Abstract:
A system for launching a plurality of projectiles from a single launch tube is disclosed. In the illustrative embodiment, the system uses an electromagnetic catapult to sequentially throw a first projectile and a second projectile. The first projectile is thrown while the second projectile is temporarily restrained within the launch tube.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The underlying concepts, but not necessarily the language, of the following cases are incorporated by reference: 
         [0002]    (1) U.S. patent application Ser. No. 10/899,234, filed 26 Jul. 2004; 
         [0003]    (2) U.S. patent application Ser. No. 11/278,988, filed 7 Apr., 2006; 
         [0004]    (3) U.S. patent application Ser. No. 11/428,697, filed 5 Jul., 2006; 
         [0005]    (4) U.S. patent application Ser. No. 11/535,480, filed 26 Sept., 2006;and 
         [0006]    (5) U.S. patent application Ser. No. 11/773,146, filed 3 Jul., 2007.If there are any contradictions or inconsistencies in language between this application and one or more of the cases that have been incorporated by reference that might affect the interpretation of the claims in this case, the claims in this case should be interpreted to be consistent with the language in this case. 
     
    
     FIELD OF THE INVENTION 
       [0007]    The present invention relates to munitions in general, and, more particularly, to munition launchers. 
       BACKGROUND OF THE INVENTION 
       [0008]    Projectiles, such as missiles, mortar rounds, countermeasure devices, and the like, are often stored, shipped, and carried to their point of deployment in canisters. Among other things, a canister protects a projectile from harsh environmental conditions. A typical canister comprises a launch tube that guides the projectile as it is launched, much like the launch tube of a gun. At deployment, the canister may be secured in a launch apparatus and the projectile is propelled from its canister, typically by means of a chemical propellant. 
         [0009]    In order to avoid damage during transport, a projectile is usually secured within its canister by attaching it to the base plate of the canister by means of a mechanical release restraint. The restraint is actuated to release the projectile and enable its propulsion from the canister at launch. Commonly used restraints include explosive bolts, marmon clamps, bullet jackets, and shape charges. Once the projectile has been launched, its canister is replaced in the launch apparatus by a fresh canister in preparation for the launch of another projectile. 
         [0010]    Often, it is desirable to be able to launch many projectiles within a short period of time, such as for the deployment of countermeasure devices. Countermeasure systems are employed by military vessels to confuse or otherwise frustrate the targeting systems of an approaching missile or similar threat. Modern missiles have targeting systems that incorporate sophisticated sensor platforms that are capable of sensing target signature information across a spectrum of signal types (e.g., radar, acoustic, thermal, etc.). An effective countermeasure system, therefore, must be capable of rapidly deploying a plurality of countermeasure devices (e.g., flares, chaff, acoustic emitters, IR emitters, etc.) to present a false image (i.e., decoy) that closely mimics the multispectral signature, shape, and behavior of the actual vessel. 
         [0011]    To achieve a high aggregate firing rate, conventional multiple-projectile launch systems constitute multiple individual projectile launchers or launch tubes, each of which propels a single projectile.  FIG. 1  depicts a schematic diagram of an exemplary prior art multiple-projectile launcher. Countermeasure launcher  100  comprises multiple launch tubes that are held in a pre-arranged configuration by a platform that is attached to the deck of a warship. The launch tubes are suitable for launching countermeasure payloads using a chemical-propellant, such as black-powder explosives. The launch tubes are pre-loaded with an array of countermeasure devices, depending on the characteristics of the vessel on which they reside. 
         [0012]    Conventional countermeasure launchers have certain drawbacks that limit their effectiveness, however. 
         [0013]    First, such systems offer limited flexibility in projectile placement. Specifically, these conventional systems typically launch their projectiles at fixed positions and fixed launch angles. Furthermore, the propulsive force from the chemical propellant of each missile is not controllable. As a consequence, effective decoy placement requires that a vessel undergo complicated maneuvers prior to and after launch. 
         [0014]    Secondly, the use of a chemical-propellant creates a characteristic signature that has thermal, aural, and visual aspects. In particular, the signature may include a thermal bloom, a cloud of smoke, noise, a thermal trail, and/or a smoke trail. In most cases, the thermal bloom heats the area immediate to the launch area, which results in a residual local thermal signature that can act as a beacon for an incoming threat. 
         [0015]    Thirdly, after launch, the launcher must be cleaned and reloaded. In the case of a countermeasure launcher, this renders the vessel relatively more vulnerable to attack. In the case of a multi-cell offensive weapon, this renders the launcher impotent for a period of time. 
         [0016]    Finally, as the number of launchers or launch tubes increases, the size of the launch system grows and contributes significantly to deck clutter. This also increases the complexity and cost of the launch system. 
         [0017]    Electromagnetic launchers have been developed as an alternative to chemical propellant launchers. Electromagnetic launchers mitigate some of the disadvantages associated with the use of chemical propellants; however, prior art electromagnetic launchers are limited to the launch of a single projectile per launch tube. As a result, an array of electromagnetic launchers must used to provide a launch system capable of the rapid launch of a plurality of projectiles. An electromagnetic propulsion system requires greater infrastructure and is more complex than a chemical propellant propulsion system, which exacerbates the problems associated with deck clutter and overall system cost. There exists a need, therefore, for a multi-projectile launch system that avoids or mitigates some or all of the problems associated with prior-art multiple projectile launch systems. 
       SUMMARY OF THE INVENTION 
       [0018]    The present invention provides a launcher for propelling multiple projectiles without some of the costs and disadvantages associated with launchers known in the prior art. 
         [0019]    An embodiment of the present invention comprises an electromagnetic propulsion system for accepting and securing a removable cartridge that contains a plurality of projectiles. The propulsion system comprises a plurality of propulsion coils for generating force to propel each of the plurality of projectiles from the cartridge. In some embodiments, the propulsion system also comprises a propulsion coil for ejecting the cartridge. In some embodiments, the cartridge is immobilized with respect to the propulsion system by a passively-actuated restraint. 
         [0020]    In some embodiments, the cartridge comprises a launch tube that contains a plurality of projectiles. Each projectile is individually secured within the launch tube by a passively-actuated restraint. In the absence of electromagnetic force, each restraint substantially immobilizes its respective projectile with respect to the launch tube. In some embodiments, a restraint comprises an electrically-conductive loop that is located on the projectile. In some embodiments, the electrically-conductive loop is located on another structure, such as an armature, that is operatively coupled to the projectile. In some embodiments, the electrically-conductive loop is mechanically coupled to the cartridge. 
         [0021]    To launch a projectile, a flow of electric current is generated through a propulsion coil. Mutual inductance between the propulsion coil and a restraint causes the restraint to actuate and release the projectile, thereby enabling motion of the projectile with respect to the cartridge. Mutual inductance between the propulsion coil and the projectile induces a propulsive force on the projectile that ejects the projectile from the launcher. Since only one restraint at a time is actuated, multiple projectiles can be stored and launched from a single launch tube. 
         [0022]    In some embodiments, a cartridge is secured within the propulsion system by a passively-actuated restraint. To eject the cartridge from the propulsion system, a flow of electric current is generated through a propulsion coil. Mutual inductance between the propulsion coil and the restraint causes the restraint to actuate and release the cartridge, thereby enabling motion of the cartridge with respect to the propulsion system. Mutual inductance between the propulsion coil and the cartridge induces a propulsive force on the cartridge that ejects the cartridge from the propulsion system. In some embodiments, cartridges are loaded into the propulsion system by an automatic cartridge loader. 
         [0023]    A method in accordance with the present invention comprises:
       engaging a cartridge and an electromagnetic propulsion system;
           wherein the cartridge comprises a tube containing a first projectile and a second projectile;   wherein the electromagnetic propulsion system comprises a first propulsion coil and a second propulsion coil; and   wherein the cartridge locates the first projectile with respect to the first propulsion coil and the second projectile with respect to the second propulsion coil when the cartridge and electromagnetic propulsion system are engaged;   
           propelling the first projectile from the electromagnetic propulsion system, wherein the first projectile is propelled by a first force that is induced by the flow of electric current in the first propulsion coil; and   disengaging the cartridge from the electromagnetic propulsion system.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  depicts a schematic diagram of an exemplary prior art multiple-projectile launcher. 
           [0031]      FIG. 2  depicts a block diagram of an electromagnetic launch system in accordance with an illustrative embodiment of the present invention. 
           [0032]      FIG. 3  depicts the details of method  300  in accordance with the illustrative embodiment. 
           [0033]      FIG. 4A  depicts a representational view of launcher  202 , prior to insertion of cartridge  408  in propulsion system  402 , in accordance with the illustrative embodiment of the present invention. 
           [0034]      FIG. 4B  depicts a cross-sectional view of details of propulsion system  402  in accordance with the illustrative embodiment of the present invention. 
           [0035]      FIG. 4C  depicts a cross-sectional view of details of cartridge  408  in accordance with the illustrative embodiment of the present invention. 
           [0036]      FIG. 5A  depicts a representational view of launcher  202 , after insertion of cartridge  408  in propulsion system  402 , in accordance with the illustrative embodiment of the present invention. 
           [0037]      FIG. 5B  depicts a cross-sectional view of details of launcher  202  in accordance with the illustrative embodiment of the present invention. 
           [0038]      FIG. 6  depicts a top view of details of a conductive loop in accordance with the illustrative embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    The following terms are defined for use in this Specification, including the appended claims:
       Locate means to place at a certain location.   Physically connected means in direct, physical contact and affixed (e.g., a mirror that is mounted on a linear-motor).   Physically coupled means in direct, physical contact, although not necessarily physically-connected (e.g., a coffee cup resting on a desktop).   Projectile means an object that is fired, thrown, or otherwise propelled. Examples of projectiles include, without limitation, artillery shells, mortar rounds, self-propelled missiles, unmanned aerial vehicles, guided missiles, and countermeasure devices, such as flares, chaff, acoustic emitters, IR emitters, and the like.       
 
         [0044]      FIG. 2  depicts a block diagram of an electromagnetic launch system in accordance with an illustrative embodiment of the present invention. Electromagnetic launch system  200  comprises multi-projectile electromagnetic launcher  202  (hereinafter, launcher  202 ), launch controller  204 , weapons control system  206 , power system  208 , data bus  210 , current bus  214 , and signal line  212 . 
         [0045]    Launcher  202  is a system that has the capability to house and expel multiple projectiles upon command. The system expels the projectiles using an electromagnetic catapult. Although in the illustrative embodiment, launcher  202  expels projectiles that comprise countermeasures, it will be clear to those of ordinary skill in the art how to make and use alternative embodiments of the present invention that expel projectiles such as munitions, unmanned vehicles, guided missiles, chaff, flares, acoustic emitters, acoustic sensors, and the like. 
         [0046]    Launch controller  204  provides targeting information to launcher  202  prior to launch. Launch controller  204  also provides the directive to initiate a launch of one or more projectiles to power system  208 . In some alternative embodiments, such as when launcher  202  expels a guided missile or unmanned vehicle, launch controller  204  also provides targeting and/or course information to launcher  202  and/or the projectile to be expelled. In some embodiments, at least one projectile comprises built-in test electronics. In these embodiments, launch controller receives self-test data from these projectiles. In some embodiments, launcher  202  comprises mechanisms for setting the elevation and azimuth at which a projectile is launched. In some embodiments, launch controller  204  communicates with these mechanisms to control elevation and azimuth. 
         [0047]    Weapons control system  206  provides targeting and firing authority to launch controller  204  prior to and during a launch of one or more projectiles. 
         [0048]    Power system  208  comprises circuitry that conditions and manages the storage and delivery of power to launcher  202  in response to signals from launch controller  204 . Power system  208  controls power generation, scavenging, storage, and delivery prior to, during, and after each launch. Power system  208  also controls the magnitude of the force with which launcher  202  propels each projectile. 
         [0049]    Data bus  210  carries targeting and self-test information between launch controller  204  and launcher  202 . Signal line  212  connects launch controller  204  to power system  208  and carries the commands that direct power system  208  to initiate and control the launch of a projectile. Current bus  214  carries power from power system  208  to launcher  202 . 
         [0050]      FIG. 3  depicts the details of method  300  in accordance with the illustrative embodiment. Method  300  depicts operations for launching multiple projectiles using launcher  202 . Method  300  is described herein with reference to  FIGS. 4A-C ,  5 A-B, and  6 . 
         [0051]      FIG. 4A  depicts a representational view of launcher  202 , prior to insertion of cartridge  408  in propulsion system  402 , in accordance with the illustrative embodiment of the present invention. Launcher  202  comprises propulsion system  402  and cartridge  408 . 
         [0052]    Propulsion system  402  comprises retainer  406  and propulsion coils  404 - 1 ,  404 - 2 , and  404 - 3 . Each of propulsion coils  404 - 1 ,  404 - 2 , and  404 - 3  comprises a helical coil of electrical conductor, capable of carrying sufficiently high voltage/amperage to enable sufficient launch power. Each of propulsion coils  404 - 1 ,  404 - 2 , and  404 - 3  generates an electromagnetic field when carrying electric current. Propulsion system  402  accepts, locates, and restrains cartridge  408 . 
         [0053]    Cartridge  408  comprises a canister for holding, locating, and restraining projectiles  412 - 1  and  412 - 2 . Cartridge  408  also comprises base plate  410 , projectiles  412 - 1  and  412 - 2 , and restraints  414 - 1  and  414 - 2 . Restraints  414 - 1  and  414 - 2  substantially immobilize projectiles  412 - 1  and  412 - 2 , respectively, with respect to cartridge  408 . Cartridge  408  provides a substantially air-tight environment for the projectiles. In some embodiments, cartridge  408  holds more than two projectiles. In some embodiments, cartridge  408  comprises more than two restraints. 
         [0054]      FIG. 4B  depicts a cross-sectional view of details of propulsion system  402  in accordance with the illustrative embodiment of the present invention. Propulsion system  402  comprises frame  416 , propulsion coils  404 , and retainer  406 . 
         [0055]    Frame  416  provides a rigid structure for holding propulsion coils  404  in well-known fashion. 
         [0056]    Retainer  406  includes seat  418  for receiving conductive loop  430 - 3  when restraint  502  is engaged. As is described below, and with respect to  FIG. 5B , retainer  406 , conductive loop  430 - 3 , and base plate  410  collectively define restraint  502 . When restraint  502  is engaged, retainer  406  receives conductive loop  430 - 3 . This substantially immobilizes base plate  410  (and cartridge  408 ) with respect to propulsion system  402 . 
         [0057]      FIG. 4C  depicts a cross-sectional view of details of cartridge  408  in accordance with the illustrative embodiment of the present invention. Cartridge  408  comprises base plate  410 , launch tube  424 , fly-through cover  426 , projectiles  412 - 1  and  412 - 2 , restraints  414 - 1  and  414 - 2 , and spacers  434 . 
         [0058]    Base plate  410  is a substantially rigid plate of structural material that is suitable for the development of mutual inductance with propulsion coil  404 - 3  when the propulsion coil carries electric current. In some embodiments, base plate  410  comprises a coil of electrically conductive wire. In some embodiments, base plate  410  comprises a material having high magnetic permeability, such as Permalloy, nickel, steel, and the like. 
         [0059]    Base plate  410  comprises shoulder  438 , which locates conductive loop  430 - 3 . Conductive loop  430 - 3  is a continuous loop of electrically-conductive material that is suitable for the development of a mutual inductance with propulsion coil  404 - 3  when this coil carries electric current. 
         [0060]    Launch tube  424  is a substantially rigid cylinder for housing and guiding launched munitions. Launch tube  424  includes seats  432 - 1  and  432 - 2 . Seat  432 - 1  receives conductive loop  430 - 1  when restraint  414 - 1  is engaged. In similar fashion, seat  432 - 2  receives conductive loop  430 - 2  when restraint  414 - 2  is engaged. 
         [0061]    Launch tube  424 , fly-through cover  426 , and base plate  410  collectively form a substantially air-tight environment for projectiles  412 - 1  and  412 - 2  in well-known fashion. 
         [0062]    Projectiles  412 - 1  and  412 - 2  (referred to collectively as projectiles  412 ) are countermeasure devices for providing decoy signals to an incoming threat, such as an approaching enemy missile. Projectile  412 - 1  comprises warhead  420 - 1 , armature  422 - 1 , and conductive loop  430 - 1 . Although in the illustrative embodiment conductive loops  430 - 1  and  430 - 2  are included in projectiles  412 - 1  and  412 - 2 , it will be clear to one of ordinary skill in the art, after reading this specification, how to make and use alternative embodiments of the present invention wherein conductive loops  430 - 1  and  430 - 2  are a part of launch tube  424  rather than projectiles  412 . It will also be clear, after reading this specification, how to make and use alternative embodiments of the present invention wherein projectiles  412  comprise any object, or combination of objects, that can be fired, thrown, or otherwise propelled using an electromagnetic propulsion system. Suitable projectiles include, without limitation:
       i. artillery shells; or   ii. mortar rounds; or   iii. self-propelled missiles; or   iv. unmanned vehicles; or   v. guided missiles; or   vi. countermeasure devices; or   vii. any combination of i, ii, iii, iv, v, and vi.       
 
         [0070]    Projectile  412 - 2  comprises warhead  420 - 2 , armature  422 - 2 , and conductive loop  430 - 2 . Projectiles  412 - 1  and  412 - 2  are immobilized with respect to cartridge  408  by restraints  414 - 1  and  414 - 2  (referred to collectively as restraints  414 ), respectively, and are separated from each other and base plate  410  by spacers  434 . 
         [0071]    Armatures  422 - 1  and  422 - 2  (referred to collectively as armatures  422 ) are suitable for the development of mutual inductance with its respective propulsion coil when the propulsion coil carries electric current. In some embodiments, at least one of armatures  422  comprises a coil of electrically conductive wire. In some embodiments, at least one of armatures  422  comprises a material having high magnetic permeability, such as Permalloy, nickel, steel, and the like. 
         [0072]    Armature  422 - 1  includes shoulder  428 - 1 , which locates conductive loop  430 - 1 . In similar fashion, armature  422 - 2  includes shoulder  428 - 2 , which locates conductive loop  430 - 2 . Conductive loops  430 - 1  and  430 - 2  are continuous loops of electrically-conductive material that are suitable for the development of a mutual inductance with propulsion coils  404 - 1  and  404 - 2 , respectively, when these coils carry electric current. 
         [0073]    Armature  422 - 1 , conductive loop  430 - 1 , and seat  432 - 1  collectively define restraint  414 - 1 . In similar fashion, armature  422 - 2 , conductive loop  430 - 2 , and seat  432 - 2  collectively define restraint  414 - 2 . 
         [0074]    Method  300  begins with operation  301 , wherein cartridge  408  is inserted into, and engages with, propulsion system  402 . In some embodiments, cartridge  408  is inserted into propulsion system  402  from the muzzle end. In some embodiments, cartridge  408  is inserted into propulsion system  402  from the breech end. In some embodiments, launcher  202  includes an automatic cartridge loading system for inserting cartridge  408  into propulsion system  402 . 
         [0075]      FIG. 5A  depicts a representational view of launcher  202 , after insertion of cartridge  408  in propulsion system  402 , in accordance with the illustrative embodiment of the present invention.  FIG. 5A  depicts launcher  202  in cross-section but, for clarity, without details of its constituent elements. When propulsion system  402  and cartridge  408  are engaged, projectile  412 - 1 , projectile  412 - 2 , and base plate  410  are located with respect to propulsion coil  404 - 1 , propulsion coil  404 - 2 , and propulsion coil  404 - 3 , respectively. Projectile  412 - 1 , projectile  412 - 2 , and base plate  410  are positioned relative to their respective propulsion coils to enable the efficient propulsion of the projectiles and the canister out of launcher  202 . 
         [0076]      FIG. 5B  depicts a cross-sectional view of details of launcher  202  in accordance with the illustrative embodiment of the present invention.  FIG. 5  depicts launcher  202  after insertion of cartridge  408  into propulsion system  402 . For clarity, the connections to and from power system  208  are not shown in  FIG. 5B . 
         [0077]    Once they are engaged, restraint  502  immobilizes canister  408  with respect to propulsion system  402 . Retainer  406 , base plate  410 , and conductive loop  430 - 3  collectively define restraint  502 . While restraint  502  is engaged, conductive loop  430 - 3  is captured by both seats  418  and shoulder  438 . Although in the illustrative embodiment conductive loop is included in cartridge  408 , it will be clear to one of ordinary skill in the art, after reading this specification, how to make and use alternative embodiments of the present invention wherein conductive loop  430 - 3  is included in propulsion system  402 . 
         [0078]    At operation  302 , power system  208  energizes propulsion coil  404 - 1 . The flow of electric current in propulsion coil  404 - 1  generates an electromagnetic field in the region of propulsion coil  404 - 1 . 
         [0079]    At operation  303 , restraint  414 - 1  is actuated to enable motion of projectile  412 - 1  with respect to cartridge  408 . Actuation of restraint  414 - 1  occurs passively as a result of a first force on conductive loop  430 - 1 , which results from a mutual inductance between conductive loop  430 - 1  and propulsion coil  404 - 1 . This force compresses conductive loop  430 - 1  into shoulder  428 - 1  while disengaging it from seat  432 - 1 . In some embodiments, restraint  414 - 1  is a non-passively actuated restraint, such as a marmon clamp, explosive bolt, and the like. 
         [0080]    At operation  304 , mutual inductance between armature  422 - 1  and propulsion coil  404 - 1  induces a second force on armature  422 - 1 . This second force propels projectile  412 - 1  through fly-through cover  426  and out of cartridge  408 . Once projectile  412 - 1  is thrown, the flow of electric current in propulsion coil  404 - 1  can be stopped. 
         [0081]    The force with which projectile  412 - 1  is thrown from launcher  202  is a function of the flow of electric current in propulsion coil  404 - 1 . The ability to vary the propulsive force on projectile  412 - 1  is an advantage that electromagnetic propulsion affords over other means of propulsion, such as chemical-engines, explosive charges, etc. Electromagnetic propulsion also enables the use of passively-actuated restraints, such as restraints  414 . 
         [0082]    At operation  305 , power system  208  energizes propulsion coil  404 - 2 . The flow of electric current in propulsion coil  404 - 2  generates an electromagnetic field in the region of propulsion coil  404 - 2 . 
         [0083]    At operation  306 , restraint  414 - 2  is actuated to enable motion of projectile  412 - 2  with respect to cartridge  408 . Actuation of restraint  414 - 2  occurs passively as a result of a first force on conductive loop  430 - 2 , which results from a mutual inductance between conductive loop  430 - 2  and propulsion coil  404 - 2 . This force compresses conductive loop  430 - 2  into shoulder  428 - 2  while disengaging it from seat  432 - 2 . In some embodiments, restraint  414 - 2  is a non-passively actuated restraint, such as a marmon clamp, explosive bolt, and the like. 
         [0084]    At operation  307 , mutual inductance between armature  422 - 2  and propulsion coil  404 - 2  induces a second force on armature  422 - 2 . This second force propels projectile  412 - 2  through fly-through cover  426  and out of cartridge  408 . Once projectile  412 - 2  is thrown, the flow of electric current in propulsion coil  404 - 2  can be stopped. 
         [0085]    In some embodiments, power system  208  sequences the flow of electric current in propulsion coils  404 - 1  and  404 - 2  to enhance the propulsive force on projectile  412 - 2 . In some embodiments, propulsion system  402  comprises additional propulsion coils to enable the enhancement of propulsive force on each projectile in a cartridge by sequencing current flow between multiple propulsion coils. 
         [0086]    At operation  308 , power system  208  energizes propulsion coil  404 - 3 . The flow of electric current in propulsion coil  404 - 3  generates an electromagnetic field in the region of propulsion coil  404 - 3 . 
         [0087]    At operation  309 , restraint  502  is actuated to enable motion of cartridge  408  with respect to propulsion system  402 . Actuation of restraint  502  occurs passively as a result of a first force on conductive loop  430 - 3 , which results from a mutual inductance between conductive loop  430 - 3  and propulsion coil  404 - 3 . This force compresses conductive loop  430 - 3  into shoulder  438  while disengaging it from seat  418 . In some embodiments, restraint  502  is a non-passively actuated restraint, such as a marmon clamp, explosive bolt, and the like. 
         [0088]    At operation  310 , mutual inductance between base plate  410  and propulsion coil  404 - 3  induces a propulsive force on base plate  410 . This propulsive force propels cartridge  408  out of propulsion system  402 . Once cartridge  408  is thrown, the flow of electric current in propulsion coil  404 - 3  can be stopped. 
         [0089]      FIG. 6  depicts a top view of details of a conductive loop in accordance with the illustrative embodiment of the present invention. Conductive loop  430 - i  is representative of any of conductive loops  430 - 1 ,  430 - 2 , and  430 - 3 . Conductive loop comprises gap  602 - i  and latch  604 - i.  The presence of gap  602 - i  enables conductive loop  430 - i  to compress when a compressive force is applied to it. Latch  604 - i  enables conductive loop  430 - i  to remain compressed even after the removal of this force. 
         [0090]    Latch  604 - i  comprises jaws  606 - i  and  608 - i.  When conductive loop  430 - i  is compressed in response to the flow of electric current in a propulsion coil, jaws  606 - i  and  608 - i  engage to keep conductive loop  430 - i  from expanding once the flow of electric current stops. Conductive loop  430 - i,  therefore, is kept in its compressed state even after the removal of the force that acts upon it. Once latch  604 - i  is engaged, it must be manually disengaged. It should be noted that latch  604 - i,  as depicted, is only one of many suitable latch designs. In some embodiments, springs are used to ensure that latch  604 - i  remains engaged throughout the actuation of a restraint. It will be clear to those skilled in the art, after reading this specification, how to specify, make, and use latch  604 - i.    
         [0091]    It is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.