The stock game needs an interface for planning interplanetary missions. I currently use external transfer window planners to find optimal dates, but the stock game just leaves players high and dry after they get to the Mun and Minmus. the built in tools are pretty poor for trying to plan something that may be kerbin-years away.
Even without a visulization in the map screen, just having contract missions offered around the window would be great. I may blow past a window to Eeloo because i'm focused on Duna and never expect a Eeloo window to open up.
Another idea is a "days to X Transfer window" countdown in the tracking station that could be a further upgrade option.
