Why does MechJeb's maneuver planner wait for such a late phase angle?

[Oddible]

I've been using http://ksp.olex.biz/ and Kerbal Alarm Clock and Kerbal Engineer to set up my phase angles for interplanetary transfer. But I always check MechJeb's Maneuver Planner and it is always late by 2-5 days. Why would this be? It always sets up a maneuver node significantly later than all the other recommendations. Curious about this.

[AmpsterMan]

I've been using http://ksp.olex.biz/ and Kerbal Alarm Clock and Kerbal Engineer to set up my phase angles for interplanetary transfer. But I always check MechJeb's Maneuver Planner and it is always late by 2-5 days. Why would this be? It always sets up a maneuver node significantly later than all the other recommendations. Curious about this.

I would imagine it is because the Olex Calculator assumes the orbits are perfect circles and not inclined. Mechjeb, however, I assume uses the current orbital parameters and the current mass, thrust, and the built in maneuver nodes system to calculate trajectories.

[Oddible]

Interesting, using this Launch Window Calculator (http://alexmoon.github.io/ksp/) it also recommends the later departure for the lowest dV use. So why does ksp.olex.biz and Kerbal Engineer recommend the earlier Phase Angle? It can't possibly know my inclination but maybe it is assuming a perfect equatorial orbit?

[Specialist290]

Again, I'd imagine that KER is using idealized circular orbits rather than the actual elliptical ones.

[Oddible]

Again, I'd imagine that KER is using idealized circular orbits rather than the actual elliptical ones.

But the website is saying the same thing as MechJeb and there is no way that the website knows my orbital offset, or anything other than my current altitude (which I enter).

[Specialist290]

In the big picture, the ideal transit window is more dependent on the relative positions of the planets themselves than it is on your precise orbit around the body of origin. Unless your orbit is significantly inclined or highly elliptical, the differences between the two aren't likely to be very great as long as they're both drawing from the same model of planetary motion.

[numerobis]

But the website is saying the same thing as MechJeb and there is no way that the website knows my orbital offset, or anything other than my current altitude (which I enter).

It knows what body you're orbiting. It probably solves assuming you're at UT 0?

[boomerdog2000]

Perhaps KAC is giving you a larger launch window instead of the exact window? There are a few days, either side of the window, if you're willing to burn a bit more fuel.