Resonant Orbits - the hard way...

[schlosrat]

Suppose you're crazy, and you'd like to deploy a network of, oh... let's say 3 communications satellites. Not that this would be anything a normal person would want to do, but work with me here and just suppose...

Here's how you can do it given the extraordinarily limited amount of orbital info you can get in KSP 2 right now. You're probably going to want to use a tool like Excel or whatever you like for some simple math (maths if you're English).

Get the mass of the body you're orbiting (I assume the old KSP 1 Wiki is at least close). For the Mun this would be 9.7599066×1020 kg

1. In your math tool of choice get ready with the following
   • G = 6.67e-11
   • M = 9.7599066e20
   • mu = G*M
     • NOTE: You can also get this from the wiki - it's the Standard Gravitational Parameter
2. Get in a nice high circular orbit around the body you want to deploy your network about.
3. Record your AP and PE from the ORBITAL.INFO block below the nav ball. You need these numbers in meters! If your orbit is showing them in km then convert.
   • AP = whatever it is in meters
   • PE = whatever it is in meters
4.  Compute your orbital eccentricity
   • e = (AP - PE)/AP + PE)
5. Compute your semi major axis
   • a = (AP + PE)/2
6. Compute your semi minor axis
   • b = SQRT(a^2*(1-e^2))
7. Compute your orbital period
   • TP1 = 2*PI()*a^(3/2)/SQRT(mu)
8. Compute the orbital period of the transfer orbit you need. If you want a network of 3 satellites you'll want a 2:3 orbital resonance, which you get by multiplying the period of your circular orbit by (2/3)
   • TP2 = TP1*2/3
9. Compute the semi major axis of your transfer orbit
   • a2 = (TP2*SQRT(mu)/(2*PI()))^(2/3)
10. Compute the periapsis for your transfer orbit
    • PE2 = 2*a2-AP
11. Release your first satellite! If you've stacked them vertically, then point your vessel in any direction other than prograde or retrograde (I like to use Normal direction, but Anti-Normal works well too if you're feeling a bit deviant)
12. Once your first satellite has cleared away from you then point retrograde and burn until you've got a PE equal to PE2 computed above
13. Complete one full orbit in this transfer orbit and circularize once you're back at the apoapsis
14. Release your next satellite
15. Rinse and Repeat as needed.

So, basically you need to do a little math with the tiny amount of info you've got, plus one assumption for the mass of the body you're orbiting, and you can get the PE you need for a resonant orbit. The rest is really up to you and your piloting skilz.

 

Edited June 9, 2023 by schlosrat
Added info about the Standard Gravitational Parameter

[Dman979]

Moved to KSP2 Tutorials. Nice stuff!

[Vortygont]

We need more orbital info! 

[SpaceJaM]

I'm lazy and I use the online tool "resonant orbit calculator" 

But my satellites do not work because they lose commnet communication every time 

[schlosrat]

On 3/16/2023 at 3:59 PM, SpaceJaM said:

I'm lazy and I use the online tool "resonant orbit calculator" 

But my satellites do not work because they lose commnet communication every time 

I recommend you consider installing the Community Fixes mod. That will solve your loss of CommNet when deploying satellite problem. I thought this was going to be fixed in 0.1.1, though. If this is still happening, then you may want to report it as a bug.

As a workaround, if when you deploy your satellite it loses CommNet, then switch to the vessel, then back to the deployer, then back to the vessel. That, or a quick F5/F9 may do the trick to get your satelite back on line. Assuming it's got EC and an antenna...

[SpaceJaM]

On 3/18/2023 at 7:38 PM, schlosrat said:

I recommend you consider installing the Community Fixes mod. That will solve your loss of CommNet when deploying satellite problem. I thought this was going to be fixed in 0.1.1, though. If this is still happening, then you may want to report it as a bug.

As a workaround, if when you deploy your satellite it loses CommNet, then switch to the vessel, then back to the deployer, then back to the vessel. That, or a quick F5/F9 may do the trick to get your satelite back on line. Assuming it's got EC and an antenna...

I've not started using mods yet, but I think I will soon.

The quickload/quicksave trick works, even if sometimes the mothership with the remaining satellites start spinning like crazy shredding the remaining satellites to pieces (already patchet to 0.1.1 and yes, I have all the antennas).

However, thank you for the detailed explanation of the math behind the resonant orbits 

[schlosrat]

5 hours ago, SpaceJaM said:

I've not started using mods yet, but I think I will soon.

When you get around to using mods, I'm currently working on a Resonant Orbit Calculator that can be used in flight mode. It will save you the effort of doing the match, and you'll be able to see what orbit you need so you can plan to get there.

You may also want to take a look at this site. It was developed for KSP1, but works fine for KSP2 as well I think. https://meyerweb.com/eric/ksp/resonant-orbits/

There's a link on that page to the KSP1 forum thread where this is also discussed.

[schlosrat]

As promissed: https://spacedock.info/mod/3332/Resonant Orbit Calculator

Forum thread here: 

 

[SpaceJaM]

18 hours ago, schlosrat said:

You may also want to take a look at this site. It was developed for KSP1, but works fine for KSP2 as well I think. https://meyerweb.com/eric/ksp/resonant-orbits/

I've always used it since ksp1, and still using now