Saturn coorbitals

[peruke]

I noticed that the Saturn co-orbitals Janus & Epimethus do not "swap" orbits but simply remain on opposite sides of Saturn and thus except for a short time every 4 years are in the wrong position.

[FarGetaNik]

The orbits for these moons are defined by simple ellicptical orbits. The effect of them swapping orbits every 4 years is due to gravitational perturbation that is not taken into account.

You could use eiher a sampled orbit definition or better a spice orbit definition to show their long term behaviour. Look at this topic on Celestial Matters for more information:
http://forum.celestialmatters.org/viewtopic.php?f=18&t=584

[peruke]

The add ons for spacecraft allow an object to have multiple orbits at different times. I assume the same means could give each of the co-orbitals an "inner" and an "outer" orbit by changing the semi-major axes on Jan 21 of each even numbered non leap year. It wouldn't be precisely correct as the swap would be an instant jump of a few km rather than the gradual change but would put them close enough to the actual positions so the Cassini flybys would actually happen.

[selden]

Celestia also has the feature called "ScriptedOrbit". If you understand the orbital dynamics, in principle you can write a Lua function which will move the moons around appropriately.

See https://en.wikibooks.org/wiki/Celestia/Trajectories#ScriptedOrbit