Aletheia's

Ah, but these aren't NASA. They're just some independent wackos. I don't think they have much chances for success... That is, precisely speaking, sure, they can launch some stuff that even might reach the space, but Mars? Come on... Actually, what bothers me most, is not even that someone could accept a one way ticket, but that they can attract people who actually will trust them and their technical abilities. For me it looks like the astronautic equivalent of the alternative medicine, even if they genuinely believe they're able to do it.

As for the theoretical possibility of the journey with no return, NASA is a public organization, they get money from the government. And, as is aptly said in the movie, they won't get financed a single paper clip anymore if they actually lose someone this way. Public opinion and all that... The movie uses the option with a series of missions (where each one leaves stuff for next ones) and... what is the opposite of lander? launcher? ...launchers send in parts and assembled on Mars. I guess there must have been also the part with making the fuel from carbon dioxide in the Martian atmosphere while waiting between missions (which requires part of the machines set off after assembling and working for some time on their own), but this part wasn't mentioned in the movie.

ETA
Oh, I forgot. The mother ship is only orbiter, of course! It never lands on Mars! Or Earth, for that matter. All the traffic between the space and surface is done by landers and, uh, launchers, if this is the proper name...