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Comment by corradio | Hacker News Reader

wait and what's the energy usage of that thing? Carbon footprint?

Musk said that the fuel (methane and oxygen) for Mars expeditions has to be produced on Mars, using solar panels, water and capturing carbon dioxide available in the atmosphere, and he also stated that the very same procedure could be used on Earth.

That doesn't mean it's anywhere close to being economical. It's just one of the few options they have there, or it's perhaps a little cheaper/more practical than carrying everything from Earth. Perhaps capturing it from Mars instead of bringing it from Earth means the project can cost "only" $5 billion per trip rather than $20 billion.

But that says absolutely nothing about doing that on Earth vs all the other much cheaper alternatives.

Sure, but the discussion was about energy and carbon footprint, not economics; I just reported what Elon Musk said the last presentation about how to produce the fuel starting from carbon dioxide. Economic viability has to be proved, but I think they are more closer to it now than when they presented the BFR for the first time.

EDIT: I forgot the fact that CH4 is being burned, not released as-is in the atmosphere.

Original comment:

Carbon footprint is just one way of measuring the impact on climate, but that's only because CO2 is the biggest pollutant. However, methane (CH4) is much much much better in trapping heat. 19 times more potent over a 5 year period, or 4 times more over a 100 year period (source: http://www.onegreenplanet.org/animalsandnature/methane-vs-ca...).

This is despite having the same number of carbon. So technically the "carbon footprint" is zero if, as Elon said, you're extracting carbon from CO2 in the atmosphere, but if you change it to CH4, you're worsening by a big factor the impact on climate. Maybe over thousands of years that factor goes down to 1x but still...

All this is assuming you extract CH4 from atmosphere, which is extremely unlikely for economical reasons, as others have pointed out.

Burning CH4 has a lower footprint than it being freely in the atmosphere, so if they could capture it from the atmosphere and then burn it would be better.

Thanks for the missing piece of the puzzle!

If they build a rocket fuel plant on Earth the carbon footprint will be negative.

So a solar powered rocket fuel generator would be a carbon sink?

If all the carbon came from Earth and some is burned in space then the footprint on Earth is negative I think

sadly this is all I started thinking, but only because of how much he pushes EVs and Solar. It seems like a complete opposite move but given current technology there isn't a clean method to do what he wants.

I would be really curious how much works has gone into neutral fuels. pretty sure lox and such can be made neutrally with solar powered chillers but what is his other fuel? a hydrogen type would be similar would it not?

He mentions the possibility of making the fuel from solar power, water and CO2 on Earth in the same way he plans to for Mars. It wouldn't make economic sense now though. If you care about the environment that much, use the same process to make the same methane and run your ICE car off it. That's old tech.

Methane + oxygen (methalox).

That produces C02, and given the energies required, would produce a lot. A retrograde step.

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