synchronous orbit
Noun
Meaning
synchronous orbit (plural synchronous orbits)
A satellite orbit where the orbital period is equal to, or multiples of, the Earth’s rotational period; i.e. making one, two, three, etc., orbits in a 24-hour period. Examples include geosynchronous (period equals Earth's rotation), semisynchronous (two orbits per day); and geostationary (geosynchronous orbit where satellite maintains a fixed position on the equator).
Related terms
Examples
Orbital decay can occur due to tidal forces for objects below the synchronous orbit for the body they're orbiting.
This is because the smaller body becomes tidally locked faster, and by the time a synchronous orbit is achieved, it has had a locked synchronous rotation for a long time already.
With an altitude of convert, Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates.