Should I believe MechJeb or KAC?

[Targa]

Trying to get to a launch window from Kerbin to Duna, and MechJeb and Kerbal Alarm Clock keep giving me different dates for an optimal transfer. For example, if KAC says today is the day, MechJeb will say the next transfer is in 7 days. To be honest, I don't even know if KAC believes KAC. I just set an alarm 1 hour and 15 minutes before the next (according to KAC) optimum transfer window to Duna. When the alarm went off, I left the space center and got on my orbiting ship. I opened the KAC transfer window and it says the next window for Duna is 28 days away...

[Alshain]

There is no one right answer. It depends on what goals you have, time (which is less relevant with the ability to time warp) or delta V, and even then there may be more than one launch window with the same Delta V or time to arrival.

If you want to be able to choose the criteria that matters to you most, the best option is here or the modded-into-ksp version made by the same author that does KAC here. That second option integrates with KAC so you can create alarms from within it's GUI. However even this does not account for gravity assists.

Edited July 15, 2015 by Alshain

[steve_v]

Use MJs "Advanced transfer to another planet" function, and you can pick your transfer burn on a pretty porkchop of dv / departure time / transit time ('tis a simplified version of the aforementioned in-game tool)

Edited July 15, 2015 by steve_v

[sarbian]

I know that there is something fishy in that MJ code for the transfer window. I wrote a test for the ascent AP to recalculate the launch time each frame instead of only doing once and ended up with a value that changed a lot each frame. I need to look into it but it s some part of the code I never worked on...

The advanced mode should not have the bug since you chose the solution yourself.

[Red Iron Crown]

IIRC KAC uses a simplified model of the solar system that assumes circular, non-inclined orbits (this makes the math involved much, much simpler). MJ and Transfer Window Planner use a more sophisticated model that takes eccentricity and inclination into account. For the ultimate in transfer planning (including gravity assists!) try Trajectory Optimization Tool.