Note: Descriptions are shown in the official language in which they were submitted.
TERMINALLY GUIDED WEA]?ON DELIVERY SYSTEM
1 BACKGROUND OF THE INVENTION
1. Field of the Invention
-
This invention relates to weapon systems,
and more specifically to weapon systems which track
maneuvering targets and launch terminally guided
projectiles toward targets.
2. Description of the Prior Art
One type of weapon system which is intended to
destroy enemy ground-based or airborne targets uses
as weapons unguided projectiles or missiles against
targets with relatively low target acceleration capability.
other systems have been developed which require a means
for tracking the target, a means for tracking a projectile
or missile initially aimed at the target, and a means
for reducing or eliminating the miss vector between
the target and the projectile or missile. The means
for reducing or eliminating the miss vector provides
guidance to the projectile or missile so that the projec-
tile or missile will proceed to either hit the target
directly or explode in such close vicinity to the target
lethal zone so as to fatally damage the target. Most
anti-airborne and anti-ground based target weapon
systems provide continuous projectile or missile trajectory
correction whereby information is sent to the projectile
or missile at some predesignated data rate, so as to
alter the course of the projectile or missile, and energy
5~
1 resources of the projectile are used throughout the
course of the flight of the projectile or missile, or
for some relatively lengthy terminal phase of the flight
of the projectile, to maneuver the projectile or missile
to within the lethal zone at the end of the flight of
the projectile or missile. Furthermore, when a missile
is used, guidance and control systems on board the missile
are often actively employed in obtaining information
about the target and/or computing corrections to its own
flight path. Such guidance and control systems on board
the missile greatly increase the cost of designing,
manufacturing, testing, and maintaining the missile.
Although the weapon guidance technique hereinbefore
described has been demonstrated to be effective against
relatively slowly accelerating targets, serious diffi-
culties have arisen in attempting to eliminate targets
which can rapidly accelerate as the weapon enters its
terminal phase of the trajectory. When the weapon has
been directed throughout its entire flight to the pre-
dicted location of the target, and uses most of itsenergy resources therefor, a rapid maneuver by a target,
wherein the target severely deviates from its expected
flight path, near the end of the flight of the weapon,
cannot generally be compensated, since system delay
times prevent the system from responding to rapid changes
and sufficient energy resources to maneuver the weapon
are no longer available to correct for extreme changes
in the miss vector during the terminal phase of the
flight of the weapon.
Modern weapon systems having purposes similar to the
invention herein disclosed have been investigated and
designed in the past two decades. A gun-fired missile
system concep-t commonly referred to as POLCAT, was
investigated by the Bulova Research and Development
Laboratories. The POLCAT concept of weapon delivery
~.2~L~5~3
1 employs a gun-launched anti-tank weapon with terminal
trajectory correction using a semiactive guidance technique
and impulse control. The POLCAT weapon system concept
employs a frame-fixed target seeker for guidance and a
single~impulse applied at the center of gravity normal
to the longitudinal axis of the weapon for trajectory
correction. The system operates by firing a missile, in
a manner similar to that of a conventional gun system,
when a target is engaged. In one version of POLCAT,
an illuminator in the missile transmits pulsed radiation
with a narrow radiation beam throughout the flight,
which is required because ground targets, in general,
do not have sufficiently intense or discrete signature.
Correction of the missile trajectory is initiated when a
line-of-sight control angle is determined which indicates
an increasing miss of the target. By this technique,
near misses are controlled close to the target and larger
deviations are controlled further from the target, because
a threshold angle for trajectory control is a constant
value. The missile incorporates a forward-looking receiver
that determines the pertinent angles to the target, so
as to provide data to alter the trajectory of the missile.
The DRAGON missile system is a light-weight system
designed to be carried by a foot soldier and fired against
tanks or other targets within an approximate range of
1,000 meters, and intended for use aQ a medium anti-tank
missile at the infantry platoon level. The system con-
sists of a cylindrical missile, a portable launcher for
firing the missile, a sighting means or "tracker" for
visually following the missile in flight after launch,
and appropriate electronic means for correcting the
flight path of the missile during the flight from the
launcher to the target. The missile is fired from a
tubular launcher after the launcher is aimed at the
designated target. The missile is required to be of a
5~.~
1 proper aerodynamic configuration and must rotate
about its longitudinal axis in flight to maintain
flight stability. The rotation, as well as aerodynamic
stability of the missile, is provided by fins located in
the aft area of the periphery of the missile. Guidance of
the missile during flight is provided in the following
manner. When the missile is launched, the soldier who
fired the weapon sights the missile through an optical
viewer throughout its flight to the target. The course
of the missile is automatically corrected in flight by
keeping the view of the missile as near as possible to
the cross hairs of the optical viewer through which the
soldier sights the missile and computing the deviation
of the missile from its course to the target. The system
lS is designed to keep the missile on a direct line-of-sight
to the target, rather than having a fixed trajectory
from the point of launch to a correction point near the
target. The missile is kept on course by discharging (by
explosion or detonation) small "thrusters" or jets which
are built into the periphery of the missile from front to
rear and discharged at an angle to the longitudinal axis
of the missile. The timing and direction of application
of the thrusters determine the direction of motion of the
missile throughout the flight of the missile. The thrust-
ers are fired electronically in the following manner. Alight source is mounted in the tail of the missile. The
beam of light from the light source impinges on an optical
detector in the tracker component which senses whether
the missile is above, below, to the right, or to the left
of the line-of-sight from the tracker to the target.
Depending upon the quadrant of the detector upon which
the beam impinges, a signal is sent over a wire to the
missile to fire one or more of the thrusters at a desig-
nated time and in a designated sequence so as to correct
for deviations of the missile from the line-of-sight. The
1 wire over which the signal is transmitted is wound on a
spool, which is mounted on the rear of the missile, and
the wire feeds out as the missile moves toward the target
and maintains the connection between the tracker and the
missile throughout the flight of the missile. The cost
goal of the weapon round is $2,000-$2,500 and for the
tracker of the missile is $8,000-$10,000, according to
Aviation Week & Space Technology, "Program Slip Delays
Export of Dragons," February 3, 1975.
SUMMARY OF THE INVENTION
The advantage of the present weapon system invention
in relation to prior art ground-based or airborne weapon
systems is the ability to provide highly accurate perfor-
mance against maneuvering airborne or ground targets withthe use of a relatively inexpensive artillery launched
round, for example. The need for an expensive weapon
and the control thereof through the entire course of
flight of the weapon is eliminated. Furthermore, the
miss vector between the weapon and the target is deter-
mined as a function of predetermined ballistic-trajectory
computations and the position of the target is determined
by radar tracking of the target. Moreover, the miss
vector is reduced during the terminal stage of flight of
the weapon by sending a single signal to the weapon to
fire thrusters located on the periphery of the weapon.
The angular orientation of the weapon, with respect to
the longitudinal axis of the weapon, governs the timing
and sequence of the firing of the thrusters so as to
force the weapon toward the target. The angular orienta-
tion of the weapon is determined from the transmission
of beacon signals from the rear of the weapon via a
polarized antenna which i5 canted by a few degrees with
1 respect to the longitudinal axis of the weapon. A
one-time correction signal is sent ~rom a ground-based
fire control system causing thrusters located on the
periphery of the weapon to rapidly detonate in a particular
sequence, so as to force the weapon to destroy the target
by exploding within a lethal zone surrounding the target.
The timing of the correction signal is based upon an
estimated position of the weapon ~as computed from bal-
listics), an estimate of the angular orientation of the
weapon (as derived from signals transmitted from a canted
antenna located at the rear of the weapon), and an estimate
of the position of the target at the end of the trajectory
of the weapon (as derived from radar tracking).
In keeping with the principles of the present inven-
lS tion, the purposes are accomplished with the unique
combination of a fire control system with a radar target
tracking system, and a weapon having small thrusters
mounted on the periphery thereof and with a small
beacon transmitter which is tracked by the ground-based
radar system. At the appropriate point in the trajectory
of the weapon, a terminal maneuver is executed by the
weapon by sequentially firing small thrusters located
around the periphery at the center of gravity of the
weapon.
Accordingly, it is a general purpose of an aspect of the present
invention to provide an improved weapon delivery system.
A purpose of an aspect of the invention is to provide a
target weapon system which uses a relatively inexpensive
weapon.
A purpose of an aspect of the invention is to provide
weapon system having day-night and zero visibility con-
ditions (including fog, smoke, and haze), all-weather
capability.
~2~1~5~
A purpose of an aspect of the invention is to
provide an improved anti-airborne or anti-ground target
weapon delivery system.
An aspect of the invention is as follows:
A weapon system for providing terminal guidance to
a projectile which rotates about its longitudinal axis
during *light and which responds to a command signal so
as to modify the flight path in such a manner as to
decrease the magnitude of the miss vector between the0 projectile and a target, said weapon system comprising:
means for tracking the target and providing
tracking signals indicative of the location of the
target;
means for launching said projectile;
means for computing the location of said projectile
after launch and for providing trajectory signals
indicative of the trajectory of said projectile;
a canted linearly polarized antenna and a
transmitter beacon both carried ~y said projectile such
that transmitter beacon energy is transmitted from said
antenna, whereby said energy is polari~ation modulated
as a function of the angular orientation of said
projectile;
means, responsive to the polari~ation modulated
transmitter beacon energy, for measuring the relative
angular orientation of said projectile about said axis;
and
means responsive to said tracking signals, said
trajectory signals and to the measured angular
orientation of said projectile for computing an
uncorrected miss vector and for providing a command
signal, during the terminal phase of flight of said
projectile, so as to cause a decrease in the magnitude
of the miss vector.
~L2~r~dS~
7a
BRIEF DESCRIPTION OF THE DRAWINGS
The following specification and the accompanying
drawings describe and illustrate an embodiment of
the present invention. A complete understanding of the
invention, including the nove:L features and purpose
thereof, will be provided by consideration of the speci-
fication and drawings.
FIG. 1 illustrates typical battlefield encounters
wherein the weapon system is employed, depicting a tank
with a yround-based fire control system (including a
radar system), a weapon, and three kinds of airborne
targets;
FIG. 2 is a schematic block diagram of the weapon
delivery system depicting the elements of the invention;
FIG. 3 is a diagram which illustrates the air defense
weapon delivery concept involved with the invention indi-
cating the flight path of the weapon and the airborne
target;
FIG. 4 depicts a typical change in flight paths of
a target and a weapon to demonstrate the guidance concept
of the weapon system~
FIG. 5 depicts in further detail the change in
flight path of the weapon as a result of thrusters acting
on the weapon
FIG~ 6 depicts the respective antenna fields of the
antenna associated with the fire control system and the
antenna associated with the weapon;
FIG. 7 depicts the envelope of the beacon signal
sent from the weapon to the ground-based radar system;
5~ ~
1 FIG. 8 depicts the modulation of the beacon signal
sent from the weapon to the ground-based radar, wherein
the antenna on the weapon is canted by a few degrees
relative to the longitudinal axis of the weapon;
S FIG. 9 further illustrates the air defense weapon
delivery concept by depicting the weapon, having forces
acting thereon by thusters located on the periphery of
the weapon, with the antenna located at the rear thereof
and the canted orientation of the antenna with respect to
the longitudinal axis of the weapon; and
FIG. 10 is a cross-sectional view of the weapon
depicting the manner in whch the thrusters are mounted on
the periphery of the weapon.
DETAILED DESCRIPTION OF THE INVENTION
1. General Description of the Weapon System
The use of the present invention is depicted in
FIG. 1. FIG. 1 illustrates fire control system 11 with
radar system 15 of the weapon system mounted on tank 10.
Tank 10 is located on a typical battlefield. Launcher 12
is a part of tank 10 and is used to launch the weapon
associated with the invention. As a part of fire control
system 11, radar system 15 is shown to be tracking, by
way of antenna tracking beam 17, various enemy airborne
targets. FIG. 1 depicts helicopter 20 as such a target;
low flying jet aircraft 21 as such a target; and missile
22 as such a target. Although only airborne targets are
shown, the weapon system has the capability of eliminating
ground targets with the use of a suitable radar system 15
and weapon 16.
FIG. 1 also pictorially illustrates the capability
of radar system 15 to track multiple targets. Radar
system 15 is shown to be simultaneously tracking the here-
inbefore described targets, viz., helicopter 20, low
flying jet aircraft 21, and missile 22.
5~;
1 2. Elements of the Weapon System
FIG. 2 is a schematic block diagram of the weapon
delivery system of the invention including the weapon,
depicting the elements of the :invention and the inter-
actions thereof, as indicated by data interfaces 51 to
58. FIG. 2 used in conjunction with FIG. 3 describes
the weapon system of the present invention.
2(a) Radar System
Radar system 15 is a conventional tracking radar
used to locate, acquire, and track airborne targets,
such as the U.S. Roland II, the APG 63 radar system used
on the F-15 military aircraft or the APG 65 radar system
used on the F/A-18 military aircraft; an advanced artillary
round tracking radar such as the TPQ 36 or TPQ 37 can
also be used. Radar system 15 is used to evaluate the
range, relative velocity, and angular position of the
weapon. It should be noted that any sensor which
accurately measures range can be used, such as a laser,
as well as a conventional microwave radar. On data
interface 51, the following data is transferred from
radar system 15 to fire control computer 14: the position
of target 21, in terms of the range and line-of-sight
angle from radar system 15 to target 21; the velocity of
target 21 relative to radar system 15; the acceleration
of target 21 in the direction of the line-of-sight from
radar system 15 to target 21; the acceleration of target
21 in the direction normal to the line-of-sight; and the
angular rate of the line-of-sight to target 21. Radar
system 15 also has a data interface 52 to weapon attitude
angle measurement device 13. An appropriate radar system
may be used to track maneuvering ground targets, when so
required.
1 o ~ 5~
1 2(b) Fire Control Computer
Fire control computer 14 calculates significant
quantities for fire control system 11 based upon informa-
tion from radar data system 15 and attitude angle
S measurement device 13. Fire control computer 14 receives
data input on data interface 51 from radar system 15 and
on data interface 53 from measurement device 13. Fire
control computer 14 determines the direction in which
launcher 12 should be pointed for weapon 16 to be launched
without terminal correction to intercept target 21,
assuming that target 21 continues on its trajectory 32
without making a terminal maneuver, and computes the lead
angle for launcher ballistics. After weapon 16 has been
launched, fire control computer 14 continues to predict
the future position of weapon 16 and compare this pre-
dicted position to the predicted target position infor-
mation by using the data obtained from radar system 15.
As previously explained, if target 21 maneuvers so that
weapon 16 cannot expect to intercept the target, weapon
16 will maneuver upon the receipt of a command signal
causing weapon 16 to intercept target 21 to within a
lethal æone surounding target 21. The time tc for com-
manding the initiation of the maneuver depends upon the
miss vector e, the roll angle of the longitudinal axis
of weapon 16 and the roll rate about the longitudinal
axis of weapon 16, which are determined by fire control
computer 14. At tha precise time tc that the maneuver
is required by weapon 1~, a command signal is initiated
on data interface 55 from fire control computer 14 to
command link 19, whereby the signal is transmitted to
weapon 16, as indicated by data interface 56.
11 ~2~5~
2(c) Measuring Device
Measurement device 13 employs a unique use of a
conventional scanning tracking system, such as those
conventional scanning tracking systems which are used on
radar tracking systems. Measurement device 13 has a
receiver used ~o monitor weapon 16 spin attitude. In
conjunction therewith, measurement device 13 has a highly
polarized antenna which receives a signal sent from
antenna 25 located at the rear of weapon 16 (as depicted
in FIG. 9) and directed in the vicinity of tank 10. The
signal indicates the relative rotational orientation
about the longitudinal axis of weapon 16, which is
further explained infra with reference to FIGS. 6 and 9.
measurement device 13 also supplies command link 19 with
a local oscillator (LO) reference signal, as indicated
by data inteface 54.
2(d) Launcher
Launcher 12 generally consists of a slaveable
gimbaled gun mounted on tank 10. Information to correctly
position launcher 12 is provided from fire control com-
puter 14 on data interface 57. The information so provided
consists of the commanded angle information to position
launcher 12 and any aiding information that is necesary
to drive launcher 12 at the large angular rates which may
be necessary. ~eapon 16 is fired in the direction in
which launcher 12 is pointing which is so indicated as
data interface 58.
2(e) Command Link
Command link 19 transmits the one-time command signal
to weapon 16. Command link 19 obtains the information
from fire control computer 14 on data interface 55. The
information on data interface 55 consists of the one-time
command to fire the initial thruster on the periphery of
weapon 16 and the time interval for firing the subsequent
thrusters. Command link 19 transmits this information on
data and interface 56 to weapon 16 in coded form.
5~
12
1 2(f) Weapon
Weapon 16 is a terminally guided artillery round.
Weapon 16 is similar to any other air defense round with
the exception that high explosive side thrusters are
located on the periphery around the center of gravity and
weapon 16 contains a receiver and logic system to detonate
the thrusters to impart a single, fixed magnitude lateral
velocity upon command from fire control system 11 via
command link 19. Weapon 16 is fired from the smooth
bore of launcher 12 using a plastic carrier called a
sabot. The plastic carrier is separated from weapon 16
immediately after it leaves launcher 12 by wind force.
Weapon 16 also has fins located on the periphery of the
weapon in order to induce spin, by canting the fins
with respect to the longitudinal axis of weapon 16,
after it leaves launcher 12, in a conventional design.
Spinning weapon 16 provides a more stable ballistic
trajectory than a conventional artillery round. ~eapon
16 also has a proximity fuse and a blast fragmentation
type warhead, which is detonated by the proximity fuse.
This combination allows a high probability of hitting the
target without actually intercepting the target. ~xplo-
sive thrusters on the periphery of weapon 16 provide the
means for the rapid maneuver of weapon 16 at the terminal
phase of the flight to eliminate target 21. The maneuver
of weapon 16 occurs in response to the command signal from
command link 19 when weapon lS has the correct angular
orientation. This command signal could be mechanized by
a special modulation added to the tracking radar radiation.
The explosive thrusters are detonated in a predetermined
sequence as weapon 16 spins so as to impute a fixed
lateral velocity (Vc) to weapon 16. Weapon 16 further
has a command link receiver and an intervalometer which
1 will fire the initial thruster of weapon 16 on command
and the subsequent thrusters at a commanded interval.
Weapon 16 has a radio frequency (RF) diplexer in order
to permit it to transmit and receive signals simultaneously
on different signal frequencies.
3. Weapon Delivery Concept
The weapon delivery concept of the present invention
is described with reference to FIGS. 3, 4, 5, and 9.
FIG. 3 pictorially illustrates in general the weapon
delivery concept involved with the invention. Radar
system 15 associated with fire control system 14 is shown
mounted on tank 10. Radar system 15 is tracking target
21 with antenna tracking beam 17. Target 21 is traversing
flight path 32. Target 21' represents target 21 at
another location on flight path 32. Weapon 16 has been
launched from launcher 12 and is traversing flight path
30. An error vector e is the magnitude of the distance
between weapon 16 and target 21 and the relative orienta-
tion of said distance, as indicated by angle ~, at any
instant in time. This distance is determined from the
combination of radar measurement of the location of target
21 and ballistic prediction calculations of the location
of weapon 16.
The vehicle used to carry launcher 12 and radar
system 15 is depicted as tank 10.
Tank 10 is one of a variety of existing state-of-
the-art military tanks. Examples thereof are the M48
tank, the M60 tank, and the Ml Main Battle Tank, which
are used by the United States Army.
FIG. 3 also depicts the kinematics of weapon 16 for
one point on trajectory 30 of weapon 16.
VL is the velocity vector of weapon 16 due to
accelerations induced by forces acting on weapon 16 as it
flies on trajectory 30; such forces include the initial
firing velocity from launcher 12, drag on the weapon,
wind, and gravity acting on the weapon.
5~6
14
Vc is the correction velocity vector when initiated.
Operationally, the guidance of weapon 16 involved
with the weapon delivery concept is explained in further
detail with reference to FIGS. 3, 4 and 5. Weapon 16
traverses flight path 30 having a rotational rate about
its longitudinal axis of between 50 revolutions per second
(r.p.s.), and 1000 r.p.s., but typically 100 r.p.s. A
beacon signal is transmitted by weapon 16 using antenna
25 located at the rear of weapon 16 (as depicted in FIG.
9) and directed toward radar system 15. Antenna 25 is
mounted at the rear of weapon 16 so as to be canted by 2
to 3 degrees with respect to the longitudinal axis of
weapon 16. The beacon transmitted signal is used to
indicate the relative angular orientation of weapon 16.
The beacon signal also could be used to track the projec-
tile to thereby improve the accuracy of the weapon system.
In order for the control signal which is sent from weapon
control system 11 to weapon 16 to properly initiate the
rapid firing seguence of the thrusters located on the
periphery of weapon 16, knowledge of the actual angular
orientation of weapon 16 when the firing sequence of the
thrusters is initiated is crucial in order for weapon 16
to eliminate target 21. Terminal flight path correction
to reduce error vector e, wherein w~apon 16 rapidly accel-
erates so as to direct the velocity in the direction oftarget 21, is employed so as to take into account any
large maneuvers produced by high accelerations by target
21, which may occcur any time after launching weapon 16
and before sending the control signal from firs control
system 11 to weapon 16. The direction of the velocity
vector is controlled by synchronizing the command signal
with the spin attitude of weapon 16, and tc is so
computed.
-15- ~25~
3(a) Computation f tc
In general, the computation of the tc involves
computing the time when the thrusters on the periphery
of weapon 16 are to be detonated, which occurs when the
product of the lateral correction velocity (Vc) and tc
equals the miss distance (Mc), which is the direct
linear distance between weapon 16 and target 21. The
command time tc is delayed by a vernier amoun-t until
weapon 16 is at the proper spin attitude to poin-t -the
lateral velocity at the proper angle, as determined by
fire control computer 14. Thus from miss distance Mc,
as derived from error vector e, tc, which is the optimum
time to detonate the thrusters located on weapon 16, is
computed to be equal to the computed miss distance (Mc)
divided by the correction velocity (Vc). A time delay
is included to account for computational processing.
FIG. 3 illustrates the nature of the error vector e
at the time tc when the command signal has been received
by weapon 16. Error vector -e is shown to have a miss
component Mc and an angle ~, both measured from a local
plane which includes weapon 16. Target aircraft 21 is
shown to be executing a high-acceleration, rapid
maneuver, producing trajectory 32, just prior to tc.
The timing of the sending of the control signal from
fire control system 11 to weapon 16 also depends upon
the value of the magnitude of error vector e. Error
veetor e is computed at any instant in time while weapon
16 is flying on trajectory 30 from the position
coordinates of target 21 and weapon 16. The position of
target 21 is estimated from measurements made by radar
system 15 which uses radar search, acquisition and
tracking techniques well known in radar art to locate
and track the position of target 21. The position of
weapon 16 is estimated by using ballistics tables and
calculations well known in the art, as documented in the
U.S. Navy report,
r ~ 6
16
1 A Ballistic Tra~ectory_Algorithm for Digital Airborne
Fire Control (A.A. Duke, T.H. Brown, K.W. Burke, R.B.
Seeley), NWC Technical Publication 5416, September 1972,
based upon the nature of the weapon used; the initial
angular orientation of the longitudinal axis of the
launch; the initial velocity of the weapon; the air
density; and local wind.
In particular, the computational requirements for
tc can be de~onstrated mathemat:ically, first by defining
the following relevant quantities:
Error vector, _xe
e(t) = Ye
l Ze
Weapon position vector,
W(t) = Yw
, _Zw,
20 Target position vector, ~xT
T(t) = YT
ZT
Weapon velocity vector, -vxw
Vw(t) = o
Vzw~gt
Target velocity vector, vxT
YT(t) = vyT
LVzT
Correction velocity vector, O
VC(t) = vyc cos ~wtc
VZc sin ~wtc .
~ ~c~ 6
17
1 K, kill radius of warhead associated with weapon 16,
which is associated with the zone aro~nd the target, in
three dimensions, wherein when the weapon warhead explodes,
it is in such close vicinity of the target that the target
is rendered fatally damaged;
~w~ angular rotational (or spin) rate of weapon 16;
g, constant of gravitational acceleration;
t, time.
0 Then, for the error vector
T = W + e, or
_
e = T - W.
From knowing that
_ t _ t _
W = j VWdt + ¦ VC(t, tC)dt,
o o
it follows that
t _ t _ t _
e = J Vt(t)dt ~ ¦ VW(t)dt - J Vc(t, tC)dt.
o o o
Substituting, and integrating as above indicated,
25 ~ xe ~ vxT ~ Vxw t
Ye = vyT t - Vyc cos ~wtC t _ O
Ze VzT VZc sin ~wtc v t _ dg2
Therefore,
Xe = vxT t - vxw t
Ye = VyT t - (t-tC) Vyc cos ~wtC
Z = VzT t ~ (t~tc) Vzc sin ~w tc ~Vzw t ~ 2
18
1 Or alternatively,
e(t) = VTt - Vct - W(t)
It is required that
S ¦e(t)¦ < K.
for tc.
At time tc, upon receipt of the command signal by
weapon 16, the thrusters located on the periphery of
weapon 16 are fired in rapid predetermined sequence so as
to decrease the magnitude of error vector e and intercept
or come within a lethal zone of target 21. The firing
sequence of the thrusters around the periphery of weapon
16 is performed in a predetermined order, so that the only
control variables contributing to the accuracy of the
hit are the angular orientation and firing rate of the
thrusters of weapon 16 at the time the control signal is
sent from fire control system 11 to weapon 16. Generally,
the firing sequence of the thrusters is initiated when
weapon 16 is within approximately the last second of
flight on trajectory 30, and typically when weapon 16 is
within the last one-half second of flight.
3(c) Weapon Flight Path/Trajectory Alteration
FIG. 4 depicts the alteration in flight path 30 of
weapon 16 resulting from the capability of fire control
2~ system 11 to track, using radar system 15, a rapid accel-
eration maneuver by target 21 on flight path 32. Fire
control system ll using radar system 15 is thereby capable
of predicting the change in the flight path of target 21
to fli.ght path 32 from flight path 32', which would have
been the flight path of target 21 had target 21 not pro-
duced a rapid acceleration maneuver at point 33 on its
flight path. Subsequent to target 21 altering its flight
path at point 33, fire control system 11 sends a command
signal to weapon 16 at time tc so as to detonate the
thrusters located at the periphery of weapon 16 in a pre-
designated order, causing flight path 30 of weapon 16 to
5~
19
1 be altered to flight path 34 at point 31 on the flight
path of weapon 16. Time tc is calculated so as to Eepre-
sent the time when the predicted position of target 21
intersects the line which represents the locus of all
positions reachable by weapon 16 after the thrusters on
the periphery of weapon 16 are fired. Cone 39 represents
the lethal ~one of the weapon warhead. Flight paths 30
and 30' depict the flight path of weapon 16 as predicted
from ballistic computations by weapon control system 11.
The ballistic computations predict a point of impact 35
of weapon 16 with target 21, assuming no variation in
flight path 32' of target 21. The weapon system guidance
using the thrusters on the periphery of weapon 16 permit
weapon 16 to rapidly alter its flight path 30 to flight
path 34 and thereby, within approximately one second,
but typically one-half second, from the receipt of the
command signal, come to within a lethal zone indicated
by cone 39 of the target 21.
3(d) Force Thrusters
FIG. 5 pictorially illustrates how the thrusters
located at the periphery of weapon 16 are fired in
sequence, thereby exerting forces on weapon 16 so as to
alter the flight path of weapon 16 from flight path 30 to
flight path 34, at point 31, deviating from flight path
30' which is a predicted flight path based on ballistic
computations. Thusters located on the periphery of weapon
16 are shown to be fired at equally-spaced intervals,
associated with points 41 to 46 on flight path 34. The
duration of the intervals is commanded by the command
signal and depends upon the angular orientation and rota-
tional rate of weapon 16, as well as error vector e, when
weapon 16 receives the command signal from weapon control
system 11.
5~6
1 FIG. 9 depicts forces Tl and T8 resulting ~rom the
firing of two of the thrusters located on the periphery
of weapon 16. The forces acting on weapon 16 as a result
o~ the thrusters produce a rapid acceleration of weapon 16
so as to create velocity Vc in the direction of target 21.
4. Weapon Con~iguration
FIG. 10, a cross-sectional view of weapon 16,
depicts the manner in which thrusters 61 to 68 are mounted
on the periphery of weapon 16. Elaborating further,
typical thruster 66 is shown comprising a frame 72 which
encompasses turning charge 73 and an explosive detonator
75; preformed inert assembly 74 is placed adjacent to the
thrusters, in effect isolating one thruster from its
adjacent thruster. Shell casing 71 of weapon 16 is also
shown in FIG. 10.
5. Terminal Guidance Technigue of Weapon
The weapon guidance technique of the invention,
whereby the angular orientation of weapon 16 is deter-
mined, is explained with reference to FIGS. 6, 7, 8 and 9.
5(a) Weapon Canted Antenna Configuration
As shown in FIG. 9, weapon 16 has polarized antenna
25 at the rear of and located in reference to weapon 16
longitudinal axis 60 of weapon 16. The plane of antenna
25 is canted (that is, skewed or tilted) by an angle
~, which is approximately 2 to 3 degrees, with respect
to a plane perpendicular to longitudinal axis 60 of
weapon 16, wherein orientation line 81 lies in said
plane. A signal is transmitted by a relatively low-power
(on the order of ~ive milliwatts) transmitter beacon 24,
which is carried by weapon 16, using linearly polarized
antenna 25. The signal is sent to angle measurement
device 13. A linearly polarized antenna associated with
angle measurement device 13, which also contains a
beacon receiver, senses the beacon signal. FIG. 6
~.2~
1 pictorally illustrates the fields of polarization of
the antenna associated with angle measurement device 13
and of antenna 25 associated with weapon 16. The
vectors E and H of antenna field of polarization are
indicated for the two antenna fields. The field of the
antenna associated with angle measurement device 13 is
indicated to be vertically polarized, Antenna 25 is
'indicated to have a spinning field since antenna 25
rotates as weapon 16 rotates in flight. While weapon 16
is in flight, antenna 25 field vectors E and H rotate at
the spin rate (typically 100 r.p.s.) of weapon 16 relative
to the respective field vectors E and H of antenna 25,
The rotation of antenna 25 field vectors E and ~ relative
to the antenna associated with angle measurement
device 13 field vectors produces a modulation of the
signal sent from weapon 16 to radar system 15.
5(b) Signal Modulation re: Antenna Configuration
The modulation of the beacon signal due to antenna
polarization produces a signal which is depicted as wave-
form 83 in FIG. 7. Waveform 83 has oscillation period
~, because each time the E field vector of antenna 25 is
aligned with the H field vector of the antenna associated
with radar system 15, a signal null is created which is
illustrated by curve 83. Curve 83 demonstrates that
nulls occur twice per spin cycle of weapon 16. Since
the spin cycle of weapon 16, while weapon 16 is in flight
and rotating (at a typical rate of 100 r.p.s.) is 2~, as
depicted by waveform 82, the modulation characteristics
of signal curve 83 is phase-angle ambiguous insofar
as defining the angular orientation of weapon 16, because
any particular point on the surface of weapon 16 could
be out of phase by ~.
22
1 Weapon 16 angular rotation and anyular rotational
rate telemetry information, which is required for correctly
commanding the firing sequence of the thrusters located
on the periphery of weapon 16, is provided by canting
linearly polarized antenna 25 with respect to a plane per-
pendicular to the longitudinal axis 60 of weapon 16, so
that the signal sent from the beacon transmitter on
weapon 16 rotates with signal cross-over at the antenna
gain 3 d8 point as weapon 16 rotates. FIG. 8 illustrates
a typical signal return indicating waveform 85 character-
istics for the E field vector of antenna 25 rotated by 90
degrees with respect to antenna weapon orientation line 81
(as depicted in FIG. 6). Waveform 85 indicates that the
beacon transmitted signal on weapon 16 has modulation
envelope with a wide null and a narrow null, wherein the
modulation envelope is produced by the canting of linearly
polarized antenna 25 with respect to a plane perpendicular
to the longitudinal axis 60 of weapon 16 and having the
E field vector of antenna 25 rotated by 90 degrees with
respect to antenna weapon orientation line 81. From the
modulation envelope of waveform 85, the rotational
- ambiguity of ~eapon 16 described supra, can be resolved
with use of the wide null and narrow null characteristics.
Each time the weapon has gone through a full rotation of
2~, only one narrGw and one wide signal null is produced.
Consequently, the signal received by radar
system 15 from antenna 25 of weapon 16 is modulated by
two effects: (1) the polarity modulation caused by the
beacon signal E vector spinning with respect to the
stationary receiving antenna's E vector of angle measure-
ment device 13; and ~2) the nutating amplitude modulation
resulting from weapon 16 rear-facing antenna which is
pointed along the ballistic path of weapon 16. As shown
by FIG. 7, the envelope signal, indicated by waveform
83, received by the polarized antenna of measurement
-23~
device 13 from weapon 16 would have equally spaced nulls
and peaks and it therefore would not be possible to
determine the exact angular orientation of weapon 16.
The canting of antenna 25 on weapon 16 induces a
modulation in the signal transmitted from antenna 25 to
measurement device 13, as depicted in FIG. 8 by waveform
85, so that the precise angular orientation of weapon 16
is known. Canting antenna 25 has no impact on the
antenna of measurement device 13 until longitudinal axis
60 of weapon 16 is displaced from the line-of-sight of
weapon 16 to radar system 15, as gravity changes the
position of antenna 25 causing a change in the character
of the signal, as depicted in FIG. 8, which will allow
the determination of the geometric relationship of the
ambiguous signal nulls that occur as weapon 16 ro-tates.
In so removing the "up-down" ambiguity of weapon 16,
while the weapon is in flight, the roll angle
orientation and angular roll rate of weapon 16 are
determined. The signal transmitted from weapon 16 also
can be used to control the relative frequency of the
local oscillator (LO) for command link 19.
Consequently, data interface 54 command link RF
frequency will be offset from this LO reference. It is
necessary to determine the roll angle orientation of
weapon 16 in order to command the terminal phase
maneuver of weapon 16, since the turning capability of
weapon 16 occurs in a single plane.
6. Alternate Implementations
To those skilled in the art, it should be apparent
that the implementation of the above-described
embodiment could be varied without departing from the
scope of the invention. In all cases, it is understood
that the above-described embodiments are merely
illustrative of but a small number of the many possible
specific embodiments which represent the application of
the principles of the
~4~5~ ~
24
1 present invention~ Furthermore, numerous and varied
other arrangements can be readily devised in accordance
with the principles of the present invention by those
skilled in the art without departing from the spirit and
scope of the invention.
