Y'see, this is something I never understood about this plan... the entire mission takes a couple of years, but they're only going to stay on Mars for 30 days? I don't get it. Why not make it a longer stay? It'd be like going somewhere really exotic on your annual 2 weeks (or whatever) holiday, but taking so long to get there you can only stay 1 day before you have to go home again! Yeah, I know, it's to do with orbital mechanics... so they'd have to stretch out the overall journey home. So what?