I underestimated my life support requirements for a Duna mission and accidentally put enough to get there, but not enough (~30 days short) to return with an optimal trajectory. At first I was convinced that my Kerbal would die in the cold void of space and started thinking of ways to at least recover the science. Then I remembered this launch window calculator that allows you to select trajectories based on time, and I started looking for the fastest one that I could take with my limited fuel supply. After some clicking around, it gave me one that would leave me with about 10 days of breathing room but would require most of my delta-v. Here's a screenshot during the burn (compare the maneuver node delta-v with my total delta-v in the bottom left corner): Here's a screenshot after the burn. Note the number of days to the Kerbin encounter, the number of days of life support remaining, and how much fuel/delta-v I have left: The encounter ended up having a periapsis of 7km, which I wanted to refine as I got closer. Unfortunately, he never returned, as this was in 0.90 and I didn't timewarp far enough to have him return home (I ran multiple missions at a time) and this save was utterly broken in 1.0.