Yeah, so.....whoops. My previous calculation was way off. Turns out that to move 0.502 AUs with constant acceleration and turnover at the half-way point would only require a bit over 2 gravities. I was suspicious of the previous number because it didn't really seem sane. So maybe that's doable, if we can figure out a fuel that lets us accelerate for that long. Plus you have to worry about Earth and Mars actually lining up in their orbits in order to make the trip that short-----which means that once it's made, you couldn't easily return for quite a while unless you were willing to take a longer trip. The good news about the return voyage: It's easier to move to a "lower" orbit around the sun than to a "higher" one. All you have to do is slow down.