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> we are talking 19 launches per day […] isn't that completely impossible!?? The US uses over 20 million barrels of petroleum every single day. We have 44,000

> we are talking 19 launches per day […] isn't that completely impossible!?? The US uses over 20 million barrels of petroleum every single day. We have 44,000 airline flights every day. I think 19 starship flights won’t even move the needle.

Someone 6y ago
https://en.wikipedia.org/wiki/SpaceX_Starship https://en.wikipedia.org/wiki/SpaceX_Starship says a starship uses 3,400,000 kg (first stage) + 1,200,000 kg = 4,600,000 kg of propellant, both methane + liquid oxygen. Let’s guess making the fuel takes 5,000,000 kg of oil (corrections welcome. I guess that’s a reasonable estimate. Less than 100% of fuel is methane, but the specific energy of methane is about 20% higher than that of oil, and creating liquid oxygen takes energy, too) Multiply by 19 gives you 95,000,000 kg, or about 700,000 barrels. That’s 3% of the oil usage in the USA. And that excludes construction, maintenance, and ground operations. ⇒ I think it would move the needle, more so given that we should work hard on getting that number down.
- ben_w 6y ago
  Why count oil as the energy source for liquefying oxygen? Why not PV? Why not use natural gas instead of cracking oil? Also, separate point: Starship return flight to Mars requires large-scale manufacture of methane from atmospheric CO2, using solar (or technically nuclear, but I don’t see that happening in this case). It’s the only way of getting back — their tanks are empty when they finish landing on Mars — but it works fine here too.
- Tuna-Fish 6y ago
  > corrections welcome. Methane is not made from oil. It's either directly pumped out of the ground as natural gas, or collected from organic decay processes. Methane is more carbon-efficient, as it has almost 2x more hydrogen per carbon compared to longer hydrocarbon fuels, and most of the energy in the molecule is in the hydrogen, to the tune of 40% more energy per ton of CO2. One ton of methane burnt produces ~2.7 tons of CO2 (and 2.2 tons of water), compared to one ton of octane producing 3.1 tons of CO2 (and 1.4 tons of water). Of the propellant in the rocket, less than a quarter is methane, and more than 3/4ths are LOX. The stoichiometric ratio would be ~1:4 (by mass), but for various reasons most rocket engines are more fuel-efficient when burning fuel-rich, so the real ratio is probably somewhere between 1:3.6 to 1:3.8. The energy cost of producing LOX is really, really low, less than 1% of the energy content of similar mass of methane. Also, this process is done with electricity, and is very amenable to intermittent production. (So the CO2 impact is effectively zero). Coming from the other direction, according to the department of energy, the US yearly CO2 emissions from all anthropogenic sources are ~6.7B tons of CO2 equivalents, while the launch of a single SS/SH produces about 2700 tons. If you were launching a thousand of them every year, they would account for 0.04% of emissions.

Someone 6y ago

https://en.wikipedia.org/wiki/SpaceX_Starship https://en.wikipedia.org/wiki/SpaceX_Starship says a starship uses 3,400,000 kg (first stage) + 1,200,000 kg = 4,600,000 kg of propellant, both methane + liquid oxygen. Let’s guess making the fuel takes 5,000,000 kg of oil (corrections welcome. I guess that’s a reasonable estimate. Less than 100% of fuel is methane, but the specific energy of methane is about 20% higher than that of oil, and creating liquid oxygen takes energy, too) Multiply by 19 gives you 95,000,000 kg, or about 700,000 barrels. That’s 3% of the oil usage in the USA. And that excludes construction, maintenance, and ground operations. ⇒ I think it would move the needle, more so given that we should work hard on getting that number down.

ben_w 6y ago
Why count oil as the energy source for liquefying oxygen? Why not PV? Why not use natural gas instead of cracking oil? Also, separate point: Starship return flight to Mars requires large-scale manufacture of methane from atmospheric CO2, using solar (or technically nuclear, but I don’t see that happening in this case). It’s the only way of getting back — their tanks are empty when they finish landing on Mars — but it works fine here too.
Tuna-Fish 6y ago
> corrections welcome. Methane is not made from oil. It's either directly pumped out of the ground as natural gas, or collected from organic decay processes. Methane is more carbon-efficient, as it has almost 2x more hydrogen per carbon compared to longer hydrocarbon fuels, and most of the energy in the molecule is in the hydrogen, to the tune of 40% more energy per ton of CO2. One ton of methane burnt produces ~2.7 tons of CO2 (and 2.2 tons of water), compared to one ton of octane producing 3.1 tons of CO2 (and 1.4 tons of water). Of the propellant in the rocket, less than a quarter is methane, and more than 3/4ths are LOX. The stoichiometric ratio would be ~1:4 (by mass), but for various reasons most rocket engines are more fuel-efficient when burning fuel-rich, so the real ratio is probably somewhere between 1:3.6 to 1:3.8. The energy cost of producing LOX is really, really low, less than 1% of the energy content of similar mass of methane. Also, this process is done with electricity, and is very amenable to intermittent production. (So the CO2 impact is effectively zero). Coming from the other direction, according to the department of energy, the US yearly CO2 emissions from all anthropogenic sources are ~6.7B tons of CO2 equivalents, while the launch of a single SS/SH produces about 2700 tons. If you were launching a thousand of them every year, they would account for 0.04% of emissions.