Page 179 - Intro to Space Sciences Spacecraft Applications

CHAPTER 8

Spacecraft Systems

The preceding chapters have discussed many of the space science topics
involved with the operation of spacecraft and spacecraft applications. The
purpose of this chapter is to describe, in more detail, the individual ele-
ments which make up a complete space system. Before continuing, we
must first define precisely what is meant by a space system. The spacecraft
itself is part of a larger system, which includes ground-based telecommu-
nication, tracking, data collection, processing, and dissemination elements
that are described in the chapter under the heading of Ground Support Sys-
tems. Other space-based assets such as communication relay satellites used
to link spacecraft data to the ground systems and navigation satellites that
provide precise geopositioning information to orbiting satellites can also
be an essential part of the larger architecture of our spacecraft system. This
constellation of interlocking space-based and ground-based systems are all
tied to a system user with a mission goal. Whether the mission applications
goal is scientific, military, civil, or commercial, the over-arching space sys-
tem, with networked space and ground elements, begins and ends with the
user. The user establishes the applications goals and operating protocols at
the beginning of the system development process and makes use of the
communications, remote sensing, and navigation information produced by
the system when it is in place. Our description of this complex end-to-end
system begins with a discussion of the spacecraft element by outlining the
rudiments of satellite design.

SATELLITE DESIGN

Figure 8-1 identifies the basic elements of a satellite system. In addition
to the payload, satellite, and launch vehicle, there are many devices that
must be added to the system to complement the payload, such as special
downlinks, tape recorders, and cryogenic coolers. The mission and pay-
load characteristics also place requirements upon the satellite bus subsys-
tems to provide special capabilities in each of the subsystem areas, for