Duna transfer

[Gogi]

Hey guys. I'm trying to plan a mission to Duna. Launch would be around day 26. Alex Moon's calculator states ejection angle 24 to prograde, delta V of 2002 m/s at phase angle of 124.11degrees. Yet when i set up a node with those parameters, I don't even get a close approach. Any advice is welcome.

[bewing]

Day 26? The first window for Duna is about day 236.

 

[Gogi]

You're partially right. Optimal window is day 236, however 2000 and a change delta v is not that bad. I have done it before in version 1.2 at about the same date, so I'm puzzled why it's not working this time around.

[OHara]

You are leaving much earlier than the transfer window, to an outer planet, so Kerbin has not yet caught up to Duna as much as it would be at the transfer window.  To catch up to Duna, the transfer path has to swing closer to the sun than the Hohmann-transfer shape you would see at the window. The exit from Kerbin is not parallel to Kerbin's apth but dives toward the sun; the approach to Duna is parallel, though, since you picked the arrival time that minimized that burn.

Sometimes the closest-approach markers give nonsense (bottom image).   You know there is a closer approach further along the orbits, so If you add another maneuver node, with zero burn, further along in your orbit, you can force KSP to find the real approach.