> that results in CO2 and CH4
The chemical reaction of O2 + CH4 -> CO2 + CH4 does not compute.
More likely is the reaction 2 O2 + CH4 -> CO2 + 2 H2O.
So no methane emissions, that's the actual fuel. Only CO2 (and water) emissions.
The chemical reaction is indeed CH4 + 2 O2 -> CO2 + 2 H2O. So, for each 16 grams of CH4 you get 64 grams of O2, that's a stoichiometric mass ratio of 1:4.
The fuel ratio for the Raptor engine is 22:78, according to Elon Musk's tweet. So, for each 100 g of propellant mixture you get 19.5 g of CH4 to burn using 78 g of O2 and you are left with 2.5 g unburned CH4.
I simply neglected the H2O resultant from the reaction because, while H2O is a very potent greenhouse gas, it has a fast cycle in nature (rain, etc). Also, I have no idea how to account for it as a greenhouse gas.
Otherwise it would have been in a comment on an Eric Berger Ars Technica article.
- each starship burns 4600 tons of methalox fuel
- the mixture ratio of the propellent is 78% O2 and 22% CH4 [1]
- that means that each 100 tons of methalox results in 53.6 tons of CO2 and 2.5 tons of CH4
- generally in the climate science it is accepted that one ton of CH4 is equivalent to 25 tons of CO2
- overall, each 100 tons of propellent will produce 116 tons of CO2-equivalent emissions
- a single launch of 4600 tons propellent will result in 5.34 kT CO2 emissions
- if we get to 5000 launches per year we end up with about 25 MT of CO2-equivalent emissions
- the current worldwide level of emissions is 45 GT CO2-equivalent as of 2017 [2]
- that means 5000 launches will increase our global emissions by 0.06%
[1] https://twitter.com/elonmusk/status/1258580078218412033
[2] https://en.wikipedia.org/wiki/List_of_countries_by_greenhous...