Communication Satellites

This paper is intended to provide a review of communication satellites starting with their comparatively brief history and continuing through present developments and future concepts and the probable impact on global communications. The advantages and disadvantages are considered for various types of passive and active devices, for various orbits, and from the standpoint of both military and commercial applications. Consideration of all major technical and economic factors leads to the conclusion that a system of 3 or 4 repeater satellites in 24-hour orbits will best meet future world-wide communication requirements. A number of system concepts are described, including time-synchronous and frequency-sharing systems. Important aspects of communication satellite design are discussed including electronics, antennas, power supply, structure, attitude and position stabilization, command control, and telemetering. Selection of frequency is shown to be not critical over a wide range. Choice of design parameters such as power output, antenna gain, stabilization accuracy, etc., is largely dependent on the desired capacity of the communication system and the available satellite payload. Some typical parameters for a high capacity system are presented. Reliability is an over-riding consideration in satellite design and it is proposed to achieve desired life by proper choice of components, by use of redundancy, and by minimization of satellite requirements at the expense of the ground equipment. Based on published information on ARPA-NASA programs and booster capabilities, some estimates are made of the rate of progress which can be expected in communication satellites, leading to their eventual use in military and commercial communications.