To be more precise: the laws of physics and chemistry will never allow to pull CO2 from the atmosphere in an energy efficient way
The consequence is that, unless all your electricity generation and raw resource extraction needed for the process has basically zero emissions, it's probably better to just use regular fuel. Burning fossil fuels to create fuel that you then burn has more CO2 emissions than just burning fossil fuels once (since you need way less fossil fuel in the first place). And the US grid is, right now, not in path of not burning fossil fuels. So the idea of pulling CO2 from the atmosphere and be carbon neutral doesn't seem plausible.
> To be more precise: the laws of physics and chemistry will never allow to pull CO2 from the atmosphere in an energy efficient way
I see. Now that is a big difference. I don’t know enough to tell if you are right.
> it's probably better to just use regular fuel
Maybe. There is one reason why spacex might still do it even if it is less energy efficient.
Their mars plan depends on in-situ resource extraction. If they can’t generate fuel on mars they can’t send their rockets back.
This will be a very hard technological challenge. If they can find a path to derisk their co2->methan plants here on earth it would be worth doing it even if it costs them money. They have to master the tech anyway.
Now clearly doing the conversion here on earth is not the same deal as doing it on mars. The atmosphere is quite different as a start. I don’t know enough to tell how much this matters. Maybe they can just tweek some process parameters and make a machine which works here on earth and on mars “sameish” enough that it helps with learning. Maybe they can process the exhaust of some industrial process into a kind of “martian atmosphere” analogue close enough that they can learn from that.
They will want to test their ISRU equipment before heading to mars. And they want to it eventually in large enough scale that the output can power their rockets back. It stands to reason that even their tests must be at a certain point on a huge scale. So why not fill the methane they get from the testing into their rockets at that point here on Earth too?
