How to measure arbitrary phase angles

[Bobshayd]

I thought I had found a solution to my problems - Protractor! Finally, a mod that would act as an on-screen protractor! I just wanted to know what my current phase was with Mun, relative to Kerbin, Kerbin's current phase with Duna relative to the Sun, Minmus' current phase to the Sun relative to Kerbin, and so on. It would be possible to muck through with accurate distance measurements, and if I were just to compute distances and stick them in the law of cosines, I could develop a massive network of satellites and compute distances to all the objects from individual satellites, but that's just a little ridiculous. I don't want Protractor or Mechjeb to do my orbital calculations for me. I want to compute my own orbit, I want to calculate exactly when my burn needs to start, and then I want to compute what angle that happens at, and then I will know exactly what my phase angle needs to be when I throttle up, and then I just want that on-screen, and I don't want to reinvent the wheel. Are there any good tools existing that will let me select three arbitrary bodies and tell me the angle between two relative to the third, wherever I am, whenever I ask?

[alexmun]

Kerbal Engineer's flight engineer component will give you the angle to your target body.

[capi3101]

Which stat is that? I've got KER installed; haven't figured out the best way to use the in-flight data just yet (other than as a measure of remaining stage delta-V)

[Bobshayd]

Does that give me the angle between Kerbin and Duna even when I'm orbiting something other than those two?

[Mr Shifty]

Does that give me the angle between Kerbin and Duna even when I'm orbiting something other than those two?

If you can get the true anomaly of the two planets (and I think KER gives this info), the phase angle is just the difference.

[Bobshayd]

The http://en.wikipedia.org/wiki/True_anomaly difference is only the phase angle if the periapses are aligned. Are all the planets' periapses aligned?

[Mr Shifty]

The http://en.wikipedia.org/wiki/True_anomaly difference is only the phase angle if the periapses are aligned. Are all the planets' periapses aligned?

No, you're right, they're all different:

https://docs.google.com/spreadsheet/ccc?key=0AuySrGPsDeq2dFdaS19xc2lobGc2aWNXUkJsZlVtWFE#gid=0

[Bobshayd]

Well, that's even worse! I have to repeatedly take the difference of the true anomalies, switching back and forth between target planets, and then add to that the angle of periapsis, and then watch that number change and hope I don't miss it while I'm computing. I guess the better way would be to compute the next instance of it occurring, compute the true anomaly of the current or the target, and then launch from there.

Hey, thank you, Mr Shifty, for the doc. That is supremely helpful, especially if I'm going to plan trips at arbitrary times. I will keep this in mind.

By the way, if the eccentricity is 0, and there is no periapsis, how does Kerbin even _have_ a true anomaly? Is it set to the angle of displacement from the KSP universal vector frame of background reference, assuming they use one for their computations?

And does anyone have other suggestions? I don't like the clutter of MechJeb, since I want to have a hand in my own orbit-planning; there's always a tool to do some planning for you, but I can always answer whatever bizarre question I have as long as I