4-15
(absence of power from solar cells), and satellite failures. The distribution of outage times is a
complicated function of time and earth-station locations. With careful coverage coordination, maximum
communications effectiveness is obtained.
Q12. Why is satellite acquisition and tracking important?
ROLE OF SATELLITE COMMUNICATIONS
In the context of a worldwide military communications network, satellite communications systems
are very important. Satellite communications links add capacity to existing communications capabilities
and provide additional alternate routings for communications traffic. Satellite links, as one of several
kinds of long-distance links, interconnect switching centers located strategically around the world. They
are part of the defense communication systems (DCS) network. One important aspect of the satellite
communications network is that it continues in operation under conditions that sometimes render other
methods of communications inoperable. Because of this, satellites make a significant contribution to
improved reliability of Navy communications.
ADVANTAGES OF SATELLITE COMMUNICATIONS
Satellite communications have unique advantages over conventional long distance transmissions.
Satellite links are unaffected by the propagation variations that interfere with hf radio. They are also free
from the high attenuation of wire or cable facilities and are capable of spanning long distances. The
numerous repeater stations required for line-of-sight or troposcatter links are no longer needed. They
furnish the reliability and flexibility of service that is needed to support a military operation.
Capacity
The present military communications satellite system is capable of communications between
backpack, airborne, and shipboard terminals. The system is capable of handling thousands of
communications channels.
Reliability
Communications satellite frequencies are not dependent upon reflection or refraction and are
affected only slightly by atmospheric phenomena. The reliability of satellite communications systems is
limited only by the equipment reliability and the skill of operating and maintenance personnel.
Vulnerability
Destruction of an orbiting vehicle by an enemy is possible. However, destruction of a single
communications satellite would be quite difficult and expensive. The cost would be excessive compared
to the tactical advantage gained. It would be particularly difficult to destroy an entire multiple-satellite
system such as the twenty-six random-orbit satellite system currently in use. The earth terminals offer a
more attractive target for physical destruction. These can be protected by the same measures that are
taken to protect other vital installations.
A high degree of freedom from jamming damage is provided by the highly directional antennas at
the earth terminals. The wide bandwidth system that can accommodate sophisticated anti-jam modulation
techniques also lessens vulnerability.
