Overview Space Segment

Abstract

Chapter 1 summarizes the space segment, introducing the “Space Environment”, “Space System Engineering” and “Space Communications”, the latter establishing the connection to the ground segment.

The space environment in which spacecraft have to operate is an alien world in which we would not survive for more than a few minutes without protection. Fortunately, in this respect, spacecraft are generally more robust than humans and it is possible for spacecraft to regularly operate continuously for more than 15 years. In the case of Voyager 1, launched over 35 years ago, the spacecraft continues to operate and to communicate with the Earth 18 billion km away. It is interesting to question how this longevity can be achieved when there is no possibility of maintenance and the environment, at first sight, appears so unattractive.

System engineering requires skills that are traditionally associated with both art and science. Good system engineering not only requires the art of technical leadership including creativity, problem solving, knowledge and communication skills but it also requires the science of systems management or the application of a systematic disciplined approach. In this section the systematic disciplined approach is considered in more detail.

Radio communication with a spacecraft has to deal with the fact that there are large distances between transmitter and receiver, possible low elevation angles resulting in a substantial attenuation by the atmosphere and large Doppler shifts due to the orbital velocity of the satellite. Moreover, the ionosphere reflects or absorbs certain frequencies that are thus unusable for space communications.