Delta-V changes if maneuver node is > 14 days

[MarvinKosh]

So, yeah. Something I've started to notice recently is that if a planned maneuver node is two weeks or more in the future, the Delta-V needed will change while the craft is loaded. Not by a lot, but enough that I should probably wait until the maneuver is almost due to fine-tune and execute it.

Is this normal?

[DD_bwest]

do you see it changing while your RCS is on to try and point towards your node?   if your rcs is on, it can slightly change your orbital parameters, the more orbits out(actually, the further out in general) your node is, the more these small changes will effect your node.  

I believe thats the case atleast, ive observed behavior like that, and by not using RCS thrusters so far in advance, the problem went away

Edited December 1, 2016 by DD_bwest

[Geschosskopf]

There are a number of causes for this.  As @DD_bwest says, having RCS activated can cause this, even if not actually being used at the time.  There are also a bunch of things going on under the hood in KSP such as rounding off and the whole thing about the orbital decay we used to have and the fixes for it that we now have, that cause things to change slightly over time.  Also, if you have Kerbal Alarm Clock, you might have set it to recalculate nodes periodically.

Basically, nothing's ever exact, perfect, or constant in KSP due to various inherent limitations of the game itself.  And even if they were, the interface prevents us from executing nodes perfectly anyway.  But you can get close enough for government work so I just quit worrying about all this some years ago, unless orbits just refuse to be stable or the dV changes more than a a couple dozen m/s.  Then there's something really wrong.