Synchronous orbit
A stationary orbit is an orbit with the same orbital period as the rotational period of the orbited body. The eccentricity is equal to 0 and the inclination is exactly 0°. A satellite on this orbit will stay in the sky at the same position at all times, the surface velocity is zero and making the communication easy as the ground based telescopes don't have to follow the satellite's relative motion.
A stationary orbit is a special kind of synchronous orbit, which all have the same orbital period but may differ in inclination or eccentricity. Satellites on a synchronous but not stationary orbit have a ground track forming an analemma. Because it is impossible to get all values exact for a stationary orbit, every satellite on a synchronous orbit form an analemma.
Some celestial bodies don't allow synchronous orbits, and thus also no stationary orbits, because the altitude lies outside the celestial bodies' sphere of influence. This is because of a very slow rotation requiring a very high altitude to allow such long orbital periods explaining why all tidally locked moons don't have a synchronous orbits. Moho is the only planet without any synchronous orbit, because it's very slow rotational period with only almost two rotations in one orbit.
See also
- KEO, the stationary orbit around Kerbin
- Synchronous orbit on Wikipedia
- Synchronous orbit on Wikipedia
- Geostationary orbit on Wikipedia
- Geosynchronous orbit on Wikipedia
