Question about Orbits

[MrZayas1]

I happened to think to myself today, like I do a lot, and I thought of a puzzling question. Is it possible for an orbit of a moon or satellite to never cross into the shadow of it's parent body? I'm pretty sure this is impossible without gravitational interference from an object with gravity, or from a preset burn, but I am wondering nonetheless thanks in advance!

[andrewas]

Sure. Put the moon in a polar orbit around its primary. Set the moons orbital period so that it orbits exactly, say, six times a year. Adjust the timing so that none of those six orbits puts it into shadow. Note that this setup is not stable in the long run, but under KSP physics it works.

[lajoswinkler]

Doesn't have to be polar, just inclined enough that, at its distance, it doesn't touch the penumbra. Also, modify distance so that the satellite's orbital period is synchronized with planet's revolution around the star.

[Bill Phil]

If the primary is giving off enough light, then any orbit won't be in its shadow.

[softweir]

Actually, there is no orbit that will never cross the parent body's shadow at some time of year. Whether the moon is in an inclined orbit or in a polar orbit, twice each year that orbit will coincide with the line between the sun and the planet and there will be the chance of the moon being in shadow. The more inclined the orbit is the fewer times the moon will be eclipsed, but it will never be zero times.

In theory, if the moon orbits the planet an exact number of times per year then it can be phased so - by apparent coincidence - it never crosses the shadow. However such resonances are very unstable, and gravitational interactions with the star will destabilise the orbit until it is no longer an exact multiple, and it can once again cross the shadow.