List of orbits

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[1]): An orbit around the planet Jupiter.
  • Saturn orbit (Kronocentric[1] 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).[2]
  • 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."[3]
  • 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).[4] 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).[3]

Inclination classifications

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.

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.[7] 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.[8] 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.[8]

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.[9][10] 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.[11] This is proposed as a possible Gateway orbit, outside EM L1 and L2.[10]
  • Decaying orbit: A decaying orbit is an orbit at a low altitude that decreases over time due atmospheric resistance. Used to dispose of dying artificial satellites or to aerobrake an interplanetary spacecraft.
  • Graveyard orbit (or disposal, junk orbit) : An orbit that satellites are moved into at the end of their operation. For geostationary satellites a few hundred kilometers above geosynchronous orbit.[12][13]
  • Parking orbit, a temporary orbit.
  • Transfer orbit, an orbit used during an orbital maneuver from one orbit to another.

Pseudo-orbit classifications

See also

Notes

  1. Orbital periods and speeds are calculated using the relations 4π2R3 = T2GM and V2R = GM, where R = radius of orbit in metres, T = orbital period in seconds, V = orbital speed in m/s, G = gravitational constant 6.673×1011 Nm2/kg2, M = mass of Earth 5.98×1024 kg.
  2. Approximately 8.6 times when the moon is nearest (363104 km ÷ 42164 km) to 9.6 times when the moon is farthest (405696 km ÷ 42164 km).

References

  1. Parker, Sybil P. (2002). McGraw-Hill Dictionary of Scientific and Technical Terms Sixth Edition. McGraw-Hill. p. 1772. ISBN 007042313X.
  2. "NASA Safety Standard 1740.14, Guidelines and Assessment Procedures for Limiting Orbital Debris" (PDF). Office of Safety and Mission Assurance. 1 August 1995. p. A-2. Archived from the original (PDF) on 15 February 2013. Low Earth orbit (LEO) - The region of space below the altitude of 2000 km., pages 37–38 (6-1,6-2); figure 6-1.
  3. "Orbit: Definition". Ancillary Description Writer's Guide, 2013. National Aeronautics and Space Administration (NASA) Global Change Master Directory. Archived from the original on 11 May 2013. Retrieved 29 April 2013.
  4. Vallado, David A. (2007). Fundamentals of Astrodynamics and Applications. Hawthorne, CA: Microcosm Press. p. 31.
  5. Hadhazy, Adam (22 December 2014). "A New Way to Reach Mars Safely, Anytime and on the Cheap". Scientific American. Retrieved 25 December 2014.
  6. Whipple, P. H . (17 February 1970). "Some Characteristics of Coelliptic Orbits – Case 610" (PDF). Bellcom Inc. Washington: NASA. Archived from the original (PDF) on 21 May 2010. Retrieved 23 May 2012.
  7. Merritt and Vasilev, ORBITS AROUND BLACK HOLES IN TRIAXIAL NUCLEI", The Astrophysical Journal 726(2), 61 (2011).
  8. Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton: Princeton University Press. ISBN 9780691121017.
  9. NASA Shapes Science Plan for Deep-Space Outpost Near the Moon March 2018
  10. How a New Orbital Moon Station Could Take Us to Mars and Beyond Oct 2017 video with refs
  11. "Asteroid Redirect Mission Reference Concept" (PDF). www.nasa.gov. NASA. Retrieved 14 June 2015.
  12. "U.S. Government Orbital Debris Mitigation Standard Practices" (PDF). United States Federal Government. Retrieved 28 November 2013.
  13. Luu, Kim; Sabol, Chris (October 1998). "Effects of perturbations on space debris in supersynchronous storage orbits" (PDF). Air Force Research Laboratory Technical Reports (AFRL-VS-PS-TR-1998-1093). Retrieved 28 November 2013.
  14. Keesey, Lori (31 July 2013). "New Explorer Mission Chooses the 'Just-Right' Orbit". NASA. Retrieved 5 April 2018.
  15. Overbye, Dennis (26 March 2018). "Meet Tess, Seeker of Alien Worlds". The New York Times. Retrieved 5 April 2018.

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