Defense
Satellite Communications System
Operations
The purpose and
operational objectives of the DSCS Characteristics and limitations of the
DSCS
Systems
Control and Terminal Equipment
Control elements
of the DSCS operations control system DSCS systems control The Air Force
satellite control facility Terminals used in the DSCS
Associated
Networks
Ground mobile
forces
In the last
volume, we discussed satellites as a transmission media. You will now see
that it’s the only system to have its own office within DCA. The system
is so vast and has so many variables that it requires the management and
supervision of a separate organization charged with the responsibility
of ensuring that timely and correct
decisions
be made for control of the various aspects of the DODs satellite programs.
In this unit, we will look at the Defense Satellite Communications System
(DSCS), one of its programs, the ground mobile forces (GMF) network, and
an integral part of the DSCS, the Air Force Satellite Control Facility.
We will also discuss the Air Force Satellite Communications System (AFSCS).
Operations
With the launching
of new satellites and the modification of terminals, the Initial Defense
Communications Satellite Program (IDCSP) entered a new phase and was renamed
the Defense Satellite Communications System. This is a triservice program
under the direction and operational control of DCA. As you read the following
sections describing the DSCS, you may wish to refer back to Volume 1 of
this course for a refresher on the operational characteristics of satellites.
The purpose
and operational objectives of the DSCS
Purpose
The DSCS was
developed to support unique and vital global communications networks for
the DOD. The DSCS is an integral part of the DCS and normally supports:
a.
Needs of the Worldwide Military Command and Control System (WWMCCS). b.
Establishment, extension, and upgrading of communications in direct support
of
combat forces.
c.
Wideband communications requirements to remote locations not adequately
served by other
means.
4– 2
d.
Navy ship- to- ship, ground mobile forces, and other authorized DCS user
requirements.
e.
Other uses as directed by the Joint Chiefs of Staff (JCS) and/ or Secretary
of
Defense.
A unique feature
of DSCS is its ability to extend communications services to remote locations
not adequately served by other means, to support Navy ship- shore- ship
communications, the GMF of the Army, Marine Corps, and Air Force, and the
Diplomatic Telecommunications System (DTS) of the Department of State (fig.
4– 1).
[figure 4–
1]
Operational
objectives
The primary operational
objective of the DSCS is to provide continuous high- quality communications
to each validated user. In stressful environments, including trans- and
postattack periods, the objective is to preserve the critical communication
needs of the WWMCCS. Operational objectives are achieved by supporting
the DSCS performance criteria and its operational priority system. These
objectives are met by ensuring that critical subscribers and systems maintain
connectivity with the DCS; that sustained quality service is maintained
through timely, effective testing and analysis in both normal and stress
environments; and that efficiency is increased in the DSCS. Also, the system
should remain flexible to serve the maximum number of potential users and
to be tactically adaptable.
4– 3
Characteristics
and limitations of the DSCS
Characteristics
Due to the importance
of defense satellite systems, they must have high reliability along with
the basic characteristics that allow them to perform effectively. All communications
systems must conform to certain basic requirements, some of which are listed
below.
Reliability
Two types of
reliability are of interest. The first is propagation reliability. The
highfrequency (HF) band has always been subject to the irregularities of
the ionospheric layers that surround the Earth. Thus, only a portion of
the HF band is actually usable at any given time over a particular path.
Also, the multipath effects of ionospheric propagation seriously limit
the amount of information that can be transmitted over a given channel.
Added to these limitations are the “blackouts” that may result from ionospheric
disturbances caused by sunspot activity. High- altitude nuclear explosions
can introduce similar disturbances. One is forced to conclude, and rightly
so, that using HF frequencies and the ionosphere as a propagation medium
yields less than desirable results. By contrast, a communications satellite
of the active- type using line- of- sight (LOS) transmission at microwave
frequencies is extremely reliable from a propagation standpoint. A communications
satellite introduces a second type of reliability problem— that of reliable
unattended operation for long periods in orbit. Systems engineers have
shown that a reliable communications satellite can be made with operational
life expectancies of more than 1 year if the following practices are used:
Components
of proven reliability are selected. All components are operated within
their ratings. The satellite design provides adequate protection during
launch and while in the
space environment.
Adequate
use is made of redundancy to further increase the chance of successful
operation.
Capacity
Through the years,
people have become dependent, almost exclusively, on frequencies in the
5- to 30- MHz range for long- range global communications. These frequencies
are shared among all countries and must support both military and civilian
applications. This narrow range of frequencies and the propagation characteristics
discussed previously seriously limit total communications capacity. It
is not surprising that a great interest exists in techniques that open
more areas of the frequency spectrum to long- range communications (e.
g., ionospheric and tropospheric scatter propagation). Communications satellites
use the complete range of frequencies to 10,000 MHz and higher for long-
range communications, thus providing more than 1,000 times the spectrum
available in the HF band.
4– 4
Flexibility
One need is to
provide sufficient flexibility in systems so that new or changing demands
can be satisfied without major overhaul or replacement of facilities. A
disadvantage of submarine cable, for instance, is lack of flexibility because
it is a fixed- plant facility. Limitations on the flexibility of other
systems include the physical size of equipment, criticality of the troposphere,
and microwave antenna aiming points and power needs. Satellite communications
systems provide a high- degree of flexibility for several reasons: (1)
They have wide bandwidths that allow versatility in traffic handling capabilities.
(2) They are flexible in positioning or location because of their compact
size. (3) By providing wide bandwidths and essentially global coverage,
they place minimum restraints on the number and location of ground stations
served and the volume of communications sent to each.
Also, the
use of solid- state devices and modular construction places minimum power
requirements on systems. Usually, all terminal power can be supplied by
small, mobile power generator plants, an advantage that further broadens
system flexibility.
Delay
Speed of communications
is a must. All too frequently, delays are caused by poor propagation conditions.
Weather, solar flares, and other atmospheric phenomena can totally disrupt
normal communications links. When compounded by congested facilities, they
cause delays in the transmission of urgent message. Satellite systems designs
have done much toward overcoming delay problems. Wide bandwidths have relieved
traffic congestion by providing the capacity for many users simultaneously.
The use of microwave frequencies and LOS principles have negated propagation
problems. The ability to locate systems at sites convenient to users has
ended or greatly reduced delivery delays.
Limitations
To understand
the capabilities of space communications more fully, we must consider certain
constraints and design limitations.
Natural
constraints
The natural constraints
that must be considered in space communications systems are listed below:
a.
Path profile. An LOS path must be established between the transmitter and
receiver.
b.
Free space loss. Power radiated from a transmitting antenna is distributed
over an
everexpanding
portion of the Earth’s spherical surface. The resulting decrease in power
density (power per unit area) reduces the energy “captured” by the receiving
antenna and is known as free space loss. This is the most serious loss
in satellite communications.
c.
Noise. Noise is introduced at each stage of the communications process.
The most
significant contributions
are from the medium through which communications are sent and from within
the receiver itself. Noise reduces the ability of a receiver to detect
weak signals.
4– 5
Design
limitations
Some design limitations
that must be considered are as follows:
a.
Transmitter power. This is a measure of the minimum signal strength with
which
a receiver can
be gainfully operated.
b.
Receiver noise figure. The inherent noise injected into a system by the
receiver
itself constitutes
a basic limit on the minimum detectable signal.
c.
Bandwith. The bandwidth of a system is limited by many considerations,
most
important of
which is the capacity of a system to transmit data directly proportional
to its usable bandwidth.
d.
Data processing. Transmitting data into space does not necessarily mean
that
effective communication
will be the result because all data does not represent information. One
can find out the effective capacity of a system only by measuring how well
transmitted data represents information. In other words, if data is transmitted
with errors, there will be wasted energy, therefore, the system will not
work as efficiently as it should.
e.
Modulation. The effectiveness of a communications system varies greatly
with
the modulation
technique used.
Systems
Control and Terminal Equipment
There are several
types of terminals in use in the DSCS, each with its own operational characteristics,
but they all must adhere to certain operational guidelines. In this section,
we will discuss the operational control of the DSCS, the control system
of the DSCS, and then take a look at the various terminals the system uses.
Control
elements of the DSCS operations control system
DOCS is the system
of operational control used in the DSCS. This control system is exercised
by the DCA satellite operations division, the area communications operations
centers, the DSCS operations centers, technical control facilities, and
DSCS Earth terminals. This structure can be seen in figure 4– 2.
4–
6
[figure 4– 2]
DCA
satellite operations division (Code B440)
B440 is the operations
manager of the DSCS within the DCA directorate. One of their responsibilities
is to develop and manage a control system (DOCS) that makes sure the DSCS
mission and operational objectives are met. The DSCS control authority
goes from B440 through the control hierarchy of the NCS/ DCAOC and ACOCs
to the DSCS operations centers.
DSCS
Operations Center (DSCSOC)
The DSCSOCs,
colocated with dual- headed Earth terminals, perform satellite communications
(SATCOM) network and satellite control. They conduct the daily operation
and control of networks associated with chosen satellites under the authority
of their ACOC. The DSCSOCs also provide operational direction of Earth
terminals and satellite payloads by using DOCS equipment to maintain correct
network parameters.
DSCS
earth terminals
Earth terminals,
or network control terminals (NCT), are operated and maintained by the
military departments (MILDEP) and are a key element in the control process.
NCT personnel perform the DOCS function by monitoring, measuring, and maintaining
performance standards of terminal equipment, and by reconfiguring and adjusting
operating parameters in response to direction from the DSCSOCs. Execution
of all terminal operations is coordinated with the local TCF and/ or the
DSCSOC, as appropriate.
4– 7
Technical
control facility
TCFs support
the DOCS by coordinating with NCTs and the DSCSOCs for channel fault isolation,
corrective action, and channel activation or deactivation.
DSCS systems
control
DSCS
systems control
DSCS system control
is an inherent part of the DCS control structure (fig. 4– 2). Systems control
will be exercised at the lowest level consistent with authority and resources.
It is the means by which DSCS assets are used to maintain and restore maximum
DSCS performance under changing traffic conditions, natural or manmade
stresses, disturbances, and equipment disruptions. The basic aspects of
systems control include the timely acquisition of systems performance data,
facility and satellite load status, and service quality indications. It
also includes rapid analysis and processing and display of information
to include real- time data base management. Decisionmaking and control
execution are a major emphasis of systems control. It takes into consideration
the support of long- range systems management and engineering objectives.
Planned
and reactive changes
The DSCS has
two methods for making changes to the systems it manages: planned and reactive.
Planned changes are caused by management decisions on reconfiguration of
DSCS subsystems and are based on a variety of engineering factors or on
operational performance analysis indicators. Reactive changes are in response
to disturbances, such as equipment failures, system outages, circuit degradation,
or unusual traffic demands. The systems control design supports DCA and
the MILDEPs in the performance of their DSCS activities. Also, it builds
on the inherent monitoring and control features of major satellite facilities
to help DCA in the execution of its network administration and management
activities.
Systems
control objectives
The primary objectives
for DSCS systems control are to:
a.
Make sure of critical subscriber and system connectivity. b. Make sure
that systems control reacts quickly and flexibly, but in such a way as
to
impose no operational
constraints on the system.
c.
Incorporate a level of control and systems management survivability consistent
with the survivability
of the DSCS.
d.
Make sure of sustained quality service through timely, effective testing
and
analysis in both
normal and stressed environments.
e.
Make sure of interoperability or compatibility with the control systems
associated
with other communications
systems.
f.
Increase DSCS efficiency. g. Improve management visibility of availability
status, quality of service, and
performance of
the DSCS.
h. Make operation
and maintenance activities easier at DSCS stations.
4– 8
i. Decrease
manpower resources and support information required for control.
The Air Force
satellite control facility
Air
Force Satellite Control Facility (AFSCF)
The Air Force
has responsibility for launching DSCS satellites and, as mentioned in Volume
1 of this course, the AFSCF is under the operational direction of the Department
of the Air Force and performs telemetry, tracking, and control of all satellites
in the DSCS. It has the responsibility of keeping satellites in their assigned
orbital positions, maintaining the prescribed altitude relative to Earth,
and supporting the housekeeping functions necessary to make sure of optimum
operations. Though the AFSCF is not really a part of the DSCS control structure,
it must coordinate all of its actions with the right DSCSOCs, as well as
with B440. As you can see in figure 4– 2, the AFSCF has a worldwide network
of remote tracking stations (RTS), which supply a constant status of all
DSCS satellites. The AFSCF is located in Onizuka AFS, California.
Terminals
used in the DSCS
At present, four
types of terminals are used in the DSCS: (1) AN/ FSC– 9. (2) AN/ MSC– 46.
(3) AN/ FSC– 78. (4) AN/ GSC– 39.
AN/
FCS– 9
The AN/ FSC–
9 is a fixed terminal maintained by the Army. There is one located at Ft.
Dix, New Jersey, and one at Camp Roberts, California. They are the primary
entry points to the continental United States for the Pacific and European
satellite communications links. They are both nodal stations.
AN/
MSC– 46
The AN/ MSC–
46 has a misleading nomenclature. It is a heavy air transportable terminal,
not a mobile terminal as the “M” (in MSC– 46) would lead you to believe.
This system is an SHF system with most of its equipment sheltered in vans.
Five vans make up the system (fig. 4– 3): (1) Operations control van (OCV).
(2) Maintenance van. (3) Transmitter van. (4) Storage van. (5) Multiplexer
van.
4–
9
[figure 4– 3]
The antenna is transportable on an antenna trailer, often called a “bogey.”
Most installations have a radome surrounding the antenna to protect it
from the weather.
Frequency
range
The terminal
has two power amplifiers. The high- power amplifier is a klystron with
a maximum power output of 10kW (70 dBm). The low- power amplifier uses
a traveling wave tube (TWT) and has a maximum power output of 2.5kW. Only
one may be selected at a time.
Antenna
system
The AN/ MSC–
46 uses a 40- foot paraboloid reflector for its antenna. Gain is approximately
57 dB at 8 GHz.
Tracking
This system tracks
satellites manually, through the use of elevation and/ or azimuth handwheels,
or automatically. In the manual method, the operator/ maintenance technician
uses inputs to a servosystem to adjust the antenna position for maximum
signal strength from the satellite. In the “autotrack” (automatic tracking)
mode, the terminal will use the satellite’s beacon frequency to fine- tune
the antenna position.
Link
and channel capability
AN/ MSC– 46 terminals
consist of a maximum of 9 uplinks (transmit) and 15 downlinks (receive).
They were originally configured to be either nodal or nonnodal systems
with different FDM multiplexer vans; however, most have been reconfigured
to use a digital subsystem van. There are several MSC– 46 terminals located
around the world being operated and maintained by the using service. Presently,
the Air Force has MSC– 46 terminals at Diyabakir, Turkey; Humosa, Spain;
and Misawa, Japan. These can be used in either a
4–
10
nodal or nonodal
configuration, depending on the requirements of the communications link.
AN/
FSC– 78
AN/ FSC– 78 terminals
are an updated version of the AN/ MSC– 46. It is a fixed SHF system using
phase II and III satellite repeaters. A typical layout of an AN/ FSC– 78
consists of an antenna group, a communication/ transmitter (C/ T) equipment
building, and an interfacility line trench connecting the two structures.
Frequency
range
The frequency
range of the AN/ FSC– 78 terminal is identical to that of the AN/ MSC–
46: receive frequencies are 7.25 to 7.75 GHz, and transmit frequencies
are from 7.9 to 8.4 GHz.
Output
power
The terminal
has two 5kW TWT power amplifiers.
Antenna
system
The AN/ FSC–
78 has a 60- foot parabolic reflector that works with a 7- foot hyperbolic
reflector to form a Cassegrain feed system. Gain is approximately 60 dB
at 8 GHz.
Tracking
Satellites may
be tracked manually, through the use of elevation and/ or azimuth handwheels,
or automatically. In the manual mode, the operator/ maintenance technician
uses the inputs to a servo system to adjust antenna position for maximum
signal strength from the satellite. In the autotrack mode, the terminal
uses a satellite beacon frequency to fine tune antenna position.
Link
and channel capability
AN/ FSC– 78 terminals
consist of a maximum of 9 uplinks (transmit) and 15 downlinks (receive).
These terminals are located at the following sites:
a. RAF Croughton,
England. b. Elmendorf AFB, Alaska. c. New Boston, New Hampshire. d. Onizuka
AFS, California. e. Offutt AFB, Nebraska.
AN/
GSC– 39
The AN/ GSC–
39 is a medium- traffic, fixed terminal. It is made up to two major equipment
groups: an antenna group and a communications equipment group. The communications
equipment group is contained in two vans, the transmitter and operations
vans that, along with a maintenance and supply van, provide all terminal
support.
Frequency
range
Frequency range
for this system is the same as for the MSC– 46 and FSC– 78.
4– 11
Output
power
This terminal
has two 5kW TWT power amplifiers.
Antenna
system
A 38- foot parabolic
main reflector provides high- gain, narrow- beam radiation of RF energy.
Tracking
The antenna has
an autotrack capability that enables it to move from <196> 2.5 to +92°
in elevation. All terminals in the DSCS have spread spectrum and antijam
capabilities. Multiple access of satellites is done using frequency division
techniques.
Associated
Networks
There are many
networks that use the satellites of the DSCS. Some of them are under the
direct control and operational direction of DCA, and others are operated
by the military departments. We will discuss two of these, the ground mobile
forces network and the Air Force Satellite Communications System.
Ground mobile
forces
Purpose
and applicability of ground mobile forces
The US Army first
made satellite terminals for its GMF to provide access into the DSCS. As
the name implies, GMF terminals were designed specifically for military
use in tactical communications. These terminals are capable of entry into
the DCS during crises through a network of DSCS gateways. They augment
other mobile communications systems and provide the quick reaction ability
needed to support tactical mission.
Gateway
station
Gateway stations
provide the deployed tactical community with the ability to extend their
communications capabilities from a point- to- point mode to an intratheater
or intertheater mode. There are 15- gateway stations.
Terminals
All GMF terminals
operate in the same frequency range as the four DSCS terminals, and all
include an automatic tracking 8- foot diameter antenna mounted as an integral
part of the equipment enclosure. They are completely self- contained and
designed to provide a full communications ability within 20 minutes of
arrival at a deployed location. There are two terminals being used by the
Air Force: the AN/ TSC– 94 and the AN/ TSC– 100.
AN/
TSC– 94
The AN/ TSC–
94 has all equipment necessary for the reception, transmission, and processing
of multiplexed voice channels. It is used for point- to- point operation
in tactical communications systems and is capable of simultaneous transmission
and reception of a single high- rate carrier. The terminal consists of
receive, transmit,
4–
12
antenna, power,
and distribution groups. Also, it has an environmental control unit (heating
and air- conditioning) for personnel comfort. The AN/ TSC– 94s 8- foot
dish must be built on- arrival at the deployed location. It can then manually
track satellites using switches on the antenna control panel, or track
automatically through a method known as random step scan. This terminal
can track either the satellite beacon or the communications signal. However,
because the autotrack system can adjust the antenna only +12.5°, antenna
movement is limited. There is an output power capability of 500 watts through
one klystron. The terminal has a single uplink and downlink, providing
a total of 12- voice channels and 1- voice orderwire.
AN/
TSC– 100
The AN/ TSC–
100 is picked for single- or multiple- carrier service with single- or
dualtracking antenna. The terminal is composed of three major components
(fig. 4– 4). They include an S– 280- type shelter, housing all of the terminal
electronics except for the receiver low- noise front end, an 8- foot ground-
mounted parabolic antenna system, and a diesel- powered generator and associated
switch gear to provide primary power. The terminal can also operate with
a 20- foot antenna.
[figure 4–
4]