I doubt people automatically assume that he's correct about being on Mars in 15 years, but if he's saying it, maybe he's got a reasonable plan/timeline for it. Musk is an engineer, and from what I've seen of him, he seems like less of a bullshitter than the average businessperson. Combined with his consistent delivery of results, I'd give him the benefit of the doubt.
As for launch windows, the energy required is at a minimum every 26 months, and there's a global min twice every ~17 years, the next two being in 12 and 14 years, so you'd have the easiest time then. [1] If they have a non-marginal plan, then maybe one of the relative minima would be sufficient.
What makes you say that action is absent? My impression is that SpaceX has actually been tackling a very aggressive timetable in general. I believe they're working on the Falcon Heavy and crew modules right now and they're proposing a launch for a Dragon capsule to Mars in 2018.
As for launch windows, the energy required is at a minimum every 26 months, and there's a global min twice every ~17 years, the next two being in 12 and 14 years, so you'd have the easiest time then. [1] If they have a non-marginal plan, then maybe one of the relative minima would be sufficient.
What makes you say that action is absent? My impression is that SpaceX has actually been tackling a very aggressive timetable in general. I believe they're working on the Falcon Heavy and crew modules right now and they're proposing a launch for a Dragon capsule to Mars in 2018.
[1] http://en.wikipedia.org/wiki/Manned_mission_to_Mars