Role of instrumentation and control in space and defence

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 ofBachelor of Technology

inInstrumentation and Control

By

Bhushan Pradeep Walnusakar(GR NO: 132054 )

Under the guidance ofProf. A. B. Kadu

Department of Instrumentation EngineeringVishwakarma Institute of Technology, Pune-411037

December – 2014

1

ROLE OF INSTRUMENTATION IN SPACE AND DEFENCE

BANSILAL RAMNATH AGARWAL CHARITABLE TRUST’SVISHWAKARMA 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

GuideProf. Sujit M. Deokar

Co-ordinator

Prof. Pramod M. KanjalkarHead of Department

2


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

3


AbstractThis 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.

4


Contents

Acknowledgement

Abstract

Table of Contents

.....................................................................................................................................vi

List of Tables vii

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

5


CHAPTER:4 CONCLUSION………………………………………………………..34

REFERENCES……………………………………………………………………….35

6


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

7


LIST OF TABLES

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

8


A. SPACE INSTRUMENTATION:- In this section we will study and try to understand thermal and attitude control of

satellite.

CHAPTER 1THERMAL CONTROL OF SATELLITE1.1PURPOSE 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.

1.2 REQUIREMENTS

9

Fig.a.1.1 Effect of radiations on satellite


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.

EQUIPMENTON-ORBIT TEMPERATURE RANGE ((C0

QUALIFICATIONRANGE (C0)

Minimum during non-operating phase

Operating OperatingElectronic 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 +50Solar generator

-180 -165 +70 -175 +80

Propellant lines

0 05 0 -10 +60

Momentum wheels

-40 -15 45 -25 +55

1.3 HOW DOES THERMAL CONTROL SYSTEM WORKS?

10

Table.a.1.2 Temperature specifications for the onboard parts


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).

11

Fig.a.1.3.1 Multi-layer insulation


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.

12

Fig.a.1.3.2 Block diagram of satellite thermal control

Network of thermal sensor

Controller (Computer)

Heaters/ Coolers

Satellite thermo-dynamics

Disturbances


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

13

gas flow


• 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

14


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

15

Fig.a.2.1Path of satellite called ‘orbit’


and desired attitude, and some mechanism by which the attitude error can be

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

16


between the satellite and the centre of the Earth, also called the “geocentric direction”

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 vec-

tors L and V and defines the roll axis. It does not coincide exactly with the velo-

city 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.

17

Fig.2.2.b. satellite position and velocity vectors


With perfect geocentric pointing,

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.

18

Fig.a.2.4 Gyroscopes


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

19

Fig.2.5 Venera Sun Sensor


normal to the orbit plane. Thus, the horizon sensor provides pitch and roll

measurement, and the gyro provides yaw.

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 :-

20

Fig.2.6 Thrusters


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

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.

21

Fig.a.2.7 Reaction/ momentum wheels


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

22


CHAPTER: 3

MISSILE LAUNCHING AND GUIDANCE

SYSTEM3.1 SYSTEM WORKING:

The missile guidance can be divided into three phases: launching, intermediate

or midcourse guidance, and terminal guidance.

23Fig. b.3.1 Missile launching and guidance system


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

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.

24

Fig.b.3.2 Missile below the beam 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.

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

25


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.

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).

26

Fig.b.3.3 Missile using heat-homing guidance


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

27

Fig.b.3.4 Missile using light homing system

Fig.b.3.5 Lead angle method approach


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.

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.

28


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

29

Fig.b.3.6 tracking radar antenna


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.

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

30


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

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

31

Fig.b.3.7 Weapon control station


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

32

Fig.b.3.8 Underwater missilr guidance


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

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.

33


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.

34


REFERENCES

1) Reference book: Control Engineering by Nagrath and Gopal2) 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%20Nuc -

lear%20Weapons.htm12) http://en.m.wikipedia.org/wiki/fighter_jet_instruments

35

http://en.m.wikipedia.org/wiki/fighter_jet_instruments

http://www.hnsa.org/doc/Principles%20of%20Guided%20Missiles%20and%20Nuclear%20Weapons.htm

http://www.hnsa.org/doc/Principles%20of%20Guided%20Missiles%20and%20Nuclear%20Weapons.htm

http://www.eugeneleeslover.com/

http://en.m.wikipedia.org/wiki/Attitude_control_system

http://spot4.cnes.fr/spot4-9b/attitude.htm

http://www.arsospress.com/Resources/satellite/attitudeandorbitcontrolsubsis.htm

http://www.esa.int/esaMI/Space_Engineering/SEMONFWNZf-1.html

http://space.au.af.mi/factsheets/afscn.htm

http://en.m.wikipedia.org/wiki/spacecraft_thermal_control

http://spot4.cnes.fr/spot4-9b/thermic.htm