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Comment by ajmurmann | Hacker News Reader

So what's the carbon footprint of one of these launches? Did I understand correctly that we can make the fuel by taking CO2 from the atmosphere? That would make the footprint negative, would it? That seems to good to be true.

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In all likelihood the carbon footprint of spectators going to watch the launch would be at least an order of magnitude higher than the launch itself.

CO2 extraction for methane production is planned on mars, where the relative ratio of CO2 in the atmosphere is much higher. On Earth, CO2 is only 0.04%, which makes it quite difficult to extract.

He also noted it's a long-term plan on Earth. Use solar power and extract CO₂ from the atmosphere.

The kicker for Earth is that it's a lot easier and cheaper to make CH4 from biological sources (fossil fuels, fermenters, etc), so nobody does it at scale. All the solutions (IIRC) need high temperature and a catalyst, which isn't surprising as we're un-burning rocket fuel. With cheap plentiful solar energy it's more practical; as Mars has no bio-sources of scale it's essential.

Not negative, since you are creating just as much CO2 burning the CH4 as you removed in the first place. Carbon neutral though.

I suppose some of it would be lost to the vacuum of space, though it would have to be an impressively large space transport market for that to start making a global difference.

Also weird to think about the long-term implications of Earth's resources leaving Earth permanently/irrecoverably.

Carbon neutral assuming you are creating the CH4 using atmospheric CO2. On Earth I suspect that most CH4 comes from natural gas. On Mars it would be carbon neutral - but that's actually a bad thing, assuming that your goal is to increase the atmospheric density on Mars.

Yes, that was the assumption of the parent question. I expect that initially all the fuel for Earth launches will be sourced from natural gas, but if they start doing regular sub-orbital passenger flights they'd have to convert to renewable energy + atmospheric CO2, otherwise they'd just (partially) undo the work Tesla is doing.

I thought CH4 was ~four times more potent in the greenhouse effect than CO2, significantly worsening the global temperature rise.

The rocket works by burning the methane, though, instead of releasing it into the atmosphere. Burning it results in water and carbon dioxide.

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