Patent Description:
Projectiles fired from a weapons barrel in the atmosphere naturally travel along generally ballistic trajectories. The shape of the trajectory is influenced by gravity, aerodynamic forces acting on the projectile including environmental conditions e.g. wind and/or atmospheric contaminants.

The term "shallow trajectories" is commonly applied to cases where the projectile is fired at low elevation angles of about <NUM>° or less, and this also referred to as very low-angle fire. The term "steep trajectories" is commonly applied to cases where the projectile is fired at elevation angles higher than about <NUM>°, and this is also referred to as high-angle fire.

Referring to <FIG>, a conventional projectile trajectory TJ is illustrated for a non-steered projectile. The conventional projectile trajectory TJ comprises an ascending branch AB culminating at the summit S of the trajectory, followed by a descending branch DB. While the weapons barrel WB may be set at a particular elevation angle θ, defining a line of elevation LE, the projectile typically leaves the weapons barrel WB at a different direction (the angle of departure γ) the instant it leaves the weapons barrel WB, defining a line of departure LD. The projectile typically hits the ground at a corresponding angle of fall φ.

It is known to provide lateral steering control to bodies moving through a fluid medium, such as air for example. In some cases, such as for example projectiles, such control allows for correction of aiming errors, for maneuvering, and for compensation for wind deflection and other effects.

It is also known to provide such lateral steering via jet thrust control, in which a lateral jet thruster arrangement provides a side thrust to the projectile. Many lateral steering systems based on jet thrust techniques are known, some of which are disclosed in at least some of the above references.

Further, <CIT> discloses a spin-stabilized projectile that is steered by taking air from an air intake at the front of the projectile, and expelling the air along an outer surface of the projectile to alter its trajectory toward the desired impact location. Air taken in through the air intake is directed toward a rotor that is able to rotate relative to the rest of the projectile. The rotor has an outlet that may direct the air taken in at the air inlet out in a direction having both radial and circumferential components. The force produced in the radial direction provides a steering force substantially normal to the projectile axis, used to steer the projectile. The force produced in the circumferential direction is used to provide impetus to spin the rotor. A brake is used to control the rotational speed of the rotor, to control the direction that the air is expelled from the projectile.

According to the invention there is provided a projectile configured for moving through a fluid medium, and having a longitudinal axis, the projectile comprising a steering assembly and a shell body rotatably mounted thereto about the longitudinal axis, and including an attitude control system, a despin module, an electromagnetic receiver and/or emitter system, and a controller, wherein:.

For example, said steering assembly comprises a nose portion of said shell, and wherein said ram air inlet is provided at a forward end of the nose portion. For example, said shell body comprises an external casing extending aft from a front edge thereof to an aft shell end, and wherein said front edge is axially spaced by a gap from said nose portion. For example, said aft external casing overlies an aft portion of the steering assembly, including said attitude control system and said despin module.

Additionally or alternatively, for example, said exhaust assembly comprises a plurality of shut-off valves corresponding to said plurality of said exhaust outlets, wherein each shut-off valve is controllable via said controller to selectively open or close fluid communication between the corresponding exhaust outlets and said ram air inflow provided via the ram air inlet during operation of the shell, to selectively enable said steering control moments to be generated.

Additionally or alternatively, for example, the projectile further comprises a plurality of first openings in said shell body in the vicinity of said exhaust assembly for allowing evacuation of exhaust gases generated by said attitude control system.

Additionally or alternatively, for example, said despin module comprises a generally cylindrical body including a central passageway, a central valve, and a despin thruster arrangement. For example, said fluid passageway is in selective fluid communication with central passageway via said central valve. For example, said despin thruster arrangement comprises two exhaust passageways extending from said central valve, each exhaust passageway comprising a respective tangential exhaust outlet at an outer end thereof for selectively generating thereat a tangential jet thrust from a ram air inflow selectively provided by said ram air inlet via said central valve. For example, the projectile further comprises a plurality of second openings in said shell body in the vicinity of said despin module for allowing evacuation of exhaust gases generated by said despin thruster arrangement.

Additionally or alternatively, for example, said steering assembly is rotatably mounted to said shell body via a bearing arrangement. For example, said bearing arrangement is axially located in a vicinity of said gap. For example, said bearing arrangement is configured for allowing axial movement between said steering assembly and said shell body to close said gap responsive to said shell being accelerated, and for re-opening said gap when the acceleration is terminated.

Additionally or alternatively, for example, wherein said shell body comprises a driving band made from a gliding metal.

Additionally or alternatively, for example, the projectile further comprises an electrical generator for generating electrical power during operation of the shell, responsive to a relative rotational movement between the steering assembly and the shell body. For example, said electrical generator comprises magnets provided in the shell body in lateral registry with coils provided in the steering assembly.

Additionally or alternatively, for example, said shell further comprises a tracer configuration for facilitating tracing the shell after being fired.

Additionally or alternatively, for example, said electromagnetic receiver and/or emitter system comprises a plurality of antennas. For example, said antennas are provided in said nose portion. Additionally or alternatively, for example, said antennas are conformal with an outer surface of said nose portion. Additionally or alternatively, for example, said antennas are monopole antennas. Additionally or alternatively, for example, the shell comprises four said antennas, accommodated in said nose portion in cruciform arrangement. Additionally or alternatively, for example, said antennas are configured for operating as a downlink/uplink module, operatively coupled to said controller. Additionally or alternatively, for example, said antennas are configured for receiving RF signals. For example, said controller is configured for controlling a trajectory of said shell via said attitude control system based on said RF signals when received by said antennas. For example, said RF signals are transmitted by a ground station and are configured for providing navigation instructions to said controller for controlling said trajectory; alternatively, for example, said RF signals are reflected by an illuminated target to said antennas, and wherein said controller is configured for controlling said trajectory based on differences between the RF signals received by each said antenna.

Additionally or alternatively, for example, said antennas are configured for transmitting RF signals. For example, said transmitted RF signals include information relating to at least one of the following: position of said shell, velocity of said shell.

Additionally or alternatively, for example, said shell is configured such that operation of said attitude control system to generate a thrust force by exhausting via a respective said exhaust outlets a ram airflow provided from said ram air inlet applies a control moment in at least one of pitch or yaw to the rotating shell body, which induces gyroscopic precession of said shell with respect to the longitudinal axis, and correspondingly induces a control moment to the shell in an orthogonal direction to said thrust force and said longitudinal axis to thereby correspondingly change an angle of attack of said shell, inducing an aerodynamic lateral force on said shell for changing the trajectory thereof in a desired direction.

According to a second aspect of the presently disclosed subject matter there is provided a system for steering a projectile moving through a fluid medium towards a target, the system comprising:.

For example, the system further comprises said weapons barrel.

Additionally or alternatively, for example, said sensor system includes an imaging system operating in the infra red (IR) and/or visual and/or ultraviolet spectrums.

Additionally or alternatively, for example, said sensor system is configured for selectively operating in a track lock mode, wherein the sensor system is continuously locked onto the target.

Additionally or alternatively, for example, said sensor system is configured for determining a position of the shell relative to a position of the target.

Additionally or alternatively, for example, said system is configured for firing said projectile along a shallow trajectory.

According to the second aspect of the presently disclosed subject matter there is also provided a method for steering a projectile moving through a fluid medium towards a target, the system comprising:.

For example, said image data is provided by a sensor system, and the method comprises selectively operating sensor system in a track lock mode, wherein the sensor system is continuously locked onto the target.

Additionally or alternatively, for example, the method comprises determining a position of the shell relative to a position of the target.

Additionally or alternatively, for example, said projectile is fired along a shallow trajectory towards the target.

According to a third aspect of the presently disclosed subject matter there is provided a system for steering a projectile moving through a fluid medium towards a target, the system comprising:.

Additionally or alternatively, for example, said electromagnetic illuminator comprises an active radar or a half-active radar.

Additionally or alternatively, for example, said projectile is configured such that the antennas thereof together with the controller thereof are configured for sensing and determining the instantaneous spatial position of the target during at least a portion of the trajectory of the shell from a predetermined range from the target or from a predetermined time after being fired, and wherein the controller is configured for generating course correction command signals to the attitude control system, responsive to receiving input from the antennas.

Additionally or alternatively, for example, the system is configured for firing said projectile along a steep trajectory.

According to the third aspect of the presently disclosed subject matter there is also provided a method for steering a projectile moving through a fluid medium towards a target, the system comprising:.

For example, said electromagnetic energy is provided by an active radar or a half-active radar.

Additionally or alternatively, for example, said projectile operates such that the antennas thereof together with the controller thereof are sense and determine the instantaneous spatial position of the target during at least a portion of the trajectory of the shell from a predetermined range from the target or from a predetermined time after being fired, and wherein the controller generates course correction command signals to the attitude control system, responsive to receiving input from the antennas.

According to another aspect of the presently disclosed subject matter there is also provided a projectile is disclosed, having: a longitudinal axis, a steering assembly, a shell body, an attitude control system, a despin module, an electromagnetic receiver and/or emitter system, and a controller. The attitude control system includes a ram air inlet in selective open fluid communication with an exhaust assembly, which includes a plurality of exhaust outlets to selectively generate each of a plurality of thrust jets from a ram air inflow provided by the ram air inlet, each thrust jet being selectively controllable via the controller. The despin module is configured for selectively de-spinning the steering assembly with respect to the shell body about the longitudinal axis. The electromagnetic receiver and/or emitter system is configured for receiving and/or emitting electromagnetic energy, and for cooperating with the controller for operating the exhaust assembly to thereby selectively provide steering control moments.

A feature of at least some examples of the presently disclosed subject matter is that the shell or projectile is compatible with standard rifled weapons, which therefore do not require to be modified or replaced with specialized weapons.

Another feature of at least some examples of the presently disclosed subject matter is that the shell or projectile can be provided on any one of a number of different scales, from relative low caliber shells to relatively high caliber shells, with little or no modification being necessary other than size.

Another feature of at least some examples of the presently disclosed subject matter is that a cost effective solution is provided for a steerable shell that can be homed to a target.

Another feature of at least some examples of the presently disclosed subject matter is that a self-contained shell is provided which operates without the need for an external power source or batteries.

Another feature of at least some examples of the presently disclosed subject matter is that a shell is provided having improved accuracy over long ranges, as compared with a conventional shell of similar caliber and fired from the same weapons barrel.

Another feature of at least some examples of the presently disclosed subject matter is that, at the system level, various configurations are possible for the controlling the shell for steering the same to a desired target. For example, the particular configuration for the system can depend on the type of target.

Another feature of at least some examples of the presently disclosed subject matter is that, at the system level, the system can be configured with an external detector, which can be useful for targets with low dynamic properties, i.e. static target or low relative angular movement of the target (within FOV of the external sensor.

Another feature of at least some examples of the presently disclosed subject matter is that, at the system level, the target sensor can be incorporated in the shell, which can be useful for targets with greater dynamic movement or greater range.

In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:.

According to the invention there is provided a steerable shell configured for being steered to a target.

Herein "shell" and "projectile" are used interchangeably.

Referring to <FIG>, a steerable shell according to a first example of the presently disclosed subject matter, generally designated <NUM>, comprises a steering assembly <NUM> and a shell body <NUM>, and has a longitudinal axis LA.

As will become clearer herein, the shell body <NUM> is rotatably mounted to the steering assembly <NUM> about longitudinal axis LA via a bearing arrangement <NUM>.

For convenience, and referring to <FIG> in particular, a Cartesian orthogonal axes system CS can be defined for the shell <NUM>, including three orthogonal axes x, y, z. The z-axis is along the longitudinal axis LA (and defined the roll axis or spin axis of the shell), while the x-axis and the y-axis are orthogonal to one another and to the longitudinal axis LA. The pitch axis of the shell <NUM> is parallel to or co-axial with the x-axis, while the yaw axis of the shell <NUM> is parallel to or co-axial with the y-axis.

The shell <NUM> comprises an attitude control system <NUM>, despin module <NUM>, controller <NUM>, and electromagnetic receiver and/or emitter system <NUM>, and these features are comprised fully or partially in the steering assembly <NUM>, as will become clearer herein.

Referring in particular to <FIG> and <FIG>, steering assembly <NUM> comprises a nose portion <NUM> of the shell <NUM>, connected to the attitude control system <NUM> via a hollow shaft <NUM>. The nose portion <NUM> has an opening at the front end thereof in the form of ram air inlet <NUM>, which is in open fluid communication with a fluid passageway provided by the lumen <NUM> of the shaft <NUM>. The nose portion <NUM> has a conical, ogive, rounded or otherwise aerodynamic profile, and an external surface <NUM> extending from the leading edge of the ram air inlet <NUM> to an aft edge <NUM> of the nose portion <NUM>.

In this example, the lumen <NUM> is centrally disposed with respect to the shaft <NUM>, and both are concentric with respect to longitudinal axis LA.

Referring also to <FIG>, attitude control system <NUM> comprises an exhaust assembly <NUM> including a generally cylindrical body <NUM> having an external diameter D1 and cylindrical surface <NUM>, a front end <NUM> and an aft end <NUM>. The cylindrical body <NUM> has an inlet <NUM>, extending aft into a central passageway <NUM>. The inlet <NUM> is connected to and in fluid communication with the aft end of lumen <NUM>. Four exhaust passageways <NUM> are formed in the cylindrical body <NUM>, each extending radially outwardly from the central passageway <NUM> along respective axes VA and away from longitudinal axis LA. In this example the axes VA intersect longitudinal axis LA. Each exhaust passageway <NUM> comprises a respective radial exhaust outlet <NUM> at a radial end thereof. The four exhaust passageways <NUM>, and thus the four corresponding exhaust outlets <NUM>, are in cruciform arrangement and are at the same axial position (i.e. lie on the same transverse plane) with respect to longitudinal axis LA.

The exhaust assembly <NUM> further comprises four shut-off valves <NUM>, one for each exhaust passageway <NUM>. Each shut-off valve <NUM> is configured for selectively opening or closing the respective radial exhaust outlet <NUM>, and thus for correspondingly selectively opening or closing fluid communication between the respective radial exhaust outlet <NUM> and the ram air inlet <NUM> (via the lumen <NUM>, inlet <NUM>, central passageway <NUM> and respective exhaust passageway <NUM>). Thus, the shut-off valves <NUM> are correspondingly actuable between an open position and a closed position.

In this example, the shut-off valves <NUM> are normally in a closed position until actively actuated to open, and are mechanically biased to the closed position. In alternative variations of this example, the shut-off valves are instead biased in the open position until actively actuated to close. In yet other alternative variations of this example, the shut-off valves are not biased to the open or closed positions; rather, they are configured to remain in the open position or in the closed position until actively actuated to change the current position.

In this example, the shut-off valves <NUM> are individually and independently actuable between an open position and a closed position, and controlled via the controller <NUM>.

Referring to <FIG>, an example of shut-off valve <NUM> is illustrated. In this example, the shut-off valve <NUM> comprises an electrically driven actuator <NUM> coupled to valve member <NUM>. Valve member <NUM> comprises a cylindrical tube <NUM> having a longitudinal axis TA, and closed at both axial ends by forward disc-shaped wall <NUM> and aft disc-shaped wall <NUM>. The valve member <NUM> comprises transverse cut-outs <NUM> on opposite sides of the cylindrical tube <NUM>, and aligned along an axis CO which is transverses to longitudinal axis TA. A pin or stop <NUM> projects axially outwards from wall <NUM>. The cylindrical tube <NUM> comprises solid cylindrical wall portions <NUM> located between transverse cut-outs <NUM>. The cylindrical tube <NUM> is rotatably mounted in the respective exhaust passageway <NUM> such as rotate with respect to the exhaust passageway <NUM> about its longitudinal axis TA, at least between an open position (<FIG>) and a closed position (<FIG>).

Referring to <FIG>, in the open position of the valve member <NUM> the axis CO is aligned with the axis VA of the exhaust passageway <NUM>, and thus the transverse cut-outs <NUM> are aligned with the exhaust passageway <NUM> allowing fluid communication transversely through the cylindrical tube <NUM>, i.e., between the central passageway <NUM> and the radial exhaust outlet <NUM>.

Referring to <FIG>, in the closed position of the valve member <NUM> the axis CO is orthogonal with the axis VA of the exhaust passageway <NUM>, and thus the solid cylindrical wall portions <NUM> are aligned with the exhaust passageway <NUM> closing any fluid communication transversely through the cylindrical tube <NUM>, i.e., preventing fluid communication between the central passageway <NUM> and the radial exhaust outlet <NUM>.

In this example, electrically driven actuator <NUM> comprises a solenoid actuator <NUM>, coupled to cylindrical tube <NUM> and comprising a return torsional spring <NUM>. The solenoid actuator <NUM> comprises coil <NUM> and core <NUM> rotatable within the coil <NUM> responsive to a current flowing in the coil <NUM>. The core <NUM> comprises an external magnet <NUM> fixed thereto. As core <NUM> rotates clockwise or anticlockwise about axis TA (responsive to operation of the solenoid actuator <NUM>), the valve member <NUM> rotates about axis TA in a clockwise or anticlockwise direction, respectively.

When de-activated (<FIG>), the solenoid actuator <NUM> is biased to a closed position via the return spring <NUM>, rotating the cylindrical tube <NUM> to the closed position, such that the solid cylindrical wall portions <NUM> are aligned with the exhaust passageway <NUM>. When activated (<FIG>) by a signal or electrical current from the controller <NUM>, the solenoid actuator <NUM> rotates the core <NUM> against the return spring <NUM> (thereby torsionally stressing the same), and rotating the cylindrical tube <NUM> about axis TA to the open position, i.e., such that the transverse cut-outs <NUM> are aligned with the exhaust passageway <NUM>. The solenoid actuator <NUM> and the cylindrical tube <NUM> stay in this position until deactivated by the controller, whereupon the solenoid <NUM> and the cylindrical tube <NUM> return to the closed position by the action of the torsion spring.

In this example, the core <NUM> can rotate only between two angular positions, corresponding to the valve open position and the valve closed position. For example, suitable mechanical stops can be provided to prevent further rotational movement past these angular positions. This enables the shut-off valve <NUM> to operate as an on-off valve.

In alternative variations of the above example of shut-off valve <NUM>, the shut-off valve <NUM> is instead biased to the open position, and activation of the solenoid actuator <NUM> results in the valve closing to the closed position.

While in the illustrated example the exhaust outlets <NUM> are located axially aft of the bearing arrangement <NUM>, in alternative variations of this example, the exhaust outlets <NUM> are located axially forward of the bearing arrangement <NUM>. In yet other alternative variations of this example, one set of exhaust outlets <NUM> is located forward of the bearing arrangement <NUM>, and another set of exhaust outlets <NUM> is located aft of the bearing arrangement <NUM>.

Referring again to <FIG> and <FIG>, the de-spin module <NUM> is configured for selectively de-spinning the steering assembly <NUM> with respect to shell body <NUM>, about longitudinal axis LA.

In this example, the de-spin module <NUM> is integrally formed with the attitude control system <NUM>, for example at aft end <NUM> of cylindrical body <NUM>, the aft end <NUM> having a diameter D2.

The de-spin module <NUM> comprises a generally cylindrical body <NUM> including an aft central passageway <NUM>, central valve <NUM>, and despin thruster arrangement <NUM>.

The aft central passageway <NUM> is in selective fluid communication with central passageway <NUM> via central valve <NUM>.

For example, and referring to <FIG>, central valve <NUM> can be similar to shut-off valve <NUM> as disclosed herein, mutatis mutandis, but with a few differences. For example, in central valve <NUM> the disc-like wall <NUM> of shut-off valve <NUM> is replaced with an open end 462A.

In this example, the central valve <NUM> is normally in an open position (or partially open position) until actively actuated to close, and is thus mechanically biased to the open position. In alternative variations of this example, the central valve <NUM> is instead biased in the normally closed position until actively actuated to open. In yet other alternative variations of this example, the central valve <NUM> is not biased to the open or closed positions; rather, the central valve <NUM> is configured to remain in the open position or in the closed position until actively actuated to change the current position.

Referring to <FIG>, the despin thruster arrangement <NUM> comprises two L-shaped exhaust passageways <NUM> formed in the cylindrical body <NUM>. Each exhaust passageway <NUM> has a radial portion extending radially outwardly from the aft central passageway <NUM>, and a tangential portion orthogonal thereto. Each exhaust passageway <NUM> comprises a respective tangential exhaust outlet <NUM> at an outer end thereof.

The two tangential exhaust outlet <NUM> face opposite directions. Thus when air flow from the ram air inlet <NUM> flows out of the exhaust outlets <NUM> (via the lumen <NUM>, inlet <NUM>, central passageway <NUM>, central passageway <NUM>, open central valve <NUM>, and respective exhaust passageways <NUM>), the exhaust outlets <NUM> operate as jet thrusters, generating thrust in opposite tangential directions, but each radially spaced from the longitudinal axis LA at opposite sides thereof. A rotational couple is thereby generated, inducing a spinning motion in direction DSM to the steering assembly <NUM>.

The rotation of the core <NUM> is controllable by controller <NUM> to control and fix the angular displacement of core <NUM> at any desired position. Thus, central valve <NUM> can be operated to selectively fully allow or prevent fluid flow through central passageway <NUM>, by opening fully or closing. Alternatively, the controller <NUM> can rotate the core <NUM> to any intermediate angular position (<FIG>) to selectively allow controlled flow rates through to the exhaust passageways <NUM>, and thus control the spin rate of the de-spin module <NUM>.

Thus the central valve <NUM> can be controlled to provide partial flow, so that the spin can be further controlled. The controller <NUM>, via accelerometer to provide feedback, provides for stabilization of the steering assembly <NUM>.

Referring again to <FIG> and <FIG> in particular, shell body <NUM> comprises an external casing <NUM> of the shell <NUM>, extending aft from a front edge <NUM> thereof to the aft, blunt end <NUM> of the shell <NUM>. The front edge <NUM> is axially spaced by gap t from the nose portion <NUM>, in particular from the aft edge <NUM> of the nose portion <NUM>. The external casing <NUM> comprises an aft casing portion <NUM> and aft plug <NUM>. The aft casing portion <NUM> is formed as a hollow tube of varying diameter, and having a forward open end <NUM> defined at front edge <NUM>, and an aft end <NUM> plugged by aft plug <NUM>.

The bearing arrangement <NUM> is axially located in a vicinity of gap t, and bearing arrangement <NUM> is configured for allowing axial movement between the steering assembly <NUM> and the shell body <NUM> to close the gap t responsive to the shell being <NUM> accelerated, and for re-opening the gap t when the acceleration is terminated.

The aft external casing <NUM> comprises driving band <NUM> made from a gliding metal. In this example the driving band <NUM> is integral with aft casing portion <NUM>, and the gliding metal is copper, for example. When the shell <NUM> is fired, the pressure provided by the propellant swages the metal of the driving band into the rifling of the weapons barrel. This has two effects: proving a seal to prevent the rapidly expanding propellant from blowing past the shell <NUM>; and causing the shell <NUM> to spin the shell <NUM> in spin direction SM (see <FIG>) to spin-stabilize the shell <NUM> via the engagement of the driving band <NUM> with the rifling of the weapons barrel.

The aft external casing <NUM> overlies an aft portion of the steering assembly <NUM>, including the attitude control system <NUM> and the despin module <NUM>.

Referring also to <FIG>, the aft external casing <NUM> comprises a plurality of first openings in said shell body in the vicinity of said exhaust assembly <NUM> for allowing evacuation of exhaust gases generated by said attitude control system <NUM>. This plurality of first openings is, in this example, in the form of a first set of radial through-openings <NUM>, equi-spaced circumferentially over the circumference of the aft external casing <NUM> and axially aligned with the axial position of the exhaust ports <NUM> with respect to the longitudinal axis LA. In this example, there are eight openings <NUM> in aft external casing <NUM>; however, in alternative variations of this example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more than <NUM> openings <NUM> can be provided instead.

The radial openings <NUM>, in cooperation with the cylindrical body <NUM>, are configured for venting to the external airstream any airflow from each of exhaust outlets <NUM>, in a manner such as to provide a corresponding net transverse force on the shell <NUM>, which indirectly provides a control moment in pitch and/or yaw, as will become clearer herein.

For this purpose, the cylindrical body <NUM> comprises a number of circumferential channels <NUM> recessed inwardly from cylindrical surface <NUM>, corresponding to the number of exhaust outlets <NUM>. Circumferentially adjacent pairs of channels <NUM> are circumferentially separated by a respective partition wall <NUM> having external diameter D1.

The internal diameter of the internal surface <NUM> of aft external casing <NUM> at the axial location of openings <NUM> is slightly greater than D1, enough to provide enough clearance to allow relative rotation between the cylindrical surface <NUM> and the internal surface <NUM> without generating unacceptable frictional forces, while at the same time being small enough to minimize or prevent circumferential flow between circumferentially adjacent pairs of channels <NUM>.

As can be seen in <FIG>, each exhaust outlet <NUM> is centrally located, circumferentially, with respect to its respective channel <NUM>, although in alternative variations of this embodiment the openings <NUM> can be replaced with a plurality of circumferential slots, and the channels <NUM> can be optionally omitted. Thus airflow from any particular exhaust outlets <NUM> first flows into the respective channel <NUM> and thereafter only out of the particular openings <NUM> that are in radial registry with the respective channel <NUM>, to provide a side force to the shell <NUM> in yaw or pitch.

It is to be noted that when there is relative rotation between the steering assembly <NUM> and the shell body <NUM>, about longitudinal axis LA, each of the openings <NUM> pass over a particular channel <NUM> once over such a spin cycle about longitudinal axis LA. In this example either one or two openings <NUM> are always in partial of full registry with each channel <NUM>. For example such relative rotation can be present when the shell body <NUM> is spinning in spin direction SM and the steering assembly <NUM> is despun and thus its orientation with respect to the Earth is substantially fixed in spin.

For example, and referring to <FIG>, when a pitch maneuver is required controller <NUM> provides the necessary control inputs to the shut-off valves <NUM>, ensuring that three shut off valves <NUM> are in the closed position, and one shut-off valve <NUM> is open to provide flow of ram air along the respective axis VA which is aligned with the desired pitch direction. Referring to <FIG>, as the shell body <NUM> spins about the non-spinning steering assembly <NUM> in spin direction SM, one opening <NUM> is in full registry with respective channel <NUM>; thus, airflow exiting the exhaust outlet <NUM> will be channeled out of this opening <NUM> only, and not through any of the other openings <NUM>. The outflow of air enables the exhaust outlet <NUM> to operate as a jet thruster, and results in a single thrust force being generated, along a corresponding general radial direction at the instantaneous position of the opening <NUM>.

In <FIG> the shell body <NUM> has turned further about longitudinal axis LA and now two openings <NUM> are in registry with respective channel <NUM> - one opening <NUM> is in full registry, while the other opening <NUM> is in partial registry with respective channel <NUM>. Thus, airflow exiting the exhaust outlet <NUM> will be channeled out of both of these openings <NUM> only, and not through any of the other openings <NUM>.

In <FIG> both openings <NUM> allow exit of gases, and generate unequal radial forces, however having relatively large force components along axis VA in the desired direction, while the force components orthogonal to axis VA can at least partially cancel out as they are in opposed directions.

In <FIG> the shell body <NUM> has turned further about longitudinal axis LA and now two openings <NUM> are equidistant from exhaust outlet <NUM>. Thus at this point the thrust generated via each of the two openings <NUM> are substantially equal, having relatively large force components along axis VA in the desired direction, while the force components orthogonal to axis VA fully cancel out as they are in opposed directions.

In <FIG> the shell body <NUM> has turned further about longitudinal axis LA and while one opening <NUM> is in full registry with channel <NUM>, the adjacent opening <NUM> is only in partial registry with channel <NUM>, so that there is relatively less airflow through this opening <NUM>. Furthermore, the first opening <NUM> is also closer to exhaust outlet <NUM>. Thus at this point the situation is similar to that of <FIG>, and there may be a small net force component orthogonal to axis VA, but this soon disappears as the shell body <NUM> continues to rotate.

As the shell body <NUM> turns further, one to two openings <NUM> cyclically come into and out of registry with channel <NUM>, enabling the required side force to be generated so long as the respective one shut-off valve <NUM> is open.

Similar considerations, mutatis mutandis, apply when requiring to execute a yaw, and optionally more than one shut-off valve <NUM> can be concurrently operated to provide complex maneuvers involving a combination of pitch and yaw.

In alternative variations of this example, at any time two or three openings <NUM> are always in partial of full registry with each channel <NUM>, for example.

In this example, the exhaust outlets <NUM> are aft of the center of gravity CG, and thus any thrust force generated by exhausting a ram airflow via any of the exhaust outlets <NUM>, coupled with the moment arm of the exhaust outlets <NUM> about the position of the bearings applies a control moment in pitch or yaw to the rotating shell body <NUM>. In turn, this induces gyroscopic precession (nutation) of the shell <NUM> with respect to the longitudinal axis LA, and correspondingly induces a control moment to the shell <NUM> in a different, though predictable direction, typically orthogonal thereto. This causes the longitudinal axis LA to become angularly displaced with respect to the forward direction in which the shell is traveling, i.e., changes the angle of attack of the shell, which in turn results in an aerodynamic lateral force being induced on the shell <NUM> for changing the trajectory thereof.

Referring also to <FIG>, the aft external casing <NUM> comprises a plurality of second openings in the shell body in the vicinity of the despin module <NUM> for allowing evacuation of exhaust gases generated by the despin thruster arrangement. The plurality of second openings is, in this example, in the form of a second set of radial through openings <NUM>, configured for venting to the external airstream any airflow from tangential exhaust outlets <NUM>, while minimizing or avoiding generating any net transverse force on the shell <NUM> thereby. In this example aft external casing <NUM> comprises a plurality of openings <NUM>, equi-spaced circumferentially over the circumference of the aft external casing <NUM> and axially aligned with the axial position of the exhaust outlets <NUM> with respect to the longitudinal axis LA. In this example, there are eight openings <NUM> in aft external casing <NUM>; however, in alternative variations of this example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more than <NUM> openings <NUM> may be provided instead. In yet other alternative variations of this example the openings <NUM> may be in the form of slots, for example circumferential slots.

The internal diameter of the aft external casing <NUM> at the axial location of openings <NUM> is significantly greater than D2, providing a radial gap GP between the internal surface of the aft external casing <NUM> and the outside of the aft end <NUM>. This radial gap GP defines a continuous internal annular chamber <NUM>. Thus airflow from tangential exhaust outlets <NUM> first flows into internal annular chamber <NUM> and vents substantially uniformly via all the openings <NUM>.

In operation of the shell <NUM>, when it is desired for the steering assembly <NUM> to be de-spun with respect to the Earth, the controller <NUM> provides the necessary control inputs to the central valve <NUM>, enabling the same to be partially or fully open and allowing ram air to flow therethrough and out of the exhaust outlets <NUM> to provide a despinning couple to the steering assembly in direction DSM. With the aid of suitable sensors coupled to the controller <NUM>, the controller maintains central valve <NUM> as open as required, and for as long as it is necessary, to provide the required despinning couple, such that the steering assembly <NUM> to be de-spun with respect to the Earth. Thereafter the central valve <NUM> can be actively closed, or further adjusted to maintain the steering assembly <NUM> de-spun with respect to the Earth. At any point in the trajectory of the shell <NUM>, and under the control of the controller <NUM>, the central valve <NUM> can be allowed to re-open to adjust the relative spin between the shell body <NUM> and the steering assembly <NUM>. The controller <NUM> generally operates to provide further despin operation as and when needed, for example to maintain the steering assembly <NUM> at the same attitude/orientation about the longitudinal axis LA with respect to the Earth, while the shell body <NUM> continues to spin.

Referring again to <FIG>, the steering assembly <NUM> is rotatably mounted with respect to shell body <NUM> about longitudinal axis LA via a bearing arrangement <NUM>. In this example, the bearing arrangement comprises two roller bearings in back-to-back relationship, axially located just aft of the nose body <NUM>. In alternative variations of this example, different bearing arrangements can be use, for example ball bearings, annular contact ball bearings, tapered roller bearings, and so on.

Referring in particular to <FIG>, the steering assembly <NUM> comprises an aftfacing first abutment surface <NUM> forward of the bearing arrangement <NUM>, and the shell body <NUM> comprises a forward-facing second abutment surface <NUM>. Initially (prior to the shell <NUM> being fired), the first abutment surface <NUM> and second abutment surface <NUM> are axially spaced by a spacing smaller than spacing t1. When the shell <NUM> is fired, the initial acceleration causes the shell body <NUM> to move forward relative to the steering assembly <NUM>, until the second abutment surface <NUM> comes to rest on the first abutment surface <NUM>. This abutment of the second abutment surface <NUM> against the first abutment surface <NUM> prevents Brinnelling of the bearing arrangement <NUM> which could otherwise occur due to the high forces induced at filing of the shell <NUM>.

Referring to <FIG> and <FIG> in particular, the shell <NUM>, and particularly the steering assembly <NUM>, comprises the electromagnetic receiver and/or emitter system <NUM> for at least one of receiving and emitting electromagnetic energy. In this example, electromagnetic receiver and/or emitter system <NUM> comprises antennas <NUM> configured for receiving RF signals. While in this example, four antennas <NUM> are provided, in alternative variations of this example one, two, three or more than four antennas can instead be provided, for receiving RF signals or other electromagnetic energy and/or for transmitting RF signals or other electromagnetic energy.

In this example, the antennas <NUM> are conformal with the external surface <NUM> of the nose portion <NUM>.

In this example, the antennas <NUM> are monopole antennas, and are accommodated in the nose portion <NUM> in four corresponding bays <NUM> in cruciform arrangement, and are therefore capable of receiving RF signals from the general forward direction (along z-axis) in four quadrants generally defined with respect the x-axis and y-axis. For further facilitating comprehension, the four antennas <NUM> are labeled as antennas 572a, 572b, 572c, 572d, and thus:.

The electromagnetic receiver and/or emitter system <NUM>, in particular the antennas <NUM>, can operate as a downlink/uplink module <NUM> (i.e., as a downlink module and/or as an uplink module). The downlink/uplink module <NUM> is configured for receiving electromagnetic energy, for example RF signals or digital data, for steering the shell <NUM> to a desired target. The downlink/uplink module <NUM> is operatively coupled to the controller <NUM>. Additionally or alternatively, the downlink/uplink module <NUM> can be configured for transmitting data or electromagnetic signals (e.g. RF signals), for example positional data (e.g. obtained via on-board GPS) to a ground station or control.

Referring again to <FIG>, the shell <NUM> in this example further comprises an electrical generator <NUM> for generating electrical power to supply the electrical needs of the shell <NUM>, in particular to power (and is thus in selective electrical communication with) the controller <NUM>, shut-off valves <NUM>, and central valve <NUM>, and electromagnetic receiver and/or emitter system <NUM>, and optionally any other radio transmitter or download link, and/or any other electrical equipment carried by the shell <NUM>.

The electrical generator <NUM> comprises magnets <NUM> and coils <NUM>. The magnets <NUM> are comprised in the shell body <NUM>, in particular accommodated and attached to the aft casing portion <NUM>. The coils <NUM> are comprised in the steering assembly <NUM> in particular concentrically mounted over the shaft <NUM>. The magnets <NUM> and coils <NUM> are in lateral or radial registry, i.e. are located at the same position axially along the longitudinal axis LA. Thus, when there is a relative rotation between the steering assembly <NUM> and the shell body <NUM>, electrical power is generated. For example such relative rotation can be present when the shell body <NUM> is spinning in spin direction SM and the steering assembly <NUM> is spinning at a different rate, or the steering assembly <NUM> is despun and thus its orientation with respect to the Earth is substantially fixed in spin.

In this example or in alternative variations of this example, an electrical battery can optionally be provided to supply electrical power to the shell <NUM>, either initially until the electrical generator comes on line, or for replacing the electrical generator, which can thus be omitted.

In examples in which electrical power is supplied solely by the electrical generator <NUM>, there is initially little or no electrical power generated initially when the shell <NUM> is fired. As will be explained in more detail below, after firing, the shell body <NUM> is spinning at a relative high spin rate, and induces a torque on the steering assembly <NUM> which spins at a lower rotational speed. The central valve <NUM> is configured to be biased in the normally open position, and thus airflow is automatically channeled to the exhaust outlets <NUM> from the ram air inlet <NUM> to provide a de-spinning couple to the steering assembly <NUM> (or at least to induce spinning in the steering assembly <NUM> in the opposite direction to the spin of the shell body <NUM>), while the shell body <NUM> continues spinning, thereby enabling the electrical generator <NUM> to come on line soon and generate electrical power. Thereafter the controller <NUM> can further control operation of the central valve <NUM> to close fully or partially to thereby provide and maintain the desired rotational speed of the steering assembly <NUM>, typically zero rotational speed with respect to the Earth. In alternative variations of this example, the central valve <NUM> is configured to be biased in the normally closed position. In this case, the difference in rotational speeds between the shell body <NUM>, which is spinning at a relative high spin rate, and the steering assembly <NUM>, which is spinning more slowly, enables the electrical generator to generate electrical power, which in turn enables the controller <NUM> to actively open central valve <NUM> and thereby to provide the desired de-spin to the steering assembly <NUM>, as well as controlling steering of the shell <NUM>.

Referring again to <FIG>, and also to <FIG>, controller <NUM> comprises, at least in this example, a microprocessor optionally coupled to one or more sensors - for example a gyroscopic sensor (for example in the form of MEMS) and/or one or more accelerometers (for example in the form of MEMS). Such sensors can provide feedback data to the controller <NUM> of the roll rate of the steering assembly <NUM> and/or of the shell body <NUM>, which can be used for controlling the spin rate of the steering assembly <NUM> so as to remain fixed with respect to the Earth.

Optionally, the controller <NUM> also comprises, or is operatively connected to, a GPS module (not shown).

In at least this example the controller <NUM> is accommodated in one or more of four platforms, plates or cards <NUM> extending longitudinally outside of the shaft <NUM> in box-like configuration concentric therewith and centrally located axially between the nose portion <NUM> and the exhaust assembly <NUM>.

The controller <NUM> is also operatively coupled to the electromagnetic receiver and/or emitter system <NUM>. In applications of this example, in which the electromagnetic receiver and/or emitter system <NUM> comprises antennas <NUM> (optionally in the form of downlink/uplink module <NUM>), the controller <NUM> is correspondingly operatively connected to antennas <NUM>.

In one application of this example, the controller <NUM> is configured for, and thus suitably programmed for processing input received from various sensors including antennas <NUM>, and for generating command signals for operating the attitude control system <NUM>, in particular the exhaust assembly <NUM>, to thereby provide correctional control moments to the shell <NUM>.

For example one or two cards <NUM> are dedicated to antennas <NUM> (for example comprising an RF receiver), a third card <NUM> is dedicated to sensors, including the various MEMS and to control/stabilization functions of the controller <NUM> (including providing despin and providing control of the attitude control system <NUM> to provide control moments in pitch and/or yaw), and the remaining fourth card <NUM> is dedicated to electrical power regulation, i.e., for regulating the electrical power generated by the electrical generator <NUM>.

For example, when the RF signals originate from a point source ahead of the shell <NUM> (for example the RF signals are reflected towards the shell <NUM> from the intended target, which can be correspondingly illuminated using a suitable illumination source - see below for example regarding the system <NUM> illustrated in <FIG>). In such a case, if the longitudinal axis LA of the shell <NUM> is aligned so as to intersect the illuminated target, then the signal received by all four antennas <NUM> will be of the same phase; no corrective action needs to be taken by controller <NUM>. However, if for example the longitudinal axis LA of the shell <NUM> is misaligned so as to miss the target and lie above and to the left of the target (corresponding to the quadrant defined by the +x and +y axes), then the signal received by antennas 572a and 572b will be correspondingly of different phase to the RF signals received by antennas 572c and 572d. In this manner, the controller <NUM>, which receives input from the four antennas <NUM> corresponding to the phase of the RF signals received by each antenna <NUM>, is able to determine where the target is in terms of the x-and y-axes, and correspondingly actuate the attitude control system <NUM> to provide correctional control moments in pitch and or yaw such as to maintain the RF signals received from all four antennas equal (within a predetermined threshold).

In another application of this example, in which the antennas <NUM> operate as downlink/uplink module <NUM>, the controller <NUM> is configured for, and thus suitably programmed for processing input received from various sensors including downlink/uplink module <NUM>, and for generating command signals for operating the attitude control system <NUM> to thereby provide correctional control moments to the shell <NUM>.

Optionally, the shell <NUM> can include a tracer configuration <NUM>, for example accommodated at the aft end of the shell body, for facilitating tracing the shell <NUM> after being fired - see below for example regarding the system <NUM> illustrated in <FIG>.

In operation of the shell <NUM>, the shell is fired from a rifled weapons barrel in the conventional manner, and a spin is initially applied to the shell body <NUM>, which in turn induces a torque and causes the steering assembly <NUM> to also rotate in the same direction, though at least initially at a lower rotational speed. Thus, at firing the shell body <NUM> spins at a relatively fast rotational rate about longitudinal axis LA due to the rifling of the weapons barrel, and the steering assembly <NUM> receives torque from the shell body <NUM> via friction therebetween, since the shell body <NUM> and the steering assembly <NUM> are essentially supported together by the contact between abutment surfaces <NUM> and <NUM>. Initially the central valve <NUM> is in the open position (or partially open position) and the shut-off valves <NUM> are in the closed position. After firing the shell <NUM>, the acceleration terminates, and the shell body <NUM> to move aft relative to the steering assembly <NUM>, until the second abutment surface <NUM> is no longer abutting the first abutment surface <NUM>. From this point, the steering body <NUM> continues to spin due to frictional forces in the bearing with respect to the shell body <NUM>, but concurrently the steering body <NUM> is being at least partially despun relative to the shell body <NUM> by automatic operation of the de-spin module <NUM>, as disclosed herein, since ram air is flowing through the ram air inlet and out of the spin module <NUM> from the time of firing. At the same time, the relative rotation between the steering body <NUM> and the shell body <NUM> enables electrical power to be generated by the electrical generator <NUM>, which in turn allows operation of the controller <NUM>. This thereby enables full de-spin of the steering assembly <NUM> so that the steering assembly <NUM> is maintained at a stable orientation with respect to the Earth, and further enables controlled steering of the shell <NUM> to a desired target, for example using a suitable steering system, for example as disclosed herein with reference to <FIG> or <FIG>.

It is to be noted that shell <NUM> can be made according to any suitable caliber, for example <NUM> inch, typically spinning at <NUM>,<NUM> rpm when fired, or <NUM> caliber, typically spinning at <NUM>,000rpm when fired, or indeed any other caliber, for example <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and so on. At the low end, the smallest caliber possible for shell <NUM> generally depends on the ability to accommodate all the necessary components of the shell within the envelope afforded by the small caliber.

According to a second aspect of the presently disclosed subject matter there is provided a system and method for steering a shell, for example shell <NUM>, to a target.

Referring to <FIG>, a steering system for steering a shell to a target according to a first example of the presently disclosed subject matter, generally designated <NUM>, is particularly configured for steering a shell, for example shell <NUM>, towards a target, where the target exhibits low dynamic properties. Herein, by "low dynamic properties" is meant that (a) the target is a static target, or (b) that even though the target can be moving there is correspondingly low relative angular movement of the target with respect to an external sensor that is configured for tracking the shell and target - for example, the low angular movement of the target maintains the target within the field of view (FOV) of the sensor.

In one application according to the second aspect of the presently disclosed subject matter, the system configured for steering the shell, once fired, towards a target (having low dynamic properties), for example along a relatively shallow trajectory. For example, such a shallow trajectory can be defined as corresponding to the shell being fired at an initial elevation angle not greater than <NUM>°. However, in other applications of the system according to the second aspect of the presently disclosed subject matter, the system can instead be used for steering the shell to a low-dynamic property target along a relatively steep trajectory.

Steering system <NUM> is particularly configured for use with a shell <NUM> as disclosed above for the first example thereof or alternative variations thereof, according to the invention, fired from a suitable weapons barrel <NUM>. For example, the weapons barrel can include any one of: a <NUM> tank gun and the shell <NUM> is of corresponding caliber, for example <NUM> caliber; or a <NUM> Bushmaster Cannon or Bofors AA gun or a Barrett <NUM> inch caliber sniper weapon, and the shell <NUM> is of corresponding caliber, for example <NUM> caliber.

Thus, the system <NUM> comprises at least one shell <NUM>, and can include the weapons barrel <NUM>, and in this example, the respective antennas <NUM> of the shell <NUM> operate as downlink/uplink module <NUM>, and in particular receive correction command signals from system <NUM> for steering the shell <NUM> to the desired target.

Steering system <NUM> comprises sensor system <NUM>, transmitter <NUM>, and control module <NUM>. The control module <NUM> is operatively coupled to the sensor system <NUM> and to the transmitter <NUM>.

The sensor system <NUM> is configured for providing imaging data of the shell <NUM> and the target T to enable sensing and determining the instantaneous spatial position of the shell <NUM> and of the target T during the trajectory of the shell <NUM> from a predetermined range from the target or from a predetermined time after being fired. For example sensor system <NUM> can be configured for providing image data of the instantaneous spatial position of the shell <NUM> and the target T from the time and position that the shell <NUM> is fired from the weapons barrel <NUM>.

The sensor system <NUM> can include any suitable sensor, in particular an imaging system operating in the infra red (IR) and/or visual and/or ultraviolet spectrums. For example, the sensor system <NUM> can include at least one IR sensor, for example a thermal imaging camera (e.g. as provided by FLIR Systems, USA), operating in the <NUM> micron to <NUM> micron range or in the <NUM> micron to <NUM> micron range, or for example a shortwave IR camera (SWIR), operating in the <NUM> micron to <NUM> micron range.

In this example, the sensor system <NUM> selectively operates in track lock mode, so that the sensor system <NUM> is always locked onto the target T even if the target T is moving. For this purpose, the sensor system <NUM> comprises a suitable tilt and pan mechanism to move the sensor system <NUM> such as to maintain the target within the field of view of the sensor system <NUM>.

Furthermore, in this example, the sensor system <NUM> also has crosshairs on the shell <NUM>, and thus determines the position of the shell <NUM> relative to the target T, in terms of the spatial displacement between the target T and the shell <NUM> as imaged by the sensor system <NUM>. In other words, the imaging provided by the sensor system <NUM> can give the position of the shell <NUM> relative to the target T in the x-y plane, while the actual range of the shell <NUM> can be estimated based on the elapsed time after being fired, and its expected speed. Optionally, the tracer configuration <NUM> of the shell <NUM> facilitates the sensor system <NUM> maintaining the crosshairs on the shell <NUM>.

The transmitter <NUM> is configured for transmitting course correction command signals to the shell <NUM>, responsive to receiving control signals from the control module <NUM>. For example, transmitter <NUM> can be a radio transmitter configured for transmitting RF energy. For example, transmitter <NUM> transmits radio signals in the L-BAND.

The control module <NUM> comprises any suitable microprocessor system, configured for receiving image data from the sensor system <NUM> and for processing these images to provide relative positions between of objects (particularly between the shell <NUM> and the target T) captured in the images. The microprocessor system is also configured for determining whether a course correction is required for the shell <NUM>, as well as for providing suitable control signals to the transmitter <NUM> to transmit course correction command signals to the shell <NUM> to effect a course correction.

The steering system <NUM> can operate as follows.

After the shell <NUM> has been fired from the weapons barrel <NUM>, the sensor system <NUM> provides images or image data of the shell <NUM> and the target T during the trajectory of the shell <NUM>, to the control module <NUM>, while having a tracking lock on the target T.

The control module <NUM> determines whether a course correction is required for the shell <NUM>, and if so generates suitable control signals to the transmitter <NUM> to transmit course correction command signals to the shell <NUM>.

For example, if the difference between the position of the shell <NUM> and of the target (in the x-y plane) as sensed by the sensor system, <NUM>, is less than a predetermined threshold, no action is taken, and the shell <NUM> continues along its trajectory. On the other hand, if this difference exceeds the predetermined threshold, the microprocessor system determines what correction is required to bring the shell <NUM> back on course (in terms of the x-y plane), and how much thrust is needed from each of the exhaust outlets <NUM> to provide the required control moments in pitch and/or yaw to achieve this course correction. The microprocessor system then generates suitable control signals and passes these to the transmitter <NUM>, which in turn transmits corresponding course correction command signals to the shell <NUM> to effect the required course correction.

The shell <NUM> receives these course correction command signals, and the controller <NUM> correspondingly opens one or more of the shut-off valves <NUM> for a specified period of time, as provided by the course correction command signals, to thereby generate a moment to the rotating shell body <NUM> about the position of the bearings, which in turn induces gyroscopic precession (nutation) of the shell <NUM> with respect to the longitudinal axis LA, and correspondingly induces a control moment to the shell <NUM> in an orthogonal direction. This causes a change in the angle of attack of the shell <NUM> and generates an aerodynamic side force which provides the required control moments in pitch and/or yaw to achieve this course correction.

The shell <NUM> continues to receive these course correction command signals until the target is hit.

A feature of the first example of the steering system <NUM> is that at least some false reflections from other objects near the target can be avoided.

Another feature of the first example of the steering system <NUM> is relatively insensitive to at least some false targets, because sensor can be locked on to the target from the start.

A feature of the first example of the steering system <NUM> is that it can be configured as a totally passive system, and does not require the target or the shell to be illuminated by the system; rather it uses electromagnetic energy naturally reflected therefrom and originating from other sources, for example the sun, or uses internal/intrinsic heat of the target, where the sensor system <NUM> includes thermal imaging systems.

Referring to <FIG>, a steering system for steering a shell to a target according to a second example of the presently disclosed subject matter, generally designated <NUM>, is particularly configured for steering a shell towards a target having significant dynamic movement and/or is at a relatively large range (one or both of which could render the first example of the system less effective, for example).

In one application according to the second aspect of the presently disclosed subject matter, the second example of the system is configured for steering the shell, once fired, to a target along a relatively steep trajectory. For example, such a shallow trajectory can be defined as corresponding to the shell being fired at an initial elevation angle of <NUM>° or greater than <NUM>°, for example <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>°, <NUM>° or any other elevation angle inbetween. Furthermore, in at least some applications of the second example of the steering system, the steering system is configured for intercepting an airborne target, for example an aircraft or hostile projectile.

Steering system <NUM> is particularly configured for use with a shell <NUM> as disclosed above for the first example thereof or alternative variations thereof, according to the invention, fired from a suitable weapons barrel <NUM>, and in this example the antennas <NUM> are configured for operating as an on-board homing sensor for the shell <NUM>. For example, the weapons barrel can include a <NUM> Bushmaster Cannon or <NUM> L70 Bofors gun, and the shell <NUM> is of corresponding caliber, for example <NUM> or <NUM> caliber.

Thus, the system <NUM> comprises at least one shell <NUM>, and can include the weapons barrel <NUM>.

Steering system <NUM> comprises an electromagnetic illuminator <NUM>, configured for at least illuminating the target T with electromagnetic energy, which when reflected by the target can be received by antennas <NUM>.

For example, illuminator <NUM> comprises a half-active radar, i.e., configured for illuminating a target with RF energy or laser energy, respectively, but that does not require to receive reflected signals. In alternative variations of this example, the illuminator <NUM> comprises an active radar, i.e., configured for illuminating a target with RF energy or laser energy, and for receiving reflected signals therefrom.

In yet other alternative variations of this example, the sensor function of the antennas <NUM> can be replaced with a suitable laser detector for receiving laser energy (the illuminator <NUM> being configured for transmitting laser energy and comprising, for example, a half-active ladar) and homing to target. In such an example the antennas <NUM> can operate as the downlink/uplink module for the shell.

In the example illustrated in <FIG>, the antennas <NUM> together with the controller <NUM> of the shell <NUM> are configured for sensing and determining the instantaneous spatial position of the target T during the trajectory of the shell <NUM> from a predetermined range from the target or from a predetermined time after being fired, for example from the time and position that the shell <NUM> is fired from the weapons barrel <NUM>. The controller <NUM> is configured for generating course correction command signals to the attitude control system <NUM>, responsive to receiving input from the antennas <NUM>.

First, a threat or target T is detected, and its position determined, and the target T is tracked until it comes into the range of the weapons barrel <NUM>. This can be accomplished for example by a regular radar installation RI. Then, the system <NUM> is activated, whereupon on receipt of suitable positional information from installation RI, the illuminator <NUM> illuminates the target T with suitable electromagnetic energy and concurrently the shell <NUM> is fired at an elevation and elevation such that its natural trajectory will nominally cause the shell <NUM> to intercept the target T as this continues along its trajectory TP.

At a certain point after the shell <NUM> is fired, the target T falls within the field of view of the antennas <NUM>, and thus the antennas <NUM> begin to receive reflected electromagnetic from the target T. The antennas <NUM> provide a measure of the deviation of the trajectory of the shell <NUM> with respect to the actual position of the target T, and the controller <NUM> of the shell <NUM> determines what correction is required to bring the shell <NUM> back on course, and how much thrust is needed from each of the exhaust outlets <NUM> to provide the required control moments in pitch and/or yaw to achieve this course correction. The controller <NUM> then correspondingly opens one or more of the shut-off valves <NUM> for a specified period of time, as required, to thereby generate a moment to the rotating shell body 300about the position of the bearings, which in turn induces gyroscopic precession (nutation) of the shell <NUM> with respect to the longitudinal axis LA, and correspondingly induces a control moment to the shell <NUM> in an orthogonal direction. This causes a change in the angle of attack of the shell <NUM> and generates an aerodynamic side force which provides the required control moments in pitch and/or yaw to achieve this course correction.

In an alternative variation of the second example, the downlink/uplink module can provide steering instructions to the shell <NUM> if required - for example for arriving at an optimal intersection point (instead of following a nominally ballistic trajectory). In other words, the radar installation RI and/or the illuminator <NUM> (which in such a case can be configured for receiving reflected radar signals from the target and/or the shell <NUM>) can be used (via a suitable control system) to provide initial maneuvering instructions to the shell <NUM> via a suitable communications link, until the shell <NUM> is head-on with respect to the target T. The target is thus within the FOV of the antennas <NUM>, after which the antennas <NUM> receive reflections from target and enables final steering to target T. For example, the electromagnetic illuminator <NUM> can be configured for illuminating a target with electromagnetic energy and also for receiving electromagnetic energy reflected by the target. For example, illuminator <NUM> comprises a fully-active radar or a fully-active ladar, i.e., configured for illuminating and detecting a target with RF energy or laser energy, respectively. Furthermore, the shell <NUM> is configured with said downlink <NUM>, and is further configured for receiving/transmitting data with respect to the electromagnetic illuminator <NUM>. In such a case, the electromagnetic illuminator <NUM> can provide positional data of the shell <NUM> and of the target T, and transmit suitable course correction command signals to the shell, and the controller <NUM> correspondingly opens one or more of the shut-off valves <NUM> for a period of time, as provided by the course correction command signals, to thereby generate a moment to the rotating shell body <NUM>, which in turn causes a change in the angle of attack of the shell <NUM> and generating an aerodynamic side force which provides the required control moments in pitch and/or yaw to achieve this course correction. In such an example, the antennas <NUM> can optionally be omitted or not used for homing.

A feature of the first example of the steering system <NUM> is that in some applications, for example when the shell is fired along a relatively steep trajectory, since the weapons barrel <NUM> is typically facing the sky any potential false reflections can be avoided or minimized.

In the method claims that follow, alphanumeric characters and Roman numerals used to designate claim steps are provided for convenience only and do not imply any particular order of performing the steps.

Finally, it should be noted that the word "comprising" as used throughout the appended claims is to be interpreted to mean "including but not limited to".

Claim 1:
Projectile configured for moving through a fluid medium, and having a longitudinal axis (LA), the projectile comprising a steering assembly (<NUM>) and a shell body (<NUM>) rotatably mounted thereto about the longitudinal axis, and including an attitude control system (<NUM>), a despin module (<NUM>), an electromagnetic receiver and/or emitter system (<NUM>), and a controller (<NUM>), wherein:
- the attitude control system (<NUM>) comprises a ram air inlet (<NUM>) in selective open fluid communication with an exhaust assembly (<NUM>) via a fluid passageway (<NUM>) provided in said steering assembly (<NUM>), the exhaust assembly comprising a plurality of exhaust outlets (<NUM>) to selectively generate each of a plurality of thrust jets from a ram air inflow provided by said ram air inlet (<NUM>), each said thrust jet being selectively controllable via said controller (<NUM>) to thereby generate steering control moments to the shell (<NUM>) in operation thereof;
- the despin module (<NUM>) is configured for selectively de-spinning said steering assembly (<NUM>) with respect to said shell body (<NUM>) about said longitudinal axis (LA); and
- the electromagnetic receiver and/or emitter system (<NUM>) is configured for at least one of receiving and emitting electromagnetic energy, and for cooperating with said controller (<NUM>) for operating said exhaust assembly (<NUM>) to thereby selectively provide said steering control moments;
characterised in that
said attitude control system (<NUM>), said despin module (<NUM>) and said controller (<NUM>) as well as said electromagnetic receiver and/or emitter system (<NUM>) are comprised fully in said steering assembly (<NUM>).