Phase angles for new planets from mplanetfactory

[kiwiak]

How can i calculate phase angles for travelling to new planets added by planet factory?

[sciguyCO]

You need two pieces of information: how long it takes for your transfer orbit (well, half of the orbit since you'll be getting captured on one end), and how far the target planet moves in that time.

1) The period of any orbit (in seconds) is:

2 * pi * sqrt ( a / mu )

where

• a = semi-major axis of the orbit = (apoapsis + periapsis ) / 2
  
• mu = Gravitational parameter of the parent body.
  

In this situation, "a" will be the average of the two planet's orbital radii (since your transfer orbit has periapsis at one and apoapsis at the other) and "mu" will be the Sun's gravitational parameter 1.1723328 * 10¹⁸ m³/s².

Half of the period will be the time required for the transfer.

2) Now to figure out how long the target planet will move in the above amount of time. If you can get the semi-major axis for the target planet, you can calculate it's orbital period (call it P) and use that in a ratio with the above (call it T for transfer time), then multiple that ratio by 360 degrees. I haven't used planet factory, but I'd imagine you can get that in the map view from either the planet info button (little circle icon on the right of the map) or from it's "height" information when it's targeted?

Phase angle = 360 * T / P

That angle should be "behind" Kerbin if the transfer is moving inwards towards the sun and "ahead" of Kerbin if moving outwards.

Final caveat: the above assume near-circular starting and ending orbits. Orbits with a high eccentricity throw complications in that make it difficult to give a single all-encompassing equation.

Edited January 27, 2014 by sciguyCO
Got phase angle directions backwards, corrected.

[kiwiak]

Time to do some old school maths... maybe i will make some php script for this for easier calculation?

[Cerberus738]

ok see, i suck at math. i see formulas and math all over this forum. its cool that you guys can calculate what your rocket needs and just build it. my rockets generally end up way overpowered for their intended purpose and die a lot from the error part of trial and error

i tried using some of the mods that calculate dV and angles and all that but it just makes no sense to me. moar engines......

[alexmun]

I've just added the ability to add new planets to my launch window calculator (http://alexmoon.github.io/ksp), so if you have the orbital elements of the new planets, you can add them and calculate whatever you need.

[kiwiak]

Thanks, it will help me a lot.

By the way, does this correctly calculates for highly eccentric orbits, like comets?

Edited January 28, 2014 by kiwiak

[alexmun]

Thanks, it will help me a lot.

By the way, does this correctly calculates for highly eccentric orbits, like comets?

Yup, it sure does.

[EtherDragon]

Here is a simple gem of an equation for you:

p = 1 / (2*sqrt (t^3 / h^3))

Given that:

t = the Target's Semi-Major Axis

h = your Hohmann Transfer Semi-Major Axis

(which is = (s+t)/2)

(s = your starting Semi-Major Axis)

You end up with P: the portion of the target's orbit that will be completed during your Hohmann Transfer.