mechjeb mun transfer incorrect periapsis

[antipro]

hi, I'm trying to learn how to use mechjeb in order to transfer from a lko to the mun.
I expect to flyby the mun to a specific and precise periapsis, but the result periapsis may vary of 10km/20km or more sometimes.

I've recorded a 3 minutes video that shows what I do.
https://www.dropbox.com/s/3r68pb9752mquns/mechjeb mun transfer.mkv?dl=0
1 - Did I do something wrong?
2 - Is there a way to have the Pe exactly where I want and NOT in the center of the target moon, without manual correction?

Edited August 22, 2020 by antipro

[Gargamel]

Moved to Add-on discussion.

Even with MJ, when you are executing burns from a long way away, the slightest difference in dV expended can make huge changes in your target orbit.  So when you do your burns, expect to make a tiny correction burn later on.   It will take a few more dV, but you can get much greater accuracy.  But basically, the way I look at it, and it might not be accurate, but it works for me, MJ is subject to rounding errors in the game, so even the most precise burn won't always be perfect.  If you needed a 100.25 m/s burn, and you could only do a 100.2 or 100.3, then the burn will be slightly off.   Just get closer (I usually wait till SOI change, makes warping easier) and then make a correction burn then for a few m/s of dV. 

[DerekL1963]

On 8/22/2020 at 10:43 AM, antipro said:

1 - Did I do something wrong?

No.
 

On 8/22/2020 at 10:43 AM, antipro said:

2 - Is there a way to have the Pe exactly where I want and NOT in the center of the target moon, without manual correction?

No.  As @Gargamel points out, even minor variations in your burn can cause large deviations at your destination.  Your best bet is to use the "fine tune closest approach to target" option in the Maneuver Planner.  (Set this burn up as soon as your transfer burn is complete.)  Even then, you still might have to trim your periapsis when you enter your target's SOI.