The path of an object that is moving around a second object or point under the influence of gravity. This field provides information about orbital parameters of a platform from which the data were taken.
- <Orbit_Altitude>: altitude of platform above the Earth’s surface.
- <Orbit_Inclination>: angular distance of the orbital plane from the
plane of the planet’s equator, stated in degrees. [Angle between orbit and equator].
- <Equator_Crossing>: time at which the platform crosses the equator.
- <Period>: time it takes a platform to make one full orbit.
- <Repeat_Cycle>: time that the satellite passes vertically over the same location.
- <Perigee>: point in the orbit where an Earth satellite is closest to the Earth. Opposite of apogee.
- <Apogee>: point in the orbit where an Earth satellite is farthest from the Earth. Opposite of perigee.
- <Orbit_Type>: Orbital types may include Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geosynchronous Orbit (GEO), Highly Elliptical Orbit (HEO), or Lagrangian Point Orbit (LPO).
With the information requested previously related to altitude, inclination, etc., one has more information than one can deduce from any one of several classification schemes. The most useful addition might be to allow the user to immediately gain information on areas of observation and overpass times. Therefore, indicating a choice within the following categories might prove to be immediately helpful to the data user:
- LEO: Low Earth Orbits
Definition: Platforms that orbit between 80 km and 2000 km.
Choices include:
- LEO > Low Earth Orbit > Inclined Non-Polar
- LEO > Low Earth Orbit > Polar Sun-Synchronous
- LEO > Low Earth Orbit > Polar Non-Sun-Synchronous
- LEO > Inclined Non-Polar
Definition: A LEO orbit that has an inclination of less than 70 degrees. Platforms in “Inclined Non-Polar” orbits are not sun-synchronous.
Examples: LEO > Inclined Non-Polar > International Space Station (360 km) [inclination 51.6 deg] LEO > Inclined Non-Polar > Space Shuttle (300-400 km) [inclination usually about 57 deg] LEO > Inclined Non-Polar > TOPEX/PoSEIDON [inclination 66.5 deg] LEO > Inclined Non-Polar > TRMM [inclination 35 deg] LEO > Inclined Non-Polar > UARS [inclination 57 deg]
- LEO > Polar Sun-Synchronous
Definition: Platform (satellite) that passes all latitudes at the same local solar time each day [through a combination of proper altitude and inclination]. Orbits lie within 20 degrees of a 90 degree inclination from the equator. To maintain this synchronicity, the orbital plane must rotate about 1 degree per day.
Examples: LEO > Polar Sun-Synchronous > Nimbus-7 [the first sun synchronous, 99.15 deg inclination] LEO > Polar Sun-Synchronous > Aqua [98.2 deg inclination] LEO > Polar Sun-Synchronous > Terra [98.2 deg inclination] LEO > Polar Sun-Synchronous > Aura [98.2 deg inclination] LEO > Polar Sun-Synchronous > Meteor-3M [1000 km orbit; 100 deg inclination] LEO > Polar Sun-Synchronous > CALIPSO [98.2 deg inclination]
- LEO > Polar Non-Sun-Synchronous
Definition: Platform (satellite) maintains a polar orbit that does not synchronize latitude passes with solar time.
Examples: LEO > Polar Non-Sun-Synchronous > Meteor2 [altitude: 850-950 km;
inclination 81-82 deg] LEO > Polar Non-Sun-Synchronous > CHAMP [inclination: 87.4 deg] LEO > Polar Non-Sun-Synchronous > ICESat [inclination: 94 deg] LEO > Polar Non-Sun-Synchronous > GRACE [inclination: 89 deg]
- MEO > Semi-Synchronous > Communications
Definition:
Satellites that are used for telecommunications such as telephony, television, mobile communications, amateur and commercial radio, and broadband internet.
Example:
- MEO > Semi-Synchronous > Geodetic/Space Environment
Definition: These are MEO platforms that perform geodetic observations (for example, LAGEOS) or space physics observations (for example, FAST). They are neither Navigation nor Communications satellites.
Examples: MEO > Semi-Synchronous > Geodetic/Space Environment > LAGEOS
MEO > Semi-Synchronous > Geodetic/Space Environment > FAST
MEO > Semi-Synchronous > Geodetic/Space Environment > Explorer-31
- GEO: Geosynchronous Orbits (aka Clarke Orbits)
Definition: Platform orbits with a revolution of exactly one day at an altitude of 35,786 km. Any orbit, which has a period equal to the Earth’s rotational period. The orbit’s eccentricity and inclination may not necessarily be zero. When the orbit is circular and the rotational period has zero inclination, the platform is considered to also be “geostationary”.
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