[toolbox]

One big limitation that was glossed over in the presentation is radiation exposure. The only time it came up was the mention of a 'solar storm shelter'. The radiation exposure during the Martian transit would be much greater than the same time spent on the ISS, somewhere on the order of 200mSv [0] (the composition of this radiation also contains significantly greater proportions of heavy-ion radiation, which appears to be more damaging, so this may need to be adjusted upwards). According to the wonderful xkcd chart [1], this would be in the 'probably no radiation sickness, but certainly not good for you' territory.

I would love to know what their plans are, since shielding is heavy. [2] seems to suggest electromagnetic deflection as viable (which would be insanely cool, and could probably reuse SpaceX's cryogenics work for superconductors).

Also, a quick search didn't turn up much on the anisotropy of interplanetary radiation, but I wonder how much a reduction would be achieved by angling the crewless area of the ship towards the solar wind (which I think Musk had touched on in an earlier talk).

[0]: http://www.srl.caltech.edu/ACE/ASC/DATA/bibliography/ICRC200... [1]: https://xkcd.com/radiation/ [2]: https://engineering.dartmouth.edu/~d76205x/research/shieldin...

EDIT: Of course these sorts of talks are really exciting! This is just one more in a laundry list of crazy-cool engineering problems that have to be/are being solved.

[krastanov]

He has stated a couple of times that the radiation will be there and it will have the same lifetime cancer risk increase as smoking. It seems the plan is to just live with the increased cancer risk.

[grondilu]

Zubrin once joked that if you send a heavy smoker to mars without any cigarette, you actually reduce his risk of dying of cancer.

[nickik]

He does not talk about this so much because its not the fundamental show stopper.

We know enough to get started and we will have to figure the rest as we go along.