I'm trying to understand this cool delta-v map, in particular I don't get how 90m/s delta-v should be enough to go from a transfer orbit to an Eve encounter:
In my attempt, I go to a transfer orbit by burning straight up against Kerbin's orbit until I get an escape:
This escape burn already gives us about half the required orbital transfer to Eve:
But it's not even close to the 90m/s that is allegedly sufficient for an encounter. For that, I need about 400m/s:
So what's going on?
52 Answers
The starting point is "elliptical orbit around Kerbin with Pe of 10 km above atmosphere (80km ASL) and Ap at the edge of SOI", not solar orbit. If you try to do the burn while in solar orbit, it's much less efficient (because of Oberth effect).
In theory this means you should be in a (correctly aligned) elliptical orbit around Kerbin, and do the burn of 90m/s at the periapsis.
In practice such an orbit is a pain to align, and it's easier to read as 930+90=1020m/s burn from LKO to Eve intercept.
Experimentally, I see a burn of ~1030m/s from LKO to Eve intercept, which seems in line with the map.(Mechjeb was used to plan this one specifically)
As stated previously by Gedas:
If you try to do the burn while in solar orbit, it's much less efficient (because of Oberth effect).
Other than this you also need to take transfer windows into account. This means that the minimum delta-V required changes with time. Calculating it is not easy, but in the case of Eve and Duna it shouldn't be that hard, you can find many guides (such as this one):
However in the case of planets with high inclinations (they don't orbit in the some plane) and highly elliptical orbits - mainly Moho and Eeloo - this method becomes less accurate.
If you have the time and patience to maximize the efficiency of your transfer, I would like to recommend mods, such as the Transfer Window Planner.
