Page 227 - Satellite Communications, Fourth Edition

The Space Segment 207

Figure 7.7 Technicians check the alignment of the Telestar 3 communica-
tions satellite, shown without its cylindrical panels. The satellite, built for
the American Telephone and Telegraph Co., carries both traveling-wave
tube and solid-state power amplifiers, as shown on the communications
shelf surrounding the center of the spacecraft. The traveling-wave tubes are
the cylindrical instruments. (Courtesy of Hughes Aircraft Company Space
and Communications Group.)

permanent magnet providing the magnetic field for motor action. The
stator of the motor is attached to the body of the satellite. Thus the motor
provides the coupling between the flywheel and the satellite structure.
Speed and torque control of the motor is exercised through the currents
fed to the stator. The housing for the momentum wheel is evacuated to
protect the wheel from adverse environmental effects, and the bearings
have controlled lubrication that lasts over the lifetime of the satellite.