Calculating the SemiMajor Axis of a Munar orbit.

[Sunsparc]

I've currently got 4 communications satellites in a ~500km circular orbit around the Mun. I want to perfect their orbit such that they are as close to 500km and a 4 hour orbital period as possible. They're pretty close right now.

According to the wiki, the equatorial radius of the Mun is 200km. Am I correct to say that the SMA would be 700km? 500km to the surface + 200km from the surface to the orbit/Mun center?

[Supernovy]

For a circular orbit, the semi major axis is the radius, which is the distance to the centre of the body. This is, as you said, the Mun's radius plus the orbit altitude. You are correct.

[blizzy78]

I'd like to add that achieving the perfect orbit you desire is not possible in KSP once you make such a vessel the active vessel. You can, however, achieve it by editing your save file to modify the orbit parameters to the desired values, then be careful to never load the vessel again. Once you do, though, KSP will recalculate the orbit from current values, introducing rounding errors again.

[Sunsparc]

I'd like to add that achieving the perfect orbit you desire is not possible in KSP once you make such a vessel the active vessel. You can, however, achieve it by editing your save file to modify the orbit parameters to the desired values, then be careful to never load the vessel again. Once you do, though, KSP will recalculate the orbit from current values, introducing rounding errors again.

I'm aware of this. I even tested to see what it would do if I passed in physics range and switched to active vessel. So far, my Kerbin relay is still in perfect orbit with no perturbations. Mun doesn't have a geosync, so if I can get as close to 500km with a 4 hour period, I'm golden.