U.S. patent application number 10/143433 was filed with the patent office on 2003-11-13 for all weather precision guidance of distributed projectiles.
Invention is credited to Krikorian, Kapriel V., Rosen, Robert A..
Application Number | 20030210170 10/143433 |
Document ID | / |
Family ID | 29400135 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030210170 |
Kind Code |
A1 |
Krikorian, Kapriel V. ; et
al. |
November 13, 2003 |
ALL WEATHER PRECISION GUIDANCE OF DISTRIBUTED PROJECTILES
Abstract
A system and method (32) for measuring line-of-sight angular
rates for all-weather precision guidance of distributed projectiles
(16) and a guidance system (10) based thereon. In accordance with
the novel method (32) for measuring line-of-sight angular rates,
first the range rates of the target (14) relative to at least two
projectiles (16) is determined, as well as the position and
velocity of each projectile (16). Then, the line-of-sight angular
rate of the target (14) relative to at least one projectile (16) is
computed from the range rates, positions, and velocities. In the
illustrative embodiment, the range rate of the target (14) relative
to a projectile (16) is determined based on a monostatic target
Doppler measurement, a monostatic projectile Doppler measurement, a
bistatic Doppler measurement of the target (14) by the projectile
(16), and the carrier frequency of a data link (26) between the
projectile and the shipboard system. The guidance system (10) of
the present invention includes a monostatic radar (18) illuminating
the target (14), bistatic receivers (44) aboard at least two
projectiles (16) fired at the target (14), and a system (32) for
determining line-of-sight angular rates to the target based on the
monostatic measurements and the bistatic measurements from at least
two projectiles. The guidance system (10) further includes a system
(34) for computing guidance command signals for at least one
projectile based on the line-of-sight angular rates, and a
projectile steering unit (52) aboard at least one projectile for
steering the projectile based on the guidance command signals.
Inventors: |
Krikorian, Kapriel V.; (Oak
Park, CA) ; Rosen, Robert A.; (Simi Valley,
CA) |
Correspondence
Address: |
PATENT DOCKET ADMINISTRATION
RAYTHEON SYSTEMS COMPANY
P.O. BOX 902 (E1/E150)
BLDG E1 M S E150
EL SEGUNDO
CA
90245-0902
US
|
Family ID: |
29400135 |
Appl. No.: |
10/143433 |
Filed: |
May 9, 2002 |
Current U.S.
Class: |
342/62 ;
244/3.14; 342/90; 342/97; 342/99 |
Current CPC
Class: |
F41G 7/305 20130101;
F41G 7/308 20130101; G01S 13/723 20130101; F41G 7/303 20130101;
G01S 13/003 20130101 |
Class at
Publication: |
342/62 ; 342/90;
342/97; 342/99; 244/3.14 |
International
Class: |
G01S 013/72; F41G
007/28 |
Claims
What is claimed is:
1. A system for determining the line-of-sight angular rate to a
target comprising: first means for determining range rates {dot
over (R)}.sub.i of the target relative to at least two projectiles;
second means for determining the position and velocity of each
projectile; and third means for calculating the line-of-sight
angular rate of the target relative to at least one projectile
{circumflex over (.omega.)}.sub.i from said range rates, positions,
and velocities.
2. The invention of claim 1 wherein said first means includes a
monostatic radar system for illuminating the target.
3. The invention of claim 2 wherein said monostatic radar is a
shipboard radar.
4. The invention of claim 2 wherein said monostatic radar is a
millimeter wave radar.
5. The invention of claim 2 wherein said monostatic radar measures
the range, range rate and angle of the target, and the range, range
rate, angle, and angle rate of each projectile.
6. The invention of claim 5 wherein said first means further
includes fourth means for obtaining a bistatic range rate {dot over
(R)}.sub.B from each of the projectiles.
7. The invention of claim 6 wherein said fourth means includes a
bistatic radar receiver aboard each projectile for measuring the
Doppler frequency of the target from each of the projectiles.
8. The invention of claim 7 wherein said fourth means further
includes fifth means for transmitting said Doppler measurements to
said system.
9. The invention of claim 8 wherein said fifth means includes a
data link having a carrier frequency synchronized to the local
oscillator of the projectile radar receiver.
10. The invention of claim 9 wherein said first means further
includes means for adjusting said Doppler measurements for
differences between the projectile receiver local oscillator
frequency and the monostatic radar local oscillator frequency.
11. The invention of claim 10 wherein said adjusted Doppler
frequencies f.sub.BDT are obtained by taking the bistatic Doppler
measurements f.sub.BD and subtracting the fractional local
oscillator frequency error .epsilon. times the frequency of the
monostatic radar f.sub.R.
12. The invention of claim 11 wherein the fractional local
oscillator frequency error is computed from 6 = f DLM f DL - 1 + R
. SM c ,where f.sub.DL is the nominal data link carrier frequency,
f.sub.DLM is the measured data link carrier frequency, {dot over
(R)}.sub.SM is the range rate of the projectile relative to the
monostatic radar, and c is the speed of light.
13. The invention of claim 10 wherein said bistatic range rate {dot
over (R)}.sub.B is calculated by taking the adjusted Doppler
frequency f.sub.BDT, multiplying by the speed of light c, and
dividing by the frequency of the mono static radar f.sub.R.
14. The invention of claim 5 wherein the range rate of the target
relative to a projectile {dot over (R)}.sub.i is determined by
subtracting the range rate of the target relative to the monostatic
radar {dot over (R)}.sub.M from the bistatic range rate {dot over
(R)}.sub.B.
15. The invention of claim 5 wherein the position and velocity of
each projectile is calculated based on the monostatic radar
measurements of the projectile.
16. The invention of claim 15 wherein said monostatic radar
measurements are enhanced by a rear corner reflector placed on each
projectile.
17. The invention of claim 1 wherein the positions b.sub.i and
velocities .DELTA.v.sub.i of the projectiles is determined relative
to the centroid of the projectiles projected onto the plane
perpendicular to s, where s is the line-of-sight unit vector from
the centroid towards the target, and the mean velocity of the
projectiles, respectively.
18. The invention of claim 17 wherein said third means includes
calculating the line-of-sight angular rate of the target relative
to the centroid of the projectiles {circumflex over (.omega.)}
using the following equation: 7 ^ = s .times. I - 1 i b i ( R . i +
v i T s ) ,where s is the line-of-sight unit vector from the
centroid towards the target and I is the second order moment matrix
of the ensemble of projectiles in the plane perpendicular to s.
19. The invention of claim 18 wherein the line-of-sight angular
rate of the target relative to each projectile .omega..sub.i is
calculated by the following equation: 8 ^ i = ^ - [ s R .times. ( v
i - b i R . R ) ] ,where R is the mean range to the target and {dot
over (R)} is the mean range rate of the target relative to the
projectiles.
20. A system for guiding projectiles to a target comprising: a
monostatic radar system for illuminating the target and measuring
monostatic returns from the target and from the projectiles; a
bistatic receiver aboard each projectile for measuring the bistatic
Doppler off the target; a target tracking system for determining
the line-of-sight angular rates to the target based on said
monostatic measurements and the bistatic measurements from at least
two projectiles; a guidance system for computing guidance command
signals for each projectile based on said line-of-sight angular
rates; a projectile steering unit aboard each projectile for
steering the projectile based on said guidance command signals; a
transceiver for receiving the bistatic measurements from the
projectiles and sending the guidance command signals to the
projectiles; and a transceiver aboard each projectile for sending
the bistatic measurements to the target tracking system and
receiving the guidance command signals.
21. A method for determining the line-of-sight angular rate to a
target including the steps of: determining range rates {dot over
(R)}.sub.i of the target relative to at least two projectiles;
determining the position and velocity of each projectile; and
calculating the line-of-sight angular rate of the target relative
to each projectile {circumflex over (.omega.)}.sub.i from said
range rates, positions, and velocities.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to radar guidance systems.
More specifically, the present invention relates to systems and
methods for measuring line-of-sight angular rates for guided
projectiles.
[0003] 2. Description of the Related Art
[0004] Navy ships are exposed to low flying, fast, and highly
maneuverable missile threats. In order to provide the ships with an
effective missile defense system, high accuracy measurements of
incoming missile targets and precision guidance of anti-missile
projectiles are required.
[0005] Many guidance systems have been developed for missiles and
projectiles (i.e.--bullets). In a typical radar based guidance
system, the projectile is guided to the target by guidance signals
developed from tracking data obtained either by a shipboard radar
system or by a radar system located totally, or partially, within
the projectile. The former system is commonly referred to as a
command guidance system and the latter as a horning guidance
system.
[0006] In a command guidance system, a high-resolution shipboard
radar system tracks both the target and the projectile, calculates
the proper guidance signals for the projectile based on the
generated tracking data, and transmits the signals to the
projectile to enable the projectile to intercept the target.
[0007] In a homing guidance system, the target tracking radar
system is located totally or partially within the projectile. An
active homing guidance system uses a monostatic radar system where
both the radar transmitter and receiver are located in the
projectile. A semi-active guidance system uses a bistatic radar
system where a radar transmitter located remotely from the
projectile (such as onboard the ship) illuminates the target and
the reflected returns are received by a receiver located on the
projectile. The tracking data from the radar measurements are then
used to calculate the proper guidance signals to direct the
projectile to the target.
[0008] Most of these systems are designed for use with missiles and
larger caliber projectiles (greater than 3 inches in diameter),
whereas the optimum caliber for high rate-of-fire guns is generally
about 1 inch in diameter. Prior art guidance systems do not work
well with smaller caliber projectiles. In particular, prior art
approaches do not accurately measure the line-of-sight angular rate
to the target with enough precision for the application. Command
guidance systems with a high resolution monostatic shipboard radar
are capable of measuring line-of-sight angular rate. However, these
measurements are generally not as accurate as measurements made
from the projectile, as with homing guidance systems. Homing
systems, however, require a radar receiver onboard the projectile.
The size of the smaller caliber projectiles places a constraint on
the size of the radar receiver antenna on the projectile. With a
small antenna, a relatively accurate range rate can be measured,
but the angular rate will be imprecise.
[0009] The critical factor required for effective projectile
guidance is an accurate measurement of the line-of-sight angular
rate to the target relative to the projectile. Guidance algorithms
depend on line-of-sight angular rate information to successfully
direct a projectile to its target. Poor line-of-sight angular rate
measurements may cause a projectile targeting error.
[0010] Hence, there is a need in the art for an improved method or
system for accurately measuring line-of-sight angular rates for
precision guidance of small caliber projectiles.
[0011] Furthermore, these guidance systems need to be effective
under all weather conditions. Laser or ladar based guidance systems
have been developed for small caliber projectiles. These systems
offer very high angular resolution; however, they typically require
favorable weather conditions to be effective. Adverse weather such
as fog, rain, or clouds may block optical electromagnetic energy,
causing a laser based guidance system to fail.
[0012] Hence, a need exists in the art for an improved method or
system for accurately measuring line-of-sight angular rates for
all-weather precision guidance of small caliber projectiles and a
guidance system based thereon.
SUMMARY OF THE INVENTION
[0013] The need in the art is addressed by the system and method
for measuring line-of-sight angular rates for all-weather precision
guidance of projectiles and the guidance system based thereon of
the present invention. This invention takes advantage of the fact
that several projectiles are usually fired at the incoming target.
While the LOS angular rate cannot be determined solely from the
range rate measurements from a single projectile, it can be
calculated if the range rate information from several projectiles
is available.
[0014] In accordance with the novel method for measuring
line-of-sight angular rates, first the range rates of the target
relative to at least two projectiles is determined, as well as the
position and velocity of each projectile. Then, the line-of-sight
angular rate of the target relative to at least one projectile is
computed from the range rates, positions, and velocities. In the
illustrative embodiment, the range rate of the target relative to a
projectile is determined based on a monostatic target Doppler
measurement, a monostatic projectile Doppler measurement, a
bistatic Doppler measurement of the target by the projectile, and
the carrier frequency of a data link between the projectile and the
shipboard system.
[0015] In an illustrative embodiment, the guidance system of the
present invention includes a monostatic radar illuminating the
target, bistatic receivers aboard at least two projectiles fired at
the target, and a system for determining line-of-sight angular
rates to the target based on the monostatic measurements and the
bistatic measurements from at least two projectiles. The guidance
system further includes a system for computing guidance command
signals for at least one projectile based on the line-of-sight
angular rates, and a projectile steering unit aboard at least one
projectile for steering the projectile based on the guidance
command signals.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagram of an anti-ship missile defense system
designed in accordance with the present teachings.
[0017] FIG. 2 is a block diagram showing the components of the
projectile guidance system of the present invention in more
detail.
[0018] FIG. 3 is a flow chart that illustrates the operation of the
guidance system of the present invention.
DESCRIPTION OF THE INVENTION
[0019] Illustrative embodiments and exemplary applications will now
be described with reference to the accompanying drawings to
disclose the advantageous teachings of the present invention.
[0020] While the present invention is described herein with
reference to illustrative embodiments for particular applications,
it should be understood that the invention is not limited thereto.
Those having ordinary skill in the art and access to the teachings
provided herein will recognize additional modifications,
applications, and embodiments within the scope thereof and
additional fields in which the present invention would be of
significant utility.
[0021] FIG. 1 is a diagram of an anti-ship missile defense system
10 designed in accordance with the present teachings showing a ship
12 and an incoming missile 14, also referred to as the target. The
ship 12 fires several projectiles 16 to intercept the missile
target 14. A shipboard radar 18 transmits a radar beam 20 towards
the target 14. The monostatic reflected return 22 is received by
the shipboard radar 18. In addition, bistatic illumination 24
reflected off the target 14 is received by each projectile 16.
These bistatic measurements are transmitted to the shipboard radar
18 by a wireless data link 26. The monostatic and bistatic
measurements are then used to calculate guidance signals to direct
the projectiles 16 to the target 14. The guidance commands are
transmitted to the projectiles 16 via the data link 26.
[0022] FIG. 2 is a block diagram showing the components of the
projectile guidance system 10 of the present invention in more
detail. On the ship 12, a monostatic radar system 18 with a radar
antenna 30 track the missile target 14 as well as the anti-missile
projectiles 16. In the preferred embodiment, the radar system is
using millimeter wave radar. A millimeter wave system is preferable
because it provides very high angular resolution, while still
providing weather penetration. The radar system 18 measures the
position and monostatic Doppler of the target 14 and of each of the
projectiles 16.
[0023] The radar measurements are used by a target tracking system
32 which calculates the range rates and line-of-sight angular rates
needed by the guidance system 34 to compute guidance signals for
the projectiles. In the illustrative embodiment, the tracking
system 32 and guidance system 34 are implemented in software in a
high-speed computer 36. A data link transceiver 38 with an antenna
40 is provided to communicate with the projectile. The data link
transceiver 38 receives bistatic projectile measurements needed by
the target tracking system 32 and roll angle measurements needed by
the guidance system 34, and transmits guidance signals from the
guidance system 34 to the projectiles.
[0024] On each projectile is a low cost bistatic radar receiver 44
and antenna 42. The projectile receiver measures the bistatic
Doppler off the target and data links these measurements back to
the shipboard radar by a data link transceiver 46 and antenna 48.
The carrier frequency of the data link is synchronized to the
receiver local oscillator (LO) 50. Thus the shipboard tracking
system 32 can derive the local oscillator offset by comparing the
data link carrier frequency with the Doppler of the skin return.
The projectile data link transceiver 46 receives the guidance
signals from the shipboard guidance system 34 and sends them to a
projectile steering system 52. The projectile may also include an
accelerometer 54 or other device for measuring properties of the
projectile needed by the guidance system 34, such as the inertial
roll angle. These measurements are transmitted to the shipboard
system by the data link transceiver 46.
[0025] The present invention includes a novel method for
determining the line-of-sight (LOS) angular rate to the target
relative to each projectile by using the range rate information
obtained from several projectiles. This invention takes advantage
of the fact that several projectiles are usually fired at the
incoming target. While the LOS angular rate cannot be determined
solely from the range rate measurements from a single projectile,
it can be calculated if the range rate information from several
projectiles is available.
[0026] In accordance with the novel method, the range rate of the
target relative to each projectile is determined based on the
monostatic target Doppler, the monostatic projectile Doppler, the
bistatic Doppler measurement of the target by the projectile, and
the frequency of the data link carrier. The position and velocity
of each projectile is also calculated based on the monostatic
range, range rate, angle, and angle rate of the projectile measured
by the shipboard radar system. Finally, the line-of-sight angular
rates to the target from each projectile are computed, which are
the key measurements in projectile guidance.
[0027] The relatively large separation between the projectiles
(compared to their diameter) leads to highly accurate measurements
of the line-of-sight angular rates. Note that unambiguous angular
accuracy relative to the separations is not required, so the
separations do not need to be measured to within a wavelength.
[0028] FIG. 3 is a flow chart that illustrates the operation of the
guidance system of the present invention. First, at Step 110, the
monostatic shipboard radar system measures the range, range rate,
and angle of the target (relative to the shipboard radar), and the
range, range rate, angle, and angle rate of the projectiles
(relative to the shipboard radar) in accordance with conventional
methods.
[0029] At Step 112, the position and velocity of each projectile is
determined. In the illustrative example, the position and velocity
of each projectile is calculated based on the monostatic radar
measurements of the projectile. The skin return of the projectile
can be enhanced by a rear corner reflector. Alternatively, the
position of each projectile may be determined by a transponder
return of the projectile. In the illustrative example, the location
of each projectile b, is determined relative to the centroid of the
ensemble of projectiles, and the relative velocity of each
projectile .DELTA.v, is calculated relative to the mean velocity of
all the projectiles.
[0030] Meanwhile, at Step 114, the receiver aboard each projectile
measures the bistatic Doppler f.sub.BD off the target.
[0031] At Step 116, properties of the projectile needed by the
guidance system such as the antenna roll angle and acceleration are
measured in accordance with conventional methods. For example, the
inertial roll angle of the projectile may be determined based on an
accelerometer that is compensated for inertial acceleration based
on the measured change of projectile velocity.
[0032] At Step 118, the bistatic Doppler measurements and antenna
roll angle and acceleration measurements are transmitted to the
shipboard system by a coded data link message. The carrier
frequency of the data link is synchronized to the local oscillator
of the projectile receiver.
[0033] At Step 120, the shipboard system receives the projectile
measurements from the data link and measures the carrier frequency
of the data link f.sub.DLM for each projectile.
[0034] At Step 122, the range rate of the target relative to the
projectile {dot over (R)}.sub.i is calculated for each projectile.
The range rate {dot over (R)}.sub.i is given by the following
equation:
{dot over (R)}.sub.i={dot over (R)}.sub.B-{dot over (R)}.sub.M
[1]
[0035] where RM is the range rate of the target relative to the
monostatic radar and {dot over (R)}.sub.B is the bistatic range
rate. The bistatic range rate {dot over (R)}.sub.B is the rate of
change of the sum of the distance from the monostatic radar
transmitter to the target plus the distance from the target to the
bistatic receiver, and is determined from the bistatic Doppler
measured by the projectile. The bistatic range rate {dot over
(R)}.sub.B is given by the following equation: 1 R . B = cf BDT f R
[ 2 ]
[0036] where c is the speed of light, f.sub.R is the frequency of
the transmitted radar, and f.sub.BDT is the true bistatic Doppler
frequency.
[0037] The true bistatic Doppler f.sub.BDT adjusts the Doppler
frequency measured by the projectile receiver to accommodate any
differences between the receiver local oscillator frequency and the
monostatic local oscillator reference. The true bistatic Doppler
frequency f.sub.BDT is calculated from the following equation:
f.sub.BDT=f.sub.BD-.epsilon.f.sub.R [3]
[0038] where f.sub.BD is the bistatic Doppler frequency measured by
the projectile and .epsilon. is the fractional frequency error of
the projectile local oscillator relative to the monostatic local
oscillator. The LO frequency error .epsilon. is given by: 2 = f DLM
f DL - 1 + R . SM c [ 4 ]
[0039] where f.sub.DL is the nominal data link carrier frequency,
f.sub.DLM is the data link carrier frequency measured by the
shipboard receiver, and {dot over (R)}.sub.SM is the range rate of
the projectile relative to the monostatic radar.
[0040] Thus, the range rate of the target relative to the
projectile {dot over (R)}.sub.i is calculated from the range rate
of the target relative to the monostatic radar {dot over
(R)}.sub.M, the range rate of the projectile relative to the
monostatic radar {dot over (R)}.sub.SM, the bistatic Doppler
frequency measured by the projectile f.sub.BD, and the data link
carrier frequency measured by the shipboard receiver f.sub.DLM.
This range rate {dot over (R)}.sub.i is computed for each
projectile.
[0041] At Step 124, the line-of-sight angular rate is computed for
each projectile. First, the line-of-sight angular rate relative to
the centroid of the ensemble of projectiles {circumflex over
(.OMEGA.)} is calculated by the following equation: 3 ^ = s .times.
I - 1 i b i ( R . i + v i T s ) [ 5 ]
[0042] where s is the line-of-sight unit vector from the centroid
towards the target, b.sub.i is the location vector of each
projectile relative to the centroid projected onto the plane
perpendicular to s, I is the second order moment matrix of the
ensemble of projectiles (given by 4 ( given by I = i b i b i T )
,
[0043] {dot over (R)}.sub.i is the range rate to the target for
each projectile as computed in Step 122 ({dot over (R)}.sub.i is
negative for closing), and .DELTA.v.sub.i is the velocity vector of
each projectile relative to the mean velocity.
[0044] After the line-of-sight angular rate relative to the
centroid {circumflex over (.OMEGA.)} is computed, the line-of-sight
angular rates relative to each projectile {circumflex over
(.OMEGA.)}.sub.i are computed using the following equation: 5 ^ i =
^ - [ s R .times. ( v i - b i R . R ) ] [ 6 ]
[0045] where R is the mean range to the target and {dot over (R)}is
the mean range rate of the target relative to the projectiles
(negative for closing).
[0046] At Step 126, the line-of-sight rates are used to compute
guidance commands in accordance with conventional methods. The
guidance commands are transmitted to each projectile via the data
link.
[0047] Finally, at Step 128, the projectiles receive their guidance
commands and, in accordance with conventional methods, adjust their
navigational fins to guide the projectiles to the target.
[0048] Thus, accurate measurements of projectile velocities,
especially in the forward direction, are essential. In the
illustrative example, this accuracy is attained because of the
enhanced projectile radar cross section, or by projectile
transponders.
[0049] The RMS accuracy .sigma..sub.W of the line-of-sight angular
rate as calculated by this method is given approximately by:
.sigma..sub.W=.sigma..sub.{dot over (R)}/({square root}{square root
over (N)}.multidot.D) [7]
[0050] where .sigma.{dot over (R)} is the bi static Doppler
accuracy of the projectile receiver, N is the number of
projectiles, and D is the RMS distance between projectiles.
[0051] While the present invention is described herein with
reference to illustrative embodiments for a particular application
(an anti-ship missile defense system), it should be understood that
the invention is not limited thereto. It may be applied to any
precision targeting application.
[0052] Thus, the present invention has been described herein with
reference to a particular embodiment for a particular application.
Those having ordinary skill in the art and access to the present
teachings will recognize additional modifications, applications and
embodiments within the scope thereof.
[0053] It is therefore intended by the appended claims to cover any
and all such applications, modifications and embodiments within the
scope of the present invention.
[0054] Accordingly,
* * * * *