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