# Patent

## Title
Multiple kill vehicle (MKV) interceptor and method for intercepting exo and endo-atmospheric targets

## Abstract

By sharing tasks between the CV and the KVs, the MKV interceptor provides a cost-effective missile defense system capable of intercepting and killing multiple targets. The placement of the acquisition and discrimination sensor and control sensor on the CV to provide target acquisition and discrimination and mid-course guidance for all the KVs avoids the weight and complexity issues associated with trying to “miniaturize” unitary interceptors. The placement of a short-band imaging sensor on each KV overcomes the latency, resolution and bandwidth problems associated with command guidance systems and allows each KV to precisely select a desirable aimpoint and maintain track on that aimpoint to impact.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to missile defense systems, and in particular, but not exclusively, to a system for intercepting and destroying exo-atmospheric missiles using kinetic energy kill vehicles.
2. Description of the Related Art
Ballistic missiles armed with conventional explosives, chemical, biological or nuclear warheads represent a real and growing threat to the United States from the former Soviet Union, terrorist states and terrorist groups. The technologies required to both create weapons of mass destruction (WMD) and to deliver them over hundreds to thousands of miles are available and being aggressively sought by enemies of the United States.
Several modern missile defense systems are under development by branches of the US Armed Services and Department of Defense. These systems use an (interceptor) missile to destroy an incoming (target) missile, warhead, reentry vehicle, etc. . . . Blast-fragmentation systems detonate high power explosives shortly before the collision of the interceptor with the target. Kinetic energy systems rely solely on the kinetic energy of the interceptor to destroy the target. Both systems require highly sophisticated guidance systems to acquire and track the target. In particular, kinetic energy systems must hit the target with great precision.
U.S. Pat. Nos. 4,738,411 and 4,796,834 to Ahlstrom describe techniques for guiding explosive projectiles toward the target. In the '411 patent, the magazine is loaded with transmitting projectiles with means for illuminating the target with electromagnetic radiation and explosive projectiles with a passive or purely receiving homing device. During the last part of its travel, the transmitting projectile illuminates the target area with electromagnetic energy. A preferred wavelength range is the so called millimeter wavelength range, suitably 3-8 mm. Energy reflected off of any targets within the target area is received by the explosive projectiles and used to guide the projectiles toward the target. The mm band is adequate to detect the target and possibly strike the target but is not adequate to select a particular aimpoint on the target. In the '834 patent, each of the explosive projectiles includes illumination means and a passive receiver. A leading projectile passively detects and then illuminates a target. A trailing projectile detects the return energy off of the illuminated target and corrects its trajectory accordingly. When the leading projectile hits the ground, the trailing projectile senses the interruption and resets itself to passive detection. When the target's own radiation is detected, the passive signature is used for final guidance. The detector device for activating the illumination source is preferably the same detector as that included in the target tracking device.
Raytheon's EKV (Exo-Atmospheric Kill Vehicle) system represents state-of-the-art in kinetic energy systems designed to locate, track and collide with a ballistic missile. The EKV is a unitary interceptor that includes a single kill vehicle (KV). The interceptor is launched on a multi-stage rocket booster. Current versions of the kill vehicle have optical sensors to support the endgame functions including: acquisition of the target complex, resolution of the objects, tracking the credible objects, discrimination of the target objects and homing in on the target warhead.
The deployment of missiles with Multiple Independently Targeted Re-entry Vehicles (MIRVs) is driving a move to develop interceptors that can deploy multiple kill vehicles. A multiple kill vehicle (MKV) interceptor would include a carrier vehicle (CV) and multiple KVs. The development of an MKV interceptor presents unique problems of weight, miniaturization, and control bandwidth to acquire, track and intercept multiple targets in addition to all the issues encountered by unitary interceptors. Consequently, an effective MKV interceptor has not yet been developed or deployed.
One concept being pursued is to simply miniaturize existing unitary interceptors such as the EKV. In this approach, each KV includes all of the intelligence needed to discriminate targets and provide guidance to impact. The CV is merely a bus to transport the KVs from launch to release. Unfortunately, the ability to “miniaturize” all the functionality into a small, lightweight KV is well beyond state-of-the-art and may never be realizable due to fundamental physics constraints.
Another concept is to “command guide” all of the KVs from the CV to impact. In this approach all of the intelligence needed to discriminate targets and provide guidance to impact is located on the CV. The KVs include minimal functionality, typically only a receiver and actuators to respond to the heading commands sent by the CV. U.S. Pat. No. 4,925,129 describes a missile defense system including a guided projectile including multiple sub-projectiles. A radar tracker is used to guide the projectile toward a target at relatively large distances. An optical tracker on the projectile is used to track the target at relatively small distances and issue guidance commands to guide the sub-projectiles to intercept the target. Although conceptually attractive, command guidance suffers from poor target resolution and latency associated with the stand-off range of the CV to keep all targets within the optical tracker's field of regard, which makes aimpoint selection and terminal guidance imprecise. Recent studies have shown precise aimpoint selection and terminal guidance to strike the aimpoint are critical to the success of kinetic energy systems. Furthermore, the CV must have sufficient bandwidth to track all of the targets simultaneously.
SUMMARY OF THE INVENTION
The present invention provides a MKV interceptor capable of acquiring, tracking and intercepting multiple targets at precise aimpoints without overstressing the design of the CV or individual KVs. This is accomplished by distributing the tasks required to acquire, track and intercept multiple incoming targets between the CV and the KVs.
In an embodiment, an MKV interceptor comprises a CV and a plurality of KVs initially stored in the CV for release to intercept incoming targets. The CV includes a first sensor subsystem for acquiring and tracking the targets and providing heading commands to the released KVs pre-handover. Each KV includes an imaging sensor subsystem for selecting a desirable aimpoint on the target post-handover and maintaining track on the aimpoint to terminal intercept. The placement of the first sensor subsystem on the CV to provide acquisition and mid-course guidance for all the KVs avoids weight and complexity issues associated with trying to “miniaturize” unitary interceptors. The placement of the imaging sensor on each KV overcomes the latency, resolution, field of regard, and bandwidth problems associated with command guided systems.
In another embodiment, the imaging sensor subsystem is preferably a short-band imaging sensor that at a certain range-to-target post-handover provides sufficient independent pixels on target to use the shape and orientation of the target to select the aimpoint. Such a short-band imaging sensor cannot adequately detect passive signatures and thus must be used in combination with external illumination. In a preferred embodiment, the external illumination is short-pulsed and the imaging sensor is gated to a very narrow window to suppress dark current and improve SNR.
In another embodiment, target discrimination is centralized in the CV and shared with the KVs at handover. The CV's first sensor subsystem includes a passive discrimination sensor subsystem for initial acquisition and discrimination of targets based on external cues and a control sensor subsystem for actively tracking the targets and providing heading commands to the released KVs pre-handover. The KVs are preferably deployed ahead of the CV allowing the control sensor subsystem to track both the KVs and targets to determine the heading commands. At some range to target, the target designations and tracking are then handed over to the individual KVs. Centralized target discrimination and “mid-course” guidance reduces both weight and complexity.
In another embodiment, the CV hands over the target designation and tracking information to each KV by illuminating each target in a time sequence. Data is uplinked in advance to each KV to tell its imaging sensor when and where to look for its target. The KV sees the return signature off the designated target to acquire the target and initiate post-handover tracking.
In yet another embodiment, the CV and KVs work together to provide post-handover guidance using semi-active tracking. The CV uses the control sensor's source to illuminate the targets and the KVs' imaging sensor detects the return signal. The power and beam pointing accuracy of the CV source in combination with the reduced range-to-target of KV sensors provides for very accurate tracking.
In yet another embodiment, the KVs are released from the CV without sufficient knowledge of their orientation to safely divert away from the CV and other KVs and/or divert to acquire the track towards the targets. Each KV initiates a spin that continuously sweeps a narrow FOV visible sensor through a star field, sufficiently 1 degree×20 degrees, and matches the imaged star field against a pre-stored star map to determine initial orientation. This simplifies the release mechanism.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which:



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified diagram of an MKV interceptor including a booster stage, a carrier vehicle lofted by the booster, and a plurality of KVs initially stored in the carrier vehicle and then released to intercept the targets;
FIG. 2 is a simplified block diagram of the hardware components on the carrier vehicle;
FIG. 3 is a diagram of an embodiment of a KV;
FIG. 4 is a simplified block diagram of the hardware components on the KV;
FIG. 5 is a diagram of an MKV interceptor launch to intercept multiple exo-atmospheric targets;
FIGS. 6a and 6b are flowcharts of the CV and KV actions from target designation to intercept;
FIGS. 7a through 7d are diagrams illustrating the release of the KVs, initiated spin to acquire KV orientation, minimum number of stars acquired for a given swath and alignment of data link receiver to the CV;
FIG. 8 is a diagram illustrating CV tracking of the KVs and targets for midcourse guidance pre-handover;
FIG. 9 is a diagram illustrating the CV laser designation of the targets to facilitate handover to the KVs and post-handover to facilitate semi-active track until the range-to-target is close enough for autonomous acquisition by the KVs,
FIGS. 10a and 10b are a timing diagram of the laser designation and gating of the KVs' imaging sensors and QWERTY scan to facilitate handover;
FIG. 11 is a diagram illustrating aimpoint selection and terminal guidance by the KV's on-board imaging sensors under external illumination; and
FIGS. 12a through 12c are sensor images of a representative target for a given aperture size for the KV's short band imaging sensor and the CV's long band discrimination sensor, and for a given short band sensor mounted on the CV at typical stand-off distance.



DETAILED DESCRIPTION OF THE INVENTION
The present invention describes a multiple kill vehicle (MKV) interceptor for intercepting targets. The particular MKV interceptor described herein is for exo-atmospheric interceptors. Atmospheric drag requires different CV and KV designs although the principles are applicable.
As an overview, the presence of an incoming target is detected and signaled to the battlefield management system by an early warning system and an MKV interceptor is launched on a path to intercept the target. At a certain range to the target cloud, the CV releases the KVs and preferably deploys them in waves out in front of the CV. An exemplary CV includes a LWIR discrimination and acquisition sensor subsystem for passively acquiring and discriminating real targets based on external cues and refining the track and a short-band control sensor subsystem for actively tracking the targets and KVs and command guiding the KVs pre-handover. The CV suitably hands over the target designation and tracking information to each KV by illuminating each target in a time sequence. Data is uplinked in advance to each KV to tell its imaging sensor when and where to look for its target. The KV sees the return signature off the designated target to acquire the target and initiate post-handover tracking. Each KV uses its imaging sensor subsystem to select a desirable aimpoint and maintain track on the aimpoint to terminal intercept. The imaging sensor is suitably a short-band signature that detects a return signature reflected off a target illuminated by an external source.
By sharing tasks between the CV and the KVs, the MKV interceptor provides a cost-effective missile defense system capable of intercepting and killing multiple targets. The placement of the first sensor subsystem on the CV to provide target acquisition and discrimination and mid-course guidance for all the KVs avoids the weight and complexity issues associated with trying to “miniaturize” unitary interceptors. The placement of an imaging sensor on each KV overcomes the latency, resolution and bandwidth problems associated with command guidance systems and allows each KV to precisely select a desirable aimpoint and maintain track on that aimpoint to impact.
The MKV interceptor is a very complex system including much functionality outside the scope of the invention. Consequently, the diagrams and descriptions of the CV, KVs and methods of discrimination, acquisition and guidance are limited to the subject matter of the present invention for purposes of clarity and brevity. Other functionality is well known to those skilled in the art of missile defense systems using kinetic energy interceptors.
As shown in FIGS. 1 and 2, an exemplary MKV interceptor 10 includes a carrier vehicle (CV) 12 and a plurality of KVs 14 initially stored in the carrier vehicle. For earth-based systems, the interceptor is launched using a multi-stage booster. A kick stage divert 16 separates the interceptor from the last stage of the booster and maneuvers the interceptor onto a nominal intercept trajectory. The kick stage may include axial and lateral divert capability through the center of gravity of the interceptor. An attitude control system includes multiple thrusters 18 offset from the center of gravity that provide yaw, pitch and roll control. Tanks 20 provide the propellant for the divert stage and ACS thrusters. Once the interceptor exits the earth's atmosphere a shroud 22 that protects the interceptor from contamination, aerodynamic pressure and heating during launch is jettisoned. An external commlink 24 is used to communicate with any source outside the interceptor. An Inertial Measurement Unit (IMU) 26 measures lateral accelerations and angular rates that are fed to the processor 28 to calculate the CV's position and attitude after a star fix initialization.
The KVs are stored in and then released from the CV by a KV retention and release mechanism 30. Conventional release mechanisms are fairly complicated in that they attempt to transfer the pre-release alignment of the KVs to the released KVs. This requires considerable control information to be exchanged between the CV and KVs and a sophisticated release mechanism. In the preferred embodiment, no requirements are placed on the release mechanism for maintaining inertial reference of the KVs. Consequently the release mechanism 30 can be a simple spring-loaded or gas-pressure mechanism without elaborate guiding mechanisms to constrain the release tip-off rate. The KVs are suitably kicked off with roughly controlled separation velocity but unknown or insufficiently known spin rate or orientation. As will be described below, the KVs are controlled to reacquire their direction to the CV to allow them to safely divert away from the CV and their inertial reference to allow them to divert to acquire track towards the targets. The KVs may be released with no knowledge or only enough knowledge to divert away from the CV but not to acquire track. This approach uses a simpler release mechanism 30. However, a conventional umbilical release mechanism may be used.
A discrimination and acquisition sensor subsystem 32 is mounted inside the CV. Discrimination optics 34 fold the light path so that the sensor is side-looking in this particular embodiment. The optics may be a fixed mirror or gimbaled mirror system. The gimbaled mirror system sweeps the sensors field-of-view (FOV) 36 over a certain angle to image a larger field-of-regard (FOR). The cues provided by the external systems are not precise enough to enable active sensing, the FOR of a laser illuminator is too narrow to acquire the targets. Therefore, the acquisition and discrimination sensor is suitably a longwave IR (LWIR) sensor having a relatively large FOV for passive detection. The sensor has a suitably large aperture to provide both the sensitivity and resolution required in a diffraction limited system. On account of the aperture size, the sensor is quite heavy, and thus the centralizing acquisition and discrimination on the CV reduces the burden on the KVs considerably. The sensor discriminates real targets from decoys, chaff, etc. and refines the tracking information for the real targets.
A control sensor subsystem 38 receives the refined tracking information for the real targets and provides active mid-course tracking to command guide the KVs until tracking is handed over to the KVs. The control sensor subsystem 38 includes a short-band laser 40, typically >10 W, a highly agile and very accurate beam pointing system (BPS) 42 that moves the laser's FOV over a FOR 43, an angle/angle/range (AAR) short-band IR receiver 44 and a controller 46 that allows the control sensor subsystem 38 to accurately track multiple targets over a considerable distance and service different modes of operation. For mid-course tracking, latency, target resolution, and update rates are not critical. Also, at these ranges the laser's FOR 43 easily covers all targets.
The control sensor subsystem 38 is suitably configured to perform several different tasks.
KV acquisition: Controller 46 controls the laser 40 to emit a low power pulsed beam and controls the BPS 42 to expand the beam to the maximum extent possible and to sweep the search volume where KVs might be located. Power is low due to the very short range and augmented KV reflective signature, but this is balanced against the expanded beam. As KVs are found the CV initializes tracks. This mode can not be used to establish the initial line-of-sigh from the KVs to the CV in cases where KVs must first divert to place themselves within the control sensor subsystem 38 FOR.
KV Tracking: Controller 46 controls laser 40 to emit very low power pulses (close range & augmented reflection off KV) in a wide beam, which reduces the update rate necessary to keep the beam on the KV. The FOR is largest just after release and diminishes as CV-KV separation increases. The BPS 42 uses the latest tracking information and moves from one target to the next. The AAR Receiver 44 detects the return signature off of each of the illuminate targets and passes the information to processor 28, which updates the tracking information. KV Tracking typically begins before Target Tracking and continues until handover to the KVs.
Target Acquisition: The Acq/Disc sensor subsystem 32 hands over the refined tracking information for the real targets to the control sensor subsystem 38. Controller 46 tells the BPS 42 where to point laser 40. The refined tracking information is still relatively coarse when compared to the narrow FOV of the laser so the BPS 42 may need to search to lock onto the targets. The laser 40 is controlled to emit the highest pulse power within a narrow beam due to the range-to-target and target cross section. Initially the laser 40 requires a small FOR to illuminate all of the targets that grows as the CV gets closer to the target cloud. It is possible to acquire targets sequentially with the laser 40 (vs. multi-plexing between them).
Target Tracking: The laser 40 is controlled to emit the highest pulse power within a narrow beam due to the range-to-target and target cross section. Initially the laser 40 requires a small FOR to illuminate all of the targets that grows as the CV gets closer to target cloud. The BPS 42 is controlled based on the last updated target track. The required update rate diminishes after a track state is established, until it increases again due to control range closure. The controller multiplexes the BPS 42 and laser to track targets and KVs.
KV Uplink/PPM: Controller 46 keeps the laser 40 on a KV for multiple pulses in order to send handover data from the CV to the KV. In one embodiment, the data is pulse position modulated (PPM), where the interval between adjacent pulses is used to encode the data.
Handover Designation: Controller 46 controls the BPS 42 to direct laser 40 to lase each of the targets (return signals are detected by the designated KVs). The controller 46 suitably lases the targets in sequence so that any target within the angle uncertainty of the laser 40 is not within the timing uncertain of KV detection. R4 loss vs. CV acquisition (CV is closer to target, and KV is closer still, light return from target to KV) but smaller receive aperture so pulse power requirements may be greater or less depending on system details. In some embodiments may suspend KV tracking when this begins. Narrowest beam for highest return.
SA Track Illumination: Same R4 loss issues as above, but expand beam as range closes to illuminate the entire target silhouette (so that the KV can measure a good aimpoint)
In a test mode, some number of KVs are replaced with a test pod 48 that stays on the CV and provides nominal CW illumination of the KV so that a electrically modulated retro reflector on the back of the KV can provide a multiple mbits per second data link back to the CV without significant imposition of power or resources. The test pod 48 receives the reflected signals and reformats and remodulates them for transmission to telemetery receiving stations. KV will typically perform this remodulation using an electrically modulated retroflector. This allows the same component to serve as signature augmentation of KV track, and allows a full bandwith test data link to be included in the KV with no significant weight or power impact to the KV.
As shown in FIGS. 3 and 4, an exemplary KV 14 includes a chassis 60 on which is mounted a processor 62 as part of the avionics electronics 63 for controlling the KV and receiving data from the CV via laser uplink receiver 64. A battery 66 supplies electrical power to the KV. An IMU 68 measures lateral accelerations and angular rates that are fed to the processor 62 to calculate the KV's position and attitude after a star fix initialization. A telemetry (TM) modulated retro-reflector 70 provides KV signature augmentation to aid CV tracking of the KV as well as modulation for the test data link described previously.
Each KV includes an imaging sensor subsystem 72. In order to provide sufficient independent pixels on target at a certain range-to-target post-handover to select a desired aimpoint, the imaging sensor must detect in a band that is not suitable for passive acquisition at typical handover ranges. Passive acquisition at these ranges requires longer wavelength sensors such as the LWIR sensor used for acquisition and discrimination. In the exemplary embodiment described herein, imaging sensor subsystem 72 comprises a short-band sensor, suitably an uncooled FPA in the visible and/or near-visible bands, generally referred to as the 1 micron band, approximately 200 nm to 1.6 μm, which are generally incapable of passive detection of typical targets. These short-band imaging sensors must be “externally illuminated” by a man-made source (not the sun). The sun is an adequate source of illumination but is not always available. The imaging sensor is shielded from stray sun light by a sun shade 74. External illumination can be provided semi-actively by the laser on the CV whose band overlaps the KV imaging sensor, a different source on the CV or by an illuminator on each KV. The imaging sensor subsystem detects the return signal from its designated and illuminated target and passes the data to processor 62. The processor updates the target track and controls the divert & attitude control system (DACS) 76 to adjust the heading of the KV to the updated target track. Fuel tanks 78 fuel the DACS thrusters and fuel pressurant 80 maintains the pressure inside the fuel tanks.
Each KV is relatively small, typically about one foot long and lightweight in some cases as little as 2 kg. But at very high closing velocities, the KV possesses considerable kinetic energy, enough to kill incoming warheads if the aimpoint on the target is properly selected and the KV impacts the target precisely on the aimpoint. The inclusion of a short-band imaging sensor subsystem 72 on each KV provides high resolution images of the targets sufficient to precisely determine the aimpoint and to provide terminal tracking to impact.
An exemplary embodiment for intercepting exo-atmospheric targets using the MKV interceptor described above is illustrated in FIGS. 5 through 12 including the stages of (1) launch & pre-release guidance, (2) KV release and divert, (3) target acquisition & discrimination, (4) active midcourse tracking (5) hand-over to the KVs, (6) semi-active track (optional) and (7) aimpoint selection and terminal guidance.
Launch & Pre-Release Guidance
As shown in FIG. 5, a hostile missile 90 is launched on a ballistic trajectory 92 towards a friendly target. The MIRV warhead 94 separates from the boost stage 96 and the multiple RVs (targets) 98 and decoys, chaff, etc. 100 for a target cloud 102 that generally follows the ballistic trajectory. The targets may deviate from this trajectory either unintentionally upon re-entry into the atmosphere or intentionally to defeat a missile defense system.
A missile defense system includes a number of external systems that detect missile launch, assess the threat, and determine external target cues 104 (ballistic trajectory, time to intercept, number of RVs, etc.). The defense system launches one (or more) MKV interceptors 106 along an initial intercept track 108 based on those external target cues. Once aloft, the interceptor drops the booster stage 110 and jettisons the shroud. The interceptor is suitably tracked by a ground based radar installation 112 and engages it's divert and ACS systems to put the interceptor on the initial intercept track.
KV Release and Divert
Once the initial intercept track 108 has been established, as shown in FIGS. 6a and 6b, the CV 114 receives initial target designation from external systems or cues (step 116) releases the KVs 118 (step 120). The CV 114 activates an illumination source (step 122), suitably a few simple LEDs 124 around the CV 114 that will allow the KV uplink sensors to “see” the CV 114 and determine its relative position and major orientation. In one implementation, the light would blink in a pattern so that a non-imaging sensor could separately measure the angle to each point on the CV 114. It is generally preferable to have the KVs 118 separate from the CV 114 early, once the interceptor is out of earth atmosphere, to give them sufficient time to achieve a desired separation from the CV 114 in order to conserve propellant. KVs 118 typically will not all be released at the same time, one ring at a time is preferable. This minimizes the risk of collisions among other benefits.
As shown in FIG. 7a, KVs 118 are suitably released with insufficient information to be able to safely divert without risking running into each other or the CV 114 and/or to be able to divert to acquire track towards the target. This lack of orientation knowledge also precludes more conventional alignment methods, such as GPS maneuver realignment, that require KV lateral divert before the orientation can be discerned. The KVs 118 will typically have a controlled separation velocity but an unknown or insufficiently known spin rate and orientation. Alternately, the CV 114 and KVs 118 may be configured using standard umbilical technology and more complex release mechanisms well known in the art to maintain their inertial reference and heading.
As shown in FIG. 7b, the KVs 118 are powered on (step 126) and initiate a spin to find stars in the CV 114 illumination (step 128). Each KV continuously sweeps its narrow FOV imaging sensor subsystem 72 perpendicular to its line of sight through as much as 360 degrees in a few seconds. This guarantees covering a swath of unoccluded stars 130 of at least 1 deg×20 deg regardless of the initial orientation. The sensor may image the earth 132, the moon 134, the CV 114 or other KVs 118. These swaths are easily discriminated from star patterns and eliminated using image processing techniques well known to those in the art. Starting at any star and sweeping the FOV +/− in any arbitrary direction, the FOR length (deg) necessary to include a given # of stars (vs. FOV) is shown in table 136 in FIG. 7c. As shown, all 1 deg×20 deg swaths contain at least 10 stars detectable by conventional uncooled focal plane arrays (FPA) at a reasonable KV spin rate (magnitude 6.5 or brighter). The map of all such stars fits easily in the processor memory. Each KV uses its swath of at least 10 stars to determine an inertial orientation (step 138) by matching against the pre-stored star map using conventional techniques. As is known in the art, five stars are sufficient to determine a precise orientation match (Kayser-Threde). Each KV also determines its direction to the CV 114 using the illumination from the CV 114 (step 140).
Using their inertial reference and direction to the CV, the KVs use DACS 76 to divert away from CV and into the FOR of the control sensor to receive their initial target divert commands (step 142). This will also allow the CV to track the KVs and reduce errors in command guidance. Each KV orients its wide FOV uplink receiver 64 to the CV as shown in FIG. 7d and awaits uplink of initial commands from the CV for each KV (step 144). This methodology precludes the need for a separate datalink to notify the CV of whether each individual KV passed its built-in-test (BIT) at power up. Only those KVs that passed divert into the control sensor's FOV. Those KVs that's do not show up, failed.
The CV's control sensor subsystem 38 acquires the KVs (step 146) and, based on the initial track from external cues, commands the KVs for an initial divert toward the toward the target areas (step 148). In most cases the KVs will be commanded to separate into waves that reach the target seconds apart. In some cases, the KVs may be given updated commands based on revised ground cues before discrimination sensor acquisition. These steps are suitably done prior to “Target Acquisition & Discrimination” to get all of the KVs moving in the right direction as early as possible to minimize divert requirements, but could be done afterwards. In the particular CV configuration shown in FIG. 1, the interceptor flies sideways toward the targets so the side-looking control sensor subsystem 38 and ACQ/DISC sensor subsystem 32 can see the KVs and targets as shown in FIG. 8.
Target Acquisition & Discrimination
The CV's LWIR passive acquisition and discrimination sensor subsystem 32 acquires the targets within its FOV 149 as shown in FIG. 8 and refines the target discrimination and tracking cues (step 150). Methods for passive LWIR acquisition and discrimination of real targets from a target cloud is known in the art and beyond the scope of the present invention. However, the centralization of the acquisition and discrimination functions on the CV greatly simplifies the design of the KVs and reduces the complexity of the target discrimination and designation process.
Active Mid-Course Guidance
Once candidate targets have been acquired and their track information refined, the CV's control sensor subsystem 38 actively track the targets with a narrow FOV 151 pulsed laser beam 152 and command guides the KVs 118 (step 154). Although it is conceptually possible to use active tracking to perform acquisition and tracking it would be very difficult. The FOV 151 of the laser is very narrow, and thus it is difficult to image a target based on the relatively coarse tracking information provided by the external cues. Furthermore, active tracking of all the potential targets in the target cloud heavily burdens the capability of the BPS. Therefore, relatively wide FOV passive LWIR sensors are more suitable for acquisition and discrimination. As shown in FIG. 8, the CV preferably actively tracks both the targets 98 and the KVs 118 to eliminate sources of error in the guidance commands.
Handover of Target Designations & Tracking to KVs
At some range-to-target, primary tracking responsibility is transferred from the CV to the individual KVs (“Handover”). The range-to-target is determined by the sensitivity (aperture size) and resolution capabilities of the KV's imaging sensors, and the power of the CV illuminator (for SA handover) or the target intensity for passive handover.
One option is to use a MWIR imaging sensor on the KV to provide both the passive handover and to provide suitable resolution for aimpoint selection and terminal guidance (step 156). The MWIR sensor can only acquire passive in earth umbra (darkness) at very close handover ranges. Another is to handover initially to an LWIR sensor, which can acquire at much longer ranges, transitioning to MWIR to provide adequate aimpoint resolution. In these cases, the KV's imaging sensor subsystem 72 would include an MWIR sensor and possibly an LWIR sensor instead of the short-band sensor. This option is described in detail in co-pending application entitled “Enhanced Multiple Kill Vehicle (MKV) Interceptor for Intercepting Exo and Endo-Atmospheric Targets”. The short-band imaging sensor can acquire the targets at handover at considerable ranges and perform aimpoint selection if illuminated by sunlight.
Another option is to use the CV's control sensor subsystem 38 and the KV's imaging sensor subsystem 72 to both designate the targets for each KV and handover the current tracking. This is enabled because the emission band of the control sensor laser 40 overlaps the detection band of the KV's imaging sensor subsystem 72. The CV initiates handover by directing the KVs to look for target designations in a particular direction at a particular time (step 158). The CV control sensor subsystem illuminates the targets with a pulsed beam 160 to designate the targets as shown in FIG. 9 (step 162) and the KVs detect return signals 164 from their designated targets and enter track (step 165). As shown in FIG. 10a, a particular KV will look for its designated target within a “designation window” 166 to detect the return signal. This approach effectively eliminates the complexities and potential failures from matching detections between passive CV and KV sensors.
To reduce the likelihood of mis-designation, the targets are illuminated in QWERTY scan order reminiscent of the typewriter keyboard layout. As shown in FIG. 10b, a QWERTY scan designates the targets in order 1, 2, 3, 4, 5, . . . so that any target within the angle uncertainty of the imaging sensor's FOV 168 is not within the timing uncertainty of the designation. As with the typewriter, this temporally separates actions that are spatially nearby.
Another common approach would be to have each KV detect nearby illumination “pings” within its FOV and correlate that information to uplinked data to determine the target designation.
Semi-Active Post-Handover Tracking
In many applications, it may be desirable prior to entering terminal guidance to intercept to “semi-actively” track the targets using the CV's control sensor lasers and BPS to illuminate the targets (step 170) and each KV's imaging sensor subsystem to detect the return signals and update the track (step 172). Semi-active tracking provides the combined benefits of the CV's powerful laser and agile BPS with the range-to-target (resolution, latency) advantages of the KV's imaging sensor. This combined with updating the guidance track on each KV provides for more accurate tracking.
Aimpoint Selection & Terminal Track to Intercept
To enable aimpoint selection on the target with sufficient accuracy and to track the target to impact the selected aimpoint, in the exemplary embodiment a man-made source 173 of external illumination 174 illuminates the targets as shown in FIG. 11. The return signals 176 are then detected by the appropriate KV. The external illumination is suitably “short pulsed” and the imaging sensors gated to suppress dark current and improve SNR.
In diffraction limited systems, for a given aperture size the only practical way to increase resolution is to use shorter wavelength sensors (super-resolution methods based on sensor motion have been proposed, but are unsuitable in such a highly dynamic environment). A KV can only support so much weight, which restricts the aperture too fairly small diameters, hence short-band sensors. These short-band sensors can not detect a passive signature for targets in the temperature range expected for missile defense systems, hence the need for external illumination.
As shown in FIG. 12a, for a given aperture size of 2-3 inches a 0.96 micron imaging sensor produces sufficient independent pixels 180 on target to resolve both the shape and orientation of the target. By comparison a 8 micron sensor with the same aperture size only produce sufficient pixels 182 on target to determine an image centroid as shown in FIG. 12b, which is typical of most systems. However, recent studies have shown that guiding based on the centroid is not optimal and may be insufficient to destroy the target. Therefore, it is very important to resolve the target to be able to pick a particular aimpoint and then guide the KV to that aimpoint at impact. Also by comparison, a 0.96 micron imaging sensor located on the CV would only image a very few pixels 184 on target as shown in FIG. 12c due to its much greater stand-off range. Again this is only adequate to determine an image centroid aimpoint.
The source 173 of external illumination 174 is generally located somewhere on the interceptor. In one embodiment, the source is located on the CV. More specifically, the control sensor's laser (or more generally a source such as a flashlamp) is a convenient source. The KVs determine the precise aimpoint on the target as resolution and range-to-target permit (step 186) and the KVs process the return signals and guide to intercept (step 188). The tracking process is the same as “semi-active tracking” except for the selection of a specific aimpoint and terminal tracking to impact that aimpoint.
This approach has the benefit of reusing the CV's high power laser and agile BPS 42 to designate the targets. A potential drawback is that the CV must stand-off to keep all of the targets within the FOR of the laser and BPS 42. In another embodiment, the source 173 is mounted on each KV as a “headlamp” as also described in co-pending application entitled “Enhanced Multiple Kill Vehicle (MKV) Interceptor for Intercepting Exo and Endo-Atmospheric Targets”. The headlamp can be much lower power and have only a limited pointing system if any. In this case, each KV active tracks the targets to select the aimpoint and guide to intercept (step 190).
While several illustrative embodiments of the invention have been shown and described, variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.

## Claims

1. A multiple kill vehicle (MKV) interceptor for launch on a multi-stage rocket booster to intercept targets, comprising:
A carrier vehicle (CV); and
A plurality of kill vehicles (KVs) initially stored on said carrier vehicle for release to intercept the targets;
Said CV including a first sensor subsystem for detecting a first signature off of the targets, a CV processor for processing the first signature to track said targets and issue guidance commands, and an external commlink for transmitting the respective guidance commands to the released KVs pre-handover; and
Each said KV including a second sensor subsystem for detecting a second signature from its target, a divert and attitude control system (DACS), and a KV processor for processing the second signature to update the target track and select a desirable aimpoint on the target post-handover and controlling the DACS to maneuver the KV to impact the target at the aimpoint relying on the kinetic energy of the KV to destroy the target.

2. The MKV interceptor of claim 1, wherein said CV's first sensor subsystem includes a passive acquisition and discrimination sensor subsystem for detecting a third signature, said processor processing the third signature to discriminate candidate targets from a target cloud and designate one of the candidate targets for each said KV.

3. The MKV interceptor of claim 2, wherein the CV's passive acquisition and discrimination sensor subsystem includes a LWIR sensor, the KVs' second sensor subsystem includes an imaging sensor having a detection band in the visible or near visible bands that at a certain range-to-target post-handover provides independent pixels on target in the second signature for the KV processor to select the aimpoint.

4. The MKV interceptor of claim 3, wherein the visible or near visible wavelength band of the imaging sensor is too short for passive acquisition of the designated target at handover.

5. The MKV interceptor of claim 3, wherein the KV processor processes the independent pixels on target to use shape and orientation of the target to select the aimpoint.

6. The MKV interceptor of claim 3, further comprising a man made airborne source of external illumination for illuminating the targets, each said KV's imaging sensor detecting the second signature returned from its illuminated target.

7. The MKV interceptor of claim 6, wherein the source of external illumination is mounted on the CV.

8. The MKV interceptor of claim 6, wherein the man made source pulses the external illumination and the KVs' second sensor subsystem gates the imaging sensor to detect the externally illuminated targets.

9. The MKV interceptor of claim 1, wherein the CV includes a mechanism for releasing the KVs, each KV's processor controlling the DACS to initiate a spin that continuously sweeps a narrow field-of-view (FOV) visible sensor through a star field area longer that the FOV width and using the imaged star field to determine initial orientation.

10. The MKV interceptor of claim 9, wherein the mechanism releases the KVs so that the KVs lack sufficient knowledge of their orientation to safely divert away from the CV and other KVs or to divert to acquire track to the target.

11. The MKV interceptor of claim 9, wherein the star field area is at least 1 deg by 20 deg.

12. The MKV interceptor of claim 1, wherein the CV's first sensor subsystem includes a control sensor subsystem having a beam pointing system that controls a laser to actively illuminate the targets and a receiver to detect the first signature.

13. The MKV interceptor of claim 12, wherein the processor controls the DACS to divert the KVs to move out ahead of the CV upon release to maintain CV control sensor coverage to illuminate and track the KVs up to at least a desired handover range.

14. The MKV interceptor of claim 13, wherein the KV processors control the respective DACS to the KVs into waves with temporally displaced intercept times.

15. The MKV interceptor of claim 13, wherein the KVs include a reflector to reflect the laser illumination to augment CV tracking of the KV.

16. The MKV interceptor of claim 1, wherein KV health is indicated when the KV diverts as commanded.

17. The MKV interceptor of claim 1, wherein the CV processor and external commlink hand over the target designation and initial track to each said KV by uplinking data to each KV directing the KV when and where to look for a return signature, said CV first sensor subsystem including a beam pointing system for controlling a laser to illuminate each target in a time sequence, each said KV processor controlling its DACS to orient the second sensor subsystem to look for its target in the designated direction at the designated time.

18. The MKV interceptor of claim 17, wherein the CV's beam pointing system controls the laser to illuminate the targets in an order whereby any target within the angle uncertainty of the KV's second sensor subsystem's FOV is not within the timing uncertainty of the designation.

19. The MKV interceptor of claim 17, wherein the CV first sensor subsystem includes a receiver that receives the first signature from the targets to provide the initial track.

20. The MKV interceptor of claim 1, wherein the CV first sensor subsystem includes a control sensor subsystem with a beam pointing system for controlling a laser to illuminate the targets post-handover to facilitate semi-active tracking by the KVs' second sensor subsystems of their designated target.

21. A multiple kill vehicle (MKV) interceptor for launch on a multi-stage rocket booster to intercept targets, comprising:
A carrier vehicle (CV); and
A plurality of kill vehicles (KVs) initially stored on said carrier vehicle for release to intercept the targets,
Said CV including an acquisition and discrimination sensor subsystem for passively detecting a first signature in a first band, a control sensor subsystem for actively detecting a second return signature in a second band, and a CV processor for processing the first signature to discriminate candidate targets from a target cloud and designate one of the candidate targets for each said KV and processing the second return signature to track the designated targets and issue guidance commands, and an external commlink for transmitting the respective guidance commands to the released KVs pre-handover; and
Each said KV including an imaging sensor subsystem for detecting a third signature in a third band, a divert and attitude control system (DACS) and a KV processor for processing the third signature to track its target post-handover and control the DACS to maneuver the KV to intercept relying on the kinetic energy of the KV to destroy the target.

22. The MKV interceptor of claim 21, wherein the acquisition and discrimination sensor subsystem includes a passive LWIR sensor.

23. The MKV interceptor of claim 21, wherein the control sensor subsystem includes a beam pointing system that controls a laser to actively illuminate the targets and an angle-angle-range receiver that detects the second return signature.

24. The MKV interceptor of claim 21, wherein the KV processor controls the DACS to divert the KVs to move out ahead of the CV upon release to maintain CV control sensor coverage to illuminate and track the KVs up to at least a desired handover range.

25. The MKV interceptor of claim 21, wherein the CV processor and external commlink hand over the target designation and track to each said KV by uplinking data to each KV directing the KV when and where to look for a return signature and the control sensor subsystem includes a beam pointing system for controlling a laser to illuminate each target in a time sequence, each said KV processor controlling its DACS to orient the imaging sensor subsystem to look for its target in the designated direction at the designated time.

26. The MKV interceptor of claim 25, wherein the CV's beam pointing system controls the laser to illuminate the targets in an order whereby any target within the angle uncertainty of the KV's imaging sensor subsystem's FOV is not within the timing uncertainty of the designation.

27. The MKV interceptor of claim 21, wherein each KV's imaging sensor subsystem includes a sensor in the visible or near visible band that resolves the third signatures returned from externally illuminated targets to select a desirable aimpoint on the target and maintain track on the aimpoint to terminal intercept.

28. The MKV interceptor of claim 27, wherein the sensor provides independent pixels on target, said KV processor processing the independent pixels to use the shape and orientation of the target to select the aimpoint.

29. A multiple kill vehicle (MKV) interceptor for launch on a multi-stage rocket booster to intercept targets, comprising:
A carrier vehicle (CV); and
A plurality of kill vehicles (KVs) initially stored on said carrier vehicle and then released to intercept the targets,
Each said KV including an imaging sensor subsystem for detecting a signature, a processor and a divert and attitude control system (DACS);
Said CV including a mechanism for releasing the KVs, each KV processor controlling the DACS to initiate a spin that continuously sweeps a narrow field-of-view (FOV) visible sensor through a star field area the FOV width and use the imaged star field to determine initial orientation, said processor controlling the DACS to divert the KV to acquire a target track whereby the processor processes the detected signature of the target and guides the KV to intercept relying on the kinetic energy of the KV to destroy the target.

30. The MKV interceptor of claim 29, wherein the mechanism releases the KVs so that the KVs lack sufficient knowledge of their orientation to safely divert away from the CV and other KVs or to divert to acquire track to the targets.

31. The MKV interceptor of claim 29, wherein the star field area is at least 1 deg by 20 deg.

32. The MKV interceptor of claim 29, wherein the KV processor matches the imaged star field against a pre-stored star map to determine initial orientation.

33. A multiple kill vehicle (MKV) interceptor for launch on a multi-stage rocket booster to intercept targets, comprising:
A carrier vehicle (CV);
A plurality of kill vehicles (KVs) initially stored on said carrier vehicle for release to intercept the targets; and
A man made airborne source of external illumination for illuminating the targets;
Said CV including a first sensor subsystem for detecting a first signature off of the targets, a CV processor for processing the first signature to track said targets and issue guidance commands, and an external commlink to transmitting the respective guidance commands to the released KVs pre-handover; and
Each said KV including a short-band imaging sensor for detecting a return signature from a target illuminated by said source post-handover, a divert and attitude control system (DACS), a KV processor for processing the second signature to select a desirable aimpoint on the target and controlling the DACS to maneuver the KV to impact the track on the aimpoint relying on the kinetic energy of the KV to destroy the target.

34. The MKV interceptor of claim 33, wherein the source of external illumination is mounted on the CV.

35. The MKV interceptor of claim 33, wherein the man made source pulses the external illumination and the KVs' short-band imaging sensor gates the return signature to detect the externally illuminated targets.

36. The MKV interceptor of claim 33, wherein the imaging sensor detects in the visible or near visible bands.

37. A kinetic energy kill vehicle (KV) for use with an MKV interceptor launched on a multi-stage rocket booster to intercept targets, comprising:
A divert and attitude control system (DACS) for controlling the heading of the kill vehicle;
A short-band imaging sensor subsystem for detecting a return signal in the visible or near visible bands from a target illuminated by an external source;
A processor that processes the return signal to select a desirable aimpoint on the target and controls the DACS to maintain track on the aimpoint to terminal intercept relying on the kinetic energy of the KV to destroy the target.

38. The KV of claim 37, wherein the short-band imaging sensor subsystem provides independent pixels on target for the processor to use the shape and orientation of the target to select the aimpoint.

39. The KV of claim 37, further comprising a telemetry modulated retro-reflector.

40. A method of intercepting targets, comprising:
Using a multi-stage rocket booster to launch a multiple kill vehicle (MKV) interceptor on a path to intercept a target cloud, said interceptor including a plurality of KVs stored on a control vehicle (CV);
Releasing the KVs from the CV and diverting them toward the targets;
Passively detecting signatures on the CV of the incoming targets to acquire the targets and refine the track of the KV towards the candidate targets;
Handing over target designation and tracking responsibility from the CV to the multiple deployed KVs;
Using a man-made airborne source to illuminate the targets;
Sensing the return signatures off of the illuminated targets at the respective KVs; and
At each KV, computing an aimpoint on the designated target from the return signature and refining the track on the aimpoint to target intercept relying on the kinetic energy of the KV to destroy the target.

41. The method of claim 40, wherein upon release each KV initiates a spin that continuously sweeps a narrow field-of-view (FOV) visible sensor through a star field area of at least 1 degrees by 20 degrees and uses the imaged star field to determine initial orientation.

42. The method of claim 40, further comprising prior to handover, actively tracking the acquired targets from the CV and transmitting guidance commands to the respective KVs to direct them toward the candidate targets.

43. The method of claim 40, wherein the CV hands over the target designation and track to each said KV by uplinking data to each KV directing the KV when and where to look for a return signature and by illuminating each target in a time sequence, each said KV looking for its target in the designated direction at the designated time.

44. The method of claim 40, wherein post-handover the CV illuminates the targets and the KVs detect the return signatures and track their respective targets.

45. The method of claim 40, wherein the KVs detects independent pixels on target to use the shape and orientation of the target to select the aimpoint.