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If they can fully synthesize the methane and oxygen using carbon neutral energy sources, then they will have essentially created a carbon-neutral orbital launch

If they can fully synthesize the methane and oxygen using carbon neutral energy sources, then they will have essentially created a carbon-neutral orbital launch platform. Realistically, it will be easier and cheaper to achieve the same goal by buying carbon offsets on the market. Let's be pessimistic. At 3400 tons of propellant per launch (not sure how much of it actually becomes CO2), and an estimated 50$ per tonne on the market, we're talking about 170 000$, so instead of 2 000 000$ per launch, we're talking about 2 170 000$ per CARBON-NEUTRAL launch. Only factoring in PR value, it's totally worth it.

gpm 6y ago
They've been promising to synthesize the methane from scratch using green energy for quite awhile now, or in other words they agree.
- skykooler 6y ago
  Which makes a fair amount of sense as they need to develop and test those technologies for synthesizing methane on Mars anyway.
- bryanlarsen 6y ago
  I don't think Musk has yet expiclitly said that he will do so. If so, I'd love a link. He's certainly hinted that they'd like to and are looking into it. Obviously they are researching it for Mars in-situ production, but Mars' atmosphere is 95% CO2, making the reaction easier.
  - gpm 6y ago
    Technically I guess this is only about launches from the old oil rigs he bought, but this is explicit and recent. I feel like there's a better tweet/quote out there somewhere which says it for all launches, but you know, limited time to search for it and all.. https://twitter.com/elonmusk/status/1364470475620044802?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1364470475620044802%7Ctwgr%5E%7Ctwcon%5Es1_c10&ref_url=https%3A%2F%2Fforum.nasaspaceflight.com%2Findex.php%3Ftopic%3D47352.260 https://twitter.com/elonmusk/status/1364470475620044802?ref_...
bryanlarsen 6y ago
That's not a bad approximation. The nominal reaction is CH4 + 2O2 -> 2H2O + CO2. Hydrogen is light and oxygen is heavy, so by weight the CO2 would be 55% of the total. However, for various reasons they run fuel rich, so a significant part of the output is CO which will combine with atmospheric oxygen to produce CO2. The total CO2 is therefore close to, but not quite 100% of the propellant mass.
- Valgrim 6y ago
  I was under the impression that the Raptor was running a full-flow staged combustion, which by definition is neither Fuel-rich nor oxygen-rich.
  - bryanlarsen 6y ago
    FFSC means it has two turbopumps, one which runs fuel rich and the other which runs oxygen rich. It doesn't force the thrust chamber to be perfectly balanced, in fact because you can run the turbopumps independently it gives you the freedom to have the mixture be whatever you want: fuel rich, oxygen rich or at the perfect stoichiometric ratio. The perfect stoichiometric ratio would get the highest exhaust velocity, but thrust is mass x velocity, and ISP is relative to propellant mass. Oxygen is relatively heavy, so optimum ISP is fuel rich.

gpm 6y ago

They've been promising to synthesize the methane from scratch using green energy for quite awhile now, or in other words they agree.

skykooler 6y ago
Which makes a fair amount of sense as they need to develop and test those technologies for synthesizing methane on Mars anyway.
bryanlarsen 6y ago
I don't think Musk has yet expiclitly said that he will do so. If so, I'd love a link. He's certainly hinted that they'd like to and are looking into it. Obviously they are researching it for Mars in-situ production, but Mars' atmosphere is 95% CO2, making the reaction easier.
- gpm 6y ago
  Technically I guess this is only about launches from the old oil rigs he bought, but this is explicit and recent. I feel like there's a better tweet/quote out there somewhere which says it for all launches, but you know, limited time to search for it and all.. https://twitter.com/elonmusk/status/1364470475620044802?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1364470475620044802%7Ctwgr%5E%7Ctwcon%5Es1_c10&ref_url=https%3A%2F%2Fforum.nasaspaceflight.com%2Findex.php%3Ftopic%3D47352.260 https://twitter.com/elonmusk/status/1364470475620044802?ref_...

bryanlarsen 6y ago

That's not a bad approximation. The nominal reaction is CH4 + 2O2 -> 2H2O + CO2. Hydrogen is light and oxygen is heavy, so by weight the CO2 would be 55% of the total. However, for various reasons they run fuel rich, so a significant part of the output is CO which will combine with atmospheric oxygen to produce CO2. The total CO2 is therefore close to, but not quite 100% of the propellant mass.

Valgrim 6y ago
I was under the impression that the Raptor was running a full-flow staged combustion, which by definition is neither Fuel-rich nor oxygen-rich.
- bryanlarsen 6y ago
  FFSC means it has two turbopumps, one which runs fuel rich and the other which runs oxygen rich. It doesn't force the thrust chamber to be perfectly balanced, in fact because you can run the turbopumps independently it gives you the freedom to have the mixture be whatever you want: fuel rich, oxygen rich or at the perfect stoichiometric ratio. The perfect stoichiometric ratio would get the highest exhaust velocity, but thrust is mass x velocity, and ISP is relative to propellant mass. Oxygen is relatively heavy, so optimum ISP is fuel rich.