6.1 Definition

Authored by Dr. Zhu with major contributions from Dr. Daniel Selva of Texas A&M

The communications subsystem in a spacecraft combines the communication link between the spacecraft and the ground. There are antennas and transceivers on both the spacecraft and on the ground to transmit and receive signals. The ultimate goal is to guarantee a communication link between the spacecraft and mission control for required phases of the mission to download clean payload data and upload spacecraft commands.

Signals are carried through space by electromagnetic waves defined at a certain radio frequency. These radio waves are transmitted and received by antennas and transceivers/transponders, which must then be translated into digital electrical signals. A communication link must travel from the original data, through data filtering, encoding algorithms, and modulation hardware, through space, through antenna and receiver hardware, to demodulation, decoding, and decompression algorithms to finally reach mission operators. This same process is true for mission operators to send commands to spacecraft. We will focus this chapter on the spacecraft side of communications but briefly discuss ground stations when the context is appropriate.