I'm having a math and physics problem: math and physics is getting in the way of the plot in Mars, Ho!
I originally thought it would be a six month trip, but math got in the way since they were getting gravity from propulsion. So I shortened it to a two month trip, and to do that I had to have Earth and Mars on opposite sides of the sun -- but orbital mechanics makes waiting shorten the time.
The best bad way around it I can see is a little hand-waving, with the captain wondering why the company didn't wait a week to launch. But I'm not satisfied with this. Does anybody have any ideas?