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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12$\begingroup$ 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 Dec 2 at 17:24
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1$\begingroup$ different but related: Does "What happens beyond Kármán, stay beyond Kármán"? $\endgroup$– uhohCommented Dec 2 at 20:50
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1$\begingroup$ @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 Dec 2 at 21:19
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1$\begingroup$ @TLW and that solar wind is radiating out in all directions, diminishing with the inverse square law. $\endgroup$– RonJohnCommented Dec 3 at 3:24
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1$\begingroup$ @RonJohn - and carrying your rocket exhaust along with it out, dissipating said exhaust through inverse-square in the process. $\endgroup$– TLWCommented Dec 3 at 15:13
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5 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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1$\begingroup$ 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 Dec 2 at 12:32
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4$\begingroup$ @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 Dec 2 at 14:26
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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 Dec 2 at 14:31
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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 Dec 2 at 21:15
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3$\begingroup$ @controlgroup apogee kick motors are often solids for reliability reasons and quick burn times. This apparently includes geostationary satellites, despite the potential weight savings with better Isp. The new horizons probe that went to pluto even used a solid kick motor as its final stage. $\endgroup$– AI0867Commented Dec 3 at 16:48
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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.
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In most space flight configurations, most if not all propellants "outside" of the Earth's atmosphere use either liquid hydrogen as fuel and LOX (liquid oxygen) as the oxidizer, or hypergolic propellants which consist of hydrazine variants as the fuel along with an oxidizer such as nitrogen tetroxide. Both of these fuel/oxidizer combos produce water vapor as a byproduct of combustion. As such, water vapor poses no threat to space.
The emissions of solid rocket fuels and other liquid fuel types used in most rocket booster stages will be confined to the Earth's atmosphere.
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Are you building engines that move planets? Like, did you lower a moon-scale thrusters into Jupiter and are burning its Hydrogen in a fusion candle to turn Jupiter into an interstellar space craft?
(You build a large hydrogen collector and two fusion engines on a planetoid (or structure on that size). You lower this into Jupiter, and fire both in balance. The inward one pushes on Jupiter itself, and the outer one provides thrust; the net effect is you have a rocket engine pushing Jupiter. You fuel it by gathering hydrogen from Jupiter atmosphere. Note that this will get insanely hot and insanely turbulent, as the rocket plume will warm up the atmosphere near you; this is K1 or K2-scale planetary engineering.)
If you are doing planetary engineering on this kind of scale, you start having to worry about your rocket exhaust messing with the solar system.
If you are merely launching rockets from a planet to do light exploration, space is insanely big, and the sun pushes a large amount of gas out of the solar system already. The existing solar wind is on the order of millions of tonnes of gas per second - spread over the entire sphere of the solar system, but still, it is a lot.
Local emissions could mess with that, but you'd have to be somewhere in that neighborhood, which is far beyond our current level of space faring capability.
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1$\begingroup$ I’d like to give you a quick heads-up. I noticed you mentioned fusion candles, which you likely got from SFIA (since that’s where these kinds of projects are often discussed). However, Space.Stackexchange primarily focuses on the present era. While some future concepts are mentioned, they’re usually not well-received. If you want to include that concept, I’d recommend adding reliable sources and numbers about the exhaust. As it stands, your answer probably will be downvoted for lacking those elements. Remember, this platform is more of a Q&A site than a discussion forum like Reddit. $\endgroup$ Commented Dec 4 at 16:43
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Small amounts of gasses and solids or not we are still governed by Sir Newton. After hundreds of years of heavily polluting Earth's atmosphere such that we can hardly breathe it, the comments here still nay say as if what happens here will not happen in space. Small changes can create large problems.
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