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Encyclopedia > Molniya orbit
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Molniya orbit is a class of a highly elliptic orbit with inclination of +/-63.4 degrees and orbital period of about 12 hours for which perturbations in argument of perigee are zero. A satellite placed in this orbit spends most of its time over a designated area of the earth, a phenomenon known as apogee dwell. Molniya orbits are named after a series of Soviet/Russian Molniya communications satellites that have been using this class of orbits since the mid 1960s. Molniya orbits are not limited to Earth orbits only as they can be computed for any celestial body for which secular variations in longitude of the ascending node and argument of perigee because of central body’s oblateness have dominant effects on bodies orbiting it. Two bodies with similar mass orbiting around a common barycenter with elliptic orbits. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... The argument of perigee is the angle subtending from the ascending node to the point of perigee in an Earth-centered orbit. ... Jump to: navigation, search Molniya (lightning) was a military communications satellite system used by the Soviet Union. ... U.S. military MILSTAR communications satellite A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. ... Earth orbit is an orbit around the planet Earth. ... Oblate also refers to a member of the Roman Catholic religious order of the Missionary Oblates of Mary Immaculate, or in some cases to a lay or religious person who has officially associated himself (or herself) with a monastic community such as the Benedictines for reasons of personal enrichment without... In astrodynamics, an orbiting body () is a body that orbits central body (). Under standard assumptions in astrodynamics: it is orders of magnitude lighter than central body (i. ...

Contents


Properties

For a stationary apogee in the northern hemisphere, the inclination must be +63.4 and -63.4 for a stationary apogee in the southern hemisphere.


Use in communications

The Molniya orbit allows for 24h communicatons coverage of polar periods by a constellation of 3 satellites. The first satellite to use this orbit was Molniya 1-01 launched on August 23, 1965.


American satellites have also used Molniya orbits, including the Satellite Data System cluster. The Satellite Data System (SDS) is a system of United States military communications satellites. ...


Other uses

Molniya orbit is not suitable for manned spacecraft as it crosses high-energy Van Allen belt. Van Allen belts The Van Allen radiation belt is a torus of energetic charged particles around Earth, trapped by Earths magnetic field. ...


According to some sources, the Soviet Fractional Orbital Bombardment System functioned by mimicking a standard satellite travelling in a Molniya orbit. Fractional Orbital Bombardment System (FOBS) was a Soviet ICBM in the 1960s with a low Earth orbit that would de-orbit for an attack. ...


Derivation

In order to achieve that position of the apogee is not severely affected by orbit perturbations, an inclination close to 63.4 degrees is chosen. This results in the argument of perigee remaining nearly constant for a long period of time. This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... The argument of perigee is the angle subtending from the ascending node to the point of perigee in an Earth-centered orbit. ...



The formula for the argument of perigee change per day is as follows:

The equation becomes zero for an inclination of 63.4 degrees.


References

See also


  Results from FactBites:
 
Molniya or Highly Elliptical Orbit (154 words)
A Molniya orbit, often referred to as a highly elliptical orbit (or HEO) is an egg-shaped orbit inclined approximately 60 degrees to the equator with a high apogee over the northern hemisphere and a low perigee over the southern hemisphere.
Molniya, which means "lightning" in Russian, was the name of the first Russian communications satellites to use it.
This type of orbit is suitable for communications services in the high-latitude areas over Russia and is also used by U.S. intelligence satellites that focus on spying on Russia and Russian missile warning satellites that are observing U.S. ICBM silos.
  More results at FactBites »

 
 

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