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List of orbits
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The following is a list of types of orbits:
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The following is a list of types of orbits:
Centric classifications
Altitude classifications
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
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.
- 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.
- 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
Pseudo-orbit classifications
- 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.
Other
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