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Satellites which orbit under influence of gravity can be expressed as a set of orbital elements which can be regarded as time - dependent fixed entities. In general, two-body approach is enough, but in reality there are saome gradual shifts which can't be ignored. There are some disturbance which occur in satellites which orbitting the earth so the performances of these satellites are not as good as expected. The main cause of this perturbation are the existence of third body, imperfection of earth's symetry, atmospheric drag, and solar radiation pressure. The effect of perturbation to the satellite orbit can be catagorized according to the periodicity of this perturbation. Secular variation shows variations which change the orbit linierly in time, so in the long run it can affect the orbit of this satellite. The most dominant cause of secular variation is the aspherity of the earth. Short term variation is a periodic variation which occur in the orbit in which the time scale is shorter than the orbital period. Long term variation is a periodic variation which occur in the orbit in which the time scale is longer than the orbital period. Atmospheric drag depends linierly on the atmospheric density and High Earth Orbit Satellites are more influenced by solar radiation pressure. |
