U.S. patent number 3,782,667 [Application Number 05/275,014] was granted by the patent office on 1974-01-01 for beamrider missile guidance method.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Jimmy R. Duke, Walter E. Miller, Jr., Teddy J. Peacher, Robert L. Sitton.
United States Patent |
3,782,667 |
Miller, Jr. , et
al. |
January 1, 1974 |
BEAMRIDER MISSILE GUIDANCE METHOD
Abstract
In the improved beamrider guidance an optical beam is
electronically modued and transmitted toward a target. A missile is
launched into the beam path and is caused to automatically seek the
center of the beam as it flies toward the target. The transmitted
beam is spatially encoded to provide guidance signals which the
missile automatically responds to in seeking the center of the
beam. The beamrider missile does not require tracking or
correctional guidance from an external source as it generates its
correctional commands internally from the beams's spatial encoding.
The missile is immune to optical countermeasures, being within the
narrow corridor of the beam and responsive only to the encoded
intelligence in the beam for seeking or maintaining flight along
the beam center.
Inventors: |
Miller, Jr.; Walter E.
(Huntsville, AL), Peacher; Teddy J. (Huntsville, AL),
Duke; Jimmy R. (Huntsville, AL), Sitton; Robert L.
(Huntsville, AL) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
23050550 |
Appl.
No.: |
05/275,014 |
Filed: |
July 25, 1972 |
Current U.S.
Class: |
244/3.13;
244/3.16 |
Current CPC
Class: |
F41G
7/263 (20130101) |
Current International
Class: |
F41G
7/20 (20060101); F41G 7/26 (20060101); F41g
007/00 (); F42b 015/02 () |
Field of
Search: |
;244/3.13,3.16 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Engle; Samuel W.
Assistant Examiner: Hanley; James M.
Attorney, Agent or Firm: Harry M. Saragovitz et al.
Claims
We claim:
1. In a missile guidance system wherein a target is tracked by
visual line-of-sight, a method of directing a missile toward a
target and comprising the steps of: visually tracking a target from
a target tracking station; directing an amplitude coded beam of
optical energy, having a high intensity center portion and a
reduced intensity outer portion, from said target tracking station
along the line-of-sight to the target; launching a missile into the
path of said optical beam toward said target; encoding said optical
energy by electronically modulating a single solid state,
photodiode source for providing an optical frequency reference; and
generating correctional guidance within the missile in response to
said optically encoded energy for maintaining missile trajectory
along the line-of-sight.
2. A method of directing a missile toward a target as set forth in
claim 1 and further comprising the steps of: simultaneously
detecting first and second intensity levels of said optical energy
by said missile for directing said missile toward the high
intensity center portion of the beam.
3. A method as set forth in claim 2 and further comprising the
steps of: nutating said amplitude coded beam, transmitting a
nutator position timing signal in said amplitude coded beam, and
detecting by said missile the variation in signal amplitude during
nutation and the timing signal for directing said missile toward
the high intensity center portion of the beam.
4. In a missile guidance system wherein a target is tracked by
visual line-of-sight a method of directing a missile toward a
target and comprising the steps of: electronically modulating a
plurality of solid state, photodiode sources with respective
individual frequencies for providing individually encoded optical
beams; forming said individually encoded beams into a single beam
of adjacent segments having a common central point by transmitting
the output of said plurality of diode sources through an optical
integrator and imaging the output face of the optical integrator to
form the projected beam; visually tracking a target from a target
tracking station; directing said beam of optical energy from said
target tracking station along the line-of-sight to the target;
launching a missile into the path of said optical beam; and
generating correctional guidance within the missile in response to
said optically encoded energy for maintaining missile trajectory
along the line-of-sight.
5. A method of directing a missile toward a target as set forth in
claim 4 and further comprising the steps of electronically
modulating first, second, third, and fourth laser diodes with
respective first, second, third, and fourth frequencies for
providing said encoded optical energy path to said target; and
forming said single segmented beams into quadrants of uniform
intensity.
6. In a missile guidance system wherein a target is tracked by
visual line-of-sight a method of directing a missile toward a
target and comprising the steps of: electronically modulating an
array of photodiodes with a plurality of individual frequencies for
providing individual modulated optical beams; shaping said beams
with respective light pipes into a plurality of optical lines;
forming said optical lines into a plural line beam having a common,
central, line terminal point with optically void zones adjacent
said optical lines; visually tracking a target from a target
tracking station; directing said plural line beam of optical energy
from said target tracking station along the line-of-sight to the
target; launching a missile into the path of said optical beam; and
generating correctional guidance within the missile in response to
said optically encoded energy for maintaining missile trajectory
along the line-of-sight.
7. A method of directing a missile toward a target as set forth in
claim 6 and further comprising the steps of: modulating first,
second, third, and fourth photodiodes with respective first,
second, third, and fourth frequencies for providing an orthogonal
optical axes energy path as said plural line beam.
8. A beamrider missile guidance system comprising: apparatus for
transmitting an optical beam toward a target; a missile for
traversing the path of said optical beam, an optical detector on
said missile responsive to said optical beam energy for directing
the missile trajectory within said beam and wherein said apparatus
for transmitting an optical beam includes a plurality of
photodiodes arranged in an array, a plurality of electronic
modulators coupled to respective of said diodes for individually
modulating said diodes, an optical integrator responsive to the
output optical energy of said diode array for directing said energy
as distinct adjacent sections of a composite beam, and a nutator
for nutating the optical output beam.
9. A missile guidance system as set forth in claim 8 wherein said
optical integrator is a plurality of light pipes for shaping
individual beam segments into a pattern segment, said photodiodes
are laser diodes, and said composite beam is a quadrant beam.
Description
BACKGROUND OF THE INVENTION
In guidance systems for directing a missile toward a target the
system must be capable of avoiding jamming signals which may be
deliberate or spurious in nature. Optical command guidance systems
are highly accurate and have reduced missile susceptibility to
jamming on counter-measure efforts. However, the missile beacon and
beacon tracker of the command guidance systems are still highly
susceptible to jamming.
An optical beamrider guidance system is disclosed in U.S. Pat. No.
3,398,918 to Girault wherein a missile is guided from a launching
site to a target. A laser source and optical means for radiating
fan shaped beams are at the launch site. The four fan shaped beams
are independently modulated and are projected toward a target,
forming four optical walls of a corridor for guiding the
projectile. The projectile ricochets or bounces within the corridor
until it reaches the target. Alternative to the optical wall method
of guidance, a proportional guidance system provides means whereby
two beams sweep the guiding volume in directions perpendicular to
each other for directing the projectile.
SUMMARY OF THE INVENTION
In the improved beamrider missile guidance the gunner or observer
at a launch site visually locates and identifies a target. A visual
line-of-sight to the target is established through a telescopic
sight. An optical transmitter, boresighted to the telescope,
directs optical energy toward the target. The transmitted optical
energy is spatially coded, allowing onboard missile sensors to
respond to missile deviations from the gunner's line-of-sight.
Deviation or error information generated in the missile allows
automatic generation of correctional commands for returning the
missile to the line-of-sight. The beamrider system provides
countermeasures hardening over existing systems by utilizing the
extreme accuracy of optical command guidance while eliminating the
susceptible missile tracker and beacon from the system. The
beamrider system has a re-usable transmitter which provides a
myriad selection of electronic signal modulation. The accuracy with
which a missile seeks the center of a beam, while moving toward a
target, is determined by the particular spatial encoding of the
transmitted beam and the resulting beam resolution .
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an embodiment of the beamrider guidance system.
FIG. 2 is a diagrammatic view of a preferred embodiment of the
beamrider transmitter encoding method.
FIGS. 3A, 3B and 3C disclose coded beam patterns A, B, and C that
can be projected toward a target.
FIG. 4 is a graph of relative intensity across the beam from a
single source such as FIG. 3C.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like numbers represent like
parts in each of the several figures, FIG. 1 discloses an optical
beamrider system. From a target tracking station 10 an optical beam
12 is directed toward a target 14 by a beam transmitter or optical
source 16 which is boresighted to follow the telescopic tracking of
the target by an observer or gunner. A missile 18 is launched from
the target tracking station into the beam path toward the target.
An optical receiver or receivers 48 on the aft end of the missile
respond to the spatially encoded light beam for directing the
missile toward the center of the beam or null axis representing the
line-of-sight axis between the target tracking station and the
target.
FIG. 2 discloses the method of optical transmission toward the
target wherein the transmitter 16 comprises a group of
symmetrically arranged diode lasers 31, 32, 33 and 34. A bank of
electronic modulators 22 provide respective output frequencies f1,
f2, f3 and f4 for respectively modulating diode lasers 31, 32, 33
and 34. Optical output energy from the diode lasers is coupled
through respective light pipes 41, 42, 43 and 44, forming the coded
beam pattern at a common junction 24 for projecting the beam. The
beam pattern 26 projected from light pipe terminal 24 is coupled to
a nutator 28. Nutation of the beam during target tracking allows
vertical and horizontal position information to be obtained onboard
the missile for generation of guidance commands. Beam nutation as
seen by a missile receiver is equivalent to moving the receiver in
a small circle within a stationary beam, as shown in FIGS. 3A, 3B,
and 3C. The output optical energy from nutator 28 is directed to
beam forming optics 29 for transmitting the beam toward the target.
The missile, launched into the beam path, has an optical energy
detector 48A on the aft end thereof for detecting the modulated
frequencies spatially coded into the formed beam and activating
correctional guidance control systems.
The beam pattern of FIG. 3A is obtained from a solid state laser
diode array wherein the separate beams generated by individual
lasers are brought together to form a single composite beam. Beam
pattern 26a is comprised of beam quadrants f1, f2, f3 and f4,
representative of the modulated frequency superimposed on
respective optical beam segments. To provide very sharp edges to
the quadrants, and relatively uniform intensity over a given
quadrant, the light pipes are placed between the diode arrays and
nutator 28. Thus, the light pipes function as optical integrators
for each quadrant and may consist of glass or quartz sections. The
integrator is sufficiently long to permit total internal
reflections to smooth out dark and bright areas of the array,
thereby providing uniform intensity over a given quadrant. For the
particular quadrant formation shown, vertical position error is the
relative duration of f1 + f2 compared to f3 + f4. Similarly,
horizontal error is given by the relative duration of f1 + f4
compared to f2 + f3. The small nutation circle within pattern 26a
represents the missile position within the beam at a given time
during flight. As shown, there is no error in the vertical
deviation, hence, no vertical correction is required. For the
horizontal direction, however, the missile will sense an error
since the relative duration of energy received from f1 + f4 is
greater. Obviously, the beam axes can be rotated in space. Encoding
of signal processing requirements would change mechanically with a
different system arrangement but the function would be
identical.
For a 4-line beam as shown in FIG. 3B the information desired from
a nutated quadrant beam is contained in the crossing times from one
quadrant to the next. Thus, four coded lines are transmitted and
the quadrant areas left blank. In response to detector 48A the
missile electronics senses the relative time between axis crossings
and processes the signals in the same manner as in the quadrant
configuration. The quadrant or line shape of the beam pattern is
determined by the optical integrators used. A linear system may
also be embodied when a reference sine or cosine voltage is sampled
at each crossing in a 4-line beam. However, the reference voltages
must be phase locked to the nutation frequency for this embodiment,
which makes the relative duration processing method more suitable
for the beamrider. An advantage of the 4-line beam over the
quadrant beam is the significant reduction in transmitter power
required. For the same intensity of transmitted energy and
effective beam size, the required power is reduced by the ratio of
the active array areas. This is approximately a factor of 10 for a
line aspect ratio of 10:1, for which linear arrays of laser diodes
are well suited.
The amplitude coded beam shown in FIG. 4 utilizes a single
frequency fixed (not nutating) beam with a high intensity center
portion, and a reduction in intensity with distance from the
center. A single diode source provides the simple beam. During
flight the missile is required to roll at least one-half the rate
that correctional commands are required. Two detectors 48B are
placed on the aft end of the missile, preferably on the wings and
as widely separated as possible. Deviation of the missile, away
from a position where the signal level is equal on both detectors,
results in a strong imbalance of signal energy due to the high
intensity center of the beam. This indicates to the missile
guidance that correction is needed. If the missile is directed
toward the detector receiving the greatest signal during each
one-half turn the average command will be towards the beam center.
Since the fall-off of beam intensity is controllable, appropriate
sensing logic on the missile allows linear error correction to be
achieved. If it is desired the tracking rate or other known bias
can also be transmitted to the missile from the launch site via the
coded beam. If it is desired not to roll the missile, four
detectors 48B can be placed on the aft of the missile, forming a
quadrant plane normal to the missile longitudinal axis. Deviation
of the missile from positions of equal intensity will indicate and
initiate correctional guidance.
The amplitude coded beam of FIG. 4 can be nutated as shown in FIG.
3C. Processing is identical on the missile to that of the
non-nutated beam except that only one optical detector is required
for this mode and the angle of rotation of nutation wedge 28 is
transmitted as a timing signal on the beam for detection by the
missile. The missile guidance then responds to a signal
proportional to the variation in signal amplitude received during
each nutation cycle. The guidance response is in a direction
determined by the received nutation angle at the time of received
maximum intensity.
The basic guidance information of a beamrider missile is angular,
measured at the transmitter, between the boresight axis and missile
position. Thus, for long range targets, the linear miss distance
increases with range. For instance if the nominal guidance accuracy
is 1/3 milliradian at 5 miles, the miss distance is 8.8 feet. Such
accuracy is acceptable for ground targets such as tanks, vehicles,
and hardened positions, since they are normally engaged at much
shorter ranges. For the longer target engagement ranges a dual mode
operation is desirable wherein the missile first rides the beam to
the vicinity of the target, then a homing seeker on the missile
activates providing homing guidance for the terminal phase of the
flight. Depending on the missile-target range at which it is
desired to initate terminal homing, the homing seeker can be
rudimentary, with the reflected energy from the target providing
the homing beam path.
Either photoemissive diodes or photodiode lasers can be used as
optical sources for the beamrider transmitter. These devices offer
a direct power conversion from electrical to modulated optical
power with typical efficiencies from 10 to 25 percent. They are
capable of high frequency modulation, which eliminates wake
modulation of background (including sun interference) as a noise
source. They are easily arrayed to provide any desired beam
configuration, and simple optics can project the array geometry
eliminating the need of beamsplitters and mechanical modulators,
since each quadrant or any portion of the array may be
independently modulated electronically.
Although a particular embodiment and form of this invention has
been illustrated, it is apparent that various modifications and
embodiments of the invention may be made by those skilled in the
art without departing from the scope and spirit of the foregoing
disclosure. Accordingly, the scope of the invention should be
limited only by the claims appended hereto.
* * * * *