I'm not that good in Physics, but I try my best to learn.

So my question is. I know that planes "damage" nature pretty hard. And they use kerosene as fuel I think. But rockets need way more power. What fuel do they use? If it is "cleaner" then kerosine, why don't planes use it as well?

I think the kerosene gets burned or something and the exhaust fumes damage the ozone layer. What happens with all the rocket fuel..?

And if rockets do produce more "damage" to nature.

What would be an alternative to move in a vacuum?

closed as off-topic by L.Dutch, Mołot, Frostfyre, sphennings, Green Oct 4 '17 at 12:32

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    Hello and welcome to Worldbuilding. Your question is almost all right but it needs some clarification: what do you mean with "eco-friendly"? "Ecological"/"Organic" is normally used as a label to characterize production, and this has almost nothing to do with the concept of "environmentally friendly". The latter is a different concept. So you have a mashup here. Space travel is neither a form of production, nor is there any kind of physical environment you are moving in, since you are moving in vacuum. So... what are you asking about? – MichaelK Oct 4 '17 at 10:49
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    Please ask one question at a time. And please, please avoid real life questions that can be answered by simply reading relevant Wikipedia page. You can know for sure what panes use. And what rockets use. And if your knowledge of propulsion is "gets burned or something", please read a bit and there go to space.stackexchange.com and space.stackexchange.com and ask for things you wasn't able to find. Such knowledge will allow you to ask better question, and to better understand answers you will get. – Mołot Oct 4 '17 at 11:18
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    @a4android I despise the use of linguistic imprecision. So when someone has expressed themselves in a fuzzy, imprecise manner, I will point out to them that they should express themselves with more clarity and precision. And when it comes to something as important as humanity's ecological footprint, the environment, climate change, sustainable development and similar such concepts, I urge people to be precise and informed, and not to be ignorant and/or too casual about them. – MichaelK Oct 4 '17 at 11:42
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    Was tossing up between answer and comment, the decision was made for me. @MichaelK has written a very good answer on basic travel, I would add one thing; if you don't want to pollute space, don't explode. Normal travel doesn't leave enough matter behind to cause any problems because space is, as a rule, too mindbogglingly huge. However, if you have routine space travel along established routes wreckage can really spoil your day. – Ash Oct 4 '17 at 12:39
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    @Ash Obligatory HHGTTG quote: Space is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is! I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space! Listen... – MichaelK Oct 4 '17 at 12:42

Space travel is not air travel

You are comparing aircraft to spacecraft. This is not a good comparison.

  • Aircraft move in the air, the atmosphere
  • Spacecraft move in space

Why do aircraft use fossil fuels but spacecraft do not? Well they do actually; for instance some spacecraft use(d) kerosene as their main propellant, the most conspicuous example being the Saturn V, the biggest rocket that ever flew successfully.

Some other rocket engines do not use fossil fuels though. The Space Shuttle had main engines that used hydrogen and oxygen. Hydrogen and oxygen burns cleanly and forms only pure water. Why do aircraft not use that?

This is because an aircraft engine is expected to be used for thousands of hours and to be very cost effective. A rocket engine is usually meant to be used for less than 10 minutes, and you do not really care much about the fuel cost of a rocket engine. And while it is very easy to make a rocket engine that can use hydrogen and oxygen as fuel, we have still not been able to do that with aircraft engines. We simply do not yet have the technology to make internal combustion engines that use hydrogen and oxygen as fuel. If we could, we would have solved a lot of environmental problems. The work to achieve that is ongoing.

What happens with the exhaust from rocket engines you ask. It is simply left in the atmosphere to be diluted by the rest of the air. And since space travel is exceedingly rare compared to air travel, by a factor of more than a million, the contribution to pollution by rocket engines is simply too small to be noticed.

What can we do to keep space travel (and air travel) "clean"?

Two things:

  1. Use fuel that can be manufactured without leaving a big footprint. The aforementioned hydrogen-oxygen combination mentioned before is good at that, if you use clean electricity to make the hydrogen oxygen.
  2. Use fuel that does not leave exhaust that affect the environment adversely. Actually RP-1 (kerosene) that the Saturn V used was quite good for that, leaving only water and carbon dioxide behind. But again, the hydrogen-oxygen combination is a good one.
  • Perfect answer. Thanks so much. I will now inform myself a bit more about "Electrolysis". (: – Daniel Oct 4 '17 at 11:26
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    It might be worth pointing out that there are also rockets which use pretty nasty chemicals as fuel. The Proton-series of heavy lift rockets, for example, runs on Dinitrogen Tetroxide and Hydrazine. – Philipp Oct 4 '17 at 11:29

The main environmental advantage of space travel is that there is vastly less of it than there is of air travel. There are about 35 or 40 million commercial flights per year, not counting military, government and private flying. There are around 100 space launches per year, fewer than 0.001% of the number of flights. At that scale, it doesn't really matter how polluting space travel is or is not, unless you live immediately next to a major launch facility.

So, let's split your question in two parts:

  1. Why don't planes use rocket fuel instead of kerosene?

Rockets carry their oxidizer with them while planes are air-breathing. Rockets bring fuel (hydrogen, kerosene, etc) and their oxidizer (usually liquid oxygen). But LOX is a pain to deal with. It costs a lot of energy to lift, and it needs to be cryogenic. But the rocket needs that, because it is going into space. An aircraft — that literally flies around in its own oxidizer — does not bother about that. It just scoops it up out of the air.

  1. What's the most ecological way to travel in space?

Travelling to space needs to be ecological, travelling in space doesn't (It's a giant vacuum, afterall) The easiest ecological way to go to space is an Space Elevator or a Hydrogen-Oxygen rocket (because it will generate steam as exhaust, nothing dangerous)

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    Point 1 is just plain nonsensical. RP-1 for instance is simply highly refined and "clean" kerosene. It is comparable to jet fuel. To quote the Wikipedia page: "RP-1 is less toxic than various jet and diesel fuels, and far less toxic than gasoline". It also has a high flashpoint, higher than ordinary gasoline. – MichaelK Oct 4 '17 at 13:05
  • @MichaelK sorry about that, I edited my answer. – Markus Appel Oct 4 '17 at 13:56
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    Your point 1 is still a complete mess. As I said out in my answer: kerosene is a rocket fuel too. The point you are trying to make is that rockets carry their oxidizer with them while planes are air-breathing. Rockets bring fuel (hydrogen, kerosene, etc) and their oxidizer (usually liquid oxygen). But LOX is a pain to deal with. It costs a lot of energy to lift, and it needs to be cryogenic. But the rocket needs that, because it is going into space. An aircraft — that literally flies around in its own oxidizer — does not bother about that. It just scoops it up out of the air. – MichaelK Oct 4 '17 at 14:30
  • @MichaelK this is a good way to put it. – Markus Appel Oct 5 '17 at 7:32

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