Well, 215,000 L for the 747, 175,000 L for a Falcon 9, and 470,000 for the Falcon Heavy so in the same rough range. The Falcon Heavy is also carrying another 780,000 L of oxygen but that doesn't contribute any extra carbon, of course.

That is a really surprising comparison, thanks for pointing it out! Do you have a source for that, it is something I expect to be repeating.

I agree. For some reason I imagined that orbital-capable rockets use order(s) of magnitude more fuel than airliners...

Depending on how you count, it does. The 747-8 freighter can carry 240k L of fuel [1], and 308k lbs of cargo [2], so 1.3 L/lb. The Falcon Heavy can launch 120k lbs of cargo into low-Earth orbit [3], and according to the grandparent, is carrying 1250k L of fuel (including oxygen, which is an essential component of "fuel" in this case), so 10.4 L/lb. Still, that's better than I expected. And if you want to go to Mars, you can take 30k lbs, so 41.7 L/lb, for only 4X LEO, quite the bargain!

(Interestingly, the average cost of a 10 hr 747 flight is about $40k [about $14k for fuel, which is about 33% of costs], compared to $90m [estimated] for a Falcon Heavy launch. So one order of magnitude more fuel, but almost 4 orders of magnitude more price.)

[1] https://www.reference.com/vehicles/much-747-weigh-8b0c48a1d8... [2] https://en.wikipedia.org/wiki/Boeing_747-8 [3] https://en.wikipedia.org/wiki/Falcon_Heavy [4] https://www.quora.com/How-much-fuel-does-a-Boeing-747-or-777... [5] https://www.quora.com/How-much-of-the-cost-of-an-airline-tic...

Would it be erreneous to say that no matter how 'green' our industries and power consumption on ground becomes, aviation and space flight would always require carbon based fuel?

An electric plane could be a possibility, depending on advancements in battery technology or power storage in general. Space flight would most likely require some kind fuel, at least in our lifetimes - so far we haven't found any other way to move mass in vacuum other than expelling propellant.

However, not all rocket fuel/propellant is carbon based, in fact, most aren't.

We may be able to develop better electricity storage to allow electric planes to be more practical than they currently are.

However, there's also a lot of interest in using biofuels for aviation, so you may see that in the mid-term future we're using carbon-based fuels but they're largely carbon-neutral.

If we can make renewable energy cheap enough it'll start making economic sense to synthesize fuel oil out of the air and water rather than mining it out of the ground, leading to no net carbon consumption.