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Douglas_Knight comments on [LINK] Waitbutwhy article on the history and future of space exploration, SpaceX and more - Less Wrong
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Is there any good writeup on the 'geophysical ignorance' anywhere? I checked out some of the comments but they all seemed to be along the lines of 'hydrogen rules, batteries drool', and I can't take hydrogen-car proposals very seriously given Tesla's demonstrated success.
In any case, I read this a few days ago and found it very interesting. He's at least up front about the fanboying, and the overoptimism seems to come from Musk directly (before I read this, I assumed that Musk's talk of going to Mars before 2030 was so much PR intended to keep his mystique alive and stock prices & valuations high and, among other things, deflect attention from the extent to which his companies are still dependent on subsidies; after, I began to take seriously the idea he might actually believe all that), and if nothing else, it seems like this is the closest thing to a comprehensive Musk manifesto - which is interesting all on its own.
What's going on in your first paragraph? How did we get from spaceflight to cars?
Without bothering to read these comments, my understanding is that fuel cells are bad for cars but good for spaceships. Batteries win on energy per volume, but lose on energy per mass. Also, fuel cells can store energy for a longer period of time, but that is relevant to the outer system, not for Mars.
The linked articles cover pretty much everything, from cars to spaceflight.
No, the issue is power density. Fuel cells win over batteries in terms of energy per mass but lose in terms of power per mass and power per volume. Fuel cells are still an order of magnitude or so behind batteries in terms of deliverable power. This is why they are best suited to applications that require power drain for an extended period of time without the possibility of recharging.
It's difficult to directly compare batteries and fuel cells, though, because in the fuel cell the actual fuel tank is separate from the electrodes and can be made as large as desired. In the limit of a very large fuel tank, huge energy densities of 20 MJ/kg or 15 MJ/L are possible with methanol. Compare this with about 1 MJ/kg for the best lithium-ion batteries. However, in the same limit, fuel cell power density drops to near zero.