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The following is a list of types of orbits:

Centric classifications

For orbits centered about planets other than Earth and Mars, the orbit names incorporating Greek terminology is less commonly used

  • Mercury orbit (Hermocentric or hermiocentric): An orbit around the planet Mercury.
  • Venus orbit (Aphrodiocentric or cytheriocentric): An orbit around the planet Venus.
  • Jupiter orbit (Jovicentric or zenocentric[3]): An orbit around the planet Jupiter.
  • Saturn orbit (Kronocentric[3] or saturnocentric): An orbit around the planet Saturn.
  • Uranus orbit (Oranocentric): An orbit around the planet Uranus.
  • Neptune orbit (Poseidocentric): An orbit around the planet Neptune.

Altitude classifications for geocentric orbits

  • Low Earth orbit (LEO): geocentric orbits with altitudes below 2,000 km (100–1,240 miles).[4]
  • Medium Earth orbit (MEO): geocentric orbits ranging in altitude from 2,000 km (1,240 miles) to just below geosynchronous orbit at 35,786 kilometers (22,236 mi). Also known as an intermediate circular orbit. These are "most commonly at 20,200 kilometers (12,600 mi), or 20,650 kilometers (12,830 mi), with an orbital period of 12 hours."[5]
  • 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 42,164 km (26,199 mi).[6] This works out to an altitude of 35,786 km (22,236 mi). 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 35,786 km (22,240 miles).[5]

Inclination classifications

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.

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.

Orbits in galaxies or galaxy models

  • Box orbit: An orbit in a triaxial elliptical galaxy that fills in a roughly box-shaped region.
  • Pyramid orbit: An orbit near a massive black hole at the center of a triaxial galaxy.[11] The orbit can be described as a Keplerian ellipse that precesses about the black hole in two orthogonal directions, due to torques from the triaxial galaxy.[12] The eccentricity of the ellipse reaches unity at the four corners of the pyramid, allowing the star on the orbit to come very close to the black hole.
  • Tube orbit: An orbit near a massive black hole at the center of an axisymmetric galaxy. Similar to a pyramid orbit, except that one component of the orbital angular momentum is conserved; as a result, the eccentricity never reaches unity.[12]

Special classifications

  • Sun-synchronous orbit: An orbit which combines altitude and inclination in such a way that the satellite passes over any given point of the planets's surface at the same local solar time. Such an orbit can place a satellite in constant sunlight and is useful for imaging, spy, and weather satellites.
  • Frozen orbit: An orbit in which natural drifting due to the central body's shape has been minimized by careful selection of the orbital parameters.
  • Orbit of the Moon: The orbital characteristics of the Moon. Average altitude of 384,403 kilometres (238,857 mi), elliptical-inclined orbit.
  • Beyond-low Earth orbit (BLEO) and beyond Earth orbit (BEO) are a broad class of orbits that are energetically farther out than low Earth orbit or require an insertion into a heliocentric orbit as part of a journey that may require multiple orbital insertions, respectively.
  • Near rectilinear halo orbit (NRHO): an orbit currently planned in cislunar space that could serve as a staging area for future missions in a 2018 NASA concept.[13][14] One proposed is approximately lunar polar with a period of about 6 days.
  • Distant retrograde orbit (DRO): A stable circular retrograde orbit (usually referring to Lunar Distant Retrograde Orbit). Stability means that satellites in DRO do not need to use station keeping propellant to stay in orbit. The lunar DRO is a high lunar orbit with a radius of approximately 61,500 km.[15] This is proposed as a possible Gateway orbit, outside EM L1 and L2.[14]

Pseudo-orbit classifications

See also

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