guidance theory and applications (lecture 1) - iit kanpur and control/debasish... · guidance...

Guidance Theory and Applications (Lecture 1)

Debasish Ghose

Professor

Department of Aerospace Engineering

Indian Institute of Science

Bangalore

School on Systems and Control

IIT Kanpur, 4-9 August 2015

D. Ghose/Guidance Theory and Applications/IIT-Kanpur/2015

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Control Theory and Flight Vehicles

Flight path planning

Navigation

Guidance

Control


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Guided Missiles

A guided missile is a space-

traversing unmanned vehicle which

carries within itself the means for

controlling its flight path


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An Operational Definition

A guided missile is one which is

usually fired in a direction

approximately toward the target and

subsequently receives steering

commands from the guidance system

to improve its accuracy


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Categories of Guided Missiles

Surface-to-Surface Missiles (SSM)

Surface-to-Air Missiles (SAM)

Air-to-Air Missiles (AAM)

Air-to-Surface Missiles (ASM)


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Other Categories

Tactical

Strategic

A Fascinating History

Tipu Sultan and William Congreve


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Source: wikipedia

Nazi Germany, Rise of Hitler, and the Second World War


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Werner von Braun and the Peenemunde

Army Research Laboratories

The German V Rockets


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Operation Paperclip, Werner von

Braun in Alabama, and the American

Missiles, Rockets, and Space Program

Raytheon Company and the Lark,

Sparrow, and Hawk Missiles

Indian Missile Program (IGMDP)


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Components of Tactical Missiles

Airframe

Flight Control System

Guidance System

Fuze

Warhead

Propulsion System


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Airframe

Cruciform

Planform


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Further Classification of Airframes

Based on source of lift and location of control surfaces

B (body)

T (tail)

W (wing)

C (canard)

l (lift)

c (control)


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Some Examples


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Examples Contd.


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This airframe generates lift using its body and its tail surfaces

The control is provided by forces acting on the canards


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How is latax generated?

The guidance computer generates the guidance command.

This guidance command is fed into the flight control system which

deflects the control surfaces by an appropriate amount.

The control surface deflection produces a small lift force

Which deflects the lifting surfaces and the body of the missile about its

CG and changes the angle of attack.

This produces a large lift force that is responsible for the lateral

acceleration needed to turn the missile or cause it to maneuver.


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Commanded and Achieved Latax

What does it mean in terms of trajectory?


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Velocity Lateral Acceleration

Actual trajectory Arc of

a circle


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Flight Control System

Stabilizes the missile

Controls the missile in its flight

Ensures that the missile airframe responds effectively to guidance commands


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Missile Motion: Roll, Pitch, and Yaw


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Lateral Autopilots

The pitch and yaw autopilots are, in principle,

similar since they control the same kind of

missile motion.

They are functionally identical and go under

the common name of lateral autopilots.


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Attitude (angle) feedback loop

The innermost loop Feeds back the attitude angle, either in

the pitch plane or in the yaw plane, of the missile.

To generate a latax in one of these planes the missile

needs to have a certain angle of attack in the respective

plane.

This requires a change in the angular attitude of the

missile. The output of the angle feedback loop is the

achieved attitude angle.

This is subtracted from the desired angle and

the difference is used to generate the

command which serves to reduce this gap.

The angular orientation of the missile is

measured using an attitude gyroscope.


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Attitude rate feedback loop

Feeds back the angular rate at which the missile is

changing its angular orientation.

This feedback is used to damp the output of the system

and drive the angular rate to zero as the required

angular orientation is achieved.

Rate feedback improves the stability of a missile. The

angular rate is measured using a rate gyroscope.


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Latax feedback loop

Used to establish when the commanded latax

has been achieved

Also to generate appropriate inputs using the

difference between the achieved and desired

latax till they become equal.


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Two Loop Autopilot

One of the main concerns during the design of a tactical

missiles is its weight which has to be kept at a minimum.

One way to achieve some weight reduction is to

eliminate the attitude gyroscope and use the rate

feedback itself to generate the angle information. This is

done by integrating the angular rate over time.


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Roll Autopilot


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Roll Autopilot

Roll autopilots use the roll angular rate feedback to

generate roll angle information.

There is no latax feedback because the roll autopilot only

changes the roll orientation of the missile.

The rate feedback improves stability. This is important in

those missiles in which roll stabilization is required.


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Roll Autopilot without Roll Stabilization

There are some missiles in which roll stabilization is not

so important.

These missiles use roll autopilots which do not use rate

feedback.

However, note that though a rate gyro is still employed,

its output is not fed back directly. Rather, it is first

integrated to extract the roll angle information.


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Adaptive Gain Control

Why is this important?

Dither technique: Low frequency low amplitude

square wave signal

Inertial reference adaptive gain control:

Integrating to obtain velocity and altitude and

then use look-up tables


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Guidance Subsystem

Sensory organ and brain

Acquires and tracks target

During tracking it decouples the seeker motion from the

missile body motion and disturbances, thus improving

the stability of the seeker system.

It collects information about the target and generates

appropriate guidance commands to guide the missile to

an intercept.


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Components of guidance subsystem

Seeker antenna

Gimbal system which is attached to the missile body

and on which the seeker is mounted

A rate gyroscope for measuring the angular rate of the

seeker head

A signal processing unit

A guidance command computer

The seeker stabilization loop decouples the

seeker from the body motions which is fed

back at an appropriate position in the loop.


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An Everyday Example


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Components of Guided Missiles

Contd ….

Proximity Fuze

Propulsion System

Warhead


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Proximity Fuze

The missile comes very close to the target. This event

is sensed by the missile and its warhead is detonated.

The proximity fuze performs this function.

The kind of proximity fuze which is used in most

tactical missiles are of the active kind.


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RF Proximity Fuze

The RF proximity fuze consists of two CW

radars placed diametrically opposite on two

sides of the missile, a little behind the

guidance subsystem.

The main-lobes generate a saucer-shaped

pattern around the missile.


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How does it work?

When the target enters this pattern, the

reflected energy is received by the

receiving antennas.

The doppler frequency is extracted from

this signal and is used to generate the fuze

pulse.


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Range Cut-off

An in-built range cut-off suppresses reflected signals

from objects at a larger distance than the lethal

radius of the warhead.

This ensures that no fuze pulse is generated for

signals reflected from the ground or the sea or from

other nearby objects like foliage, buildings, etc.


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Other Checks to Avoid False Alarms

A bandpass filter to ascertain whether the signal is within a

specified bandwidth (sea skimming missiles).

A threshold detector to check if it satisfies the minimum level

of reflected signal which identifies a target.

The threshold detector suppresses second-time-around

echoes and eliminates ambiguous range measurements.


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Laser proximity fuze Uses a laser source as the active transmitter and an infra-red

detector as the receiver.

High frequency energy gives very accurate information about

target.

Four emitters are mounted around the missile at 90 degrees,

each producing a sector-shaped pattern with 90 degrees.

The combination produces a circular pattern of a definite radius

and very small thickness.


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Different patterns

Using different number and arrangement of

transmitters, various laser beam patterns can be

obtained.

Using these, warhead explosion can be timed suitably,

depending on the time instants at which the target

intercepts the two beams, to ensure that the blast

occurs nearer to the center of the target.


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Operation of Laser Fuze

A receiver is mounted next to each emitter.

The signal received from the target is used to

generate the fuze pulse.

Due to its inherent accuracy the possibility of false

alarm in laser fuzes is very small compared to the RF

fuze.


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Propulsion System

Provides the required thrust to the missile.

Two phases in missile propulsion:

Boost: Provides high level of missile acceleration

over a relatively short period of time (1-15 secs)

Sustain: Maintains the missile speed at a desired

level for most of the remaining missile flight.


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Combinations

Combinations of boost and sustain propulsion

All-boost

Boost-sustain

All sustain

In principle, the all-sustain configuration is never used.

Even in the air-to-air missile, which does not have a booster

motor, a short boost is provided by the sustainer motor itself.


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All-boost Boost-sustain All sustain


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Types of Propulsion

The booster motor is typically a solid propellant

motor.

The sustainer motor could be solid propellant one or a

jet engine.

Some modern missiles nowadays use integrated

rocket-ramjet propulsion.


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Warhead

Consists of shell, explosives, and a detonator

The fuze pulse activates the detonator which in turn triggers the

explosive.

The shell breaks into fragments which are propelled outward in a 60-

90 degrees spread and penetrates target components.

Basic fragmentation type of warhead

Continuous-rod warhead

Annular blast fragmentation warhead

Selectively aimable warhead


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End of Lecture 1 THANK YOU

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