Patent Grant
7150428
The present invention relates to a missile guidance system and in, particular, to a system where sensors on the missile detect light scattered from a laser beam directed towards a target, signals generated by the sensors being applied to processing electronics in the missile that determines, from the signals, the distance the missile is from the beam and then provides guidance signals to the missile's guidance system to maintain the missile's trajectory at a predetermined position with respect to the laser beam.
Precision guidance for missiles is a subject of high interest for all military organizations throughout the world. The required precision has high costs due, in great part, to the complexity of the guidance techniques generally used. Radar, RF, GPS, TV, IR or lasers are examples of technologies that have been used to meet the guidance precision requirements. The majority of the present approaches are based on terminal homing seekers. The problem with these approaches is the high costs associated with seeker components such as gimbals, domes, high performance electronics and software. Other techniques make use of a human in the loop to reduce the complexity and costs of the components installed aboard a missile. In these techniques, a human operator provides assistance to a missile's guidance system by correcting its trajectory through a data link such that a satisfactory trajectory of the missile to the target is achieved. This approach substantially reduces the costs of the guidance system but the precision is directly proportional to the operator's skill and this can be highly variable.
One technique using an operator to guide missiles during flight is described in U.S. Pat. No. 4,234,141 by Walter E. Miller Jr., which issued on 18 Nov. 1980. In this guidance system, an observer establishes and maintains a visual line-of-sight contact with a target through a telescope. In tracking the missile's trajectory towards the target, short pulses of collimated light are transmitted from the launch site towards the missile, which pulses are received by an optical receiver on the missile and are simultaneously reflected by a retro reflective prism on the missile. The reflected pulses follow a path parallel to the incident wave and are thus directed back to the launch site. A missile tracker at the launch site responds to the reflected pulses and measures any deviation of the missile from the visual line-of-sight maintained between the launch site and the target. Guidance commands are then transmitted towards the missile for maintaining the missile on a proper trajectory, which pulses contain correctional signals for the missile's guidance system. The guidance precision of this technique is proportional to the observer's (operator's) skill in maintaining the visual line-of-sight contact with the target and this can be rather variable.
Another missile guidance system is a scatterider guidance system that utilizes a designating beam of laser pulses directed from the launch pad towards a target. Atmospheric particles scatter the laser pulses and sensors on the missile detect the laser light scattered by the atmospheric particles and onboard guidance electronics calculate the radial distance between the laser beam and the longitudinal axis of the missile. That distance is then used to generate deflection commands for the aerodynamic control surfaces of the missile such that it stays close to the laser beam. In the embodiment described by McCowan et al in U.S. Pat. No. 6,138,944, laser light scattered from atmospheric particles for one laser pulse is detected by eight aft-looking optical sensors mounted around the circumference of the missile and one annular forward-looking sensor mounted on the nose section. The aft-looking sensors are mounted with their centrelines angled such that they point 60 degrees aft of the perpendicular to the missiles' longitudinal axis and each has a field-of-view of 45 degrees so the eight sensors provide a 360 degree coverage around the missile. The detection of back-scatter laser light is provided by one annular forward-looking sensor that is mounted such that it stares at a 45 degree angle forward of the perpendicular to the missile's longitudinal axis.
In U.S. Pat. No. 6,138,944, when light scattered from a single laser pulse is detected by one of the eight aft-looking sensor and by the forward-looking sensor, this detection as well as the time lapse between the detection by the aft-looking sensor and detection by the forward-looking sensor are provided as inputs to guidance electronics. That time lapse will be directly dependent on the radial distance between the missile's longitudinal axis and the laser beam due to the time it takes the laser pulse to travel from the aft-looking detection point and the forward-looking detection point. The guidance electronics is coupled to the aft-looking sensors to derive which one actually detected the scattered light and then calculates the radial distance between the laser beam and the missile using principles of geometry and trigonometry. That distance as well as the aft-looking detector that detected the scattered laser light is used to generate commands for the guidance system to maintain the missile on the desired trajectory with respect to the laser beam. The precision of this guidance system is dependent on the precision of the geometric and trigonometry calculations. The annular forward-looking sensor will limit what type of countermeasure may be effective since no sensor is looking directly at the target. It does, however, require inertial rate sensors and a roll sensor.
Another laser guidance system for a missile is described in JP Patent No. 2000039296 (Application No. JP 98209942) based on three laser beams directed along vertices of an equilateral triangle between which a missile flies and determines its position by the relative level of scattered laser light detected by a number of sensors on the missile.
A further laser guidance system for a missile is described by Walter E. Miller Jr., in US Statutory Invention Registration H299 that was published on 7 Jul. 1987. In this system the operator maintains sight of a target through optics at a fire control station. A laser transmitter on the missile directs a laser beam towards the fire control station where it is received and coupled to a phase conjugated amplifier and redirected back through a spatial encoder to the missile. The encoding provides guidance instructions for the missile where the redirected beam is received and applied to the missile's guidance control system. This guidance system does not have any sensor directed toward the target and this limits what type of countermeasures may be effective. It does, however, require an operator in the loop that has to maintain visual sight of the target.
The majority of guidance techniques, other than those taught by McCowan et al and Walter E. Miller Jr., share a common weakness in that they are susceptible to detection by the target which can employ countermeasure since the field-of-view of their guidance sensor have to continuously look at the target. Countermeasure that may be employed including dazzling or destruction of the sensor which would ruin the precision guidance of the missile. The majority of these missiles still rely on complex and costly gyroscopes and accelerometers to assist in guidance.
A new generation of hypervelocity missiles presently being developed inevitably call for a highly profiled fuselage nose that denies any possibility of using a forward-looking sensor because that would require a dome at the tip of the missile. There is, as a result, a requirement for a new guidance system for missiles that would be almost immune to known countermeasures while permitting use of a highly profiled nose and provide for a low cost implementation.
It is an object of the present invention to provide a guidance system for a vehicle that is less costly to implement.
A guidance system for a vehicle, according to one embodiment of the present invention, comprises a laser beam source directing at least one laser beam towards a required designated final location for the vehicle on which at least one sensor is located, that sensor rotating around an axis in the direction of travel of the vehicle and having a field-of-view (FOV) that is generally directed sideways to the direction of travel of the vehicle, the sensor generating a signal in response to detecting radiation from the laser beam scattered by an atmosphere through which the laser beam propagates, the width of said signal being proportional to the distance between the beam and said vehicle, signals from said at least one sensor being applied to a vehicle guidance system in the vehicle that determines the distance from the vehicle to the beam and then provides correction commands to the guidance system to correct the direction of travel of the vehicle.
Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawing, in which:
Precision guidance for missiles is a subject of high interest for all military organizations throughout the world. The required precision has high costs due, in great part, to the complexity of the guidance techniques generally used. Radar, RF, GPS, TV, IR or lasers are examples of technologies that have been used to meet the guidance precision requirements. The majority of the present approaches are based on terminal homing seekers. The problem with these approaches is the high costs associated with seeker components such as gimbals, domes, high performance electronics and software. Other techniques make use of a human in the loop to reduce the complexity and costs of the components installed aboard a missile. In these techniques, a human operator provides assistance to a missile's guidance system by correcting its trajectory through a data link such that a satisfactory trajectory of the missile to the target is achieved. This approach substantially reduces the costs of the guidance system but the precision is directly proportional to the operator's skill and this can be highly variable.
Many of the present guidance techniques share a common weakness in that they are susceptible to detection and countermeasures (CM) being applied by a target since the field-of-view (FOV) of their guidance sensor have to continuously look at the target. Countermeasures that may be employed include dazzling or destruction of the sensor, which would ruin guidance of the missile. Moreover, the majority of guidance systems for missiles still rely on complex and costly gyroscopes and accelerometers to assist in guidance.
One technique using an operator to guide missiles during flight is described in U.S. Pat. No. 4,234,141 by Walter E. Miller Jr. which issued on 18 Nov. 1980. In this guidance system, an observer establishes and maintains a visual line-of-sight contact with a target through a telescope. In tracking the missile's trajectory towards the target, short pulses of collimated light are transmitted from the launch site towards the missile, which pulses are received by an optical receiver on the missile and are simultaneously reflected by a retro reflective prism on the missile. The reflected pulses follow a path parallel to the incident wave and are thus directed back to the launch site. A missile tracker at the launch site responds to the reflected pulses and measures any deviation of the missile from the visual line-of-sight maintained between the launch site and the target. Guidance commands are then transmitted towards the missile for maintaining the missile on a proper trajectory, which pulses contain correctional signals for the missile's guidance system. The guidance precision of this technique is proportional to the observer's (operator's) skill in maintaining the visual line-of-sight contact with the target and this can be rather variable.
Another missile guidance system is a scatterider guidance system that utilizes a designating beam of laser pulses directed from the launch pad towards a target. Atmospheric particles scatter the laser pulses and sensors on the missile detect the laser light scattered by the atmospheric particles and onboard guidance electronics calculate the radial distance between the laser beam and the longitudinal axis of the missile. That distance is then used to generate deflection commands for the aerodynamic control surfaces of the missile such that it stays close to the laser beam. In the embodiment described by McCowan et al in U.S. Pat. No. 6,138,944, laser light scattered from atmospheric particles for one laser pulse is detected by eight aft-looking optical sensors mounted around the circumference of the missile and one annular forward-looking sensor mounted on the nose section. The aft-looking sensors are mounted with their centrelines angled such that they point 60 degrees aft of the perpendicular to the missiles' longitudinal axis and each has a field-of-view of 45 degrees so the eight sensors provide a 360 degree coverage around the missile. The detection of back-scatter laser light is provided by one annular forward-looking sensor that is mounted such that it stares at a 45 degree angle forward of the perpendicular to the missile's longitudinal axis.
In U.S. Pat. No. 6,138,944, when light scattered from a single laser pulse is detected by one of the eight aft-looking sensor and by the forward-looking sensor, this detection as well as the time lapse between the detection by the aft-looking sensor and detection by the forward-looking sensor are provided as inputs to guidance electronics. That time lapse will be directly dependent on the radial distance between the missile's longitudinal axis and the laser beam due to the time it takes the laser pulse to travel from the aft-looking detection point and the forward-looking detection point. The guidance electronics is coupled to the aft-looking sensors to derive which one actually detected the scattered light and then calculates the radial distance between the laser beam and the missile using principles of geometry and trigonometry. That distance as well as the aft-looking detector that detected the scattered laser light is used to generate commands for the guidance system to maintain the missile on the desired trajectory with respect to the laser beam. The precision of this guidance system is dependent on the precision of the geometric and trigonometry calculations. The annular forward-looking sensor will limit what type of countermeasure may be effective since no sensor is looking directly at the target. It does, however, require inertial rate sensors and a roll sensor.
Another laser guidance system for a missile is described in JP Patent No. 2000039296 (Application No. JP 98209942) based on three laser beams directed along vertices of an equilateral triangle between which a missile flies and determines its position by the relative level of scattered laser light detected by a number of sensors on the missile.
A further laser guidance system for a missile is described by Walter E. Miller Jr., in US Statutory Invention Registration H299 that was published on 7 Jul. 1987. In this system the operator maintains sight of a target through optics at a fire control station. A laser transmitter on the missile directs a laser beam towards the fire control station where it is received and coupled to a phase conjugated amplifier and redirected back through a spatial encoder to the missile. The encoding provides guidance instructions for the missile where the redirected beam is received and applied to the missile's guidance control system. This guidance system does not have any sensor directed toward the target and this limits what type of countermeasures may be effective. It does, however, require an operator in the loop that has to maintain visual sight of the target.
The majority of guidance techniques, other than those taught by McCowan et al and Walter E. Miller Jr., share a common weakness in that they are susceptible to detection by the target which can employ countermeasure since the field-of-view of their guidance sensor have to continuously look at the target. Countermeasure that may be employed include dazzling or destruction of the sensor which would ruin the precision guidance of the missile. The majority of these missiles guidance systems still rely on complex and costly gyroscopes and accelerometers to assist in guidance.
A new generation of hypervelocity missiles presently being developed inevitably call for a highly profiled fuselage nose that denies any possibility of using a forward-looking sensor because that would require a dome at the tip of the missile. There is, as a result, a requirement for a new guidance system for missiles that would be almost immune to known countermeasures while permitting use of a highly profiled nose and provide for a low cost implementation.
The basic Beam Laser Atmospheric Scattering Trajector (BLAST) guidance system according to the present invention is illustrated in
Each sensor 3 has a photodetector 4, a lens 5 to focus light scattered from laser beam 8 directed to target 9 onto photodetector 4 and an optical filter 6 in the optical path to the photodetector to block light from sources other than that scattered from laser beam 8 from reaching photodetector 4. Signal from the sensors 3 are supplied to processing electronics 7 located inside the missile 10 that analysis signal outputs from the laser sensors 3 to determine the distance the missile 10 is from beam 8 and then generate the necessary trajectory corrections to the guidance system (not shown) for the missile 10. The laser sensors 3 and processing electronics 7 represent the guidance sensor device and are located on and aboard the missile 10.
The laser beam 8 directed to target 9 may be either continuous wave (CW) or temporally and/or spatially modulated by the beam encoder 2 to bear information that will be used by the missile 10 for its guidance. The guidance schemes are numerous and could include either temporal modulation such as sinusoidal or square wave modulation or a complex series of pulses. Spatially encoder multi-element beams may also be used or combinations of both. In a basic embodiment, a simple CW beam 8 can be used which is projected in the direction of target 9 and which is switched on prior to or simultaneously with the launch of missile 10. The laser beam 8 (or beams 8 and 8, in
Since the missile 10 is spinning, each laser sensor's 3 FOV will intercept scattered radiation from the laser beam 8 having a known diameter once per revolution and generate an output signal pulse with a pulse-width that is proportional to the distance between the laser beam 8 and the missile 10 as illustrated in
When a pulsed laser source is used, as illustrated by pulses 81, 82, 83 . . . 8n in
One laser sensor 3 on a missile 10 would be sufficient but adding more sensors 3 on the missile 10 will increase the refresh rate of the distance measurement. One laser beam is sufficient for basic distance measurement of a missile 10 from that beam. By adding more laser beams, however, more position information of the missile relatively to the beams can be obtained. This more advanced embodiment of the BLAST guidance technique where two CW laser beams 8 and 8′ are used is illustrated in
The measured angle θ is used to remove the uncertainty as to if the missile is above or below the beam pair. There are always two physical positions (one above and one below) for which the values of the two positions d1 and d2 are the same. If the angle θ is not measured, then the missile will require an attitude sensor onboard to continuously determine its roll position and remove any uncertainty.
Various modifications may be made to the preferred embodiments without departing from the spirit and scope of the invention as defined in the appended claims. The same type of guidance system could, for instance, be used for remote guidance of vehicles other than missiles.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3614025 | Maillet | Oct 1971 | A |
| 4234141 | Miller, Jr. et al. | Nov 1980 | A |
| H299 | Miller, Jr. | Jul 1987 | H |
| 4696441 | Jones et al. | Sep 1987 | A |
| 5374009 | Miller et al. | Dec 1994 | A |
| 5878977 | Hosaka et al. | Mar 1999 | A |
| 6138944 | McCowan et al. | Oct 2000 | A |
| 6568627 | Jones et al. | May 2003 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20060049299 A1 | Mar 2006 | US |
