Spurious Signals in Satellite Command Systems

The Project RELAY command system is described with emphasis given to the spacecraft equipment. Errors in the RELAY command system are discussed, and the probability of error in a single command word and the probability of a spurious command are given as a function of the signal-to-noise ratio (SNR) at the output of the command receiver in the satellite. The performance of the actual RELAY command system is discussed and shown to differ considerably from the performance predicted by theory. The results of an analysis of the orbiting command system are presented. The probable cause for the anomalous performance of the command system is shown to be Radio Frequency Interference from ground based transmitters. The techniques which are available to the system designer to avoid the problems experienced by the RELAY system are discussed in detail.