This is a list of types of gravitational orbit classified by various characteristics.
Common abbreviations
List of abbreviations of common Earth orbits Orbit NameGEO Geostationary orbitLEO Low Earth orbitMEO Medium Earth orbitSSO Sun-synchronous orbit
List of abbreviations of other orbits Orbit NameGSO Geosynchronous orbitGTO Geostationary transfer orbitHCO Heliocentric orbitHEO Highly elliptical orbitNRHO Near-rectilinear halo orbitVLEO Very Low Earth Orbit
Classifications The following is a list of types of orbits:
Centric classifications Galactocentric orbit: An orbit about the center of a galaxy. The Sun follows this type of orbit about the Galactic Center of the Milky Way. Heliocentric orbit: An orbit around the Sun. In the Solar System, all planets, comets, and asteroids are in such orbits, as are many artificial satellites and pieces of space debris. Moons by contrast are not in a heliocentric orbit but rather orbit their parent object. Geocentric orbit: An orbit around the planet Earth, such as that of the Moon or of artificial satellites. Selenocentric orbit (named after Selene): An orbit around Earth's Moon. Areocentric orbit (named after Ares): An orbit around the planet Mars, such as that of its moons or artificial satellites.
For orbits centered about planets other than Earth and Mars and for the dwarf planet Pluto, the orbit names incorporating Greek terminology are not as established and much less commonly used:
Mercury orbit (Hermeocentric orbit, named after Hermes): An orbit around the planet Mercury. Venus orbit (Cytherocentric orbit, named after Cytherea, or Aphrodiocentric, after Aphrodite): An orbit around the planet Venus. Jupiter orbit (Zenocentric orbit, named after Zeus, or Latin equivalent Jovicentric): An orbit around the planet Jupiter. Saturn orbit (Kronocentric orbit, named after Cronus, or Latin equivalent Saturnicentric): An orbit around the planet Saturn. Uranus orbit (Uranocentric orbit, named after Uranus): An orbit around the planet Uranus.
Altitude classifications for geocentric orbits Transatmospheric orbit (TAO): geocentric orbits with an apogee above 100 km and perigee that intersects with the defined atmosphere. Very low Earth orbit (VLEO) is defined as altitudes between approximately 100 - 450 km above Earth’s surface. Low Earth orbit (LEO): geocentric orbits with altitudes below ., pages 37–38 (6–1,6–2); figure 6-1. Medium Earth orbit (MEO): geocentric orbits ranging in altitude from to just below geosynchronous orbit at . Also known as an intermediate circular orbit. These are used for Global Navigation Satellite System spacecraft, such as GPS, GLONASS, Galileo, BeiDou. GPS satellites orbit at an altitude of with an orbital period of almost 12 hours. Geosynchronous orbit (GSO) and geostationary orbit (GEO) are orbits around Earth matching Earth's sidereal rotation period. Although terms are often used interchangeably, technically a geosynchronous orbit matches the Earth's rotational period, but the definition does not require it to have zero orbital inclination to the equator, and thus is not stationary above a given point on the equator, but may oscillate north and south during the course of a day. Thus, a geostationary orbit is defined as a geosynchronous orbit at zero inclination. Geosynchronous (and geostationary) orbits have a semi-major axis of . This works out to an altitude of . Both complete one full orbit of Earth per sidereal day (relative to the stars, not the Sun). High Earth orbit: geocentric orbits above the altitude of geosynchronous orbit ().
For Earth orbiting satellites below the height of about 800 km, the atmospheric drag is the major orbit perturbing force out of all non-gravitational forces. Above 800 km, solar radiation pressure causes the largest orbital perturbations. However, the atmospheric drag strongly depends on the density of the upper atmosphere, which is related to the solar activity, therefore the height at which the impact of the atmospheric drag is similar to solar radiation pressure varies depending on the phase of the solar cycle.
Inclination classifications Inclined orbit: An orbit whose inclination in reference to the equatorial plane is not 0. Polar orbit: An orbit that passes above or nearly above both poles of the planet on each revolution. Therefore, it has an inclination of (or very close to) either 90 degrees or −90 degrees. Polar Sun-synchronous orbit (SSO): A nearly polar orbit that passes the equator at the same local solar time on every pass. Useful for -taking satellites because shadows will be the same on every pass. Non-inclined orbit: An orbit whose inclination is equal to zero with respect to some plane of reference. Ecliptic orbit: A non-inclined orbit with respect to the ecliptic. Equatorial orbit: A non-inclined orbit with respect to the equator. Near equatorial orbit: An orbit whose inclination with respect to the equatorial plane is nearly zero. This orbit allows for rapid revisit times (for a single orbiting spacecraft) of near equatorial ground sites.
Directional classifications Prograde orbit: An orbit that is in the same direction as the rotation of the primary (i.e. east on Earth). By convention, the inclination of a Prograde orbit is specified as an angle less than 90°. Retrograde orbit: An orbit counter to the direction of rotation of the primary. By convention, retrograde orbits are specified with an inclination angle of more than 90°. Apart from those in Sun-synchronous orbit, few satellites are launched into retrograde orbit on Earth because the quantity of fuel required to launch them is greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocity equal to the rotational velocity of the planet at its launch latitude.
Eccentricity classifications There are two types of orbits: closed (periodic) orbits, and open (escape) orbits. Circular and elliptical orbits are closed. Parabolic and hyperbolic orbits are open. Radial orbits can be either open or closed. Circular orbit: An orbit that has an eccentricity of 0 and whose path traces a circle. Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse. Geostationary or geosynchronous transfer orbit (GTO): An elliptic orbit where the perigee is at the altitude of a low Earth orbit (LEO) and the apogee at the altitude of a geostationary orbit. Hohmann transfer orbit: An orbital maneuver that moves a spacecraft from one circular orbit to another using two engine impulses. This maneuver was named after Walter Hohmann. Ballistic capture orbit: a lower-energy orbit than a Hohmann transfer orbit, a spacecraft moving at a lower orbital velocity than the target celestial body is inserted into a similar orbit, allowing the planet or moon to move toward it and gravitationally snag it into orbit around the celestial body. Coelliptic orbit: A relative reference for two spacecraft—or more generally, satellites—in orbit in the same plane. "Coelliptic orbits can be defined as two orbits that are coplanar and confocal. A property of coelliptic orbits is that the difference in magnitude between aligned radius vectors is nearly the same, regardless of where within the orbits they are positioned. For this and other reasons, coelliptic orbits are useful in [spacecraft] rendezvous". Parabolic orbit: An orbit with the eccentricity equal to 1. Such an orbit also has a velocity equal to the escape velocity and therefore will escape the gravitational pull of the planet. If the speed of a parabolic orbit is increased it will become a hyperbolic orbit. Escape orbit: A parabolic orbit where the object has escape velocity and is moving away from the planet. Capture orbit: A parabolic orbit where the object has escape velocity and is moving toward the planet. Hyperbolic orbit: An orbit with the eccentricity greater than 1. Such an orbit also has a velocity in excess of the escape velocity and as such, will escape the gravitational pull of the planet and continue to travel infinitely until it is acted upon by another body with sufficient gravitational force. Radial orbit: An orbit with zero angular momentum and eccentricity equal to 1. The two objects move directly towards or away from each other in a straight-line. Radial elliptic orbit: A closed elliptic orbit where the object is moving at less than the escape velocity. This is an elliptic orbit with semi-minor axis = 0 and eccentricity = 1. Although the eccentricity is 1, this is not a parabolic orbit. Radial parabolic orbit: An open parabolic orbit where the object is moving at the escape velocity. Radial hyperbolic orbit: An open hyperbolic orbit where the object is moving at greater than the escape velocity. This is a hyperbolic orbit with semi-minor axis = 0 and eccentricity = 1. Although the eccentricity is 1, this is not a parabolic orbit.
Synchronicity classifications
Synchronous orbit: An orbit whose period is a rational multiple of the average rotational period of the body being orbited and in the same direction of rotation as that body. This means the track of the satellite, as seen from the central body, will repeat exactly after a fixed number of orbits. In practice, only 1:1 ratio (geosynchronous) and 1:2 ratios (semi-synchronous) are common. Geosynchronous orbit (GSO): An orbit around the Earth with a period equal to one sidereal day, which is Earth's average rotational period of 23 hours, 56 minutes, 4.091 seconds. For a nearly circular orbit, this implies an altitude of approximately . The orbit's inclination and eccentricity may not necessarily be zero. If both the inclination and eccentricity are zero, then the satellite will appear stationary from the ground. If not, then each day the satellite traces out an analemma (i.e. a "figure-eight") in the sky, as seen from the ground. When the orbit is circular and the rotational period has zero inclination, the orbit is considered to also be geostationary. Also known as a Clarke orbit after the writer Arthur C. Clarke. Geostationary orbit (GEO): A circular geosynchronous orbit with an inclination of zero. To an observer on the ground this satellite appears as a fixed point in the sky. "All geostationary orbits must be geosynchronous, but not all geosynchronous orbits are geostationary." Tundra orbit: A synchronous but highly elliptic orbit with significant inclination (typically close to 63.4°) and orbital period of one sidereal day (23 hours, 56 minutes for the Earth). Such a satellite spends most of its time over a designated area of the planet. The particular inclination keeps the perigee shift small.This answer explains why such inclination keeps apsidial drift small: https://space.stackexchange.com/a/24256/6834 Areosynchronous orbit (ASO): A synchronous orbit around the planet Mars with an orbital period equal in length to Mars' sidereal day, 24.6229 hours. Areostationary orbit (AEO): A circular areosynchronous orbit on the equatorial plane and about 17,000 km (10,557 miles) above the surface of Mars. To an observer on Mars this satellite would appear as a fixed point in the sky. Subsynchronous orbit: A drift orbit close below GSO/GEO. Semi-synchronous orbit: An orbit with an orbital period equal to half of the average rotational period of the body being orbited and in the same direction of rotation as that body. For Earth this means a period of just under 12 hours at an altitude of approximately 20,200 km (12,544.2 miles) if the orbit is circular. Molniya orbit: A semi-synchronous variation of a Tundra orbit. For Earth this means an orbital period of just under 12 hours. Such a satellite spends most of its time over two designated areas of the planet. An inclination of 63.4° is normally used to keep the perigee shift small.