Page 71 - Communications Satellites Global Change Agents

2. EVOLUTION OF SATELLITE TECHNOLOGY 47

FIG. 2.5. Comparison of different size, scale, and types of satellites—"spinning"
spacecraft.

can be manufactured in high volume and at an increasingly lower cost. Spe-
cifically, receive-only terminals such as those used with Direct Broadcast Satel-
lite (DBS) services have dropped in cost to only a few hundred dollars when pro-
duced in millions of units. There are a number of excellent books on satellite
communications, as listed in the reference section, that describe these many tech-
nical innovations as well as other more detailed improvements.
• New ways have been developed to maintain satellites precisely in orbit.
These satellites are thus always pointed exactly to the same position on the earth.
This new three-axis stabilization technique typically uses momentum or inertia
wheels (similar to the spinning motion used in a gyroscopic top) and has elimi-
nated the need to "spin" the entire spacecraft. The differences in the size of satel-
lites and the differences between three-axis stabilized "birds" with solar wings
and the can-shaped "spinners" are illustrated in Figs. 2.5 and 2.6.