuel is tiny are right, but it should be noted that the fuel mass of the Apollo lunar landers is on the same order of magnitude of the whole mass of the lunar atmosphere. Therefore, there was a time half a century ago when a sizeable part of the lunar atmosphere was made of rocket exhaust. However, it's unlikely that it had any detrimental effect. $\endgroup$– PereCommented 13 hours ago
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1$\begingroup$ different but related: Does "What happens beyond Kármán, stay beyond Kármán"? $\endgroup$– uhohCommented 12 hours ago
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$\begingroup$ @Pere A large percent increase in a small number is still a small number; obligatory xkcd. Even after all current landings the atmosphere is still considered vacuum for all intents and purposes (only around a thousand times the pressure of vacuums we can artifice for scientific purposes). $\endgroup$– controlgroupCommented 11 hours ago
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2 Answers
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No, this isn't an issue. Space is big, and the exhaust gases rapidly disperse, eventually merging with the solar wind. Exhaust can produce some solids, eg carbon, but these particles are microscopic and unlikely to condense. Some exhaust gas and dust can orbit the Sun, but most of it will dissipate.
From my answer https://physics.stackexchange.com/a/551141/123208
the solar wind [is] a stream of charged particles released from the upper atmosphere of the Sun which blows through the solar system. This wind is very thin - in Earth terms it's a hard vacuum, but it is moving quickly.
The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind. Near Earth, the slow solar wind has a speed of 300 - 500 km/s, and a temperature around 100,000 K, the fast solar wind has a typical speed of 750 km/s and a temperature around 800,000 K.
So the solar wind and solar radiation pressure tends to push exhaust gases to the far reaches of the solar system, and into the interstellar medium.
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$\begingroup$ I'm not 100% on board with how absolutely you phrased this answer. What's true is that the combustion in liquid-fueled rockets produces exhaust that consists almost exclusively of gases that then disperse, but there are some details where it's less clear-cut: ablatively cooled nozzles, solid-fueled stages, ignition mechanisms... $\endgroup$ Commented 20 hours ago
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2$\begingroup$ @leftaroundabout I tried to not make an absolute statement. Sure, there are other solids possible, apart from carbon, especially with solid fuels, eg metals and metallic oxides, nitrides, chlorides, etc. But those solid particles are tiny, and don't tend to form clumps when ejected at high speed and temperature. I think "these particles are microscopic and unlikely to condense" covers that adequately. $\endgroup$– PM 2RingCommented 18 hours ago
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1$\begingroup$ OTOH, yes, some solids can condense on nozzle surfaces, and then clumps of that "soot" can be dislodged... $\endgroup$– PM 2RingCommented 18 hours ago
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$\begingroup$ Plus, I don't know of any solid rocket motors that are used in interplanetary space. The only ones I know of are ullage motors (very small) and SRBs (used in the first stage and usually fall back down to Earth). $\endgroup$ Commented 11 hours ago
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The total mass of the (natural) interplanetary dust cloud is approximately $3.5×10^{16}$ kg. That's 7 billion Starship launchers. There is no conceivable way for humans to add significantly to interplanetary dust with present technology.
