How often Kerbin is in phase with other planets?

[frik]

I wonder if there's some calculator or math way to calculate it? I have couple ships in Kerbin orbit waiting to be shot towards, Duna, Eve and Joolian system. But they are mostly probes, as I never yet been outside Kerbin and it's moons. I'd like to see how my present design are doing in interplanetary journey before attempting crewed missions. And I wonder how long would I have to wait for next launch window? If for example after arriving at Jool I find that I don't have enough fuel for return trip I will send tanker, but if waiting for correct planet alignment will take years poor Kerbals will be bored to death so far from home...

[Guest]

This is indispensable: Interactive illustrated interplanetary guide and calculator for KSP

[Gniuz]

There is a calculator that a lot of people use here is a link: http://ksp.olex.biz/

I remember Duna is at about 42 degrees from videos I have watched.

[Noticeably FAT]

I had a thread asking pretty much the same question, and there is a pretty simple equasion to figure out when your next launch window will be. The thread is 'http://forum.kerbalspaceprogram.com/showthread.php/showthread.php/45624-Calculate-time-to-phase-angles', but Google's cache only displays the second page, and the well-written answer is on the first. I have it written down at home, I'll post it this evening if nobody else answers.

If you don't want to do the match yourself and are willing to install a mod, Kerbal Alarm Clock is pretty handy, and now lets you set alarms for phase angles.

[air805ronin]

Just as a side note, with the calculator you will know angles. Then you can fast forward to a launch window while sitting on the pad.

[ComradeGoat]

The protractor mod is so very totally your friend.

[frik]

To all posting calculator, thanks I know it. Question was about TIME between launch windows, not angles. And I don't want to warp months on launchpad. I have other ideas and flights going on.

If you don't want to do the match yourself and are willing to install a mod, Kerbal Alarm Clock is pretty handy, and now lets you set alarms for phase angles.

That'll be great!

The protractor mod is so very totally your friend.

I'll look into that, thanks.

[SteevyT]

To all posting calculator, thanks I know it. Question was about TIME between launch windows, not angles. And I don't want to warp months on launchpad. I have other ideas and flights going on.

You could look into the Kerbal Alarm Clock mod.

[ComradeGoat]

Time: If all the other planets were stationary, you'd have one launch window per planet per year.

But they move too. The nearer the planet to Kerbin, the less frequent the launch window. Jool has 2-3 times as many launch windows as Duna, for example.

[cxg2827]

Kerbal alarm clock gives you time until the next encounter. I've made an excel graph that you can get the frequency of encounters between all the different planets. Its a bit rough, But I think I got the equation right.

[Noticeably FAT]

Ok, here's the math as it was given to me. I can't remember who that was, if that person sees this please let me know so I can properly attribute this.

theta 1: Your current phase angle

theta 2: Your desired phase angle

T1: Current orbital period

T2: Target orbital period

w1: Current angular velocity

w2: Target angular velocity

delta-w = w2 - w1

w1 = 360 / T1

w2 = 360 / T2

The equation for the time to your desired phase angle is:

theta 1 = theta 2 + (delta-w)T

If you come up with a negative number for T, just add 360 to theta 2. Olex's calculator with give you the necessary phase angle (theta 2), various mods (I use MechJeb) will give you your current phase angle (theta 1). The KSP wiki will give you the orbital periods for each planet (T1 and T2).

Here's an example from one of my Duna missions

theta 1 = 28.97°

theta 2 = 44.36°

T1 = 106.52 days

T2 = 200.44 days

w1 = 3.38°/d

w2 = 1.80°/d

delta-w = -1.58°/d

28.97° = (44.36° + 360°) + (-1.58°/d)T

T = 237.589d

Wolfram Alpha is awesome for doing the math, and converting decimal days to D/H/M.

[cxg2827]

here is a table i made to see how often you will encounter a launch window to other planets. Pretty sure i got the equations and numbers correct (rounded to the nearest 1/4 day).

[maltesh]

Alternatively, use the synodic period formula.

If T1 is the longer of the periods in the target/destination pair, and T2 is the shorter, the synodic period between Hohmann windows is equal to (T1*T2)/(T1-T2)