4 ms·
Isn't the exhaust just water?!?
by jfoutz 10y ago
Isn't the exhaust just water?!?
- daeken 10y agoNot with the fuels used by the Falcon rockets. They use LOX + RP1 (kerosene), rather than LOX + LH (which does produce water).
- CommieBobDole 10y agoNot for the Falcon 9/Falcon Heavy that will be used in this launch; it uses RP-1 (basically very pure jet fuel, AKA kerosene) and liquid oxygen as fuel. The Shuttle and the new Space Launch System will use hydrogen/LOX, which exhausts basically water vapor.
- kobeya 10y agoWell, not the SRB part.
- deleted 10y ago[deleted]
- greglindahl 10y agoYeah, in both cases, the SRBs are the majority of the launch thrust.
- lutorm 10y agoRP-1/LOX also exhausts basically water vapor, plus CO2. There should be little NOx emission since it's not burning air, but there's probably some organic emissions from unburned fuel.
- coryfklein 10y agoIs it? I know very little about rocket fuel, but I always assumed that CO2 is involved. A short bit of Googling "composition of rocket fuel exhaust" wasn't immediately helpful. :/
- azernik 10y agoOther responses go into this in more detail, but basically there are a few very chemically different types of rocket fuel. Usually for main engines these are bipropellants, with a fuel component and an oxidizer component. The expensive, exotic, high-specific-impulse, but low-density and dangerous option is liquid hydrogen + liquid oxygen (hydrolox), which does indeed create water vapor as exhaust. This particular rocket, however, uses RP-1 (similar to jet fuel - just highly refined kerosene) + liquid oxygen - still burning hydrocarbons, still releasing CO2, but favored because it's cheap, dense, safe, and doesn't need cryogenic cooling. For comparison, the ITS (and many other Mars mission concepts) use liquid methane + liquid oxygen (methalox), which also outputs CO2, needs cryogenic cooling and is not as safe or dense as RP-1/LOX, but is still safer and denser than hydrogen, doesn't need to be kept quite as cold, and is easy to synthesize on-site on another planet.
- wiredfool 10y agoAnd then there are the more out-there toxic ones like hydrazine and whatever fuel they use with oxidizers like nitric acid and the chloroflourines.
- skookumchuck 10y agoJust look at the composition of the rocket fuel, and add oxygen to that. It the fuel has lots of carbon atoms in it, CO2 will be the result in the same proportion.
- homerowilson 10y agoMostly CO2 and CO, see for instance https://en.wikipedia.org/wiki/RP-1 https://en.wikipedia.org/wiki/RP-1
- Retric 10y agoThe H in hydrocarbons mostly ends up as water, so ideally it's about 50/50 H2O + CO2. But, you do get a little bit other stuff. https://en.m.wikipedia.org/wiki/Kerosene https://en.m.wikipedia.org/wiki/Kerosene The combustion reaction can be approximated as follows, with the molecular formula C12H26 (dodecane): 2 C12H26(l) + 37 O2(g) → 24 CO2(g) + 26 H2O(g); ∆H˚ = -7513 kJ
- schiffern 10y agoIt's about 50/50 by moles, but one mole of CO2 masses 44/18th = 2.44x as much as one mole of water. The atomic makeup of RP-1 is about CH1.97[1], so at stoichiometric ratio[2] that would yield 71.3% CO2 and 28.7% H2O by mass. [1] http://www.qrg.northwestern.edu/projects/vss/docs/propulsion/3-what-are-some-rocket-propellants.html http://www.qrg.northwestern.edu/projects/vss/docs/propulsion... [2] in reality Falcon 9 burns fuel-rich
- lftl 10y agoAs an interesting bit of trivia: the most prevalent greenhouse gas in the atmosphere? Water vapor.
- DennisP 10y agoWhich doesn't mean that emitting water vapor from a rocket adds to global warming. It just adds to the rain.
- morsch 10y agoTrue as long as you intend to fly your rocket within the troposphere, the lower ~10 miles of the atmosphere. Above that, water vapor seems to stick around a long time and is currently understood to be quite harmful[1]. This is also an issue with high-flying planes (not that flying low is better, due to the decreased efficiency). However, more research is needed[2]. [1] http://www.grida.no/publications/other/ipcc_sr/?src=/climate/ipcc/aviation/076.htm http://www.grida.no/publications/other/ipcc_sr/?src=/climate... (kind of old, but I think the more recent IPCC reports are in a similar vein) [2] https://eos.org/research-spotlights/the-forgotten-water-vapor-at-high-altitudes https://eos.org/research-spotlights/the-forgotten-water-vapo...
- DennisP 10y agoWow, learn something new every day. Thanks!
- morsch 10y agoDoesn't really matter what it exhausts, it expends energy either way. If it ran on hydrogen, you'd probably have to use electrical energy to produce that. Even if you somehow got the hydrogen "for free", there are other things you could use it for. This is all quite separate from the moral issue, to which I have nothing to add.
- coryfklein 10y ago> Doesn't really matter what it exhausts, it expends energy either way. Energy usage is not the only consideration, and it certainly does matter what it exhausts. Exhausting an inert gas is definitely preferable to a greenhouse gas, which would be preferable to exhausting anthrax, etc. The composition of the exhaust is going to affect the positivity of the public reaction to a billionaire burning it into public air space for leisure.
- hamandcheese 10y ago> the moral issue Uhh, what moral issue, exactly?