Abstract:
Miniature arm fire and safe and arm devices include an electrically operated pyrotechnic initiation device ( 5 ) to generate a detonation wave upon command and a movable pressure barrier ( 9 ) that blocks propagation of the detonation wave if the device is not intended to be fired and opens a window ( 12 ) to transfer the detonation wave externally of the device. The detonation wave may in alternate embodiments be a subsonic flame front and pressure wave or a supersonic shock wave, respectively. An electromagnet ( 7 ) may serve to move the pressure barrier. Detonation waves output from the device have application in igniting an explosive train, either directly or indirectly, the latter by operating an electrical switch. In the arm fire device, the barrier automatically prevents a detonation output when electrical power is removed from the device. In the safe and arm device, the barrier, once moved out of the way, remains out of the way, even when electrical power is removed. Various forms of miniature single operate electrical switches are described that may be operated by the foregoing devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Reference is made to the copending, commonly assigned U.S. patent application, Ser. No. 08/912,709, filed Aug. 18, 1997 entitled Integrated Pulsed Propulsion and Structural Support System for Micro-satellite, the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to micro-electromechanical systems (“MEMS”) and, more particularly, to micro-miniaturization of electrical switches and arming and firing devices having application in missiles, rockets, and like apparatus. 
     BACKGROUND 
     In order to prevent a rocket motor, warhead, explosive separation device or energetic material, collectively sometimes referred to as target devices, from being unintentionally operated during flight or in any circumstance that could produce an extreme hazard to personnel or facilities, an “arm fire” device is customarily incorporated in the firing control circuit for the foregoing devices as a safety measure. The arm fire device electrically and mechanically interrupts the “ignition train” to the target device so as to prevent accidental operation. The arm fire device includes a mechanism that permits the target device to be armed, ready to fire, only while electrical power is being applied to the target device. When that electrical power is removed, signifying the target device is disarmed, the mechanism of the arm fire device returns to a safe position, interrupting the path of the ignition train. 
     Another known device of similar purpose, is called the “safe and arm” device, and is a variation of the arm fire device. The mechanism of the safe and arm device enables the target device, such as the rocket motor, warhead and the like, earlier mentioned, to remain armed, even after electrical power is removed. The device may be returned to a “safe” position only by applying (or reapplying) electrical power. The safe and arm device is commonly used to initiate a system destruct in the event of a test failure, for launch vehicle separation and for rocket motor stage separation during flight. Typically, the safe and arm device uses a pyrotechnic output which may be either a subsonic pressure wave or which may be a flame front and supersonic shock wave or detonation to transfer energy to another pyrotechnic device (and serves as the trigger of the latter device). 
     The foregoing safety devices have been proven in service. Constructed using existing technology, those safety devices are typically of the size of a person&#39;s fist, and possess a noticeable weight of several pounds. If the weight and volume of those devices can be reduced, the payload and propulsion systems can be increased in weight and/or volume to increase the range and capability of a weapon system. Given the goal of reducing weight and volume, the arm fire device and the safe and arm device are candidates for significant miniaturization in the system. As an advantage the present invention addresses the function of arm fire devices and safe and arm devices, and accomplishes the functions of the foregoing devices in an electromechanical apparatus that is significantly smaller in size and weight than the presently existing counterparts. 
     Micro-electromechanical systems (“MEMS”) have become known to a degree. The MEMS devices reported in the literature represents an achievement milestone in miniaturization and integration of electromechanical machines and devices. That technology provides, as example, a toothed gear that is smaller in size than a speck of dust, invisible to the eye. MEMS devices are sometimes fabricated by employing the photo-lithograph mask and etch techniques familiar to those in the semiconductor fabrication technology to form micro-miniature parts of silicon, which are annealed to strengthen the part. In copending application Ser. No. 08/912,709, a micro-miniature pyrotechnic gas generator, called a micro-thruster is described that is capable of issuing a microburst of gas in which the expelled gas is applied to produce thrust for a micro-satellite or other small craft. 
     Accordingly, a principal object of the invention is to micro-miniaturize arm fire and safe and arm devices. 
     Another object of the invention is to provide electrical single operation switch designs for fabrication using MEMS fabrication techniques. 
     An ancillary object of the invention is to produce micro-miniature single operate electrical switches. 
     SUMMARY OF THE INVENTION 
     Miniaturized light-weight arm fire and safe and arm devices are made possible by incorporating the advantages of micro-electromechanical system (“MEMS”) technology in the devices. In accordance with the invention, arm fire and safe and arm devices include an electrically operated pyrotechnic initiator or, as variously termed, MEMS ignition device to generate a pyrotechnic output upon command and an electro-mechanically movable pyrotechnic barrier that blocks propagation of the shock wave and expanding gases of the pyrotechnic output if the device is not intended to be fired. The pyrotechnic output is transferred from the device for use in igniting an explosive train, either directly or indirectly, the latter, as example, by operating an electrical switch. To prevent output through unintended operation of the MEMS ignition device the pyrotechnic barrier is normally positioned to block the output; and the barrier is moved out of the way when output is desired. In the arm fire device, the barrier automatically prevents an output when electrical power is removed from the unit. In the safe and arm device, the barrier, once moved out of the way, remains out of the way, even when electrical power is removed. 
     As an additional feature, the switch operator of a micro-miniature electrical switch receives the pyrotechnic output and is moved in position by the pyrotechnic output to close a pair of normally open electrical contacts. The contacts may be included in an electrically operated explosive train. 
     An ancillary invention in a miniature single operation electrical switch includes an electrically operated MEMS gas generator, a movable switch operator and a pair of electrical contacts. On applying a current pulse, a microburst of hot gas is generated that forces the switch operator to shift in position to change the condition of a DC current path through the electrical contacts. 
     The foregoing and additional objects and advantages of the invention together with the structure characteristic thereof, which was only briefly summarized in the foregoing passages, will become more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment of the invention, which follows in this specification, taken together with the illustrations thereof presented in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an embodiment of an arm fire device as the embodiment appears in the unarmed (or safe) mode; 
     FIG. 2 shows the embodiment of FIG. 1 as the embodiment appears in the fire mode; 
     FIG. 3 illustrates in a partially exploded view a MEMS ignition device used in the embodiment of FIG. 1; 
     FIG. 4 is an embodiment of a safe and arm device as the embodiment appears in the safe mode; 
     FIG. 5 shows the embodiment of FIG. 4 as the embodiment appears in the arm mode; 
     FIG. 6 illustrates a rotary form of the movable barrier that may be substituted for the slidable barrier component in an alternative embodiment of the arm fire device of FIG. 1; 
     FIGS. 7 and 8 illustrate an embodiment of a single operation digital gas motivated electrical switch in respective standby and operated modes; 
     FIG. 9 partially illustrates an alternative embodiment of a single operation digital gas motivated electrical switch; 
     FIG. 10 partially illustrates a further alternative embodiment of a single operation digital gas motivated electrical switch; and 
     FIGS. 11 and 12 illustrate a still further alternative embodiment of a single operation digital gas motivated electrical switch in normal and operated positions, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 to which reference is a not-to-scale pictorial view of an embodiment of an arm fire device  1  constructed in accordance with the invention illustrating the device in a top plan view and in the unarmed (safe) position. The device includes a base  3 , suitably of a conventional resin based printed circuit board, ceramic substrate or other substrate, and the various components attached to the top surface of base  3 . Those components include a MEMS ignition device  5 , electromagnet solenoid  7 , and a multi-part mechanical slider assembly  9 . That slider assembly includes a movable slider  10 , a firing piston  11 , a firing piston channel  13  and shear pin  15 . The slider  10  is oriented perpendicular to the firing piston channel  13  for transverse movement. The slider contains an upper portion that is solid and serves as a barrier, a like bottom portion  16  and a window  12  between the two cited portions, as later more fully described herein. A tension spring  14  attaches to the remote end  16  of slider  10  and the armature  6  of solenoid  7  connects to the upper end of slider  10 . Metal leads  17  and  18 , plated on the base, electrically connect the terminals of electromagnet  7  to respective edge pins on an edge of the base  3 . Likewise plated-on metal leads  19  and  20  electrically connect the terminals of the MEMS ignition device  5  to respective edge pins on the right edge of base  3 . 
     A pair of contact pins mounted to base  3  connect via respective plated-on leads  21  and  23  to respective edge contacts on the base. The contact pins are positioned to contact a conductive metal end on slider  10 , which serves as an electrical bridging contact, when the slider is in the safe position illustrated in the figure. Through the edge contacts, the circuit through the pin contacts connect to an indicator circuit, not illustrated, so that when the slider is in the safe position the circuit through leads  21  and  23  is closed and an indicator, such as a lamp, will illuminate indicating “safe”, to the operator. As a mechanical indicator, the slider  10  may be painted with green  71  and red  73  colored patches, only one of which may be viewed through an indicator window in the cover, not illustrated, to the arm fire device. Normally the green patch is visible in the safe mode. When the unit is placed in the arm mode, later herein described, the red patch is then visible through the indicator window in lieu of the green patch. If a safe condition is not indicated for any reason, then personnel should investigate to determine the cause. 
     Further, leads  24  and  26  are connected to leads  19  and  20  that lead to the ignition device  5 , and to respective contacts located on the side of the slider  10 . The latter contacts are in contact with another electrical bridging contact on the lower side of slider  10 , when the slider is in the unarmed mode, as illustrated in the figure. The bridging contact places a short-circuit across the electrical circuit to the MEMS ignition device  5  to prevent inadvertent electrical energization of that device as an added safeguard. 
     Packaged similar to the packing used for semiconductor chips, preferably the unit may be plugged into a standard integrated circuit chip socket to mount and connect the device to external control and power circuitry, not illustrated. Although the foregoing components are three-dimensional in geometry, the components are of a very short height in this miniature device. Hence, a side view of the components does not offer any details of particular note and, accordingly, need not be illustrated. 
     Firing piston channel  13  may be constructed of flat rectangular tubing that has a rectangular passage cut through the sides to provide the mounting for the slider assembly  9 . Using a microscope the firing piston  11  is inserted into the channel and a passage in a side of that piston is aligned with a hole drilled or cut into the side of the rectangular tubing of the channel  13 . The shear pin  15  is then inserted into place to hold firing piston  11  in place in the channel. 
     Slider  10  is rectangular in cross section and sufficient in size to fill the lateral passages in the firing piston channel but with sufficient clearance on the sides to move freely through that channel. If found necessary or desirable, guide rails may be included in the slider assembly  9  to guide slider  10  as it moves, as described herein, assuring that the slider does not bind. 
     Slider  10  may be formed of a metal or a magnetic metal material. The central section of the slider assembly contains an opening or passage  12  and another passage orthogonal thereto, not visible in the figure, that leads to the right and opens into channel  13 . The window portion is bounded by four straight frame members, only two of which are visible in this top view, joining the upper portion of the slider to the lower section  16 . The bottom surface of the slider underlying window  12  is closed by a panel, and the left vertical side of the slider adjacent window  12  is also closed by a panel, not illustrated. 
     On assembly of the device, the slider is pushed to the position illustrated with the upper barrier portion of slider  10  blocking firing channel  13 . With the assistance of a microscope, the ends of spring  14  are hooked into holes, not illustrated, formed in the base  3  and in slider assembly  9 , or may be soldered to those components. Preferably, a fusible link  40  is mechanically coupled across spring  14 , such as by soldering, to normally restrain the spring, preventing the spring from expanding. The fusible link restrains slider  10  from changing in position at this stage, notwithstanding shock or vibration, as might occur when the arm fire device is being transported. Leads  41 A and  41 B extend the circuit from the link to contacts at the edge of base  3 . That restraint is removed at the appropriate time by applying current over those leads to break the link. 
     The length of the upper portion of slider  10  is about equal to the distance to the front of electromagnet solenoid  7  so that when the slider is moved through the firing channel  13  to, as example, into abutment with the solenoid or the uppermost position of travel, as later herein described during operation, the right hand side window, not visible in the figure, that is perpendicular to window  12 , is centrally positioned in the firing piston channel  13  and provides a clear passage through that channel into the slider  10 , and, through a right hand turn, (upwardly from the plane of the drawing) through window  12 . 
     The foregoing components may be fabricated to the requisite miniature size by any of the many available precision metal machine shops, particularly those firms having some experience with the MEMS technology or other miniaturized fabrication. The electromagnet  7  and firing piston channel  13 , the latter supporting slider assembly  9 , are attached to base  3 , as example, with epoxy. MEMS ignition device  5  is also mounted at the end of the channel  13 , through an end cut-out in that channel to base  3 , suitably by epoxy. 
     MEMS ignition device  5  is preferably constructed as described in copending application Ser. No. 08/912,709, referred to earlier. In that structure a quantity of solid pyrotechnic material, such as lead styphenate or zirconium potassium perchlorate, is confined within millimeter (micro-miniature) sized cavity and the cavity is sealed by a wall. In other embodiments in which sub-sonic velocity of gas is desired, lead phtalate may be substituted. By design, that sealing wall is constructed to be weaker in strength than other walls in the cavity or contains a portion of that wall that is weakened. To complete the ignition unit, the cavity is mounted in thermal conductive relationship to an electrical resistance heater element associated therewith. 
     The MEMS ignition device produces a pyrotechnic output, typically a subsonic pressure wave or supersonic detonation wave, occurring, typically over an extremely short time interval of less or equal to one-thousand micro-seconds. A typical MEMS ignition device in size measures about 900 μm by 900 μm×1400 μm. When one desires the unit to provide a pyrotechnic output, electric current is applied to the heater. Within a millisecond or so, the heat generated couples into the cavity and ignites the confined pyrotechnic material, which instantaneously produces expanding hot gas and a shock wave sufficient in force to break through the weaker wall of the unit. 
     Such MEMS ignition devices can be provided in many different forms. As illustrated in FIG. 3, a suitable pyrotechnic device  5 ′ may be fabricated on a substrate  27 , such as a circuit board, ceramic layer or other conventional substrate material. A thermal resistive material  28  is deposited on the substrate, a small pot or cavity  29 , about {fraction (1/16)} th  inch in diameter is attached by epoxy atop the resistive material, pyrotechnic ingredient  30  is inserted into the pot, and the weak-strength cover  31  is sealed in place closing the cavity. Electrical contacts  32  and  33  and the associated wiring on the circuit board or substrate permit electrical current to be applied to resistance heater  28 . The foregoing pyrotechnic device may be positioned in the combination of FIG. 1, as  5 , oriented so that the lid is in the channel facing the direction of firing piston  11 . 
     Returning to FIG. 1, the operation of the device is next considered. In safe mode, which FIG. 1 illustrates, electromagnet solenoid  7  remains unenergized. The slider  10  is positioned blocking channel  13 . Firing piston  11  is held in place by shear pin  15  and the electrical triggering circuit to MEMS ignition device  5  remains short circuited by the bridging contact at the side of the slider. 
     Should the MEMS ignition device  5  be fired inadvertently, as example, should an ill-trained technician rest a hot soldering iron on the ignition device, piston  11  will be forced forward to break shear pin  15 . However, the lateral force is not great enough to force slider  10  out of channel  13  or otherwise remove that barrier. Thus the pyrotechnic blast cannot propagate through window  12 . In the latter regard, it is noted that the side walls of the firing channel shown to the left in the figure adds further support to the side of the upper portion of slider  10 , forming, so to speak, a flying buttress to prevent further lateral movement of the firing piston  11 . The hot gas and pressure remains confined and cannot reach a “secondary ignitor”, not illustrated, external of the arm fire device of the system in which the arm fire device is installed. Everything thus remains “safe”. 
     Once the arm fire device  1  has been transported and installed in a system, personnel apply electrical current to the fusible link  40  via leads  41 A and  41 B, and the current melts the link. That removes the restraint from spring  14 . When one desires to arm a target device, the electromagnet solenoid  7  must be energized. By applying current to electromagnet  7  over leads  17  and  18 , the device transitions into the “arm” mode. The electromagnet solenoid magnetically draws armature  6  within the coil of the solenoid, pulling slider  10  to which the armature is connected toward the solenoid against the restraint of spring  14 , which expands and is placed in tension. As the slider  10  is drawn to solenoid  7 , the barrier portion of the slider is moved out of channel  13 , removing the blockage from the channel, such as is illustrated in FIG. 2 to which reference is made. When the slider reaches the uppermost position of travel, the device is ready to “fire”. 
     The circuit through leads  21  and  23  is broken to result in a signal for personnel. In the indicator window in the cover, not illustrated, the green colored patch on the slider moves out of view and is replaced by the red patch  73 . The device is thus in the arm mode, ready to be fired. As long as the electromagnet solenoid  7  remains energized, the device remains in the armed condition. Should the solenoid be de-energized, spring  14  pulls slider  10  back to the normal “safe” position. The shear pin  15 , another safety precaution, is strong enough to obstruct travel of the firing piston  11  when the latter is motivated only by vibration and/or acceleration, since the piston is thin, light weight, relatively flat and possesses insufficient moment of inertia. 
     To fire the device, electrical current is next applied to the input terminals of MEMS ignition device  5  via leads  19  and  20 . The ignition device produces a “micro-burst” of hot gas and pressure that is directed against firing piston  11 . Under the force exerted by the rapidly expanding hot gas and pressure wave, the shear pin  15  breaks and the firing piston  11  is propelled through channel  13  to the left, ultimately striking the side wall, not illustrated, to window  12  in slider  10 , covering a portion of window  12 , but leaving a portion of that window unobstructed. 
     The hot gases and pressure wave exit through window  12 , perpendicular to the plane of the paper in FIG. 2, through which the gas and pressure may be applied to initiate a larger explosive device, the secondary ignitor, either directly or indirectly. As later herein described the foregoing may be combined with an electrical switch of micro-miniature size to electrically trigger an electrically actuated explosive device, such as illustrated in FIGS. 6 through 10 later herein described. 
     In a practical example the base  3  of the foregoing embodiment is 2.5 cm by 2.5 cm square and 0.1 cm thick; and the entire unit weights about 2 grams. Compared to the “fist” sized units currently being used, weighing approximately 32 ounces, the arm and fire device of the present invention represents an improvement in weight alone of more than 99.9%, and a volume savings of about 99.99%. 
     A safe and arm device constructed in accordance with the invention is illustrated in FIGS. 4 and 5 to which reference is made. As recalled, in this kind of device, the device is armed by application of electrical power, and remains armed even when the electrical power is subsequently withdrawn. The device is reset to the safe mode by application of power. As generally observed from the figures, the structure of the safe and arm device employs many of the same components that are included in the arm fire device of FIG.  1 . To avoid unnecessary repetition and to facilitate understanding of the embodiment, the elements of this embodiment are given the same denomination as the corresponding element of the prior embodiment. Only those components added or the modifications to those components are given a new denomination. 
     A second electromagnet solenoid  8  is included in the embodiment of FIG. 4, in lieu of the tension spring  14  used in FIG.  1 . Leads  72  and  74  are included on base  3  to connect current to the solenoid  8 , when the solenoid is to be operated. A pair of spring clip formed latches are mounted to the base, one on each side of the path of movement of slider  10  and at the bottom end of the slider, respectively. The upper and lower ends of slider  10  are notched on each side to form the catches for the releasable latches. The latches are designed to release their grip on the slider, when the solenoid exerts a linear pull on the slider. The latches should hold the slider against foreseeable shock and vibration. 
     As in the prior embodiment in the “safe” condition illustrated, should MEMS ignition device  5  inadvertently fire, the hot expanding gases and the pressure wave will be sufficient to force firing piston  11  to the left and break shear pin  15 , which otherwise holds that piston stationary. However the piston strikes the side of slider  10  and cannot move any further to the left. When current is applied to electromagnet solenoid  7  (via leads  17  and  18 ), the solenoid pulls in the armature  6 , and, thereby releases latch  76 , and pulls the slider assembly close, the uppermost position of travel, as shown in FIG. 5 to which reference  25  is made. 
     The window  12  in slider  10  is moved into place in firing channel  13 , removing the barrier from the channel. As in the prior embodiment, the device is ready to fire. When moved to electromagnet solenoid  7 , the spring clips  75  engage the notches in the side of the upper end of slider  10  to latch the slider in place. Should the power to the electromagnet solenoid  7  be removed, the latches prevent the slider from moving. Hence, the slider remains in the armed position illustrated, ready to fire. 
     As in the prior embodiment, when the device is in safe mode, an indicator circuit is closed through leads  21  and  23 , the contacts abutting the side of piston  16  and the conductive bridging contact on the side of the piston and the green patch  71  is visible through the indicator window in the cover. 
     The firing of the device is the same as in the prior embodiment, and need not be repeated. If one wishes to halt the arm condition of the device and return to the safe mode, then current is applied to electromagnet solenoid  8 . The electromagnet produces a magnetic field that pulls the solenoid armature  4  into the solenoid. Since armature  4  is attached to the lower end of slider  10 , the slider is pulled back to the normal position illustrated in FIG.  4 . The force produced by the solenoid is sufficient to overcome the restraining force of the latches  75 . The spring clips of the latch are forced out of the notches as the slider is pulled toward electromagnet  8 . On completion, the device is restored to the position shown in FIG. 4, and the indicator circuit and the mechanical indicator both indicate “safe”. 
     The foregoing embodiment of FIG. 1 employed a slide type of arming device. The function served by slider assembly  9  may alternatively be served by a rotary type device, such as the device pictorially illustrated in FIG. 6 to which references is made. In this a motor mechanism  34 , containing electromagnetic coil  35 , turns the shaft of a cylindrical valve  36  by ninety degrees against the restraint of a spring when electromagnet coil  35  is energized with DC current. The side of the cylinder contains two openings  38  and  39  that are spaced ninety degrees apart about the cylindrical axis. The cylinder also contains an internal passage between those openings. In application, when the motor winding is energized the shaft turns by ninety degrees, to orient the two passages one way. When the winding is deenergized, the magnetic pull of the winding collapses, and spring  37  turns the shaft in the reverse directing reorienting the passages in cylinder  36  to the normal position. As placed into the device, as example, of FIG. 1, the orientation in the normal position normally prevents gas from passing through the cylinder when the motor winding is not energized. 
     In such application, the side of cylinder  36  is positioned against the end wall of a passage, such as passage  13  in FIG. 1, whose end edges are for this adaptation shaped to the diameter of the cylinder so as to mate with the right and left hand cylindrical surfaces of the cylinder. Normally, when motor winding  35  is not energized, passage  39  faces into the firing channel  13 , but the connected passage  38  faces the bottom of the mounting  3 , thereby blocking the escape of any pressurized gas, should the gas generator  5  inadvertently fire. When the motor winding  35  is energized, the shaft turns by ninety degrees, orienting passage  39  upwardly, and passage  38  into passage  13 . If the MEMS ignition device  5  is fired, the pyrotechnic output travels through passage  13  as earlier described in connection with the operation of FIG. 1, then through the cylinder and out passage  39 . If the power extinguishes before firing the ignition device, the spring restores the cylinder to the blocking orientation, the “safe” position. As one appreciates in this embodiment and in all of the other embodiments, the side walls of the passages, such as passage  13  must be of a material and/or thickness and strength that is sufficient to withstand the force of the anticipated pyrotechnic output without falling apart or distorting in shape. 
     Reference is made to FIGS. 7 and 8 which illustrate an alternative MEMS single operation electrical operated MEMS gas generator motivated electrical switch prior to and following operation. The switch includes a pair of electrical leads or conductive metal contacts  42  and  43 , elongate in geometry, positioned at the lower end of a rectangular shaped housing  44 . A pair of relatively thick interior sidewalls or supports  45  and  46  are affixed to opposite walls of the housing. Both the housing walls and the sidewalls supports  45  and  46  are formed of electrically non-conductive material, such as Silicon. Contact  42  lies on the bottom of the housing extending over a considerable portion of the bottom surface. The contact further extends through support  45  and the adjacent wall to the housing exterior so that the contact may be accessed by external circuitry. 
     Contact  43  is held in a cantilever fashion by support wall  46  in a position overlying contact  42  and extends parallel to the latter contact. Contact  43  is sufficient in length to extend over a major portion of that portion of contact  42  that is located interior of housing  44 ; and also extends through the wall to the housing exterior. Metal contacts  42  and  43  define a normally open electrical circuit through the switch housing. Contact  43  is sufficiently rigid to maintain sufficient clearance to the adjacent contact in the presence of any foreseeable shock and vibration. 
     A bar membrane  47  extends across the housing interior, supported by the upper ends of sidewalls  45  and  46  to which the bar is affixed. A rectangular block of non-conductive material  48 , suitably of silicon, is supported in between side walls  45  and  46  from the underside of bar membrane  47 , leaving a slight clearance on each of the right and left hand sides of the block, suitably less than one micron in clearance. Block  48 , sometimes referred to as the “silicon hammer”, overlies and is spaced from contact  43 . The upper end of housing  44  contains the MEMS gas generator  49 , pictorially illustrated, that was earlier described. Electrical power for initiating the generator  49  is supplied via electrical leads  50   a  and  50   b . A small ledge  51 , only portions of which are illustrated, extends about the upper walls of housing  44  and serves to support a covering membrane  52 , that divides the internal region above, containing gas generator  49 , from that below. Together with bar membrane  47 , covering membrane  52  defines a plenum for gas. Both membranes  47  and  52  are rupturable. 
     When the switch is to be operated, a short pulse of current is applied via leads  50   a  and  50   b  to the MEMS gas generator, which, in response, explodes the confined pyrotechnic material, producing a burst of hot expanding gas. The force produced by the gas is released against membrane  51 , which ruptures, and further expands into the plenum region, applying the force of the gas against the membrane bar  47 . The membrane bar and the silicon hammer  48  are driven down by the force, rupturing membrane bar  47  and driving silicon hammer  48  into contact  43 . As illustrated in FIG. 8, silicon hammer presses against contact  43  and being fragile the contact deforms and/or bends and presses against contact  42 , closing an electrical circuit through the switch. 
     In a practical example, in overall dimension the switch of FIG. 7 may be one millimeter square, membrane  52  may be one mm in thickness and be of any appropriate material, such as a metal foil. Membrane bar  47  man be about one-half micron in thickness and comprise a more thick metal foil. Side walls  45  and  46  may be about 100 microns thick and be formed of silicon. The housing may comprise any insulator material. Using conventional techniques the cantilever contact  43  is formed of silicon. An electrode, a conductive load pad is manufactured and positioned under the cantilever contact. When the switch is fired, the pressure of the pyrotechnic blast breaks the plenums and drives the hammer. In turn the hammer impacts the cantilever contact, forcing the cantilever into contact with the electrode  42 , thereby closing the switch. 
     Electrical switches may be of a mechanical design different from that of FIGS. 7 and 8, all of which make use of the MEMS digital propulsion gas generator to operate the switch. Several of those alternative designs are illustrated in FIGS. 9,  10 ,  11  and  12 . 
     The switch of FIG. 9 includes the pair of relatively thick side walls  54  and  55 , as in the preceding embodiment, a pair of electrical contacts  56  and  57 , and a movable block  58 , the hammer. In this embodiment hammer  58  is of electrically conductive material or has electrically conductive sides so that the hammer may also serve as a bridging contact between contacts  56  and  57 . The switch contains the same upper section, not illustrated, as in the switch of FIG.  7 . When the MEMS device operates and creates the force to rupture the membranes and drive the hammer  58  down, the side of the hammer brushes against wiper contact  57  and the front moves into contact with contact  56 , such as illustrated in the operated mode, in the figure. The electrical circuit completes through the conductive sides of the hammer  58 . In this embodiment, as an improvement, the face of the hammer includes a projection in the shape of a truncated right cone, and the contact  56  includes a conical shaped passage that is aligned with the cone. The conical passage provides a mechanical device that allows for slight misalignment between the conductive cone of the hammer and the axis of the passage, providing for self-alignment. Additionally since the cone may scrape against the conical walls when the hammer  58  is descending and essentially clean the contact of any dirt resulting in a more reliable electrical contact as compared to a contact that simply is pressed against the contact surface. 
     In the switch embodiment partially illustrated in FIG. 10, an electrically conductive metal diaphragm,  62  resembling a coffee can or oil can lid is used to provide a bridging contact for the spaced contacts  63  and  64 . A second metal diaphragm  61  is mounted in overlying relationship, leaving a gas chamber there between. Both diaphragms are attached about the peripheral edge to the walls  59  and  60 , at respective vertical locations along the wall. In the switch, contacts  63  are mounted through passages in insulating walls  59  and  60  with ends of the two contacts facing one another across an air gap. The membrane  62  normally bulges in one direction, the upward direction, as example. When a force applied to that membrane in the opposite direction attains a sufficient level, the membrane inverts, and bulges in the opposite direction. In the switch, force is applied by the expanding gas released by the MEMS thruster, not illustrated, against diaphragm  61  and forces the diaphragm downward, compressing the gas in the confined region. In turn that compressed gas creates a force on diaphragm  62 , which rises to a sufficient level to invert diaphragm  62 . By design, the downward bulge is great enough to permit the metal diaphragm to contact both contacts  63  and  64  bridging a circuit between the contacts. 
     Another micro-miniature switch structure is partially illustrated in FIGS. 11 and 12 in normal and operated positions, respectively. As with the prior switch embodiments the MEMS gas generator is omitted from the illustration. In this embodiment the switch operator is a plunger  67 . Electrical terminals  68  and  69  serve as the switch contacts. Each electrical terminal is an elongate strip of conductive metal, attached to housing  70 . Each strip extends from the exterior of the housing, through the housing wall and through a portion of the housing interior with electric terminal strip  69  overlying and parallel to a portion of electric terminal strip  68  disposed on the bottom of the housing. Housing  70  includes two side walls and a top wall  71 , the latter containing a passage for the shaft of plunger  67 . 
     The plunger includes a wide diameter head, greater in diameter than the shaft; and the head is located within the upper housing region that receives the micro-blast of gas from the micro-thruster, not illustrated. The plunger may be formed of a light weight rigid metal or plastic material. On assembly, the shaft of plunger  67  is inserted through the passage and the end of the shaft abuts the upper surface of contact  69 . The rigidity of the contact strip  69  should be sufficient to permit the contact to bear the weight of the plunger without significant deflection, maintaining clearance with the other contact strip  68 . The shaft of the plunger is of sufficient length to permit the head of the plunger to be slightly elevated above the upper surface of wall  71  when the end of the shaft is supported on contact strip  69 . This is the normal position of plunger  67 . When the switch is operated, the plunger is moved down to the second position with the head abutting the upper surface of wall  71 , as later herein described in connection with FIG.  12 . 
     As in the switches earlier described, when the switch is to be operated to close a DC circuit between contacts  68  and  69 , a pulse of current is applied to the input of the micro-thruster, not illustrated, of the switch. The current pulse heats the resistance material of the igniter, and ignites the pyrotechnic material in the housing of the micro-thruster, in the manner earlier herein described. The micro-thruster produces a micro-blast of hot expanding gas accompanied by a spiked rise in pressure. That gas and pressure impulse is directed into the chamber above wall  71 , and, hence, against the head of plunger  67 . 
     As shown in FIG. 12, the plunger is thereby driven downward until the head abuts the wall  71 . In moving down, the shaft of the plunger presses against and bends the cantilevered end of contact  69  into contact with contact  68 , which completes a DC circuit through the switch. Contact  69  may be constructed to be deformable in character, in which event the switch remains closed even after termination of the micro-blast. The contact may alternatively be flexible in character, such as spring copper alloy, so as to restore to the first position when the micro-blast extinguishes. 
     It is appreciated that the foregoing electric switch structures are of the normally open variety. That is, the switch contacts are normally separated to interrupt a DC current path through the contacts of the switch, and, when the switch is operated, the contacts are in abutment closing a DC current path there through. The foregoing mode of switch operation is consistent with present requirements for electrically detonated explosive devices that require the application of a current to ignite the device. However, in alternative embodiments some designers may chose to require the interruption or opening of a normally closed DC circuit to signify the onset of an electrically initiated explosive train. In that case the foregoing switch structures of FIGS. 7-12 should be modified so that the switch contacts are normally in electrical contact, and separate to break the DC circuit with the switch is operated. 
     It is believed that the foregoing description of the preferred embodiments of the invention is sufficient in detail to enable one skilled in the art to make and use the invention. However, it is expressly understood that the detail of the elements presented for the foregoing purpose is not intended to limit the scope of the invention, in as much as equivalents to those elements and other modifications thereof, all of which come within the scope of the invention, will become apparent to those skilled in the art upon reading this specification. 
     Thus, the invention is to be broadly construed within the full scope of the appended claims.