Semi-synchronous orbit

A semi-synchronous orbit is an orbit with a period equal to half the average rotational period of the body being orbited, and in the same direction as that body's rotation.

For Earth, a semi-synchronous orbit is considered a medium Earth orbit, with a period of just under 12 hours. For circular Earth orbits, the altitude is approximately 20,200 kilometres (12,600 mi).^[1]^[2]

Semi-synchronous orbits are typical for GPS satellites.

References

^ NASA Technical Standard 8719.14 (draft) (Report). NASA Orbital Debris Program Office. 8 Aug 2006. Archived from the original (PDF) on 2006-08-23.
^ "Catalog of Earth Satellite Orbits". 6 Sep 2012.

Gravitational orbits

Types

General	Box Capture Circular Elliptical / Highly elliptical Escape Horseshoe Hyperbolic trajectory Inclined / Non-inclined Kepler Lagrange point Osculating Parabolic trajectory Parking Prograde / Retrograde Synchronous semi sub Transfer orbit
Geocentric	Geosynchronous Geostationary Geostationary transfer Graveyard High Earth Low Earth Medium Earth Molniya Near-equatorial Orbit of the Moon Polar Sun-synchronous Transatmospheric Tundra Very low Earth
About other points	Mars Areocentric Areosynchronous Areostationary Lagrange points Distant retrograde Halo Lissajous Libration Lunar Sun Heliocentric Earth's orbit Mars cycler Heliosynchronous Other Lunar cycler

Parameters

Shape Size	e Eccentricity a Semi-major axis b Semi-minor axis Q, q Apsides
Orientation	i Inclination Ω Longitude of the ascending node ω Argument of periapsis ϖ Longitude of the periapsis
Position	M Mean anomaly ν, θ, f True anomaly E Eccentric anomaly L Mean longitude l True longitude
Variation	T Orbital period n Mean motion v Orbital speed t₀ Epoch