CA2085847C - Autonomous precision weapon delivery using synthetic array radar - Google Patents
Autonomous precision weapon delivery using synthetic array radarInfo
- Publication number
- CA2085847C CA2085847C CA002085847A CA2085847A CA2085847C CA 2085847 C CA2085847 C CA 2085847C CA 002085847 A CA002085847 A CA 002085847A CA 2085847 A CA2085847 A CA 2085847A CA 2085847 C CA2085847 C CA 2085847C
- Authority
- CA
- Canada
- Prior art keywords
- target
- weapon
- navigation
- sar
- platform
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41G—WEAPON SIGHTS; AIMING
- F41G7/00—Direction control systems for self-propelled missiles
- F41G7/007—Preparatory measures taken before the launching of the guided missiles
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41G—WEAPON SIGHTS; AIMING
- F41G7/00—Direction control systems for self-propelled missiles
- F41G7/34—Direction control systems for self-propelled missiles based on predetermined target position data
- F41G7/346—Direction control systems for self-propelled missiles based on predetermined target position data using global navigation satellite systems, e.g. GPS, GALILEO, GLONASS
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F41—WEAPONS
- F41G—WEAPON SIGHTS; AIMING
- F41G7/00—Direction control systems for self-propelled missiles
- F41G7/34—Direction control systems for self-propelled missiles based on predetermined target position data
- F41G7/36—Direction control systems for self-propelled missiles based on predetermined target position data using inertial references
Abstract
A system and method that uses differential computation of position relative to aglobal positioning system (GPS) coordinate system and the computation of an optimum weapon flight path to guide a weapon to a non-moving fixed or relocatable target. The system comprises an airborne platform that uses a navigation subsystem that utilizes the GPS satellite system to provide the coordinate system and a synthetic array radar (SAR) to locate desirable targets. Targeting is done prior to weapon launch, the weapon there-fore requires only a navigation subsystem that also utilizes the GPS satellite system to provide the same coordinate system that the platform used, a warhead and a propulsion system (for powered weapons only). This results in a very inexpensive weapon with a launch and leave (autonomous) capability. The computational procedure used in the platform uses several radar measurements spaced many degrees apart. The accuracy is increased if more measurements are made. The computational algorithm uses the radar measurements to determine the point in a plane where the target is thought to be and the optimum flight path through that point. The weapon is flown along the optimum flight path and the impact with the ground results in a very good CEP when a sufficientnumber of radar measurements are made. The present invention provides fully autono-mous, all-weather, high precision weapon delivery while achieving a relatively low cost. High precision weapon guidance is provided by the unique differential guidance technique (if a sufficiently accurate and stable navigation system is used).
Description
20Q58~7 AUTONOMOUS PRECISION WEAPON
DELIVERY USING SYI~ I H~; l lC ARRAY RADAR
BACKGROUND
The present invention related to guidance systems, and more particularly, to a method and ap~alus for providing autonomous precision gl~ n~e of ail ~ 1C
weapons.
Although many of the ~._apons utilized during the Desert Storm conflict were 5 lc~ k~bly effective, this exercise demonstrated the limited usefulness of the current WCa~ll inventory in adverse weather conditions. Because of the integral relationship b~ sensors (for targeting) and weapons, it's logical to look at a radar sensor to help resolve the adverse weather proble~ Radar SAR (synthetic array radar) targeting has been employed for many years, but never with the concictently precise accuracies 10 demonstrated by TV, FLIR and laser guided weapons in Desert Storm. High resolu-tion radar missile secekers have been in development for several years; however, these concepts still lc~l~sent much more technical risk and cost than the Air Force can bcar for a near-term all-weather, precision guided munition.
Therefore it is an objective of the present invention to provide an autonomous lS precision weapon guidance system and method for use in guiding of aillull~e weapons, and the like.
*
DELIVERY USING SYI~ I H~; l lC ARRAY RADAR
BACKGROUND
The present invention related to guidance systems, and more particularly, to a method and ap~alus for providing autonomous precision gl~ n~e of ail ~ 1C
weapons.
Although many of the ~._apons utilized during the Desert Storm conflict were 5 lc~ k~bly effective, this exercise demonstrated the limited usefulness of the current WCa~ll inventory in adverse weather conditions. Because of the integral relationship b~ sensors (for targeting) and weapons, it's logical to look at a radar sensor to help resolve the adverse weather proble~ Radar SAR (synthetic array radar) targeting has been employed for many years, but never with the concictently precise accuracies 10 demonstrated by TV, FLIR and laser guided weapons in Desert Storm. High resolu-tion radar missile secekers have been in development for several years; however, these concepts still lc~l~sent much more technical risk and cost than the Air Force can bcar for a near-term all-weather, precision guided munition.
Therefore it is an objective of the present invention to provide an autonomous lS precision weapon guidance system and method for use in guiding of aillull~e weapons, and the like.
*
SUMMARY OF THE INVENTION
The invention comprises a system and method that uses a differential computa-tion of position relative to a launching aircraft and then computes an optimum weapon flight path to guide a weapon payload to a non-moving fixed or relocatable target. The invention comprises a radar platform having synthetic array radar (SAR) capability.
The weapon comprises an inertial navigational system (INS) and is adapted to guide itself to a target position. Since the weapon does not require its own seeker to locate the target, or a data link, the weapon is relatively inexpensive. The present invention uses the radar to locate the desired targets, so that long standoff ranges can be achieved.
Once the weapon is launched with the apyloyliate target coordinates, it operatesautonomously, providing for launch-and-leave capability.
The targeting technique employs the SAR radar on board the launching aircraft (or an independent targeting aircraft). Operator ~3eci n~tions of the target in two or more SAR images of the target area are combined into a single target position estim~te.
By synchronizing the weapon navigation system with the radar's navigation reference prior to launch, the target position estimate is placed in the weapon's coordinate frame.
Once provided the target position coor lin~tes, the weapon can, with sufficient accuracy in its navigation system (GPS aided navigation is preferred), guide itself to the target with high accuracy and with no need for a homing terrninal seeker or data link.
The present invention relies on a very stable coordinate system to be used as a radar reference. One good example is the ~. rollllance provided by the GPS naviga-tional system. The GPS navigational system uses four widely spaced c~t~llitçs The GPS receiver uses time of arrival measurements on a coded waveform to measure the range to each of the four s~tellites The receiver processcs the data to calculate its position relative to the earth. Most position errors are caused by non-compensated errors h the models for tr~ncmicsion media (ionosphere and troposphere). If the GPS
receiver moves a small ~ist~llce~ the media transmission errors are still applu~ ately the same; lllelefore the GPS receiver can measure that ~ t~nf e change very accurately.
As a result, the position and velocity estim~tes for the launching aircraft carrying a GPS
receiver e,~ ;en~es very little drift over a period of several ~ S or more. Thisstability is more difficult and expensive to achieve with other navigation systems.
The SAR radar measures the coordinates of the target relative to the launching aircraft. Therefore, the target position is known in the sarne coordinate frarne as the radar. If the weapon's navigation system is synchronized and matched with the radar's navigation system reference, the target position is also in the weapon's coordinate systerIL An effecti~e way of synchronizing the radar reference and the weapon naviga-tion system is to use GPS receivers on the weapon and in the launching aircraft. If the 20858~7 weapon is comm~n-led to operate using the same GPS constellation (nominally foursatellites) as the radar, the weapon will navigate in the same coordinate frame as the radar (and the target) without requiring a transfer align sequence between the aircraft and the weapon ~S. This use of relative, or differential, GPS elimin~t~s the position S bias inherent in the GPS system. In addition, the accuracy requirements of the INS
components on the weapon are less stringent and therefore less expensive. However, if the weapon ~S is sufficiently accurate and a transfer align prooedure is exercised in an adequately stable env~ el1t, this approach can be used for an inertially-guided weapon without GPS aiding and provide a~ oxilllately equivalent performance.
When the operator desi~n~tes a pixel in the SAR image corresponding to the target, the radar computes the range and range rate of that pixel relative to the aircraft at some time. Since the radar does not know the altitude difference bel~.~n the target and the platform, the target may not be in the image plane of the SAR map. As a result, the target's honzontal position in the SAR image may not coll~ ond to its true horizontal position. Although the range and range rate are colllpu~ed coll~;lly, altitude unc~ y results in a potentially incorrect estim~te of the target's horizontal position. The present invention rernoves this error by coLu~uling a flight path in the vicinity of the ground plane which causes the weapon to pass through the correct target point independent of the altitude error.
The present invention thus provides a highly accurate but relatively inexpensive~on system. It has a launch-and-leave capability that enables a pilot to ~lrc, otha duties (such as ~esign~ting otha targets) instead of weapon guid~nre The launch-and-leave c~bility of the present invention requires only that the pilot desig-nate the target on a SAR image once; the weapon system p~.Ç~ s the re!n~in~er of the functions without further pilot intervention. The pilot can then designate other targets on the same image or other images and multiple weapons may be l~llnrhe~ ~iml-lt~nr-ously. The pilot can then exit the targe~ area.
The present invention therefore provides fully autonomous, all-weather, high pleci~ion .~apon guidance while achieving a very low ~ on cost. High precision ~e~n guidance is provided by the unique differential gUi~1~nr~ technique (if a sllfficif ntly ac~ ale and stable navigation system is used). The present invention provides for a weapon targeting and delivery technique which (l) is very accurate (10-20 ft. CEP (Circular Error Probability)); (2) suffers no degradation in performance or utility in adverse weather conditions (smoke, rain, fog, etc.); (3) is applicable ~o non-moving relocatable targets (no extensive mission planning required); (4) supports a launch and leave (autonomous) weapon; (5) supports long stand-offrange; (6) may be applied to glide or powered weapons; and (7) requires a relatively inexpensive weapon.
3a 2o85847 Other aspects of this invention are as follows:
An autonomous weapon targeting and guidance system for identifying a non-moving fLl~ed or relor~-~ble target and guiding a weapon to the target, s~ud system compnsing:
an airbome platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving, fLsed ar relocatable target, a navigation subsystem, andp..Jcessing means for plocessing SAR data and navigation data to compute the position of the target and an optimum weapon flight path f~om the platform to the target using a predete,~fined comput~ion~l procedure; and a weapon having a navigation subsystem which ut~ cs a transf ~ nm~nt algorithrn to align the weapon's navigation system with the airborne platform's navigation system prior to launch, which weapon is adapted to rca~ d to data t~Lnsferred to it by the platform to pe~nit it to navigate relative to the navigation system of the airborne platform and autonomously navigate to the location of the target along the optimunl weapon flight path.
An autQ~omous weapon targeting and guidance system for identifying a non-moving target and guiding a weapon to the target, said system cornprising:
a global positioning system (GPS) comprising a plurality of sateUites that broadcast position data to pr~vide a coordinate r~ference f~ame;
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving target, a navigation subsystem that utilizes a glo~al positioning system (GPS) s2~ellirc system and which is adapted to respond to signals provided by the GPS s~ c system to pamit the platfonn to navigate relative thereto, and processing means for pl~csc;ng SAR data and navigation data to COL~ UIC the position of the target and an O~ J wc~n flight path ~m the platform to the target using ap,cdcte,.~ned c~ .u~ n~l proccdure; and a ~ .~n comprising a navigation subsystem that is ~ pte~l to utilize the GPS
s~tellite system and which responds to signals provided by the GPS c~telli~e sysum and dau transferred to it by the platform to permit it to navigate xlative tO the GPS ~r~llite system and autonomously navigate to the location of the target along the optimum weapon flight path.
3b 208584 7 A method for dc~r~ing a non-~ing urgct and guiding an airbome weapon to the targct, saud m~th~A compnsing thc steps of:
S providing a glo~oal poS;t;Qning system comprised of a plurality of $~11itcs that each b~adcast coc~dinate ~cf~cc dau for usc in navigation~
flying an a~ c platfo~n ov a targct area and naviga~ng using a naviga~on system that utilizes thc GPS S;~tC'~ system which pro~des the co~.linate reference f~me;
mapping the targct area using a synthe~c a~ay radar (SAR) system located on 10 the ai,l.wc platform to producc an original SAR map of thc targct area;
*s~ tin~ a targ on thc SAR map;
rc-mapping thc targct a~a a prlctermined numbcr of additional timcs at different angles relative to the target using the synthetic array radar system to produce a l,lcdctc,l. ine nllr,nl~ of ~iAition~l SAR maps of thc target area;
computing a precise target l~catioll and flight pa~h in the c~ linatc system pro ~idcd by thc global positioning system using thc navigation data and thc info~nation from each of the SAR rnaps;
transfemng s~lc~tc~A infGIIllation to thc weapon prior to its Launch comprising data indicative of an op~iml)m flight path to the target that should bc flown by the weapon, navigation system init~ on info~mation tha~ permits the w~n to acquire the satellites uscd by the plarform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquirc the satellit~s used by the platform for navigation and guide the weapon ~o the target based on the optimurn flight path computed in the platfomL
A method for ~eterting a non-rnoving target and guiding an airbome weapon to the target, said mcthod cornprising thc stcps of:
pr~viding a global ~ ;oning system comprised of a plu~lity of ~t~!lites that each br~adcast c~ iinate lcf~.cnce data for usc in navigation;
aying an a~ c pLatfo~m ov a targct arca and na~igating using a navigation system that ut~ cs thc GPS s~tellitc systcm which providcs the Coo~inaLc r~fcrcnce ~mc; , mapping ~e target area using a synthctic array radar (SAR) system locatcd on the ;hll~l,c platf~m t~ produce an onginal SAR map of thc target area;
d~cigr~ring a targa on the SAR map;
3c ~0~5847 rc-mapping thc target area a predctennined numb of additional t~m-~5 at differcnt anglcs rclativc to thc targct using thc synthetic a~ay radar systcm to p~ducc a S 1~ ~d~ ine numbcr of ~ ition~l SAR maps of the target ar~a;
corrclating thc imagcs from the additional SAR maps with thc original SAR map to e!imin~tc thc nced for rcpr~t~ targct designation;
computing a precise target location and flight path in thc coordinatc system provided by thc global positioning system using thc navigation data and the infor~nation f~m cach of thc SAR maps;
transfcrring sclccted information to the weapon prior to its launch comprising data indicative of an optimum flight path to thc target that should bc flown by thc weapon, navigation systcm initialization information that permits thc weapon to acqui~
thc satellitcs used by the pla~form for navigation, and target po.sition information; and launching the wcapon using a nav~gation system in the weapon to acquire the s~-ellit~s uscd by the platfonn for navigation and guidc the wcapon to thc target based on thc optimum flight path computed in thc platfonn BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the present invention may be more read-ily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like struc-S tural elements, and in which:
FIG. 1 is a diagram illustrating a weapon guidance system in accordance with the principles of the present invention shown in an operational envil~"~nt;
FIG. 2 is a block diagram of the system archite~t~lre of the system of FIG. l;
FIG. 3 shows the terminal weapon guidance path comy~ed in accordance with the principles of the present invention;
FIG. 4 shows an e~mple of the performance that is achievable with the system of the present invention for a 50 n~lltic~l mile range to a target.
DETAILED DESCRIPTION
Referring to the drawing figures, nG. 1 is a diagram illustrating a ~pon delivery system 10 in accordance with the principles of the present invention, shown in an operational en~ The weapon delivery system 10 is shown employed in conjunction with the global positioning system (GPS) 11 that employs four s~te~ . s 12a-12d that are used to deterrnine the position of an a ll,ol,le platform 13, or aircraft 13, having a deployable ~4eapon 14. Both the aircraft 13 and the deployable weapon 14 have co~lpatible inertial guidance systems (shown in FIG. 2) that are used to control the flight of the weapon 14.
As is shown in FIG. 1, the aircraft 13 flies over the earth, and a non-moving target 15 is located thereon. The aircraft 13 has a synthetic array radar (SAR) 16 that maps a target area 17 on the earth in the vicinity of the target 15. This is done a plural-ity of times to pl~luce multiple SAR maps 18a, 18b of the target area 17. At some point along the flight path of the aircraft 13, subsequent to weapon flight path cOIII~ula-tion, the ~.~apon 14 is l~lmrhed and flies a trajectory 19 to rhe target area 17 that is co...pu~ d in accordance with the present invention. Global positioning satellite system data 20 (GPS data 20) is l~n~ r~ from the s~t~llites 12a-12d to the aircraft 13 prior to launch, and to the .~apon 14 during its flight. Inertial leÇ~ nce data derived from the global positioning satellite system 11 is transferred to the weapon 14 prior to launch along with target flight pa~h data that directs the weapon 14 to the target 15.
FIG. 2 is a block diagram of the system architecture of the weapon delivery system 10 of FIG. 1. The weapon delivery system 10 comprises the following subsys-tems. In the aircraft 13 there is a radar targeting system 16 that includes a SAR mode execution subsystem 31 that comprises electronics that is adapted to process ~adar data s 208~847 to generate a SAR irnage. The SAR mode execution subsystem 31 is coupled to a target ~lesign~tion subsystem 32 that comprises electronics that is adapted to permit an operator tO select a po~ential target located in the SAR image. The target designation subsystem 32 is coupled to a SAR map selection subsystem 33 that deteImines the 5 number of additional maps that are r~uu~,d for target position co..l~utation. The SAR
map selection subsystem 33 is coupled to a rnap matching subsystem 34 that automati-cally ensures that subsequent SAR maps 18b are correlated to the first SAR map 18a, so that the target ~esign~teA in each subsequent map 18b is the sarne target designated in the first map 18a. The map matching subsystem 34 is coupled to a target position 10 co~ u~Lion subsystem 35 that co~ ules the target position and the optimum flight path 19 to the target 15 that should be flown by the weapon 14.
A support function subsystem 36 is provided that provides for automated target cueing 37 and precision map matching 38, whose outputs are .~,s~.,~i~ely coupled to the target design~tion subsystem 32 and the target position coLul)u~tion sub~y~ 35.
15 A navigation subsystem 39 is provided that comprises a GPS receiver 40 that receives data from the global positioning system 11, an inertial measuring unit (~MU) 42 that measures aircraft orientation and accelerations, and a K~lman filter 41 that computes the platform's position and velocity. The output of the Kalman filter 41 is coupled to the target position col~u~Lion subsystem 35. The system on the aircraft 13 couples pre-20 launch data such as target position, the GPS s~t~llites to use, Kalman filter initi~li7~tionpa~ c~.~ and weapon flight path inforrnation 43 to the ~.~,apon 14 prior to its launch.
The weapon 14 compri~es a weapon launch subsystem 51 that is coupled to a navigation and g~ nre unit 52 that steers the weapon 14 to thc target 15. A naviga-tion subsystem 55 is provided that comprises a GPS receiver 53 that receives data from 5 the global positioning system 11, an inertial measuring unit (IMU) 56 that measures OI~ o. ;e Il ~l ;on and accele.~tions, and a Kalman filter 54 that computes the ~rea~ll's ~i~n and velocity. The output of the Kalman filter 54 is coupled to the navigation and g~ n~e unit 52 that guides the weapon 14 to the target 15.
Ln operation, the present weapon delivery system 10 relies on a stable coordi-30 nate system that is used as the radar reference. One good example is the performanceprovided by the GPS navigational system 11. The GPS navigation~l system 11 uses the four widely spaced s~tellites 12a- 12d. The GPS receiver 40 in the aircraft 13 uses tirne of arrival measulc.llents on a coded waveform to mea~sure the range to each of the four s~te!lites 12a-12d. The receiver 40 processes the data to calculate its position on 35 the earth. Most of the errors in position are caused by noncompensated errors in the models for the tr~nsmicsion tnediums (ionosphere and llopo~h~le). ~f the GPS
re~eiver 40 moves a small distance, the m~il-m tr~nsmicsion errors are still approxi-mately the sarne; therefore the GPS receiver 40 can measure that ~ nre change veryaccurately. As a result, the posinon and velocity estimates for the aircraft 13 carrying the GPS receiver 40 experiences very little drift over a period of several minutes or more. This stability is more difficult and e,.~nsi-/e to achieve with other navigation 5 systems.
The radar targeting system 16 co~u~es the coordinates of the target 15 relative to the aircraft 13. Therefore, the target 15 position is known in the same coordinate frame that the radar 16 uses. The .~,a~n's navigation system 55 is synclu~,nized and matched with the radar's navigation system 39, and therefore the position of the target 10 15 will also be in the weapon's coordinate system. An effective way of synchronizing the radar's navigation system 39 and the weapon's navigation system 55 is to command the ~.~apon to operate using the ~me GPS conctell~tion (nominally four s~tellites 12a-12d) as the radar, the weapon 14 then will navigate in the same coordinate frame as the radar 16 (and the target 15). This use of relative, or differential GPS elimin~tes the 15 position bias inherent in the GPS syste~
When the o~lator ~esi~n~tes a pixel in the SAR image co~ ollding to the target 15, the radar targeting system 16 COlll~uL~S the range and range rate of that pixel relative to the aircraft 13 at some tirne. Since the radar targeting system 16 does not know the altitude diLrel.,llce between the target 15 and the platform 13, the target 15 20 may not be in the image plane of the SAR map 18. As a result, the target's horizontal position in the SAR irnage 18 may not cc,llc~ol d to its true horizontal position.
Although the range and range rate are c~lpuLcd COll~lly~ altitude uncc, Lainty results in a ~b~ ially illCvll~L estim~te of the target's horizontal position. The present invention removes this error by co,l-pu~,ng a flight path l9 in the vicinity of the ground plane 25 which causes the ~ )u" 14 to pass through the true target 15 plane in~l-,~nde.~t of the ~ltit~lde error.
The details of the implem~nt~A computational procedures used in the present invention is describe(i in detail in the atIached Appendix. The target c ,~ ;on algo-rithm optimally cc,-lbines the radar mea~ with navigation e ,~ ,s to a~ive at 30 the target loc~ti~ n in the radars navigation coordinate syste~
A more de~i1p~ descli~on of the operation of the weapon delivery system 10 is l~lesent~ below. The ~._apon delivery system lO uses the stability of the GPS navi-gational system 11 to provide accurate platform location for weapon delivery. The GPS navigational system 11 is comprised of four widely spaced s7~tellites 12a-12d that 35 br{~adcast coded tr~ncmicsions used by the aircraft's GPS receiver 40 to compute the aircraft location and velocity with great precision. While the GPS navigational system 11 p~o~ndes position measurements with a very small variance, the position bias may be 7 20s5s47 si~nific~nt However, most of the bias in GPS position estimates are caused by un-coil,~usated errors in the atmospheric models. If the GPS receiver 40 traverses small distances (e.g., 40 n~lltic~l miles), the effects of the atmospheric tr~ncmicsion delays remain relatively conct~nt Therefore, the GPS receiver 40 can detennine its location in 5 the biased coordinate frame with great precision. Since the location of the target 15 is provided by the radar 16 in coordinates relative to the ai~raft 13 and the weapon 14 uses the same displaced coordinate system, the effect of the GPS position bias is elimi-nate~ Thelefo-~, the ~ea~ll delivery system 10 may use the GPS system 11 to pro-vide highly accurate targeting and weapon delivery.
Using the weapon delivery system 10 is a relatively simple process. FIG. 1 shows the typical targeting and weapon launch sequence for the weapon delivery sys-tem 10. As the aircraft 13 passes near the target 15, the operator ~clrOllllS a high reso-lution SAR map 18a (approximately 10 feet) of the target area 17. Once the operator has verified the target 15 as a target of interest, the o~.dtor deci~n~tes the target 15 with a cursor. To improve the accuracy of the weapon delivery, the o~idtor performs one 0 more ad~lition~l maps 18b of the target area 17 from a different g~LU~IliC orien-tation. The weapon delivery system 10 ~lltom~*r~lly correlates the additional map 18b (or maps) with the initial map 1 8a used for target ~lesign~*nn. The target posi*on illfc~ lation from all the maps is used by the model (col,lpu~tional process) to compute a re precise target location in the relative GPS coordinate system. Typically, only one ~d-li*--n~l map 18b is n~es~ ~ to provide sllffirient target position accuracy for the high p~cision ~.~a~n delivery. The operator then launches the .~ 14 againstthe ~1~si~n~ted target 15. The navigation and guidance unit 52 in the .~n 14 guides it on the op~uuLu flight path 19 to ensure accuracy.
There are five key fe~ ,s that make this weapon delivery system 10 superior to other weapon delivery systems. The first and primary feature of the weapon delive~y system 10 is its ~llton~mous~ all-weather weapon delive~y c~pability. Ihis feature alone provides many b~nefitc over conventional weapon delive~y systems. Once thev~ea~on 14 is l~ chloA no post-launch aircraft support is ne~c~ to ensure accurate ~eapon delivery. The second major feature of the weapon delivery system 10 is the e1imin~tion of the need for weapons 14 conr~ining sensors. The çlimin~tion of sensors allows substantial financial savings in weapon costs. The third major feature of the weap~on delivery system 10 is that the operator (pilot) is ~equired to designate the target 15 only once. This not only reduces pilot workload and allows the pilot to m~int~in situational awareness, but also reduces eIrors caused by not designating ~e same point in subsequent maps. A fourth feature of the weapon delivery system 10 is its versa-tility. The weapon delivery system 10 may be used to deliver glide bombs or air to 2085~47 ground missiles, for example. A fifth benefit of the weapon delivery system 10 is its differential GPS guidance algorithm. Since the weapon 14 is guided using a GPS
aided navigational system 11, an all weather precision accuracy of 10-15 ft is achiev-able. A more accurate weapon 14 allows the use of smaller, less expensive warheads S which allows the platform 13 to carry more of them and enh~nce mission capability.
The block diagram of the weapon delivery system 10 is shown in FlG. 2. This figure outlines the functional elements of the weapoll delivery system 10 as well as the operational procedure necessary to use the system 10. The weapon delivery system 10 requires three basic elem~nts These three elements include the GPS satellite system 11, the radar targeting system 16, and the ~.,apon 14 cont~ining a GPS aided naviga-tion system 55. These aspects of the weapon delivery system 10 are described in greater detail below.
The GPS satellite system 11 is comprised of the four s~tellites 12a-12d which broadcast coded waveforms which allow the GPS receivers 40, 53 in the ai~ft 13 15 and in the weapon 14 to CO~ u~ their locations in the GPS coordinate frame. The SAR platform 13, or aircraft 13, contains a GPS aided navigation subsystem 39 and a radar targeting system 16 with a high-resolution SAR capability. The SAR platform 13 detects the target 15 and co~ ul~,s the weapon flight path 19 to deliver the weapon 14 to the target 15. The ~.ea~n 14 receives pre-launch target position information 20 from the SAR platform 13 and uses its own GPS aided navigation system 55 to autono-mously navigate to the target location.
As is illustrated in FIG. 2, the operation of the weapon delivery system 10 is comprised of seven basic steps. The first step is target ~etection As the SAR platform 13 approaches the target area 17, the operator co,.,.,.~n-ls the SAR mode to perfonn a 25 high resolllti~n map 18a of the desired target area 17. The second step is target desig-nation. Once the ope~aL~ has verified that the ~lete~te~ target 15 is a target of interest, the o~~ designates the target 15 with a cursor. The thLrd step is to acquire addi-tional SAR maps 18b of the target from different target angles. These ~rlrlition~l maps allow the weapon delivery system 10 to compute the target position more accurately.
30 The number of maps nP~ess~- y to achieve a specific OEP requirement varies with the geometry at which the SAR maps 18 are obtained. However, in general, only one ortwo additional maps 18b are re~luired to achieve a 1~15 foot CEP.
The fourth event in the weapon delivery system 10 operational scenario is map matching. The weapon delivery system 10 autom~tic~lly correlates the images of the 35 additional SAR maps 18b with the original SAR rnap 18a to elimin~te the need for repeat~d operator target 3çsign~tion. The fifth step is to CO~ )Ut~ the target position and the weapon flight path 19 through that position. The target position information f~m all the maps is used by the weapon delivery system 10 to compute a more precise target location in the relative GPS coordinate system. The sixth step is comprised of the auto-rnatic loading of the pre-launch weapon information. The weapon 14 receives flight path information, navigation initi~li7~tion infoml~ion, and target position inforrnation 5 prior to launch. The seventh event in the weapon delivery system 10 operational scenario is weapon launch. Once the pre-launch inforrnation has been loaded into the weapon 14, the operator is free to launch the weapon 14 against the design~te~ target 15. The weapon's GPS aided navigation system 55 autom~ti~lly acquires the same GPS 5~tPllites 12a-12d used by the aircraft 13 for navigation and the weapon's naviga-tion and guidance unit 52 then guides the weapon 14 to t'ne target 15 based on the flight path information co.lll.ut~d by the SAR platform 13.
Most of the processing required for the weapon delivery system 10 takes placeon the SAR platform 13. The SAR platform 13 contains the GPS aided navigation system 39 for aircraft position and velocity computation as well as the radar largel~ng system 16 which dc~e .. ;.-es t'ne position of the target 15 with respect to the aircraft 13.
The ~ cessing which occurs on the SAR platform 13 may be ~ d in five steps:(1) SAR mode e~ce~ution initial detection of the desired target 15. (2) Target designa-tion: operator design~tion of the target of interest. (3) ~ lition~l SAR maps: additional SAR maps 18b of target area 17 to provide improved target po~iLion accuracy. (4)20 A~1t~)m~ted map ...~ching a~ ;c ~cl~lng of ~ ition~l maps 18 to cnsure accurate target ~esi~n~tion (5) Target position computation: co~ a~ion of target positionbased on the posilion and velocity estim~tes of the ai~raft 13 and SAR map measure-ments. Each of these five proces~ing steps are discussed in detail below.
The first step in the use of the weapon delivery system 10 is the SAR mode 25 ex~ tion The initial SAR mode execution p~ovides the operator with a SAR image of the target area 17. The operator may perform several low resolution maps 18 of the target arca 17 before pe-ro ~ng a high resolution map of the target 15. Only high rcsolP~ on maps 18 of the target area 17 are used as an initial map in thc . ~àpon deliv-ery system 10 since small OEPs are desirable for weapon delivery. Therefore, all SAR
30 maps 18 used for targeting typically have pixel sizes of 10 feet or less.
Once the O~latu~ has ~erified the target 15 as a target of interest, ~e operatordesignates the target 15 with a cursor. Although m~lltiple SAR maps 18 are m~rle to ensure precision weapon delivery, the operator only needs to ~ ign~te the target 15 once. To aid in target designation, a library of target templates is provide~ ~is target 35 t~mp!~te library, part of the target cueing function 37, provides the operator with an image of what the target 15 should look like and which target pixel should be designat-e~ The target cueing function 37 provides the templates to assist the operator in targeting and desi~nAtion. The computer-aided target cueing function 37 not only aids the o~ atur in designating the correct target 15, but also minimi7es the design~tion error by providing a zoom capability.
After the ~yelalol has designated the target 15, additional high resolution SAR
5 maps of the target 15 must be ~.rolll,ed to improve the accuracy of the target position compulation. These addition rnaps should be ~.fo~ cd at a dirre.e,~t o~ientation with respect to the target 15. As more maps of the target 15 are obtained from difr~l~nt g~ll~Lfic aspects, the accuracy of the coll,~u~ed position increases. Typically only one additional map 18 is necessAry to achieve a srnall OEP (~10-15 feet). However, the 10 requisite number of adrlitionAl maps 18 required to achieve a small CEP will vary according IO a nurnber of factors including target-to-aircraft geometry, SAR mapresolution, platform velocity, and platform ~Ititude Once A~l~litionAl maps 18 of the design~ted target 15 are performed, the ope.~o is not required to designAte the targets 15 in the new images. ~ncteA~l, the weapon 15 delivery system 10 pe-r~ s high precision map ll~tching to accurately locate the same decigrAted target 15 in the additional SAR maps 18. The map rnatching algorithm used to design~te the targets 15 in the subsequent images is provided by the precision map-mAt~hing function 38. The high precision map ma~ching function 38 ~ lA~ Ally determines the coordinate transformations necessary to align the two SAR images.20 While the accuracy of the n~A~h;ng algoliLhlll may vary with image content and size, subpixel accuracy is poscible with irnages of only modest contrast ratio.
The target e,~ l;Qn algorithm combines all of the SAR radar ~-l~ule.lRnt~
with the aircraft navigation position and velocity e~ llAtc s to obtain the target location in the relative GPS coordinate system. The outputs of the platform's GPS receiver 40 25 and IMU 42 are pnxe~c~ by the Kalrnan filter 4l and the outputs of the Kalman filter 41 ~e rY~i At~ to the time the SAR map 18 was formed to ~ t~ ;nÇ the position and vdocity vector to associate with the SAR image data Once the map I~A~ç~ g pr~xe.lL~e is completed and all SAR target measurementc are ~lful~d, the p~llcLers of the target içcignAted by the operator are computed in the GPS coordinate system 30 concisten~ witn the GPS system 11. After the target location is CUlllpul~d. the weapon delivery system 10 COl~ 't~ S an optimal weapon flighl path 19 to ensure precise. e~on delivery. The flight path 19 of the weapon that is c-ol~ ed by the weapon delivery system 10 is the best flight path through the e~timAted target position. If the missile is flown along this path, it is guaranteed to intersect the target plane near the 35 target regardless of the actual altitude ûf the target, as is illustrated in FIG. 3.
Before weapon launch, the weapon delivery system 10 downloads the comput-ed flight patn into the weapon's navigation and guidance unit 52. The sys~em 10 also 11 2~85847 downloads the coefficients necessary for the weapon to initialize its navigation subsys-tem 55 to elimin~te any initial errors between the SAR platform's navigation system 39 and the weapon's navigation system 55. Additionally, the SAR platform 13 provides the weapon 14 with infolulation regarding which GPS s~tellites 12a-12d to use for 5 position cc,.~plllation. Use of the same GPS satellites 12a-12d for aircraft and weapon position deterrnination ensures the same precise differential GPS coordinate system is used for both the weapon 14 and the aircraft 13. Other information the weapon receives prior to launch includes the target po~iliol,. Once the initi~li7~tiQn parameters are received from the SAR platform 13 and the weapon 14 initi~li7~s its navigation 10 subsystem 55, the weapon 14 is ready for launch.
After launch, the navigation subsystem 55 in the weapon 14 is used by the navigation and guidance ~ JpUl~ 52 to guide the weapon 14 along the pre-computedflight path 19 to the target 15. After launch, no co.. ~ tions between the weapon 14 and the SAR platform 13 are necessary. The SAR platfo~ 13 is free to leave the 15 target area 17.
To determine the accuracy of the weapon delivery system 10, the basic error sources must first be identified. In general, there are two sets of error sources which can degrade the accuracy of weapon delivery using the wc~on delivery system 10.
The first set are the errors associated with the radar targeting system 16. These errors 20 include errors in the aircraft position and velocity data from thc navigation system 39, errors in the radar mea~ulcu~r,b (range and range rate) from the SAR rnode 31, and errors associated with the design~tion function 32. The second set of errors are associ-ated with the navigation and guidance errors of the ~.capon 14. The navigation errors are ~csoci:~t~A with incorrect position e~ es of the ~.~apon's navigation subsystem 25 55. The ~irl~nre erTors are associated with not guiding the weapon 14 along the cor~t fligh~ path 19 (e.g., due to wind) by the navigation and guidance unit 52 of the .eal~on 14.
Given the navigation subsystem 39 position and velocity estim~ts accuracies and the SAR mode L~UlCllb lll accuracies, the accuracy of the weapon delivery 30 system 10 may be analyzed The accuracy of the ~.~n delivery system 10 also depends upon the accuracy of the designation and the .. ea~on's ability to na~igate to the target 15 along the collll~u~ed flight path 19. The more mea~ ~nls that are made, the lower the variance of the estim~ted target position. To reduce the target position error, each SAR target position measurement is optimally combined in a filter tO exploit 35 the full benefits of multiple target detections.
FIG. 4 shows the targeting performance of the weapon delivery system 10 when the SAR platform 13 is flying in a straight line pa~h toward the target 15 from an initial range of 50 n~utic~l miles and squint angle of 20 degrees. For the targeting per-formance chart shown in FIG. 4, the horizontal axis represents the elapsed time for the last mea~u~c,llent since the first SAR map 18 was performed (mea~ cnts are made at equal angles). The speed of the aircraft 13 is ~s..med to be 750 feet per second and the altitude is 45,000 fee~ The left vertical axis represents the squint angle in degrees or the ground range to the target 15 in n~utic~l miles. The right vertical axis represents the OEP in feet. The performance of FIG. 4 ~ s the following values for the error sources:
a radar navigation position error of 1.29 feet (1 ~), a radar navigation velocity error of 0.26 feetlsecond (1 ~), and a radar range mea~ t error of ~r2(n).
The radar range rate measurement error ar (n) is given by ~r(n) (38411) + 25~
where r(n) is the range at time n.
Thus, the radar range rate measul~en~ error is ar(n) = (36(n)3) + 12.5 750 - v2(n), where v(n) is the range rate at time n, the designation error is 4 feet (OEP), the weapon navigation error is S feet (CEP), and the weapon guidance e~or is 3 feet (OEP).
For the 50 n~utic~l mile case shown in FIG. 4, the ~eapon delivery system 10 can achieve a 14 foot OEP by making a second mea~ ;~nt 5 n~i nutC S after the first.
At this point the aircraft 13 has flown through an angle of 40 degrees and is 20 n~tit~l miles from the target. Ma~ng more than two measulc.~nls does not improve the OEPvery much. The time required to make these extra measule~llerlt~ is better utilized by im~ing other target areas. re~ro~ nce of this weapon delivery system 10 depends only on the location of the SAR platform 13 relative to the target 15 when the measu-re-ments are made and is in~epen~lerlt of the aircraft flight path used to get the SAR plat-form 13 to those meaaul~nt locations.
Thus there has been described a new and improved method and appa-ratus for providing ~ ono.,.ous precision guidance of airborne weapons. It is to be understood that the above-described emk~liment is merely illustrative of some of the many specific embolim~nt~ which l~ s-,nt applications of the principles of the present invention.
Clearly, numerous and other arrangements can be readily devised by those sl~lled in the art without depar~ing from the scope of the inven~ion.
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The invention comprises a system and method that uses a differential computa-tion of position relative to a launching aircraft and then computes an optimum weapon flight path to guide a weapon payload to a non-moving fixed or relocatable target. The invention comprises a radar platform having synthetic array radar (SAR) capability.
The weapon comprises an inertial navigational system (INS) and is adapted to guide itself to a target position. Since the weapon does not require its own seeker to locate the target, or a data link, the weapon is relatively inexpensive. The present invention uses the radar to locate the desired targets, so that long standoff ranges can be achieved.
Once the weapon is launched with the apyloyliate target coordinates, it operatesautonomously, providing for launch-and-leave capability.
The targeting technique employs the SAR radar on board the launching aircraft (or an independent targeting aircraft). Operator ~3eci n~tions of the target in two or more SAR images of the target area are combined into a single target position estim~te.
By synchronizing the weapon navigation system with the radar's navigation reference prior to launch, the target position estimate is placed in the weapon's coordinate frame.
Once provided the target position coor lin~tes, the weapon can, with sufficient accuracy in its navigation system (GPS aided navigation is preferred), guide itself to the target with high accuracy and with no need for a homing terrninal seeker or data link.
The present invention relies on a very stable coordinate system to be used as a radar reference. One good example is the ~. rollllance provided by the GPS naviga-tional system. The GPS navigational system uses four widely spaced c~t~llitçs The GPS receiver uses time of arrival measurements on a coded waveform to measure the range to each of the four s~tellites The receiver processcs the data to calculate its position relative to the earth. Most position errors are caused by non-compensated errors h the models for tr~ncmicsion media (ionosphere and troposphere). If the GPS
receiver moves a small ~ist~llce~ the media transmission errors are still applu~ ately the same; lllelefore the GPS receiver can measure that ~ t~nf e change very accurately.
As a result, the position and velocity estim~tes for the launching aircraft carrying a GPS
receiver e,~ ;en~es very little drift over a period of several ~ S or more. Thisstability is more difficult and expensive to achieve with other navigation systems.
The SAR radar measures the coordinates of the target relative to the launching aircraft. Therefore, the target position is known in the sarne coordinate frarne as the radar. If the weapon's navigation system is synchronized and matched with the radar's navigation system reference, the target position is also in the weapon's coordinate systerIL An effecti~e way of synchronizing the radar reference and the weapon naviga-tion system is to use GPS receivers on the weapon and in the launching aircraft. If the 20858~7 weapon is comm~n-led to operate using the same GPS constellation (nominally foursatellites) as the radar, the weapon will navigate in the same coordinate frame as the radar (and the target) without requiring a transfer align sequence between the aircraft and the weapon ~S. This use of relative, or differential, GPS elimin~t~s the position S bias inherent in the GPS system. In addition, the accuracy requirements of the INS
components on the weapon are less stringent and therefore less expensive. However, if the weapon ~S is sufficiently accurate and a transfer align prooedure is exercised in an adequately stable env~ el1t, this approach can be used for an inertially-guided weapon without GPS aiding and provide a~ oxilllately equivalent performance.
When the operator desi~n~tes a pixel in the SAR image corresponding to the target, the radar computes the range and range rate of that pixel relative to the aircraft at some time. Since the radar does not know the altitude difference bel~.~n the target and the platform, the target may not be in the image plane of the SAR map. As a result, the target's honzontal position in the SAR image may not coll~ ond to its true horizontal position. Although the range and range rate are colllpu~ed coll~;lly, altitude unc~ y results in a potentially incorrect estim~te of the target's horizontal position. The present invention rernoves this error by coLu~uling a flight path in the vicinity of the ground plane which causes the weapon to pass through the correct target point independent of the altitude error.
The present invention thus provides a highly accurate but relatively inexpensive~on system. It has a launch-and-leave capability that enables a pilot to ~lrc, otha duties (such as ~esign~ting otha targets) instead of weapon guid~nre The launch-and-leave c~bility of the present invention requires only that the pilot desig-nate the target on a SAR image once; the weapon system p~.Ç~ s the re!n~in~er of the functions without further pilot intervention. The pilot can then designate other targets on the same image or other images and multiple weapons may be l~llnrhe~ ~iml-lt~nr-ously. The pilot can then exit the targe~ area.
The present invention therefore provides fully autonomous, all-weather, high pleci~ion .~apon guidance while achieving a very low ~ on cost. High precision ~e~n guidance is provided by the unique differential gUi~1~nr~ technique (if a sllfficif ntly ac~ ale and stable navigation system is used). The present invention provides for a weapon targeting and delivery technique which (l) is very accurate (10-20 ft. CEP (Circular Error Probability)); (2) suffers no degradation in performance or utility in adverse weather conditions (smoke, rain, fog, etc.); (3) is applicable ~o non-moving relocatable targets (no extensive mission planning required); (4) supports a launch and leave (autonomous) weapon; (5) supports long stand-offrange; (6) may be applied to glide or powered weapons; and (7) requires a relatively inexpensive weapon.
3a 2o85847 Other aspects of this invention are as follows:
An autonomous weapon targeting and guidance system for identifying a non-moving fLl~ed or relor~-~ble target and guiding a weapon to the target, s~ud system compnsing:
an airbome platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving, fLsed ar relocatable target, a navigation subsystem, andp..Jcessing means for plocessing SAR data and navigation data to compute the position of the target and an optimum weapon flight path f~om the platform to the target using a predete,~fined comput~ion~l procedure; and a weapon having a navigation subsystem which ut~ cs a transf ~ nm~nt algorithrn to align the weapon's navigation system with the airborne platform's navigation system prior to launch, which weapon is adapted to rca~ d to data t~Lnsferred to it by the platform to pe~nit it to navigate relative to the navigation system of the airborne platform and autonomously navigate to the location of the target along the optimunl weapon flight path.
An autQ~omous weapon targeting and guidance system for identifying a non-moving target and guiding a weapon to the target, said system cornprising:
a global positioning system (GPS) comprising a plurality of sateUites that broadcast position data to pr~vide a coordinate r~ference f~ame;
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving target, a navigation subsystem that utilizes a glo~al positioning system (GPS) s2~ellirc system and which is adapted to respond to signals provided by the GPS s~ c system to pamit the platfonn to navigate relative thereto, and processing means for pl~csc;ng SAR data and navigation data to COL~ UIC the position of the target and an O~ J wc~n flight path ~m the platform to the target using ap,cdcte,.~ned c~ .u~ n~l proccdure; and a ~ .~n comprising a navigation subsystem that is ~ pte~l to utilize the GPS
s~tellite system and which responds to signals provided by the GPS c~telli~e sysum and dau transferred to it by the platform to permit it to navigate xlative tO the GPS ~r~llite system and autonomously navigate to the location of the target along the optimum weapon flight path.
3b 208584 7 A method for dc~r~ing a non-~ing urgct and guiding an airbome weapon to the targct, saud m~th~A compnsing thc steps of:
S providing a glo~oal poS;t;Qning system comprised of a plurality of $~11itcs that each b~adcast coc~dinate ~cf~cc dau for usc in navigation~
flying an a~ c platfo~n ov a targct area and naviga~ng using a naviga~on system that utilizes thc GPS S;~tC'~ system which pro~des the co~.linate reference f~me;
mapping the targct area using a synthe~c a~ay radar (SAR) system located on 10 the ai,l.wc platform to producc an original SAR map of thc targct area;
*s~ tin~ a targ on thc SAR map;
rc-mapping thc targct a~a a prlctermined numbcr of additional timcs at different angles relative to the target using the synthetic array radar system to produce a l,lcdctc,l. ine nllr,nl~ of ~iAition~l SAR maps of thc target area;
computing a precise target l~catioll and flight pa~h in the c~ linatc system pro ~idcd by thc global positioning system using thc navigation data and thc info~nation from each of the SAR rnaps;
transfemng s~lc~tc~A infGIIllation to thc weapon prior to its Launch comprising data indicative of an op~iml)m flight path to the target that should bc flown by the weapon, navigation system init~ on info~mation tha~ permits the w~n to acquire the satellites uscd by the plarform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquirc the satellit~s used by the platform for navigation and guide the weapon ~o the target based on the optimurn flight path computed in the platfomL
A method for ~eterting a non-rnoving target and guiding an airbome weapon to the target, said mcthod cornprising thc stcps of:
pr~viding a global ~ ;oning system comprised of a plu~lity of ~t~!lites that each br~adcast c~ iinate lcf~.cnce data for usc in navigation;
aying an a~ c pLatfo~m ov a targct arca and na~igating using a navigation system that ut~ cs thc GPS s~tellitc systcm which providcs the Coo~inaLc r~fcrcnce ~mc; , mapping ~e target area using a synthctic array radar (SAR) system locatcd on the ;hll~l,c platf~m t~ produce an onginal SAR map of thc target area;
d~cigr~ring a targa on the SAR map;
3c ~0~5847 rc-mapping thc target area a predctennined numb of additional t~m-~5 at differcnt anglcs rclativc to thc targct using thc synthetic a~ay radar systcm to p~ducc a S 1~ ~d~ ine numbcr of ~ ition~l SAR maps of the target ar~a;
corrclating thc imagcs from the additional SAR maps with thc original SAR map to e!imin~tc thc nced for rcpr~t~ targct designation;
computing a precise target location and flight path in thc coordinatc system provided by thc global positioning system using thc navigation data and the infor~nation f~m cach of thc SAR maps;
transfcrring sclccted information to the weapon prior to its launch comprising data indicative of an optimum flight path to thc target that should bc flown by thc weapon, navigation systcm initialization information that permits thc weapon to acqui~
thc satellitcs used by the pla~form for navigation, and target po.sition information; and launching the wcapon using a nav~gation system in the weapon to acquire the s~-ellit~s uscd by the platfonn for navigation and guidc the wcapon to thc target based on thc optimum flight path computed in thc platfonn BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the present invention may be more read-ily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like struc-S tural elements, and in which:
FIG. 1 is a diagram illustrating a weapon guidance system in accordance with the principles of the present invention shown in an operational envil~"~nt;
FIG. 2 is a block diagram of the system archite~t~lre of the system of FIG. l;
FIG. 3 shows the terminal weapon guidance path comy~ed in accordance with the principles of the present invention;
FIG. 4 shows an e~mple of the performance that is achievable with the system of the present invention for a 50 n~lltic~l mile range to a target.
DETAILED DESCRIPTION
Referring to the drawing figures, nG. 1 is a diagram illustrating a ~pon delivery system 10 in accordance with the principles of the present invention, shown in an operational en~ The weapon delivery system 10 is shown employed in conjunction with the global positioning system (GPS) 11 that employs four s~te~ . s 12a-12d that are used to deterrnine the position of an a ll,ol,le platform 13, or aircraft 13, having a deployable ~4eapon 14. Both the aircraft 13 and the deployable weapon 14 have co~lpatible inertial guidance systems (shown in FIG. 2) that are used to control the flight of the weapon 14.
As is shown in FIG. 1, the aircraft 13 flies over the earth, and a non-moving target 15 is located thereon. The aircraft 13 has a synthetic array radar (SAR) 16 that maps a target area 17 on the earth in the vicinity of the target 15. This is done a plural-ity of times to pl~luce multiple SAR maps 18a, 18b of the target area 17. At some point along the flight path of the aircraft 13, subsequent to weapon flight path cOIII~ula-tion, the ~.~apon 14 is l~lmrhed and flies a trajectory 19 to rhe target area 17 that is co...pu~ d in accordance with the present invention. Global positioning satellite system data 20 (GPS data 20) is l~n~ r~ from the s~t~llites 12a-12d to the aircraft 13 prior to launch, and to the .~apon 14 during its flight. Inertial leÇ~ nce data derived from the global positioning satellite system 11 is transferred to the weapon 14 prior to launch along with target flight pa~h data that directs the weapon 14 to the target 15.
FIG. 2 is a block diagram of the system architecture of the weapon delivery system 10 of FIG. 1. The weapon delivery system 10 comprises the following subsys-tems. In the aircraft 13 there is a radar targeting system 16 that includes a SAR mode execution subsystem 31 that comprises electronics that is adapted to process ~adar data s 208~847 to generate a SAR irnage. The SAR mode execution subsystem 31 is coupled to a target ~lesign~tion subsystem 32 that comprises electronics that is adapted to permit an operator tO select a po~ential target located in the SAR image. The target designation subsystem 32 is coupled to a SAR map selection subsystem 33 that deteImines the 5 number of additional maps that are r~uu~,d for target position co..l~utation. The SAR
map selection subsystem 33 is coupled to a rnap matching subsystem 34 that automati-cally ensures that subsequent SAR maps 18b are correlated to the first SAR map 18a, so that the target ~esign~teA in each subsequent map 18b is the sarne target designated in the first map 18a. The map matching subsystem 34 is coupled to a target position 10 co~ u~Lion subsystem 35 that co~ ules the target position and the optimum flight path 19 to the target 15 that should be flown by the weapon 14.
A support function subsystem 36 is provided that provides for automated target cueing 37 and precision map matching 38, whose outputs are .~,s~.,~i~ely coupled to the target design~tion subsystem 32 and the target position coLul)u~tion sub~y~ 35.
15 A navigation subsystem 39 is provided that comprises a GPS receiver 40 that receives data from the global positioning system 11, an inertial measuring unit (~MU) 42 that measures aircraft orientation and accelerations, and a K~lman filter 41 that computes the platform's position and velocity. The output of the Kalman filter 41 is coupled to the target position col~u~Lion subsystem 35. The system on the aircraft 13 couples pre-20 launch data such as target position, the GPS s~t~llites to use, Kalman filter initi~li7~tionpa~ c~.~ and weapon flight path inforrnation 43 to the ~.~,apon 14 prior to its launch.
The weapon 14 compri~es a weapon launch subsystem 51 that is coupled to a navigation and g~ nre unit 52 that steers the weapon 14 to thc target 15. A naviga-tion subsystem 55 is provided that comprises a GPS receiver 53 that receives data from 5 the global positioning system 11, an inertial measuring unit (IMU) 56 that measures OI~ o. ;e Il ~l ;on and accele.~tions, and a Kalman filter 54 that computes the ~rea~ll's ~i~n and velocity. The output of the Kalman filter 54 is coupled to the navigation and g~ n~e unit 52 that guides the weapon 14 to the target 15.
Ln operation, the present weapon delivery system 10 relies on a stable coordi-30 nate system that is used as the radar reference. One good example is the performanceprovided by the GPS navigational system 11. The GPS navigation~l system 11 uses the four widely spaced s~tellites 12a- 12d. The GPS receiver 40 in the aircraft 13 uses tirne of arrival measulc.llents on a coded waveform to mea~sure the range to each of the four s~te!lites 12a-12d. The receiver 40 processes the data to calculate its position on 35 the earth. Most of the errors in position are caused by noncompensated errors in the models for the tr~nsmicsion tnediums (ionosphere and llopo~h~le). ~f the GPS
re~eiver 40 moves a small distance, the m~il-m tr~nsmicsion errors are still approxi-mately the sarne; therefore the GPS receiver 40 can measure that ~ nre change veryaccurately. As a result, the posinon and velocity estimates for the aircraft 13 carrying the GPS receiver 40 experiences very little drift over a period of several minutes or more. This stability is more difficult and e,.~nsi-/e to achieve with other navigation 5 systems.
The radar targeting system 16 co~u~es the coordinates of the target 15 relative to the aircraft 13. Therefore, the target 15 position is known in the same coordinate frame that the radar 16 uses. The .~,a~n's navigation system 55 is synclu~,nized and matched with the radar's navigation system 39, and therefore the position of the target 10 15 will also be in the weapon's coordinate system. An effective way of synchronizing the radar's navigation system 39 and the weapon's navigation system 55 is to command the ~.~apon to operate using the ~me GPS conctell~tion (nominally four s~tellites 12a-12d) as the radar, the weapon 14 then will navigate in the same coordinate frame as the radar 16 (and the target 15). This use of relative, or differential GPS elimin~tes the 15 position bias inherent in the GPS syste~
When the o~lator ~esi~n~tes a pixel in the SAR image co~ ollding to the target 15, the radar targeting system 16 COlll~uL~S the range and range rate of that pixel relative to the aircraft 13 at some tirne. Since the radar targeting system 16 does not know the altitude diLrel.,llce between the target 15 and the platform 13, the target 15 20 may not be in the image plane of the SAR map 18. As a result, the target's horizontal position in the SAR irnage 18 may not cc,llc~ol d to its true horizontal position.
Although the range and range rate are c~lpuLcd COll~lly~ altitude uncc, Lainty results in a ~b~ ially illCvll~L estim~te of the target's horizontal position. The present invention removes this error by co,l-pu~,ng a flight path l9 in the vicinity of the ground plane 25 which causes the ~ )u" 14 to pass through the true target 15 plane in~l-,~nde.~t of the ~ltit~lde error.
The details of the implem~nt~A computational procedures used in the present invention is describe(i in detail in the atIached Appendix. The target c ,~ ;on algo-rithm optimally cc,-lbines the radar mea~ with navigation e ,~ ,s to a~ive at 30 the target loc~ti~ n in the radars navigation coordinate syste~
A more de~i1p~ descli~on of the operation of the weapon delivery system 10 is l~lesent~ below. The ~._apon delivery system lO uses the stability of the GPS navi-gational system 11 to provide accurate platform location for weapon delivery. The GPS navigational system 11 is comprised of four widely spaced s7~tellites 12a-12d that 35 br{~adcast coded tr~ncmicsions used by the aircraft's GPS receiver 40 to compute the aircraft location and velocity with great precision. While the GPS navigational system 11 p~o~ndes position measurements with a very small variance, the position bias may be 7 20s5s47 si~nific~nt However, most of the bias in GPS position estimates are caused by un-coil,~usated errors in the atmospheric models. If the GPS receiver 40 traverses small distances (e.g., 40 n~lltic~l miles), the effects of the atmospheric tr~ncmicsion delays remain relatively conct~nt Therefore, the GPS receiver 40 can detennine its location in 5 the biased coordinate frame with great precision. Since the location of the target 15 is provided by the radar 16 in coordinates relative to the ai~raft 13 and the weapon 14 uses the same displaced coordinate system, the effect of the GPS position bias is elimi-nate~ Thelefo-~, the ~ea~ll delivery system 10 may use the GPS system 11 to pro-vide highly accurate targeting and weapon delivery.
Using the weapon delivery system 10 is a relatively simple process. FIG. 1 shows the typical targeting and weapon launch sequence for the weapon delivery sys-tem 10. As the aircraft 13 passes near the target 15, the operator ~clrOllllS a high reso-lution SAR map 18a (approximately 10 feet) of the target area 17. Once the operator has verified the target 15 as a target of interest, the o~.dtor deci~n~tes the target 15 with a cursor. To improve the accuracy of the weapon delivery, the o~idtor performs one 0 more ad~lition~l maps 18b of the target area 17 from a different g~LU~IliC orien-tation. The weapon delivery system 10 ~lltom~*r~lly correlates the additional map 18b (or maps) with the initial map 1 8a used for target ~lesign~*nn. The target posi*on illfc~ lation from all the maps is used by the model (col,lpu~tional process) to compute a re precise target location in the relative GPS coordinate system. Typically, only one ~d-li*--n~l map 18b is n~es~ ~ to provide sllffirient target position accuracy for the high p~cision ~.~a~n delivery. The operator then launches the .~ 14 againstthe ~1~si~n~ted target 15. The navigation and guidance unit 52 in the .~n 14 guides it on the op~uuLu flight path 19 to ensure accuracy.
There are five key fe~ ,s that make this weapon delivery system 10 superior to other weapon delivery systems. The first and primary feature of the weapon delive~y system 10 is its ~llton~mous~ all-weather weapon delive~y c~pability. Ihis feature alone provides many b~nefitc over conventional weapon delive~y systems. Once thev~ea~on 14 is l~ chloA no post-launch aircraft support is ne~c~ to ensure accurate ~eapon delivery. The second major feature of the weapon delivery system 10 is the e1imin~tion of the need for weapons 14 conr~ining sensors. The çlimin~tion of sensors allows substantial financial savings in weapon costs. The third major feature of the weap~on delivery system 10 is that the operator (pilot) is ~equired to designate the target 15 only once. This not only reduces pilot workload and allows the pilot to m~int~in situational awareness, but also reduces eIrors caused by not designating ~e same point in subsequent maps. A fourth feature of the weapon delivery system 10 is its versa-tility. The weapon delivery system 10 may be used to deliver glide bombs or air to 2085~47 ground missiles, for example. A fifth benefit of the weapon delivery system 10 is its differential GPS guidance algorithm. Since the weapon 14 is guided using a GPS
aided navigational system 11, an all weather precision accuracy of 10-15 ft is achiev-able. A more accurate weapon 14 allows the use of smaller, less expensive warheads S which allows the platform 13 to carry more of them and enh~nce mission capability.
The block diagram of the weapon delivery system 10 is shown in FlG. 2. This figure outlines the functional elements of the weapoll delivery system 10 as well as the operational procedure necessary to use the system 10. The weapon delivery system 10 requires three basic elem~nts These three elements include the GPS satellite system 11, the radar targeting system 16, and the ~.,apon 14 cont~ining a GPS aided naviga-tion system 55. These aspects of the weapon delivery system 10 are described in greater detail below.
The GPS satellite system 11 is comprised of the four s~tellites 12a-12d which broadcast coded waveforms which allow the GPS receivers 40, 53 in the ai~ft 13 15 and in the weapon 14 to CO~ u~ their locations in the GPS coordinate frame. The SAR platform 13, or aircraft 13, contains a GPS aided navigation subsystem 39 and a radar targeting system 16 with a high-resolution SAR capability. The SAR platform 13 detects the target 15 and co~ ul~,s the weapon flight path 19 to deliver the weapon 14 to the target 15. The ~.ea~n 14 receives pre-launch target position information 20 from the SAR platform 13 and uses its own GPS aided navigation system 55 to autono-mously navigate to the target location.
As is illustrated in FIG. 2, the operation of the weapon delivery system 10 is comprised of seven basic steps. The first step is target ~etection As the SAR platform 13 approaches the target area 17, the operator co,.,.,.~n-ls the SAR mode to perfonn a 25 high resolllti~n map 18a of the desired target area 17. The second step is target desig-nation. Once the ope~aL~ has verified that the ~lete~te~ target 15 is a target of interest, the o~~ designates the target 15 with a cursor. The thLrd step is to acquire addi-tional SAR maps 18b of the target from different target angles. These ~rlrlition~l maps allow the weapon delivery system 10 to compute the target position more accurately.
30 The number of maps nP~ess~- y to achieve a specific OEP requirement varies with the geometry at which the SAR maps 18 are obtained. However, in general, only one ortwo additional maps 18b are re~luired to achieve a 1~15 foot CEP.
The fourth event in the weapon delivery system 10 operational scenario is map matching. The weapon delivery system 10 autom~tic~lly correlates the images of the 35 additional SAR maps 18b with the original SAR rnap 18a to elimin~te the need for repeat~d operator target 3çsign~tion. The fifth step is to CO~ )Ut~ the target position and the weapon flight path 19 through that position. The target position information f~m all the maps is used by the weapon delivery system 10 to compute a more precise target location in the relative GPS coordinate system. The sixth step is comprised of the auto-rnatic loading of the pre-launch weapon information. The weapon 14 receives flight path information, navigation initi~li7~tion infoml~ion, and target position inforrnation 5 prior to launch. The seventh event in the weapon delivery system 10 operational scenario is weapon launch. Once the pre-launch inforrnation has been loaded into the weapon 14, the operator is free to launch the weapon 14 against the design~te~ target 15. The weapon's GPS aided navigation system 55 autom~ti~lly acquires the same GPS 5~tPllites 12a-12d used by the aircraft 13 for navigation and the weapon's naviga-tion and guidance unit 52 then guides the weapon 14 to t'ne target 15 based on the flight path information co.lll.ut~d by the SAR platform 13.
Most of the processing required for the weapon delivery system 10 takes placeon the SAR platform 13. The SAR platform 13 contains the GPS aided navigation system 39 for aircraft position and velocity computation as well as the radar largel~ng system 16 which dc~e .. ;.-es t'ne position of the target 15 with respect to the aircraft 13.
The ~ cessing which occurs on the SAR platform 13 may be ~ d in five steps:(1) SAR mode e~ce~ution initial detection of the desired target 15. (2) Target designa-tion: operator design~tion of the target of interest. (3) ~ lition~l SAR maps: additional SAR maps 18b of target area 17 to provide improved target po~iLion accuracy. (4)20 A~1t~)m~ted map ...~ching a~ ;c ~cl~lng of ~ ition~l maps 18 to cnsure accurate target ~esi~n~tion (5) Target position computation: co~ a~ion of target positionbased on the posilion and velocity estim~tes of the ai~raft 13 and SAR map measure-ments. Each of these five proces~ing steps are discussed in detail below.
The first step in the use of the weapon delivery system 10 is the SAR mode 25 ex~ tion The initial SAR mode execution p~ovides the operator with a SAR image of the target area 17. The operator may perform several low resolution maps 18 of the target arca 17 before pe-ro ~ng a high resolution map of the target 15. Only high rcsolP~ on maps 18 of the target area 17 are used as an initial map in thc . ~àpon deliv-ery system 10 since small OEPs are desirable for weapon delivery. Therefore, all SAR
30 maps 18 used for targeting typically have pixel sizes of 10 feet or less.
Once the O~latu~ has ~erified the target 15 as a target of interest, ~e operatordesignates the target 15 with a cursor. Although m~lltiple SAR maps 18 are m~rle to ensure precision weapon delivery, the operator only needs to ~ ign~te the target 15 once. To aid in target designation, a library of target templates is provide~ ~is target 35 t~mp!~te library, part of the target cueing function 37, provides the operator with an image of what the target 15 should look like and which target pixel should be designat-e~ The target cueing function 37 provides the templates to assist the operator in targeting and desi~nAtion. The computer-aided target cueing function 37 not only aids the o~ atur in designating the correct target 15, but also minimi7es the design~tion error by providing a zoom capability.
After the ~yelalol has designated the target 15, additional high resolution SAR
5 maps of the target 15 must be ~.rolll,ed to improve the accuracy of the target position compulation. These addition rnaps should be ~.fo~ cd at a dirre.e,~t o~ientation with respect to the target 15. As more maps of the target 15 are obtained from difr~l~nt g~ll~Lfic aspects, the accuracy of the coll,~u~ed position increases. Typically only one additional map 18 is necessAry to achieve a srnall OEP (~10-15 feet). However, the 10 requisite number of adrlitionAl maps 18 required to achieve a small CEP will vary according IO a nurnber of factors including target-to-aircraft geometry, SAR mapresolution, platform velocity, and platform ~Ititude Once A~l~litionAl maps 18 of the design~ted target 15 are performed, the ope.~o is not required to designAte the targets 15 in the new images. ~ncteA~l, the weapon 15 delivery system 10 pe-r~ s high precision map ll~tching to accurately locate the same decigrAted target 15 in the additional SAR maps 18. The map rnatching algorithm used to design~te the targets 15 in the subsequent images is provided by the precision map-mAt~hing function 38. The high precision map ma~ching function 38 ~ lA~ Ally determines the coordinate transformations necessary to align the two SAR images.20 While the accuracy of the n~A~h;ng algoliLhlll may vary with image content and size, subpixel accuracy is poscible with irnages of only modest contrast ratio.
The target e,~ l;Qn algorithm combines all of the SAR radar ~-l~ule.lRnt~
with the aircraft navigation position and velocity e~ llAtc s to obtain the target location in the relative GPS coordinate system. The outputs of the platform's GPS receiver 40 25 and IMU 42 are pnxe~c~ by the Kalrnan filter 4l and the outputs of the Kalman filter 41 ~e rY~i At~ to the time the SAR map 18 was formed to ~ t~ ;nÇ the position and vdocity vector to associate with the SAR image data Once the map I~A~ç~ g pr~xe.lL~e is completed and all SAR target measurementc are ~lful~d, the p~llcLers of the target içcignAted by the operator are computed in the GPS coordinate system 30 concisten~ witn the GPS system 11. After the target location is CUlllpul~d. the weapon delivery system 10 COl~ 't~ S an optimal weapon flighl path 19 to ensure precise. e~on delivery. The flight path 19 of the weapon that is c-ol~ ed by the weapon delivery system 10 is the best flight path through the e~timAted target position. If the missile is flown along this path, it is guaranteed to intersect the target plane near the 35 target regardless of the actual altitude ûf the target, as is illustrated in FIG. 3.
Before weapon launch, the weapon delivery system 10 downloads the comput-ed flight patn into the weapon's navigation and guidance unit 52. The sys~em 10 also 11 2~85847 downloads the coefficients necessary for the weapon to initialize its navigation subsys-tem 55 to elimin~te any initial errors between the SAR platform's navigation system 39 and the weapon's navigation system 55. Additionally, the SAR platform 13 provides the weapon 14 with infolulation regarding which GPS s~tellites 12a-12d to use for 5 position cc,.~plllation. Use of the same GPS satellites 12a-12d for aircraft and weapon position deterrnination ensures the same precise differential GPS coordinate system is used for both the weapon 14 and the aircraft 13. Other information the weapon receives prior to launch includes the target po~iliol,. Once the initi~li7~tiQn parameters are received from the SAR platform 13 and the weapon 14 initi~li7~s its navigation 10 subsystem 55, the weapon 14 is ready for launch.
After launch, the navigation subsystem 55 in the weapon 14 is used by the navigation and guidance ~ JpUl~ 52 to guide the weapon 14 along the pre-computedflight path 19 to the target 15. After launch, no co.. ~ tions between the weapon 14 and the SAR platform 13 are necessary. The SAR platfo~ 13 is free to leave the 15 target area 17.
To determine the accuracy of the weapon delivery system 10, the basic error sources must first be identified. In general, there are two sets of error sources which can degrade the accuracy of weapon delivery using the wc~on delivery system 10.
The first set are the errors associated with the radar targeting system 16. These errors 20 include errors in the aircraft position and velocity data from thc navigation system 39, errors in the radar mea~ulcu~r,b (range and range rate) from the SAR rnode 31, and errors associated with the design~tion function 32. The second set of errors are associ-ated with the navigation and guidance errors of the ~.capon 14. The navigation errors are ~csoci:~t~A with incorrect position e~ es of the ~.~apon's navigation subsystem 25 55. The ~irl~nre erTors are associated with not guiding the weapon 14 along the cor~t fligh~ path 19 (e.g., due to wind) by the navigation and guidance unit 52 of the .eal~on 14.
Given the navigation subsystem 39 position and velocity estim~ts accuracies and the SAR mode L~UlCllb lll accuracies, the accuracy of the weapon delivery 30 system 10 may be analyzed The accuracy of the ~.~n delivery system 10 also depends upon the accuracy of the designation and the .. ea~on's ability to na~igate to the target 15 along the collll~u~ed flight path 19. The more mea~ ~nls that are made, the lower the variance of the estim~ted target position. To reduce the target position error, each SAR target position measurement is optimally combined in a filter tO exploit 35 the full benefits of multiple target detections.
FIG. 4 shows the targeting performance of the weapon delivery system 10 when the SAR platform 13 is flying in a straight line pa~h toward the target 15 from an initial range of 50 n~utic~l miles and squint angle of 20 degrees. For the targeting per-formance chart shown in FIG. 4, the horizontal axis represents the elapsed time for the last mea~u~c,llent since the first SAR map 18 was performed (mea~ cnts are made at equal angles). The speed of the aircraft 13 is ~s..med to be 750 feet per second and the altitude is 45,000 fee~ The left vertical axis represents the squint angle in degrees or the ground range to the target 15 in n~utic~l miles. The right vertical axis represents the OEP in feet. The performance of FIG. 4 ~ s the following values for the error sources:
a radar navigation position error of 1.29 feet (1 ~), a radar navigation velocity error of 0.26 feetlsecond (1 ~), and a radar range mea~ t error of ~r2(n).
The radar range rate measurement error ar (n) is given by ~r(n) (38411) + 25~
where r(n) is the range at time n.
Thus, the radar range rate measul~en~ error is ar(n) = (36(n)3) + 12.5 750 - v2(n), where v(n) is the range rate at time n, the designation error is 4 feet (OEP), the weapon navigation error is S feet (CEP), and the weapon guidance e~or is 3 feet (OEP).
For the 50 n~utic~l mile case shown in FIG. 4, the ~eapon delivery system 10 can achieve a 14 foot OEP by making a second mea~ ;~nt 5 n~i nutC S after the first.
At this point the aircraft 13 has flown through an angle of 40 degrees and is 20 n~tit~l miles from the target. Ma~ng more than two measulc.~nls does not improve the OEPvery much. The time required to make these extra measule~llerlt~ is better utilized by im~ing other target areas. re~ro~ nce of this weapon delivery system 10 depends only on the location of the SAR platform 13 relative to the target 15 when the measu-re-ments are made and is in~epen~lerlt of the aircraft flight path used to get the SAR plat-form 13 to those meaaul~nt locations.
Thus there has been described a new and improved method and appa-ratus for providing ~ ono.,.ous precision guidance of airborne weapons. It is to be understood that the above-described emk~liment is merely illustrative of some of the many specific embolim~nt~ which l~ s-,nt applications of the principles of the present invention.
Clearly, numerous and other arrangements can be readily devised by those sl~lled in the art without depar~ing from the scope of the inven~ion.
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The cxpected value of Term (1) is zero; ~ efo,e thc variance of the first term is calculated by taking the e~cted value of the square of Term (1). The random variables in this e~plession (x(n), y(n), z(n) and r(n)) are ~cs~lmed to be independent of each other.
E(T (1))2 2( ) [x(n) ~t]2 2( ) [y(n) - Yl] 2( ) +[z(n) - ZLl2~(n) + ~2(n) where ~(n) is the variance of x(n), ~(n) is the variance of y(n), ~(n) is the variance of z(n), ~r2(n) is the variance of r(n). If the navigation S system position enors are coordinate system and time independent (a~(n) = c~2y(n) = ~(n) = ~J2p) then the weight used with Term (1) is the following: ~(n) = cr2p + ~(n). S
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Terrn (2) = v,~(n) ~x(n) -~x~ + vy(n) [y(n) - y~ + vz(n) [z(n) - Ztl - v(n) Re(n) The variance of the second term is used as the second weight. It is co..,puted by expanding the second terrn in a Taylor series around the mean of each of the random variables. r~
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Since the expected value of the second term is also zero, the variance of the second term is calculated by taking the expected value of the 15 square of Te~m (2). The random variables in this expression are assumed to be independent of each other.
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The cxpected value of Term (1) is zero; ~ efo,e thc variance of the first term is calculated by taking the e~cted value of the square of Term (1). The random variables in this e~plession (x(n), y(n), z(n) and r(n)) are ~cs~lmed to be independent of each other.
E(T (1))2 2( ) [x(n) ~t]2 2( ) [y(n) - Yl] 2( ) +[z(n) - ZLl2~(n) + ~2(n) where ~(n) is the variance of x(n), ~(n) is the variance of y(n), ~(n) is the variance of z(n), ~r2(n) is the variance of r(n). If the navigation S system position enors are coordinate system and time independent (a~(n) = c~2y(n) = ~(n) = ~J2p) then the weight used with Term (1) is the following: ~(n) = cr2p + ~(n). S
The second terrn uses the radar rangc rate mcasurement, v(n).
Terrn (2) = v,~(n) ~x(n) -~x~ + vy(n) [y(n) - y~ + vz(n) [z(n) - Ztl - v(n) Re(n) The variance of the second term is used as the second weight. It is co..,puted by expanding the second terrn in a Taylor series around the mean of each of the random variables. r~
Re(n) ) [x(n) - x(n)] + (vy(n) - v(n) Y(R)( )Y~) [y(n) y(n)l +
(vz(n) - v(n) R (n) I) lz(n) - z(n)l + [x(n) -~x~ ¦ [v,~(n) - V~(n + [y(n) -^y~ I [vy(n) - vy(n)l + [z(n) ~ Zt] I [vz(n) - vz(n)l - Re(n) I [v(n) - v(n)]
Since the expected value of the second term is also zero, the variance of the second term is calculated by taking the expected value of the 15 square of Te~m (2). The random variables in this expression are assumed to be independent of each other.
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Claims (13)
1. An autonomous weapon targeting and guidance system for identifying a non-moving fixed or relocatable target and guiding a weapon to the target, said system comprising:
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving, fixed or relocatable target, a navigation subsystem, and processing means for processing SAR data and navigation data to compute the position of the target and an optimum weapon flight path from the platform to the target using a predeterminedcomputational procedure; and a weapon having a navigation subsystem which utilizes a transfer alignment algorithm to align the weapon's navigation system with the airborne platform's navigation system prior to launch, which weapon is adapted to respond to data transferred to it by the platform to permit it to navigate relative to the navigation system of the airborne platform and autonomously navigate to the location of the target along the optimum weapon flight path.
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving, fixed or relocatable target, a navigation subsystem, and processing means for processing SAR data and navigation data to compute the position of the target and an optimum weapon flight path from the platform to the target using a predeterminedcomputational procedure; and a weapon having a navigation subsystem which utilizes a transfer alignment algorithm to align the weapon's navigation system with the airborne platform's navigation system prior to launch, which weapon is adapted to respond to data transferred to it by the platform to permit it to navigate relative to the navigation system of the airborne platform and autonomously navigate to the location of the target along the optimum weapon flight path.
2. The system of Claim 1 wherein the navigation subsystems of the airborne platform and weapon are each adapted to utilize a global positioning system (GPS) satellite system.
3. The system of Claim 1 wherein the airborne platform is adapted to transfer target position, satellite, and flight path information to the weapon prior to its launch for use by the weapon during its flight along the optimum weapon flight path to the target.
4. The system of Claim 2 wherein the airborne platform is adapted to transfer target position, satellite, and flight path information to the weapon prior to its launch for use by the weapon during its flight along the optimum weapon flight path to the target.
5. The system of Claim 1 wherein the target is a fixed target.
6. The system of Claim 1 wherein the target is relocatable target.
7. An autonomous weapon targeting and guidance system for identifying a non-moving target and guiding a weapon to the target, said system comprising:
a global positioning system (GPS) comprising a plurality of satellites that broadcast position data to provide a coordinate reference frame;
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving target, a navigation subsystem that utilizes a global positioning system (GPS) satellite system and which is adapted to respond to signals provided by the GPS satellite system to permit the platform to navigate relative thereto, and processing means for processing SAR data and navigation to compute the position of the target and an optimum weapon flight path from the platform to the target using a predetermined computational procedure; and a weapon comprising a navigation subsystem that is adapted to utilize the GPS satellite system and which responds to signals provided by the GPS satellite system and data transferred to it by the platform to permit it to navigate relative to the GPS satellite system and autonomously navigate to the location of the target along the optimum weapon flight path.
a global positioning system (GPS) comprising a plurality of satellites that broadcast position data to provide a coordinate reference frame;
an airborne platform comprising a synthetic array radar (SAR) system adapted to detect a non-moving target, a navigation subsystem that utilizes a global positioning system (GPS) satellite system and which is adapted to respond to signals provided by the GPS satellite system to permit the platform to navigate relative thereto, and processing means for processing SAR data and navigation to compute the position of the target and an optimum weapon flight path from the platform to the target using a predetermined computational procedure; and a weapon comprising a navigation subsystem that is adapted to utilize the GPS satellite system and which responds to signals provided by the GPS satellite system and data transferred to it by the platform to permit it to navigate relative to the GPS satellite system and autonomously navigate to the location of the target along the optimum weapon flight path.
8. The system of Claim 7 wherein the airborne platform is adapted to transfer target position, satellite, and flight path information to the weapon prior to its launch for use by the weapon during its fight along the optimum weapon flight path to the target.
9. A method for detecting a non-moving target and guiding an airborne weapon to the target, said method comprising the steps of:
providing a global positioning system comprised of a plurality of satellites that each broadcast coordinate reference data for use in navigation;
flying an airborne platform over a target area and navigating using a navigation system that utilizes the GPS satellite system which provides the coordinate reference frame;
mapping the target area using a synthetic array radar (SAR) system located on the airborne platform to produce an original SAR map of the target area;
designating a target on the SAR map;
re-mapping the target area a predetermined number of additional times at different angles relative to the target using the synthetic array radar system to produce a predetermine number of additional SAR maps of the target area;
computing a precise target location and flight path in the coordinate system provided by the global positioning system using the navigation data and the information from each of the SAR maps;
transferring selected information to the weapon prior to its launch comprising data indicative of an optimum flight path to the target that should be flown by the weapon, navigation system initialization information that permits the weapon to acquire the satellites used by the platform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquire the satellites used by the platform for navigation and guide the weapon to the target based on the optimum flight path computed in the platform.
providing a global positioning system comprised of a plurality of satellites that each broadcast coordinate reference data for use in navigation;
flying an airborne platform over a target area and navigating using a navigation system that utilizes the GPS satellite system which provides the coordinate reference frame;
mapping the target area using a synthetic array radar (SAR) system located on the airborne platform to produce an original SAR map of the target area;
designating a target on the SAR map;
re-mapping the target area a predetermined number of additional times at different angles relative to the target using the synthetic array radar system to produce a predetermine number of additional SAR maps of the target area;
computing a precise target location and flight path in the coordinate system provided by the global positioning system using the navigation data and the information from each of the SAR maps;
transferring selected information to the weapon prior to its launch comprising data indicative of an optimum flight path to the target that should be flown by the weapon, navigation system initialization information that permits the weapon to acquire the satellites used by the platform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquire the satellites used by the platform for navigation and guide the weapon to the target based on the optimum flight path computed in the platform.
10. The method of Claim 9 which further comprises the step of correlating the images from the additional SAR maps with the original SAR map prior to computing the precise target location and flight path to eliminate the need for repeated target designation.
11. The method of Claim 9 which further comprises the step of providing target cueing information that is adapted to assist an operator in designating a target.
12. The method of Claim 9 which further comprises the step of matching subsequent SAR maps to the initial SAR map by automatically determining a coordinate transformation that aligns all SAR images to ensure that the additional SAR maps are correlated to the initial SAR map, such that the target designated in each subsequent map is the same target designated in the first map.
13. A method for detecting a non-moving target and guiding an airborne weapon to the target, said method comprising the steps of:
providing a global positioning system comprised of a plurality of satellites that each broadcast coordinate reference data for use in navigation;
flying an airborne platform over a target area and navigating using a navigation system that utilizes the GPS satellite system which provides the coordinate reference frame;
mapping the target area using a synthetic array radar (SAR) system located on the airborne platform to produce an original SAR map of the target area;
designating a target on the SAR map;
re-mapping the target area a predetermined number of additional times at different angles relative to the target using the synthetic array radar system to produce a predetermine number of additional SAR maps of the target area;
correlating the images from the additional SAR maps with the original SAR map toeliminate the need for repeated target designation;
computing a precise target location and flight part in the coordinate system provided by the global positioning system using the navigation data and the information from each of the SAR maps;
transferring selected information to the weapon prior to its launch comprising data indicative of an optimum flight path to the target that should be flown by the weapon, navigation system initialization information that permits the weapon to acquire the satellites used by the platform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquire the satellites used by the platform for navigation and guide the weapon to the target based on the optimum flight path computed in the platform.
providing a global positioning system comprised of a plurality of satellites that each broadcast coordinate reference data for use in navigation;
flying an airborne platform over a target area and navigating using a navigation system that utilizes the GPS satellite system which provides the coordinate reference frame;
mapping the target area using a synthetic array radar (SAR) system located on the airborne platform to produce an original SAR map of the target area;
designating a target on the SAR map;
re-mapping the target area a predetermined number of additional times at different angles relative to the target using the synthetic array radar system to produce a predetermine number of additional SAR maps of the target area;
correlating the images from the additional SAR maps with the original SAR map toeliminate the need for repeated target designation;
computing a precise target location and flight part in the coordinate system provided by the global positioning system using the navigation data and the information from each of the SAR maps;
transferring selected information to the weapon prior to its launch comprising data indicative of an optimum flight path to the target that should be flown by the weapon, navigation system initialization information that permits the weapon to acquire the satellites used by the platform for navigation, and target position information; and launching the weapon using a navigation system in the weapon to acquire the satellites used by the platform for navigation and guide the weapon to the target based on the optimum flight path computed in the platform.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US810,630 | 1991-12-19 | ||
| US07/810,630 US5260709A (en) | 1991-12-19 | 1991-12-19 | Autonomous precision weapon delivery using synthetic array radar |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2085847A1 CA2085847A1 (en) | 1993-06-20 |
| CA2085847C true CA2085847C (en) | 1996-12-03 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002085847A Expired - Lifetime CA2085847C (en) | 1991-12-19 | 1992-12-18 | Autonomous precision weapon delivery using synthetic array radar |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US5260709A (en) |
| EP (1) | EP0547637B1 (en) |
| JP (1) | JP2525539B2 (en) |
| KR (1) | KR960014821B1 (en) |
| AU (1) | AU640091B1 (en) |
| CA (1) | CA2085847C (en) |
| DE (1) | DE69218143T2 (en) |
| ES (1) | ES2098433T3 (en) |
| IL (1) | IL104181A (en) |
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-
1991
- 1991-12-19 US US07/810,630 patent/US5260709A/en not_active Expired - Lifetime
-
1992
- 1992-12-18 DE DE69218143T patent/DE69218143T2/en not_active Expired - Lifetime
- 1992-12-18 EP EP92121647A patent/EP0547637B1/en not_active Expired - Lifetime
- 1992-12-18 ES ES92121647T patent/ES2098433T3/en not_active Expired - Lifetime
- 1992-12-18 IL IL10418192A patent/IL104181A/en not_active IP Right Cessation
- 1992-12-18 CA CA002085847A patent/CA2085847C/en not_active Expired - Lifetime
- 1992-12-19 KR KR1019920024847A patent/KR960014821B1/en not_active IP Right Cessation
- 1992-12-21 JP JP4356214A patent/JP2525539B2/en not_active Expired - Lifetime
- 1992-12-21 AU AU30326/92A patent/AU640091B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE69218143T2 (en) | 1997-10-09 |
| KR960014821B1 (en) | 1996-10-21 |
| AU640091B1 (en) | 1993-08-12 |
| IL104181A (en) | 1995-12-31 |
| EP0547637B1 (en) | 1997-03-12 |
| US5260709A (en) | 1993-11-09 |
| CA2085847A1 (en) | 1993-06-20 |
| ES2098433T3 (en) | 1997-05-01 |
| JP2525539B2 (en) | 1996-08-21 |
| JPH0688698A (en) | 1994-03-29 |
| EP0547637A1 (en) | 1993-06-23 |
| KR930013756A (en) | 1993-07-22 |
| DE69218143D1 (en) | 1997-04-17 |
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Effective date: 20121218 |