Role of instrumentation and control in space and defence

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A Seminar Report on
Role of Instrumentation in Space and Defence
Submitted to
Vishwakarma Institute of Technology, Pune
(An Autonomous Institute Affiliated to Savitribai Phule Pune University)
in partial fulfillment of the requirements of Third Year
For the degree of
Bachelor of Technology
in
Instrumentation and Control
By
Bhushan Pradeep Walnusakar
(GR NO: 132054 )
Under the guidance of
Prof. A. B. Kadu
Department of Instrumentation Engineering
Vishwakarma Institute of Technology, Pune-411037
December – 2014

ROLE OF INSTRUMENTATION IN SPACE AND DEFENCE
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BANSILAL RAMNATH AGARWAL CHARITABLE TRUST’S
VISHWAKARMA INSTITUTE OF TECHNOLOGY, PUNE -411037
(An Autonomous Institute Affliated to Savitribai Phule Pune University)
Department of Instrumentation Engineering
CERTIFICATE
This is to certify that the Seminar entitled “Role of Instrumentation in Space
and Defence” has been completed in the academic year 2014-15 by Bhushan
Pradeep Walnusakar (Gr.No:132054), under the supervision of Prof. A. B.
Kadu, in Instrumentation And Control Engineering Department.
Date:
Prof. Tejas. G. Patil
Guide
Prof. Sujit M. Deokar
Co-ordinator
Prof. Pramod M. Kanjalkar
Head of Department

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Acknowledgements
We are profoundly grateful to Prof. Anil B. Kadu for his expert guidance
and continuous encouragement throughout to see that this project rights its
target since its commencement to its completion.
We would like to express deepest appreciation towards Dr. R. M.
Jalnekar, Director, Vishwakarma Institute of Technology, Prof. Pramod M.
Kanjalkar, Head of Instrumentation & Control Engineering and Prof. Sujit M.
Deokar, Seminar Coordinator whose invaluable guidance supported us in
completing this seminar.
At last I must express my sincere heartfelt gratitude to all the staff
members of Instrumentation & Control Engineering Department who helped me
directly or indirectly during this course of work.
Bhushan P. Walnusakar

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Abstract
This seminar report contains the application of instrumentation technology in
space and defense. The report is divided into two sections: space
instrumentation and defense instrumentation.
The satellite can generally be regarded as a space craft that receive signal and
send them back to Earth. However, these spacecraft are extremely complex and
expensive- each one costs millions of Rupees – because they have to work and
survive in space for periods up to 15 years. To make this possible, a well-built
thermal and attitude control must be used. In space instrumentation section of
this paper we will discuss the satellite thermal and attitude control.
After the World War II it became important to design and constructs the
tracking system, missile guidance system, etc. In defense instrumentation
section we will discuss and try to understand the missile launching and
guidance system.

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Contents
Acknowledgement ....................................................................................................... iii
Abstract ........................................................................................................................iv
Table of Contents..........................................................................................................v
List of Figures ..............................................................................................................vi
List of Tables ............................................................................................................ vii5
A. SPACE INSTRUMENTATION…………………………………………………..8
CHAPTER:1 THERMAL CONTROL SYSTEM OF SATELLITE…………………8
1.1 Purpose of Thermal Control……………………………………………………8
1.2 Requirements………………………………………………………………….10
1.3 How Does Thermal Control System Works…………………………………..11
1.4 Thermal Control of Satellite…………………………………………………..13
CHAPTER:2 ATTITUDE CONTROL SYSTEM OF SATELLITE………………. 15
2.1 What is an Attitude Control……………………………………………….......15
2.2 Attitude Control of Satellite…………………………………………………...16
2.3 Attitude Sensors and Actuators………………………………………………..18
B. DEFENCE INSTRUMENTATION……………………………………………...22
CHAPTER:3 MISSILE LAUNCHING AND GUIDANCE SYSTEM……………...23
3.1 System working………………………………………………………………..23
3.2 Homing System………………………………………………………………..24
3.2.1 Sound…………………………………………………………………….25
3.2.2 Radio……………………………………………………………………..25
3.2.3 Radar……………………………………………………………………..25
3.2.4 Heat………………………………………………………………………25
3.2.5 Light (LIDAR)…………………………………………………………...26
3.3 Lead angle cource……………………………………………………………...27
3.4 Components of Missile Guidance System……………………………………..28
3.5 Weapon Control System……………………………………………………….30
3.6 Underwater Missile Guidance…………………………………………………32

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CHAPTER:4 CONCLUSION………………………………………………………..34
REFERENCES……………………………………………………………………….35

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LIST OF FIGURES
Figure.a.1.1 Effect of radiations on satellite………………………………………………9
Figure.a.1.3.1 Multi-layer insulation……………………………………………………..11
Figure.a.1.3.2 Block diagram of satellite thermal control…………………….………….12
Fig.a.2.1Path of satellite called ‘orbit’ ………………………………………………...…15
Fig..2.2.a. Block diagram of attitude control loop………………………………………..16
Fig.2.2.b. satellite position and velocity vectors………………………………………….17
Fig.a.2.4 Gyroscopes……………………………………………………………………...18
Fig.2.5 Venera Sun Sensor………………………………………………………………..19
Fig.2.6 Thrusters…………………………………………………………………………..20
Fig.a.2.7 Reaction/ momentum wheels…………………………………………………...21
Fig. b.1.1 Missile launching and guidance system………………………………………..23
Fig.b.1.2 Missile below the beam axis…………………………………………………....24
Fig.b.1.3 Missile using heat-homing guidance……………………………………………26
Fig.b.1.4 Missile using light homing system……………………………………………...26
Fig.b.1.5 Lead angle method approach……………………………………………………27
Fig.b.1.6 tracking radar antenna…………………………………………………………..28
Fig.b.1.7 Weapon control station………………………………………………………….30
Fig.b.1.5 Underwater missilr guidance…………………………………………………....32

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LIST OF TABLES
Table.a.1.2 Temperature specifications for the onboard parts……………………………10

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A. SPACE INSTRUMENTATION:-
In this section we will study and try to understand thermal and attitude control of
satellite.
CHAPTER 1
THERMAL CONTROL OF SATELLITE
1.1PURPOSE OF THERMAL CONTROL
Throughout the mission, thermal control ensures that each item of equipment is
maintained at temperatures consistent with nominal operation.
Most equipment only operates correctly if maintained at right temperature and
temperature changes are within acceptable limits. In our terrestrial environment or in
laboratories, temperature is often regulated “naturally”. Satellite environment in orbit
are completely different (vaccum, microgravity, radiations, etc.). This means that
thermal conditions are very particular and likely to cause dangerous change in
temperature. Correct temperature can only be achieved by applying scientific method
and specific “thermal control” technology.
Fig.a.1.1 Effect of radiations on satellite

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1.2 REQUIREMENTS
To guarantee normal operation of equipment, thermal control must ensure
that an item’s temperature remains within predefined limits (specification):
Table a.1.2 shows maximum and minimum temperature specifications for
the onboard parts.
EQUIPMENT
ON-ORBIT TEMPERATURE RANGE
(0C(
QUALIFICATION
RANGE)0C(
Minimum
during non-
operating
phase
Operating Operating
Electronic
units
MIN MAX MIN MAX
“
TWT
(travelling
wave tubes)
-30 0 +75 -10 +80
“
Electronic
power
conditioner
-30 0 +50 -10 +60
“ Input Filters -30 +5 +50 -5 +60
“
Microwave
equipment
(transmitter,
receivers)
-30 -10 +50 -20 +60
“
Output
multiplexers
-30 +20 70 +10 +80
“
Data
processing
units
-30 -10 +50 -20 +60
“
IR and sun
sensors
-45 -30 +50 -40 +60
“
Battery Ni-
H2
-20 -5 +25 -15 +35
Non-
electronic
units
Tanks 0 0 40 -10 +50
Solar
generator
-180 -165 +70 -175 +80
Propellant
lines
0 05 0 -10 +60
Momentum
wheels
-40 -15 45 -25 +55
Table.a.1.2 Temperature specifications for the onboard parts

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1.3 HOW DOES THERMAL CONTROL SYSTEM WORKS?
External Thermal Insulation:-
To maintain the satellite at a mean temperature close to 200C and to
protect the satellite from thermal radiations, the surfaces of satellite are covered
by so-called “super-insulating” blankets which are incredibly efficient in the space
vaccum (one hundred times better than polystyrene).
In photographs of the satellite, the radiators look like blueish mirrors.
The multi-layer insulation has a golden yellow colour due to the use of
aluminium-coated polymide films, which consists of number of layer of vapour
deposited aluminium, silver or gold(fig.a.1.3.1).
Fig.a.1.3.1 Multi-layer insulation

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Internal Thermal Control Arrangement:-
In internal thermal control arrangement instrumentation must include.
The typical block diagram of thermal control arrangement is as shown in
fig.a.1.3.2.
V
During cold or too hot mission phase and in particular when the equipment is not
very active, it has to be kept warm by resistive electric heaters or cold by thermoelectric
coolers. The flight software manages the thermal control system. The temperature
measurements are recorded by network of sensors, are compared to the reference values.
The heaters and coolers are then switched on and controlled strictly according to need.
Some items require very precise temperature control. This is the case for
gyroscopes or on-board clock, which are controlled to within 10th or 100th of degree
Celsius respectively. To ensure this stability, these components are installed in fairly cold
environment then heated using PI (Proportional-integral) control law.
In the event of serious satellite failure, the satellite automatically adopts a fixed
attitude relative to the Sun and only essential equipment will be powered. A network of
electric heaters controlled by mechanical thermostats (bimetallic strips) is used to
maintain an adequate temperature to protect the equipment.
Throughout the satellite operational life, a few hundred sensors (thermisters)
located in strategic area are used to ensure nominal equipment operation. Measurement of
Temperature and heater control law can be change from ground. If a heater network fails,
a backup network can be switched on.
Fig.a.1.3.2 Block diagram of satellite thermal control
Networkof
thermal sensor
Controller
(Computer)
Heaters/
Coolers
Satellitethermo-
dynamics
Disturbances

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1.4 Thermal Control Components
• Electric heaters
– Used in cold-biased equipment
– Controlled by thermostats (local or central)
– Flat sheet heaters use the Joule effect
• Space radiators
– Heat exchanger on outer surface radiates waste heat into space
• Cold plates
– Structural mounts for electronic equipment
– May use flowing fluids for convective heat transfer
• Doublers
– Passive aluminium plates that increase heat exchange surface area
• Heat pipes
– Used to transfer heat from one area to another
– Heat at one end evaporates the working fluid, absorbing heat
– Vaporized working fluid flows to cold end and condenses, releasing heat
– Wicking material returns fluid to hot end
– Provide high heat transfer rates even with small temperature differences
Hot end Cold end
liquid flow in wick
gas flow

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• Louvers
– Shield radiator surfaces to moderate heat flow to space
• Temperature sensors
– Thermistors – Semiconductors whose resistance varies with temperature
– Resistance thermometers – Pure platinum conductor whose resistance changes with
temperature
• Thermal isolators
– Low conductivity materials used to isolate instruments and other components from the
spacecraft body
• Thermoelectric coolers
– Electric current induces cooling of junction between dissimilar metals
– Relatively low efficiency

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CHAPTER: 2
ATTITUDE CONTROL SYSTEM OF SATELLITE
(ORBIT CONTROL SYSTEM)
2.1 WHAT IS AN ATTITUDE CONTROL
The path of the satellite through space is called its orbit; the orientation of the
satellite in space is called its attitude. Control of the orbital path is required to ensure
that the satellite is in the correct location in space to provide the services required of
it. Attitude control is essential on the spacecraft to prevent the satellite from tumbling
in space and to ensure that the antennas remain pointed at a fixed point on the Earth’s
surfaces. These functions are the responsibility of the Attitude and Orbit control
subsystem.
Orbit control is required to correct for perturbation forces and to transfer
orbits, or orbital location. The major means of changing orbits or to move or maintain
current location are to fire the thrusters.
A basic attitude control system comprises three elements: an ability to sense
the current attitude of a platform, an ability to compute errors between current attitude
and desired attitude, and some mechanism by which the attitude error can be
Fig.a.2.1Path of satellite called ‘orbit’

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controlled and corrected.
2.2 ATTITUDE CONTROL OF SATELLITE
Unlike an aircraft which uses its attitude to control its trajectory (pitching to
go up, banking to turn, etc.) the angular motion of a satellite, which is travelling in a
vaccum, has practically no effect of its trajectory (i.e. its orbit).
The satellite orbit is determined by the initial velocity given it by the Ariane
launcher, and then by the small corrections made regularly by micro-thrusters. The
disturbances to the attitude control (angular orientations) are torque produced by the
environment, gravity due to the Earth and the Moon, and movement of mechanical
parts, etc.
The attitude is continuously controlled by a programmed control loop
(fig.a.2.2). Sensors measure the satellite’s attitude, the onboard computer then
processes these measurements and generates commands which are carried out by the
actuator, to ensure correct pointing.
Fig..2.2.a. Block diagram of attitude control loop
“Three axis stabilization” which means that its orientation is fully
controlled relative to three axes. One of these directions corresponds to the line
between the satellite and the centre of the Earth, also called the “geocentric direction”

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another is perpendicular to geocentric axis, in the direction of this geocentric axis, in
the direction of the satellite’s velocity vector; the third is perpendicular to the first
two. These three form the local orbital reference system.
The local orbital reference system is defined at each point of the orbit by
three unit vectors. These vectors are derived from the satellite position and velocity
vectors shown in fig.a.2.3.
1) Vector L is collinear with position vector P (on the axis between the Earth’s centre
and the satellite). It defines yaw axis.
2) Vector T is perpendicular to the orbital plane (vector L, vector V). It defines the
pitch axis.
3) Vector R completes the set of orthogonal axes. It lies in the plane defined by
vectors L and V and defines the roll axis. It does not coincide exactly with the
velocity vector due to the eccentricity of the orbit.
Axes Xs, Ys, Zs represents an orthogonal reference frame related to satellite
(satellite axes). Nominal attitude pointing consists of the best possible alignment
of this set of axes with the local orbital reference system.
With perfect geocentric pointing,
Fig.2.2.b. satellite position and velocity vectors

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Xs= -T
Ys= -R
Zs= L
2.3 ATTITUDE SENSORS AND ACTUATOR
Attitude control is exercise of control over the orientation of an inertial
frame of reference or another entity (the celestial sphere, certain fields, nearby
objects, etc)
Controlling satellite attitude requires sensors to measure satellite
attitude, actuators to apply the torques needed to reorient the satellite to a desired
attitude and algorithms to command the actuators based on 1) sensor measurement
of the current attitude and 2) specification of a desired attitude.
Many sensors generate outputs that reflect the rate of change of
attitude. These require a known initial attitude, or external information to use them
to determine attitude. Many of this class of sensor have some noise, leading to
inaccuracies if not corrected by absolute attitude sensors.
2.3. a. Sensors:-
1) Gyroscopes :-
Gyroscopes are devices that sense rotation of three-dimensional space
without reliance on the observation of external objects. The orientation of
oscillation is fixed in inertial space, so measuring the orientation of the
oscillation relative to the satellite can be used to sense the motion of the
satellite.
Fig.a.2.4 Gyroscopes

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2) Horizon Sensor/Earth Sensor :-
A horizon sensor is an optical instrument that detects light from the
‘limb’ of the earth’s atmosphere that is at horizon. Thermal infrared sensing is
often used, which senses comparative warmth of the atmosphere, compared to
the much colder cosmic background. This sensor provides orientation with
respect to the earth about two orthogonal axes. It tends to be less precise than
sensors based on stellar observation. Sometimes refer to as an earth sensor.
3) Sun Sensor :-
A sun sensor is a device that senses the direction to the sun. This can
be as simple as some solar cells and shaded, or as complex as a steerable
telescope, depending on mission requirements.
4) Gyrocompass :-
Similar to the way that a terrestrial gyrocompass uses a pendulum to
sense local gravity and force its gyro into alignment with earth’s spin vector
and therefore point north, an orbital gyrocompass uses a horizon sensor to
sense the direction to earth’s centre, and a gyro to sense rotation about an axis
normal to the orbit plane. Thus, the horizon sensor provides pitch and roll
measurement, and the gyro provides yaw.
Fig.2.5 Venera Sun Sensor

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2.3. b. Actuators:-
Attitude control can be obtained by several mechanisms,
1) Thrusters :-
Thrusters are the most common, as they may be used for station
keeping as well. Thrusters must be organised as a reaction control system
to provide tri-axial stabilisation. Their limitations are fuel usage, engine
wear and cycles of the control valves. To minimise the fuel limitation on
mission duration, auxiliary attitude control system , may be used to reduce
satellite rotation to lower levels, notable smaller, lower thrust venire
thrusters that accelerate ionised gases to extreme velocities electrically,
using power form solar cells.
2) Momentum/Reaction Wheels :-
These are electric motor driven rotors made to spin in the direction
opposite to that required to re-orient the satellite. Since momentum wheels
make up a small fraction of satellite mass and computer controlled, give
precise control. Momentum wheels are generally suspended on magnetic
Fig.2.6 Thrusters

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bearings to avoid bearing fraction and breakdown problems. To maintain
orientation in Three-dimensional space a minimum of two must be used,
with additional units providing single failure protection.
3) Solar Sails :-
Small solar sails (devices that produce thrust as a reaction force
induced by reflecting incident light ) may be used to make small attitude
control and velocity adjustments. This application can save large amounts
of fuels on a long duration mission by producing control moments without
fuel expenditure. For example- Mariner 10 adjusted its attitude using its
solar cells and antennas as small solar sails.
Fig.a.2.7 Reaction/ momentum wheels

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B. DEFENCE INSTRUMENTATION
The use of automatic control in defence has tremendously increased since the
World War II. During the World War II it became necessary to design and construct
automatic aeroplane pilot, gun positioning systems, radar tracking systems, and other
military equipments based on feedback control principle. This gave a great impetus to
automatic control theory.
There are several such type of systems in which the proper instrumentation is
necessary. Some of them have discussed here in defence chapter of this paper. They
are,
1. Missile launching and guidance system

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CHAPTER: 3
MISSILE LAUNCHING AND GUIDANCE
SYSTEM
3.1 SYSTEM WORKING:
The missile guidance can be divided into three phases: launching, intermediate
or midcourse guidance, and terminal guidance.
The missile launching and guidance system of Fig.B.1.1 is a sophisticated example
of military applications of feedback control. The target plane is sited by a rotating radar
antenna which then locks in and continuously tracks the target. Depending upon the position
and velocity of the plane as given by the radar output data, the launch computer calculates the
firing angle in terms of a launch command signal, which when amplified through a power
amplifier drives the launcher (drive motor). The launcher angular position is feedback to the
launch computer and the missile is triggered as soon as the error between the launch
Fig. b.3.1 Missile launching and guidance system

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command signal and the missile firing angle becomes zero. After being fired the missile
enters the radar beam which is tracking the target. The control system contained within the
missile now receives a guidance signal from the beam which automatically adjusts the control
surface of the missile such that the missile rides along the beam, finally homing on to the
target.
It is important to note that the actual missile launching and guidance system is far
more complex requiring control of gun’s bearing as well as elevation. The simplified case
discussed above illustrates the principle of feedback control.
Missile guidance system must determine three things,
1) Whether or not the missile is on beam axis,
2) If not, how far it is off the axis, and
3) Which way to go to get back on the axis.
There are five methods to approach the target.
3.2 HOMMING SYSTEM
As we have previously explained, missile guidance can be divided into three phases:
launching, intermediate or midcourse guidance, and terminal guidance. The proper
functioning of the guidance system during the terminal phase, when the missile is rapidly
approaching its target, is of extreme importance. A great deal of work has been done to
develop extremely accurate equipment for use in terminal-phase guidance.
Fig.b.3.2 Missile below the beam axis

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Basic principles: Some homing guidance systems are based on use of the
characteristics of the target itself as a means of attracting the missile. In other words the
target becomes a lure; in much the same manner as a strong light attracts bugs at night.
Just as certain lights attract more bugs than others, certain target characteristics provide
more effective homing information than others. And some target characteristics are such
that missiles depending on them for homing guidance are very susceptible to
countermeasures.
Types of missile response: When the control surfaces of the missile are activated by
one of the guidance systems, the missile is showing response to the guidance system. These
sources are:
3.2.A. SOUND. If we go through the frequency spectrum from low to high, we can list
systems in order of frequency and start in the audio (low) range. Sound has been used for
guidance of naval torpedoes, which home on noise from the target ship's propellers. But a
guidance system based on sound is limited in range. The missile or torpedo must use a
carefully shielded sound pickup, so that it will not be affected by its own motor noise. And
while the speed of a torpedo is low compared to the speed of sound, most guided missiles are
supersonic. Because of these limitations, no current missile uses a guidance system based on
sound.
3.2.B. RADIO. Most homing guidance systems use electromagnetic radiations. Radio waves
are used in one passive homing system. Homing is accomplished by an automatic radio
direction finder in the missile. This homing system is not restricted by weather or visibility.
3.2.C. RADAR. Although radar can be used for all classes of homing guidance, it is best
suited for the semi active and active classes. At present, radar is the most effective source of
information for homing guidance systems. It is not restricted by weather or visibility, but
under some conditions it may be subject to jamming by enemy countermeasure equipment.
3.2.D. HEAT. One form of homing system uses heat as a source of target information
(Fig.b.3.3). Another name applied to this system is INFRARED homing guidance. Heat
generated by aircraft engines or rockets is difficult to shield. In addition, a heated path is left
in the air for a short time after the target has passed, and an ultra-sensitive heat sensor can
follow the heated path to the object. One present limitation is the sensitivity of sensor units.

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As sensor units of higher sensitivity become available, infrared homing guidance will become
increasingly effective. Such systems will make it difficult to jam the homing circuits, or to
decoy the missile away from the target.
3.2.E. LIGHT. Now a day there is another homing system is used called LIRAD (Light
detection and ranging). A homing system could be designed to home on light given off by the
target. But, like any optical system, this one would be limited by conditions of weather and
visibility. And it would be highly susceptible to enemy countermeasures (fig.b.3.4).
Fig.b.3.3 Missile using heat-homing guidance
Fig.b.3.4 Missile using light homing system

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3.3LEAD ANGLE COURCE
The second method of approach to the target is called LEAD ANGLE course. It is
also known as a CONSTANT BEARING or COLLISION course. The trajectory of a
ground-to-air missile using this method of approach is shown in figure b.1.5.
Notice that the missile path from the launcher to the collision point is a straight
line. The missile has been made to lead the target in the same manner as a hunter leads a bird
in flight. In order to lead the target and obtain a hit, a computer must be used. The computer
continually predicts the point of missile impact with the target. If the target takes no evasive
action, the point of impact remains the same from launching time until the missile strikes.
Should the target take evasive action, the computer automatically determines a new collision
point. It then sends signals to the autopilot in the missile, to correct the course so that it bears
on the new collision point.
As shown in figure b.3.5, the collision point and the successive positions of
missile and target form a series of similar triangles. If the missile path is the longer leg of the
triangle, as it is in the figure, the missile speed must be greater than the target speed-but not
as great proportionally as with a zero-bearing approach.
Fig.b.3.5 Lead angle method approach

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The transverse acceleration required of a missile using the lead-angle approach is
comparatively small.
3.4COMPONENTS OF MISSILE GUIDANCE SYSTEM
There are several important components other than the missile and radar, in a
complete guidance system. As explained earlier in the text, a major part of the equipment is at
the launching site. We will describe individual components that might be found in a complete
system.
1) Tracking and guidance RADAR:
We have mentioned that the tracking radar furnishes information as to
the position of the target. All target position references are made with respect to
the scan axis of the tracking lobe. As we mentioned earlier, the tracking system is
automatic. After the tracking radar has acquired the target, tracking is maintained
without the help of a human operator. But the action of the tracking system is
monitored by an observer, who may take over and track the target manually if the
automatic system fails. At the monitor station, indications of target position
relative to the scan axis of the tracking beam are presented on two cathode-ray
tubes (CRT's). The target tracking and guidance RADAR is shown in Figure
b.1.6.
Fig.b.3.6 tracking radar antenna

29
2) Rotating reflector:
When the antenna rotates, as described above, the relative motion
between antenna and reflector produces a conically scanned beam. It is apparent
that the same relative motion can be produced by using a stationary antenna and
rotating the reflector about a point of its axis.
3) Reference Unit:
The comparison voltage is taken from the reference unit. This voltage
may be obtained from an outside source, or it may be taken from recorded
information that was put into the missile before launching. Actual operation of
the missile guidance controls takes place only when an error signal is present.
Note that the reference unit is connected to both the pitch (up-down) and yaw
(left-right) comparators.
4) Comparators:
The comparators are electronic calculators that rapidly compare
reference and signal voltages and determine the difference (error), if any,
between the two signals. It is possible for an error signal to be developed in the
pitch comparator while no error signal is developed in the yaw comparator.
Should this happen, the missile would be higher or lower than the desired
trajectory. The output voltage from the pitch comparator is then fed to the missile
automatic pilot.
5) Signal convertor:
The output of the sensor unit is an extremely small voltage. This voltage
is fed to a signal converter, which builds up the strength of the signal and
interprets the information contained in it. The output of the signal converter is
fed to the pitch and yaw comparators along with the signal from the reference
unit.

30
6) Autopilot:
The automatic pilot, or autopilot, operates missile flight controls in
much the same way as a human pilot operates airplane controls. The components
making up the autopilot assembly have been described elsewhere in this text. In
order to shift the flight controls, the autopilot must get "orders" from of error
signal voltages operate motors or hydraulic valves which in turn, operate the
flight control surfaces. There are two autopilots one for the pitch control surfaces
and other for the yaw control surfaces.
7) Rotating RADAR antenna and gun (launcher) positioning:
The rotating RADAR antenna not only detects the target but also helps in
guidance of missile. The gun (launcher) which automatically moves in
accordance with the target position triggers the missile. The positioning system
of both rotating radar antenna and gun is based on the feedback control using
servomechanism.
3.5 WEAPON CONTROL SYSTEM
This is the third major subsystem of guided missile. It encompasses both
the gun and missile fire control equipment. Because it is comparatively new, and
unique in gunnery, the weapons control system will be described in some detail in
Fig.b.3.7 Weapon control station

31
this and the succeeding section (fig.b.1.7).
Consider that an aircraft at 20,000 feet, travelling at 600 knots, will reach its
bomb-release point more than 10,000 yards from its target. Consider, also, that
this aircraft is travelling 20,000 yards a minute, and that the total problem may
consist of two, three, or more aircraft. Finally, recall that in order to destroy an
aircraft with a missile or a projectile it will be necessary to do all of the following
BEFORE the target aircraft reaches its bomb-release point:
(1) Detect the target aircraft with radar
(2) Identify the target as "friend or enemy"
(3) Designate to a selected director until the target is acquired
(4) Obtain a solution with director's associated computer
(5) Assign weapons to the tracking director on a priority basis, and position these
weapons in train and elevation
(6) Fire
(7) Wait until the projectile or missile reaches the point of impact with the target

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3.6Underwater Missile guidance
First of all, neither optical instruments nor radar can be used to detect submerged
submarines, since neither light rays nor radio waves can penetrate water sufficiently to make
these devices effective in locating underwater targets. Radar waves are reflected from the
ocean's surface, and light rays leaving the sub are dissipated after they travel a few yards.
Therefore sonar, a device which uses sound waves under water in much the same way that
radar uses radio waves, is used to detect the target and determine its present position.
Secondly, modifications to the basic fire control problem solution are necessitated by the
nature of the weapons and the manner in which these weapons are used. Surface and
antiaircraft guns can be trained and elevated to fire their projectiles at any target within range,
regardless of its position or the position of the firing ship. Thus the relative position of gun
and target at the time of firing is not critical, except insofar as it affects the gun settings. On
the other hand, the primary weapons used against submarines are depth charges and ahead
thrown missiles. These weapons are either dropped from the stern of the attacking ship, or are
thrown a short distance ahead of or to one side of the ship. Thus, in order to carry out a
Fig.b.3.8 Underwater missilr guidance

33
successful antisubmarine attack, it is necessary to maneuverer the ship into a position from
which the dropped or thrown missiles will sink to the submarine's future position. It is also
necessary to compute the correct time for firing.
The antisubmarine problem then becomes primarily a tactical one, in that the final outputs of
the fire control system are (1) the course along which the attacking ship must be steered, and
(2) the time to fire.

34
CHAPTER:4
Conclusion
There are several systems which are based on feedback control principle. Out of these those
which have illustrated in this seminar are the applications of this feedback control in space and
defence that are, thermal and attitude control of satellite, guided missile, etc. The paper also gives
knowledge of different control system components used in each space and defence related systems
discussed in this seminar.
For the satellite it is important to survive and function continuously for the periods up-to 15
years. Without proper instrumentation and control it is very difficult to survive satellite many years
for space mission. Continuous determination of satellite parameters such as temperature, attitude, etc.
is important to control them with desires manner.
Many defence appliances need proper instrumentation. For manufacturing, maintenance,
and calibration of these instruments used in fighter jets, navy ships etc, defence department needs an
instrumentation engineer. It is also necessary to design and construct autopilot, gun positioning
system, radar tracking system and other military equipment based on feedback control principle.
Thus the instrumentation field plays a dominant role in both space and defence.

35
REFERENCES
1) Reference book: Control Engineering by Nagrath and Gopal
2) http://spot4.cnes.fr/spot4-9b/thermic.htm
3) http://www.isro.gov.in
4) http://en.m.wikipedia.org/wiki/spacecraft_thermal_control
5) http://space.au.af.mi/factsheets/afscn.htm
6) http://www.esa.int/esaMI/Space_Engineering/SEMONFWNZf-1.html
7) http://www.arsospress.com/Resources/satellite/attitudeandorbitcontrolsubsis.htm
8) http://spot4.cnes.fr/spot4-9b/attitude.htm
9) http://en.m.wikipedia.org/wiki/Attitude_control_system
10) http://www.eugeneleeslover.com
11) http://www.hnsa.org/doc/Principles%20of%20Guided%20Missiles%20and%20Nucle
ar%20Weapons.htm
12) http://en.m.wikipedia.org/wiki/fighter_jet_instruments

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