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.

        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> Medium Earth Orbit [aka Intermediate Circular Orbits]
        Definition: Platform orbits lie between 2000 km to 35,786 km, but most commonly at 20,200 km or 20,650, with an orbital period of 12 hours). Note that the Van Allen Belts of high energy protons lie within the MEO orbital range ands.
        Choices include:

        • MEO > Semi-Synchronous > Navigation
        • MEO > Semi-Synchronous > Communications
        • MEO > Semi-Synchronous > Geodetic/Space Environment

      • MEO > Semi-Synchronous > Navigation
        Satellites in Medium Earth Orbits (MEO) that perform navigation processes, using techniques to establish position and velocity of an object (or platform).

      • Examples:
        MEO > Semi-Synchronous > Navigation > NAVSTAR (NAVigation System using Timing And Ranging)

        MEO > Semi-Synchronous > Navigation > GLONASS (GLObal NAvigation Satellite System)

      • MEO > Semi-Synchronous > Communications
        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.

          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”.

      • GEO > Geosynchronous > Geostationary
        A geosynchronous satellite with a circular orbit, which has a period equal to the Earth’s rotational period, with zero inclination.
        Choices include:
        • GEO > Geosynchronous > Geostationary
        • GEO > Geosynchronous > Non-Geostationary
      • Examples:
        GEO > Geosynchronous > Geostationary (GEO) > GOES
        GEO > Geosynchronous > Geostationary (GEO) > Syncom 3
        GEO > Geosynchronous > Geostationary (GEO) > Meteosat
        GEO > Geosynchronous > Geostationary (GEO) > GMS
        GEO > Geosynchronous > Geostationary (GEO) > INSAT

      • GEO > Geosynchronous > Non-geostationary
        Definition: A geosynchronous orbit that is not stationary. Geosynchronous orbits that are not geostationary do not have a fixed position relative to the Earth. All geostationary orbits must be geosynchronous, but not all geosynchronous orbits are geostationary.

        GEO > Geosynchronous > Non-geostationary > Syncom 2

        • HEO: High Earth Orbits/Highly Elliptical Orbits
          Definition: A High Earth Orbit is any orbit above geosynchronous (above 35,786 km). A Highly Elliptical Orbit is an orbit of low perigee (about 1000 km) and a high apogee over 35,786 km). These orbits have an inclination between 50 and 70 degrees. Highly elliptical orbits are mainly perturbed by the Earth’s oblateness and by gravitational attraction of the Sun and Moon. HEOs are popular orbits for Earth magentospheric measurements and astronomical observatories.

          Choices include:
          • HEO > Highly Elliptical Orbit
          • HEO > Highly Elliptical Orbit > Molniya
          • HEO > Highly Elliptical Orbit > Tundra

            HEO > Highly Elliptical Orbit > Cluster II [Perigee:17,200km Apogee: 120,500 km, Period=620 m]
            HEO > Highly Elliptical Orbit > Orbiting Geophysical Observatory 1 (OGO)
            [Perigee: 281 km Apogee: 149,385 km, Period=3839 m]
            HEO > Highly Elliptical Orbit > Advanced Composition Explorer (ACE) [Perigee: 179 km Apogee: 1,256,758 km, Period=1398 h]
            HEO > Highly Elliptical Orbit > IMP-8 [Perigee: 22.11RE Apogee: 45.26RE, Period=11.99 d]
            HEO > Highly Elliptical Orbit > Molniya > [Perigee: 495 km Apogee 39.587 km]
            HEO > Highly Elliptical Orbit > Tundra [inclination 33.4 degrees; orbital period about 12 hours]

        • LPO: Lagrangian Point Orbits
          Definition: A location in space around a rotating two-body system (such as the Earth-Moon or Earth-Sun) where the pulls of the gravitating bodies combine to form a point at which a third body of negligible mass would be stationary relative to the two bodies. Lagrangian points are named after the Italian-born French mathematician and astronomer Joseph Louis de Lagrange who first showed their existence There are five Lagrangian points in all, three of which are unstable because the slightest disturbance to any object located at one of them causes the object to drift away permanently. Until recently, this meant that the unstable Lagrangian points seemed to have no practical application for spaceflight. Now, however, they are known to have immense significance and have become the basis for chaotic control. In addition, growing numbers of spacecraft are being placed in halo orbits around the L1 and L2 points; station-keeping, in the form of regular thruster firings, are needed to maintain these orbits. (Source: The Encyclopedia of Astrobiology, Astronomy and Spaceflight: http://www.daviddarling.info/encyclopedia/L/Lagpoint.html

        • Choices include:

          • LPO > L1 > Lissajous Orbit > Halo Orbit
          • LPO > L1 > Lissajous Orbit > Lyapunov Orbit
          • LPO > L2

          LPO > L1 > Lissajous Orbit > Halo Orbit > SOHO
          LPO > L1 > Lissajous Orbit > Halo Orbit > ACE


<Orbit_Altitude>real number or text expressed in km</ Orbit_Altitude>
<Orbit_Inclination>real number or text expressed in degrees (°) </Orbit_Inclination>
<Equator_Crossing> real number or text expressed as a usually a local time in hh:mm format followed by “am” or “pm”.</Equator_Crossing>
<Period> real number or text expressed in minutes</Period>
<Repeat_Cycle> real number or text expressed in days and/or revolutions </Repeat_Cycle
<Perigee> real number or text expressed in km</Perigee>
<Apogee> real number or text expressed in km </Apogee>
<Orbit_Type>type of orbit keyword </Orbit_Type>

* All fields may contain 1 to 80 characters of the printable UTF-8 character set.

  • Field is highly recommended and may be used only once.
  • None of the fields within <Orbit> may be repeated.
  • Units should be provided as specified in the Syntax.
  • <Orbit_Type> can be selected from the list of controlled orbit type keywords.
  • <Orbit>
    <Orbit_Altitude>705 km</Orbit_Altitude>
    <Equator_Crossing>1:30 pm (south to north) and 1:30 am (north to south) </Equator_Crossing>
    <Period> 98.8 minutes</Period>
    <Repeat_Cycle>16 days (233 revolutions)</Repeat_Cycle>
    <Perigee>673 km (Periapsis)</Perigee>
    <Apogee>686 km (Apoapsis)</Apogee>
    <Orbit_Type>LEO > Polar Sun-Synchronous</Orbit_Type>


This document should be cited as:
Ancillary Description Writer's Guide, 2013.
Global Change Master Directory.
National Aeronautics and Space Administration.

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