safe file editing

[Noud]

Dear kerbonauts 

recently i heard something about putting relays on 'rail' by editing the safe file and not touching them again. to make sure they don't drift. and your com net stays nice and divided in orbit.

so i went to my safe file and changed something. where i thought this would make the orbit circular and at the specific hight, it did... nothing.

maybe one of you can help me

Spoiler

 

this is one of the crafts i am talking about. i want to make a system with 3 relays. because i am going to duna soon and it wil have some high warp speed i was hoping i can put the relays all in exactly the same orbit so they don't drift over a long period of time. 

so in sort

which values do i need to change?
what do they mean? (in not rocket scientist language)

 

thank you

[Starman4308]

2 hours ago, Noud said:

which values do i need to change?
what do they mean? (in not rocket scientist language)

First off: welcome to Rocket Science: The Video Game.

 

Second, the very quick version:

Find the vessels' ORBIT nodes.

SMA should be identical. This is the most important thing, since orbital period (how long it takes to complete one orbit) is a function only of SMA.

ECC should be very low but preferably not exactly zero.

INC should be either identical or close to identical, close to 0 for equatorial, close to 90 for polar.

LPE should be identical.

LAN should be identical.

MNA should be: 0 for one relay, 2.0944 for the second, and 4.1888 for the third

EPH should be identical.

REF should be identical, and presumably refers to Duna.

 

Third, the rocket scientist's version.

A typical orbit, such as the Moon around the Earth, is just one kind of orbit, called an elliptical orbit. There are also circular orbits (a special case of elliptical), hyperbolic (an escape trajectory), and parabolic (a special case of an escape trajectory).

An elliptical orbit is an ellipse (an oval), in a plane, with one focus of the ellipse at the body that you are orbiting around.

 

The oval is defined by the semi-major axis (which specifies 1/2 of its length along its long axis), and its eccentricity (how oval vs. circular it is).

Semi-major axis is equal to (1/2 * (Pe + Ap)), where periapsis and apoapsis are measured from the center of the orbited body, not its surface. This, by the way, is the only orbital element necessary to calculate orbital period (how long each orbit takes).

Eccentricity is equal to ((Ap - Pe) / (Ap + Pe)) for an elliptical orbit. A perfectly circular orbit has an eccentricity of 0, though that might give KSP a fit because of the other orbital elements that depend on periapsis.

 

The plane of the orbit is defined by inclination (how tilted it is with respect to the orbited body's equator) and longitude of the ascending node (at what point it crosses the equator going up). Inclination varies from 0 to 180 degrees, with 0 being an equatorial prograde orbit, 90 being exactly polar, and 180 being retrograde equatorial. Longitude of the ascending node is defined with respect to the First Point of Aries, which for KSP, is an arbitrarily chosen point in the skybox.

 

How the oval is oriented with respect to the plane of the orbit is defined by the longitude of periapsis (in the save file) or argument of periapsis (if using Hyperedit). Longitude of periapsis is where your periapsis is with respect to the First Point of Aries, while argument of periapsis is the angle from the ascending node to periapsis.

If you're wondering what that means: you could imagine an orbit where periapsis is close to the equator, close to the poles, etc: this is what LPE/AOP represent.

 

These five define the track of the orbit... but not where a vessel is in that orbit. That is usually defined with two parameters: epoch (an arbitrary point in time), and mean anomaly at epoch. Mean anomaly is related to the angle between periapsis and your current point in the orbit, and mean anomaly at epoch is "what was the value of mean anomaly at that arbitrary point in time".

Incidentally, the exact angle between periapsis and your current point in the orbit is true anomaly, and is exactly equal to mean anomaly for a circular orbit, but is more complicated to deal with for elliptical orbits.

[Allocthonous]

You may find it less nerve-wracking to use the in-game cheat menu to do this. Alt-F12 opens up the debug menu, from which you can access the 'Set Orbit' interface. It still has all the fancy abbreviations and everything, but you can fiddle around with them and see what they do a lot more easily than with a save file.

[Spricigo]

16 hours ago, Allocthonous said:

You may find it less nerve-wracking to use the in-game cheat menu to do this. Alt-F12 opens up the debug menu, from which you can access the 'Set Orbit' interface. It still has all the fancy abbreviations and everything, but you can fiddle around with them and see what they do a lot more easily than with a save file.

IIRC debug menu set orbit only works for the active vessel.  (Someone correct me If I'm wrong)

So the issue is that the game may mess with this settings when you switch to/from each relay because. My personal approach is just to have redundancy, but for someone relying on precision and efficiency those errors can be really annoying.