Question

A customer wishes to create a single-plane low-frequency satellite communications system in which the satellite footprints just meet at the surface of the Earth. At the selected frequency, the satellites must operate an elevation angle of at least 10 degrees.

a) Calculate how many satellites are required to meet this requirement if the selected orbit is at an altitude of 800 km.

b) The customer has a better idea with the satellites operating at the same altitude but the minimum elevation angle is 19 degrees. Re-calculate the number of satellites required to meet this new requirement.

Answer 1

On placing a sequence of satellites in a circular orbit. All satellites follow the same orbit. The orbit is in the Earth's equatorial plane. You want to know, how many satellites you will need in total, if you want that an observer, located on a specific point on the Equator, can always "see" at least one satellite, where "seeing" means "having a direct line of sight which is at least 5 degrees above the horizon". The Earth is assumed to be a perfect ellipsoid, and we don't take into account refraction of light and radio waves in the upper atmosphere.