How similar do orbits need to be so the drift won't be noticed over time?

[CrashyMcCrashFace]

I did a KSO but then realized it's not necessary to achieve coverage with 3 satellites at almost any orbit as long as they aren't super low. That's not really the question. I've been really meticulous and placing them within 1-2 meters altitude of each other. This is pretty easy with a tiny sat with an RA-2 relay and worth the time if I never touch them again. Now I have 2 relay sats and a station with a relay antenna around the Mun at 660km. This works great but every time I dock/undock with the station it changes altitude and sometimes by a lot which is understandable. It's getting close to 50 tons now and even though I have plenty of fuel and thrusters it's still kind of a bear to maneuver. Am I worried about 50-100 meters for nothing or will I notice it advancing/retreating? I'm betting there's some math that can answer this but might be over my head without a little explanation.

If this become too much of a problem my backup plan is just to undock the relay sat and forget trying to have them combined. But combined is still fun.

PS, I've been getting great answers to other questions. Thanks for all that.

Edited April 16, 2018 by CrashyMcCrashFace

[Geonovast]

First, what's really important here, more than AP/PE, is orbital period.  You can easily have small variations in what your PE and AP are, what you want to watch is keeping your orbital period the same among your network.

I'm sure there's a fairly easy to use equation to calculate that.  However, if you're lazy like me, just use KER and have it display the orbital period.  Stick a small fuel tank and engine (weaker is better here, and probably set the thrust limiter to 0.5) on each satellite, so you can tweak the orbit to maintain that period.

[GoSlash27]

CMcCF,

 The orbital period of a 600 km orbit is almost 5 hours. A difference in SMA of 100 m equates to a little over 3 seconds per orbit; about .0007° error per orbit. It'd take about 1200 days for a sat to get 1° out of position with that discrepancy; approximately 3 years. It probably won't be visibly noticeable until 10 years or so.

HTHs,
-Slashy

Edited April 16, 2018 by GoSlash27