It's mostly a question of dv. Getting the perfect transfer window is hard, but eyeballing a good enough one and doing some mid course correction is significantly easier.
If you put the sun at the center and kerbal at 3 o'clock, you get a good enough transfer window by waiting to having duna at 1 o'clock. You can then eject tangentially from kerbal sphere of influence and correct half way trough.
The only real plugin that I strongly suggest there is the aereobrake plugin, that'll show you the predictoion for aerobraking directly on the ksp map.
Back when KSP released their first version with other planets (2012 or so), I was a forum mod and tester for them, and I build a small website to simplify interplanetary transfers: http://ksp.olex.biz. It's still running and up-to-date, and apparently still used, despite there being a ton of other sites and ingame plugins that provide the same data in much better ways.
Thanks for your contribution! I've flown many interplanetary missions with your tool.
For more accurate and realistic missions, there's this tool [0] to calculate pork chop plots [1] to find minimum energy transfers. (you surely know about this)
I think calculators and mission planners like this should be a part of the game proper. Switching to a web browser mid-game to do mission planning is a big turn off for me.
It might be a part of their game design, there are very few numbers and data presented in game. But I don't think it works very well apart from some very basic moon missions. A lot of the information is there but it's just difficult to find (e.g. want to know your inclination? select moon, and then look at ascending/descending nodes in map view).
I enjoyed the eyeball method initially but you grow out of it soon. I liked the "fire prograde when moon rises over horizon" moon missions and I even achieved a rendez-vous in 0.17 [2] before there were maneuver nodes or other helpful gadgets in the map view.
But once we got maneuver nodes, intersection markers, etc that playing style was out of the window. Now I'd really want to have some proper mission planning utilities (similar to some MFD modes in Orbiter).
I think the game should (at minimum) have a transfer window planner, a patched conics solver (with optimization), a pork chop plotter and a rocket burn planner for ascent and powered descent. Perhaps a Clohessy-Wiltshire-Hill equation solver for pinpoint accuracy rendez-vous too.
yeah that tool is great if you know how to translate it in game, but you know the original protractor method[1] ain't bad and one can kinda eyeball it like in the old days when we timed the mun burn based on the moment it dawned on kerbin... good times XD
If you put the sun at the center and kerbal at 3 o'clock, you get a good enough transfer window by waiting to having duna at 1 o'clock. You can then eject tangentially from kerbal sphere of influence and correct half way trough.
The only real plugin that I strongly suggest there is the aereobrake plugin, that'll show you the predictoion for aerobraking directly on the ksp map.