List of orbits

Summary

Comparison of geostationary Earth orbit with GPS, GLONASS, Galileo and Compass (medium Earth orbit) satellite navigation system orbits with the International Space Station, Hubble Space Telescope and Iridium constellation orbits, and the nominal size of the Earth.[a] The Moon's orbit is around 9 times larger (in radius and length) than geostationary orbit.[b]
Various Earth orbits to scale; innermost,   the red dotted line represents the orbit of the International Space Station (ISS);   cyan represents low Earth orbit,   yellow represents medium Earth orbit, and   the black dashed line represents geosynchronous orbit.   The green dashed line represents the orbit of Global Positioning System (GPS) satellites.

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[2]): An orbit around the planet Jupiter.
  • Saturn orbit (Kronocentric[2] 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.[citation needed]

Altitude classifications for geocentric orbits

  • Low Earth orbit (LEO): geocentric orbits with altitudes below 2,000 km (1,200 mi).[3]
  • Medium Earth orbit (MEO): geocentric orbits ranging in altitude from 2,000 km (1,200 mi) 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."[4]
  • 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).[5] 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 or 22,236 mi).[4]

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

Geostationary orbit as seen from the north celestial pole. To an observer on the rotating Earth, the red and yellow satellites appear stationary in the sky above Singapore and Africa respectively.
  • 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.
  • 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.[citation needed]
      • 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.[8]
  • Supersynchronous orbit: Any orbit in which the orbital period of a satellite or celestial body is greater than the rotational period of the body which contains the barycenter of the orbit.

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.[9] 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.[10] 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.[10]

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, as a selenocentric orbit that will serve as a staging area for future missions. [11][12] Planned orbit for the NASA Lunar Gateway in circa 2024, as a highly-elliptical seven-day near-rectilinear halo orbit around the Moon, which would bring the small space station within 3,000 kilometers (1,900 mi) of the lunar north pole at closest approach and as far away as 70,000 kilometers (43,000 mi) over the lunar south pole.[13][14][15]
  • 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.[16] This was proposed[by whom?] in 2017 as a possible Gateway[clarification needed] orbit, outside EM L1 and L2.[12]
  • 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.
  • Earth-trailing orbit, a heliocentric orbit that is placed such that the satellite will initially follow Earth but at a somewhat slower orbital angular speed, such that it moves further behind year by year. This orbit was used on the Spitzer space telescope in order to drastically reduce the heat load from the warm Earth from a more typical geocentric orbit used for space telescopes.[17]
  • 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.[18][19]
  • Parking orbit, a temporary orbit.
  • Transfer orbit, an orbit used during an orbital maneuver from one orbit to another.
  • Repeat Orbit: An orbit where the ground track of the satellite repeats after a period of time.

Pseudo-orbit classifications

A diagram showing the five Lagrangian points in a two-body system with one body far more massive than the other (e.g. the Sun and the Earth). In such a system, L3L5 are situated slightly outside of the secondary's orbit despite their appearance in this small scale diagram.

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 (363 104 km ÷ 42 164 km) to 9.6 times when the moon is farthest (405 696 km ÷ 42 164 km).

References

  1. ^ "Definition of GALACTOCENTRIC". www.merriam-webster.com. Retrieved 3 June 2020.
  2. ^ a b Parker, Sybil P. (2002). McGraw-Hill Dictionary of Scientific and Technical Terms Sixth Edition. McGraw-Hill. p. 1772. ISBN 007042313X.
  3. ^ "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.
  4. ^ a b c d "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.
  5. ^ Vallado, David A. (2007). Fundamentals of Astrodynamics and Applications. Hawthorne, CA: Microcosm Press. p. 31.
  6. ^ Hadhazy, Adam (22 December 2014). "A New Way to Reach Mars Safely, Anytime and on the Cheap". Scientific American. Retrieved 25 December 2014.
  7. ^ 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.
  8. ^ a b This answer explains why such inclination keeps apsidial drift small: https://space.stackexchange.com/a/24256/6834
  9. ^ Merritt and Vasilev, ORBITS AROUND BLACK HOLES IN TRIAXIAL NUCLEI", The Astrophysical Journal 726(2), 61 (2011).
  10. ^ a b Merritt, David (2013). Dynamics and Evolution of Galactic Nuclei. Princeton: Princeton University Press. ISBN 9780691121017.
  11. ^ NASA Shapes Science Plan for Deep-Space Outpost Near the Moon March 2018
  12. ^ a b How a New Orbital Moon Station Could Take Us to Mars and Beyond Oct 2017 video with refs
  13. ^ Angelic halo orbit chosen for humankind's first lunar outpost. European Space Agency, Published by PhysOrg. 19 July 2019.
  14. ^ Halo orbit selected for Gateway space station. David Szondy, New Atlas. 18 July 2019.
  15. ^ Foust, Jeff (16 September 2019). "NASA cubesat to test lunar Gateway orbit". SpaceNews. Retrieved 15 June 2020.
  16. ^ "Asteroid Redirect Mission Reference Concept" (PDF). www.nasa.gov. NASA. Retrieved 14 June 2015.
  17. ^ "About Spitzer: Fast Facts". Caltech. 2008. Archived from the original on 2 February 2007. Retrieved 22 April 2007.
  18. ^ "U.S. Government Orbital Debris Mitigation Standard Practices" (PDF). United States Federal Government. Retrieved 28 November 2013.
  19. ^ 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.
  20. ^ Keesey, Lori (31 July 2013). "New Explorer Mission Chooses the 'Just-Right' Orbit". NASA. Retrieved 5 April 2018.
  21. ^ Overbye, Dennis (26 March 2018). "Meet Tess, Seeker of Alien Worlds". The New York Times. Retrieved 5 April 2018.