Weir's The Martian.

[Glom]

And if they used 1/3 bar pure oxygen then that airlock "malfunction" wouldn't have been so catastrophic.

[ka9q]

And if they used 1/3 bar pure oxygen then that airlock "malfunction" wouldn't have been so catastrophic.

I think the pressure for pure O₂ corresponding to the same ppO₂ as sea level air on earth would be even lower, about 210 mb. But that's still a lot of pressure. A 2-meter diameter circular piece of polyethylene sheeting would still be subjected to

pi*(1)² * 0.21e+5 N/m²

= ~ 66 kN

That's a lot of force: the earth weight of a 6700 kg mass.

[ka9q]

There is still the fire hazard problem for any large spacecraft or habitat that uses pure O₂, even at the same partial pressure as sea level air on earth. The presence of nitrogen (and argon) diminishes the fire hazard by carrying away heat.

The Apollo program was never able to completely eliminate the risk of fire even after a major campaign to minimize potential fuels. They added N₂ to the prelaunch atmosphere, but there was no practical alternative to pure O₂ during flight.

And that was just a small capsule carrying three guys who didn't have to do much on the way. A working Mars habitat would be a lot bigger (like the fictional one here) and have more people, more activities and a lot more material that could potentially burn. I'm not sure how you would mitigate the fire risk here without adding a diluent gas that would increase the total pressure, make the structure heavier, and complicate EVAs. One possibility is to inert as many of the equipment and storage areas as possible with argon or nitrogen at the same pressure as the living areas. You could work in those areas in shirtsleeves if you wear an oxygen mask. But there would still be a serious risk of accidental suffocation. You get no warning when you breathe an inert atmosphere; you just pass out.

[smartcooky]

And if they used 1/3 bar pure oxygen then that airlock "malfunction" wouldn't have been so catastrophic.

Perhaps not, but his first attempt to make rain inside his "greenhouse" might have been.

Overall, I think the science in this movie was so good that we really are looking a lot harder to find fault and nitpicking some minor technicalities which we would not even bother with for other films since they are often making monumental errors in the science. e.g., Mission to Mars and the "abandon ship" scene which was great from a drama and tension perspective, but complete rubbish with regard to orbital mechanics. Contrast that with the Rich-Purnell manoever, from The Martian, which is not fictional and is completely sound from an orbital mechanics point of view.  Nozomi, a failing Mars probe lanched by Japan in 1998 used a similar Earth-flyby trajectory in a second attempt to get to Mars after electrical failures crippled it.

[ka9q]

Yup. Though I have problems with his water-making method too....

Hydrazine is extremely toxic. He probably should have poisoned himself doing what he did.

If you just want to convert hydrazine into water, there's no need to decompose it first; just burn it directly. Decomposing it tends to make a mixture of nitrogen, hydrogen and ammonia. Ammonia has a negative enthalpy of formation meaning it's more stable than hydrazine (which is positive) and therefore somewhat harder to burn. But even ammonia is much less toxic than hydrazine.

That said, a large rocket engine would not be using straight hydrazine as fuel, especially not when it has to sit for months on a cold planet like Mars. Straight hydrazine freezes at +1C, and the same property that makes it useful in monopropellant thrusters (catalytic decomposion) makes it less than desirable for regenerative cooling, an important design feature of most larger rocket engines. They would be using either Aerozine-50 (50-50 mixture of straight hydrazine and UDMH, used by the larger Apollo spacecraft engines) or more likely monomethyl hydrazine. Both contain carbon that would quite likely produce toxic amounts of carbon monoxide unless burned very carefully in a surplus of oxygen.

[VQ]

Overall, I think the science in this movie was so good that we really are looking a lot harder to find fault and nitpicking some minor technicalities which we would not even bother with for other films since they are often making monumental errors in the science.

Absolutely. Nitpicking is an expression of love.