| Molniya Orbit |
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Properties For a stationary apogee in either hemisphere, the inclination must be 63.4°. The Argument Of Perigee then remains relatively unchanged, and is set at either 90° or 270°, which locates apogee in the southern or northern hemisphere, respectively. Use in communications The Molniya orbit allows for 24h communications coverage of polar periods by a constellation of 3 satellites. The first satellite to use this orbit was [http://www.astronautix.com/craft/molniya1.htm Molniya 1-01] launched on August 23, 1965. American satellites have also used Molniya orbits, including the Satellite Data System cluster. Other uses Molniya orbit is not suitable for manned spacecraft as it crosses high-energy Van Allen Belt . According to some sources, the Soviet Fractional Orbital Bombardment System functioned by mimicking a standard satellite travelling in a Molniya orbit. Classified American electronic intelligence satellites called Jumpseat and their successors called Trumpet are also reported to use Molniya orbits. 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. The formula for the argument of perigee change per day is as follows: : The equation becomes zero for an inclination of 63.4 degrees. Interesting Fact The Molniya orbit originates from the Russian word for lightning. It is a fitting name, as the satellite passes close to the earth relatively quickly. The Russian " Molniya (satellite) " was the first to be sent into this orbit and earned the rights to the name. References
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