Circular Orbit—_an orbit whose altitude from the earth remains constant;
it makes a circle that has the center of the earth as a center_.
Elliptical Orbit—_an orbit whose altitude from the earth varies from one
extreme to another; it makes an ellipse with the center of the earth as
one focus. The orbit’s lowest altitude is called the perigee, its
highest altitude is called the_ apogee.
Equatorial Orbit—_an orbit in the plane of the earth’s equator_.
Polar Orbit—_an orbit in a plane formed by the North and South Poles_.
Synchronous Orbit—_an orbit whose period is 24 hours, the same as that
of the earth revolving on its axis—so that the satellite’s and the
earth’s angular velocities are the same. Although there are many
possible kinds of synchronous orbits, each must have an average altitude
above the earth’s surface of approximately 22,300 statute miles_.
Stationary Orbit—_an orbit that is circular, equatorial, and
synchronous—so that the satellite will appear stationary from any point
on the earth_.
Inclined Synchronous Orbit—_an orbit that is synchronous but not
stationary, since it does not follow the plane of the equator. From a
point on earth, it will appear to follow a figure_ eight _pattern about
a line of constant longitude_.
part 2
Satellite Communications Case Histories
[Illustration: Title image]