Spacecraft Communications System Design Steps

A spacecraft communications system is defined as including not only two-way voice links, but also command channels from the earth, telemetry (and in some cases TV) to the earth, as well as tracking transmitters or transponders. These links have varying significance for the common vehicle phases of launch, orbit (either parking or mission) , objective trajectory adjustment and/or return; some of the features of these operational phases are illustrated for their effect on communications. In the course of designing such communications systems for major spacecraft programs, certain fundamental areas inevitably appear, and lend themselves to a systematic approach. By applying the eight design steps subsequently discussed in the sequence indicated, a logical analysis of the various tradeoffs can be made with a minimum of time and effort. These design steps involve the basic mission, number and choice of operating frequencies (including safeguards) , radiation pattern coverage (antenna configurations) and duration of operating signal strength margins, and trade-offs between electrical power; thermodynamic, weight, and control dynamics limitations, as well as consideration of the environment, reliability, and availability of equipment to fill the requirements thus defined. Consideration is given to the choice and complexity of possible data to be handled, as well as various transmission techniques