Introduction

Abstract

The idea of satellite communications was born a long time ago, in 1945, when Arthur C. Clarke wrote his famous paper “Extra-Terrestrial Relays” [Cla45]. In this paper, Clarke anticipated the concept of a geostationary sa tellite constellation consisting of three approximately equidistantly spaced artificial satellites in a specific orbit, such that the satellites revolve syn chronously with the earth. Clarke also foresaw manned spaceflight, and indeed thought that his satellites would house a crew which would be provisioned and relieved by a regular rocket service. Moreover, he anticipated the use of directive satellite antennas and linking the satellites by radio or optical beams. He intended to use these satellites for bidirectional communications and for broadcast services.