Satellite Orbits and Constellations

Abstract

This chapter begins with Kepler's laws, equations that describe the motion of Earth orbiting satellites under idealized conditions using a set of Keplerian parameters. It then discusses the deviation of actual satellite orbits from those predicted by Kepler's laws, and how these deviations from ideal are handled in satnav. The chapter introduces some basics of satnav constellations, since satnav requires multiple satellites both to provide coverage over large portions of the Earth's surface and to provide the needed number of measurements. Constellations are typically designed to provide graceful degradation of satellite geometry in the absence of a few satellites, as well as to accommodate additional satellites that may be launched before an on-orbit satellite has failed and needs replacement. The chapter presents some useful calculations of geometry between satellites and receivers, showing how the geometry maps into characteristics of received signals.