List of orbits

Various Earth orbits to scale; cyan represents low Earth orbit, yellow represents medium Earth orbit, the black dashed line represents geosynchronous orbit, the green dash-dot line the orbit of Global Positioning System (GPS) satellites, and the red dotted line the orbit of the International Space Station (ISS).

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 our 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 planet.
• Geocentric orbit: An orbit around the planet Earth, such as the Moon or artificial satellites. Currently there are approximately 2,465 artificial satellites orbiting the Earth.^{[citation needed]}
• Areocentric orbit: An orbit around the planet Mars, such as moons or artificial satellites.
• Lunar orbit (also selenocentric orbit): An orbit around the Earth's moon.

Altitude classifications for geocentric orbits

• Low Earth orbit (LEO): Geocentric orbits ranging in altitude from 0–2,000 km (0–1,240 miles)
• Medium Earth orbit (MEO): Geocentric orbits ranging in altitude from 2,000 km (1,240 miles) to just below geosynchronous orbit at 35,786 km (22,240 miles). Also known as an intermediate circular orbit.
• Geosynchronous Earth orbit (GEO): The orbit around Earth matching Earth's sidereal rotation period. All geosynchronous orbits have a (semi-major axis) of 42,164 km (26,199 mi).^[1]
• High Earth orbit: Geocentric orbits above the altitude of geosynchronous orbit 35,786 km (22,240 miles).

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) 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 image 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.
  • Ecliptical 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.

Eccentricity classifications

• 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: 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.
• Hyperbolic trajectory: 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.
• 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 and travel until its velocity relative to the planet is 0. If the speed of such an orbit is increased it will become a hyperbolic orbit.
  • Escape orbit (EO): A high-speed parabolic orbit where the object has escape velocity and is moving away from the planet.
  • Capture orbit: A high-speed parabolic orbit where the object has escape velocity and is moving toward the planet.

Synchronous classifications

• Synchronous orbit: An orbit where the satellite has an orbital period that 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 (GEO): 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 35,786 km (22,240 miles). 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 (figure 8) in the sky, as seen from the ground.
  • Geostationary orbit (GSO): 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.
    • Clarke orbit: Another name for a geostationary orbit. Named after the writer Arthur C. Clarke.
• Tundra orbit: A synchronous but highly elliptic orbit with inclination of 63.4° and orbital period of one sidereal day (roughly 24 hours 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.
• 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.
• Supersynchronous orbit: A disposal / storage orbit above GSO/GEO. Satellites will drift west. Also a synonym for Disposal orbit.
• Subsynchronous orbit: A drift orbit close to but below GSO/GEO. Satellites will drift east.
• Graveyard orbit: An orbit a few hundred kilometers above geosynchronous that satellites are moved into at the end of their operation.
  • Disposal orbit: A synonym for graveyard orbit.
  • Junk orbit: A synonym for graveyard orbit.
• Areosynchronous orbit: A synchronous orbit around the planet Mars with an orbital period equal in length to Mars' sidereal day, 24.6229 hours.
• Areostationary orbit (ASO): 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 the ground this satellite would appear as a fixed point in the sky.
• Heliosynchronous orbit: An heliocentric orbit about the Sun where the satellite's orbital period matches the Sun's period of rotation. These orbits occur at a radius of 24.360 Gm (0.1628 AU) around the Sun, a little less than half of the orbital radius of Mercury.

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.
• Orbit of the Moon: The orbital characteristics of Earth's moon. Average altitude of 384,403 kilometres (238,857 mi), elliptical-inclined orbit.

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, L₃–L₅ will appear to share the secondary's orbit, although in fact they are situated slightly outside it.

• Horseshoe orbit: An orbit that appears to a ground observer to be orbiting a certain planet but is actually in co-orbit with the planet. See asteroids 3753 Cruithne and 2002 AA₂₉.
• Exo-orbit: A maneuver where a spacecraft achieves an orbit that is unstable due to atmospheric drag.
• Lunar transfer orbit (LTO)
• Prograde orbit: An orbit with an inclination of less than 90°. Or rather, an orbit that is in the same direction as the rotation of the primary.
• Retrograde orbit: An orbit with an inclination of more than 90°. Or rather, an orbit counter to the direction of rotation of the planet. Apart from those in sun-synchronous orbit, few satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much 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.
• Halo orbits and Lissajous orbits: These are orbits around a Lagrangian point. Lagrange points are shown in the diagram on the right, and orbits near these points allow a spacecraft to stay in constant relative position with very little use of fuel. Orbits around the L₁ point are used by spacecraft that want a constant view of the Sun, such as the Solar and Heliospheric Observatory. Orbits around L₂ are used by missions that always want both the Earth and Sun behind them. This enables a single shield to block radiation from both the Earth and Sun, allowing passive cooling of sensitive instruments. Examples include the Wilkinson Microwave Anisotropy Probe and the James Webb Space Telescope.

See also

• Box orbit
• Ecliptic orbit
• Osculating orbit
• Parking orbit
• Artificial satellite orbit

Notes

v • d • e Orbits   Types General Box · Capture · Circular · Elliptical / Highly elliptical · Escape · Graveyard · Hyperbolic trajectory · Inclined / Non-inclined · Osculating · Parabolic trajectory · Parking · Synchronous (semi · sub) Geocentric Geosynchronous · Geostationary · Sun-synchronous · Low Earth · Medium Earth · Molniya · Near-equatorial · Orbit of the Moon · Polar · Tundra · Two-line elements About other points Areosynchronous · Areostationary · Halo · Lissajous · Lunar · Heliocentric · Heliosynchronous   Parameters Classical  Inclination ·  Longitude of the ascending node ·  Eccentricity ·  Argument of periapsis ·  Semi-major axis ·  Mean anomaly at epoch Other  True anomaly ·  Semi-minor axis ·  Linear eccentricity ·  Eccentric anomaly ·  Mean longitude ·  True longitude ·  Orbital period   Maneuvers Bi-elliptic transfer · Delta-v budget · Geostationary transfer · Gravity assist · Gravity turn · Hohmann transfer · Low energy transfer · Oberth effect  · Inclination change · Phasing · Rendezvous · Transposition, docking, and extraction   Other orbital mechanics topics Apsis · Celestial coordinate system · Direct motion · Epoch · Ephemeris · Equatorial coordinate system · Ground track · Interplanetary Transport Network · Kepler's laws of planetary motion · Lagrangian point · n-body problem · Orbit equation · Orbital speed · Orbital state vectors · Perturbation · Retrograde motion · Specific orbital energy · Specific relative angular momentum List of orbits