| MadSci Network: Astronomy |
A spacecraft orbiting the Moon is not in an orbit that is fixed with respect to any other point in the Solar System. The object orbits the Moon; the Moon orbits the Earth (actually, the Earth and Moon orbit one another about a point inside the Earth); the Earth orbits the Sun. If you were to view the path of the spacecraft orbiting the Moon from above the Solar System, it would appear quite complex- an epicycle on an epicycle, whereas orbits are elliptical with respect to the body being orbited.
In any system with more than two bodies (which includes the Solar System), orbits tend to be chaotic. That means they are not 100% stable, so given long enough the subtle tugs on the spacecraft from the Earth, Sun, and other planets may disrupt the orbit. But in practice, a lunar orbit can reasonably be treated as stable- if the orbit is set at an inclination designed to avoid mascons, it will stay in that orbit a long time, and therefore never encounter the mascons.
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