The tenth
Keplerian orbital element, specifying the orientation , (in degrees) that a
satellite hold in relation ship to the center of the earth. This value represents orientation at the perigee relative to the orbital plane. Orientation towards the center of the earth is taken to be (0°,0°). As many satellites are
spin stabilized, the reference point on the satellite must be chosen carefully. Usually this reference will be the feed horn of a communications antenna. Not all satellites maintain strict attitude control, (i.e.
ISS) or may lose the ability as fuel supply is spent. Not expressed in most formats.
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