ABSTRACT
Radio is integral to almost all uses of space.1 It is essential for most tracking, for all telemetry, command and control functions and for the very fulfilment of the purpose of most satellites. Although tracking can be done by ground-based radar, satellites are mostly tracked through the signals which they themselves transmit. Telemetry monitors the health and performance of a satellite through diagnostic information supplied by radio by the satellite itself. Command and control of a satellite is exercised through ground signals.2 The fulfilment of the function or purpose of a satellite depends on its ability to receive and to transmit data to Earth. The frequencies required by modern satellites lie in the very high frequency range and above since it is only these that can penetrate the Heaviside layer of ionised gases above the Earth, and only in these ranges is a sufficient precision of signal obtained which allows the modulation and band width necessary for the carrying of very sophisticated digital signals. Any degradation of the quality of the signal to or from a satellite at best diminishes its efficiency and at worst renders it useless. On-board computers control satellites and respond to radio signals in accordance with their programming. However, as is well known, computers only act in accordance with input received. They do not ‘know’ what is ‘meant’ by a particular signal or intended by its sender. A degraded signal may have no effect whatsoever, or it might have an unexpected effect. Problems of interference are therefore of importance in the use of radio in relation to space.
