Space Telecommunications

Abstract

Radio communications to and from a spacecraft are its lifeline, with which commands are received from the ground control centres and information collected in space is returned. Particular electromagnetic links provide also the possibility of very precise measurements of distance and velocity and of very accurate determination of the orbit of the spacecraft and the earth. Similar techniques are also used in radar ranging to the moon, to passive artificial satellites and to the planets (both in the radio and optical band). In this chapter we discuss the energetics of radio communications in space and introduce spectral theory, a necessary tool to describe their noise performance. Particular attention is devoted to coherent propagation, a particular radio link used to measure the relative velocity, and to the effect of media upon electromagnetic propagation.