Patent Publication Number: US-11644291-B1

Title: Autoignition material capsule

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application claiming priority under 35 U.S.C. § 121 of co-pending U.S. patent application Ser. No. 15/391,418, entitled “MULTISTAGE THERMAL TRIGGER”, filed on Dec. 27, 2016, issued as U.S. Pat. No. 10,677,576, which is a nonprovisional claiming priority under 35 U.S.C. § 119 of U.S. Provisional Patent Application No. 62/273,165, entitled “MULTISTAGE THERMAL TRIGGER”, filed on Dec. 30, 2015. The prior applications are incorporated by reference herein. 
    
    
     STATEMENT OF GOVERNMENT SUPPORT 
     This invention was made in part with Government support under Agreement W15QKN-09-9-1001 awarded by the U.S. Department of Defense. The Government has certain rights in this invention. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     A thermal trigger may be used to activate, or “trigger” any system, such as fire safety systems and the like, responsive to temperature. It will be appreciated that there are a wide variety of current and potential future applications for thermal triggers. For example, thermal triggers may be used in virtually any environment presenting a risk of fire or overheating. Thermal triggers may be useful in building and vehicle safety, nuclear and coal fired power plants, electrical transmission lines and substations, storage of combustible or explosive materials, storage of fragile heat-sensitive materials, protection of supercomputers, protection of servers in datacenters, mining operations, rocket motor or fuel ignition systems, storage, transport, and tactical use of solid rocket motors, shipping containers for rocket motors or heat sensitive materials, explosives or hazardous waste, warheads, munitions, propulsion systems, combustion engines, and/or any number of other environments. 
     SUMMARY 
     A multistage thermal trigger device is disclosed. In some embodiments, multistage thermal trigger devices may include a first stage and a second stage, wherein the first stage activates at a first temperature, and wherein the second stage activates at a second temperature. The first stage may comprise, e.g., a thermal actuator which activates at the first temperature. The thermal actuator may be coupled with an arming assembly having a disarmed position and an armed position. The first stage may reposition the arming assembly from a disarmed position to an armed position in response to activation of the first stage. 
     The second stage may comprise, e.g., an autoignition material (AIM) capsule which activates at the second temperature, wherein the second temperature is higher than the first temperature. When the second stage is activated, it may in turn activate an output assembly via the arming assembly. The multistage thermal trigger may be configured such that the second stage may activate the output assembly when the arming assembly is in the armed position, and the output assembly cannot be activated by the second stage when the arming assembly is in the disarmed position. 
     An AIM capsule such as may be used in multistage thermal trigger devices is also disclosed herein. In some examples, AIM capsules may include a hermetically or environmentally sealed capsule; an autoignition material disposed inside the hermetically or environmentally sealed capsule; a gas permeable retainer system which retains the autoignition material in position; a stabilizer disposed inside the hermetically or environmentally sealed capsule; and a burst disc comprising a burst orifice for gas output upon activation of the autoignition material. 
     Additional aspects of this disclosure are described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings, in which: 
         FIG.  1    is a block diagram illustrating an example multistage thermal trigger device and operation thereof to arm and initiate an application; 
         FIG.  2    is a block diagram illustrating an example output assembly and application; 
         FIG.  3    is a side cross sectional view of an example uninstalled multistage thermal trigger device; 
         FIG.  4    is a side cross sectional view of an example installed multistage thermal trigger device; 
         FIG.  5    is a perspective view and top cross sectional view of an example multistage thermal trigger device; 
         FIG.  6    is a perspective view and top cross sectional view of an example multistage thermal trigger device; 
         FIG.  7    illustrates an example AIM capsule which may be included in a multistage thermal trigger device; 
         FIG.  8    illustrates a side cross sectional view the example AIM capsule illustrated in  FIG.  7   ; 
         FIG.  9    illustrates a side cross sectional view of another example AIM capsule, prior to activation of the AIM capsule, which may be included in a multistage thermal trigger device; and 
         FIG.  10    illustrates a side cross sectional view the example AIM capsule illustrated in  FIG.  9   , after activation of the AIM capsule. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, may be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. 
     The present disclosure is generally drawn, inter alia, to technologies including multistage thermal trigger devices and methods for manufacturing and operating such devices, as well as AIM capsules which may be deployed in connection with the disclosed multistage thermal trigger devices or other devices. In some embodiments, multistage thermal trigger devices may include a first stage and a second stage, wherein the first stage activates at a first temperature, and wherein the second stage activates at a second temperature. The first stage activates an arming assembly so that the thermal trigger device is armed. The second stage may then activate an output of the multistage thermal trigger device, via the arming assembly, when the second temperature is reached. If the arming assembly is not armed by the first stage, then the second stage is prevented from activating the output. Also, if the multistage thermal trigger device does not reach the second temperature, the second stage need not activate the output, even if the arming assembly is armed by the first stage. The multistage thermal trigger device may further include a mechanism to disarm the arming assembly when the thermal trigger device drops below the first temperature, and/or prior to reaching the second temperature, as well as a variety of other useful features disclosed herein. 
     This disclosure will generally use storage of combustible or explosive materials as an example scenario in which thermal triggers may be deployed, understanding that multistage thermal trigger devices may be deployed in any number of other scenarios as noted in the background section, and the disclosed multistage thermal trigger devices are not limited to any particular scenario. Energetic materials, such as explosives and propellants, are often found in confined spaces within munitions such as solid rocket motors. When these munitions are exposed to extreme heat (as from a fire) or when impacted by bullets or fragments from other munitions, the energetic materials may be initiated. Initiation of the propellants or explosives in this manner in a confined configuration leads to over pressurization of the munition followed by an explosion or detonation. This poses a significant hazard to military personnel, fire fighters and first responders in these scenarios. 
     Efforts have been made to develop “Insensitive Munitions,” which are munitions that are generally incapable of detonation except in its intended mission to destroy a target. In other words, if fragments from an explosion strike an IM, if a bullet impacts the IM, or if the insensitive munition is in close proximity to a target that is hit, it is less likely that the insensitive munition will detonate. Similarly, if the insensitive munition is exposed to extreme temperatures, as from a fire, the insensitive munition will likely only burn, rather than explode. The extreme temperatures from a fire may be described as fast cook off (FCO) and slow cook off (SCO). To prove effectiveness, insensitive munitions may be tested in both FCO and SCO conditions. SCO may be described as a heating rate of 6° F./h or slower, and FCO may be described as direct impingement from a fuel fire with a flame temperature of up to 1600° F. or hotter within seconds. Multistage thermal trigger devices may respond in SCO and FCO environments, at faster and slower heating rates, and/or at heating rates in between those produced in SCO and FCO. Multistage thermal trigger devices may respond in any type fire or extreme heat environment. 
     One way that insensitive munitions may be made more insensitive is through active or passive mitigation approaches that include venting by splitting the case or ejecting the nozzle to increase the vent area and prevent over pressurization in FCO or SCO. Thus in some embodiments, multistage thermal trigger devices as disclosed herein may be configured to trigger thermally initiated venting systems or linear shaped charges (LSCs) installed on munitions and/or solid rocket motors. Multistage thermal trigger devices may be designed to respond to extreme fire conditions and initiate venting systems or LSCs. For example, the disclosed multistage thermal trigger devices may be adapted to initiate an output assembly comprising a detonation transfer line that is attached to an application comprising a linear shaped charge device that cuts or scores a munition casing. 
       FIG.  1    is a block diagram illustrating an example multistage thermal trigger device and operation thereof to arm and initiate an application, in accordance with at least some embodiments of this disclosure. The illustrated thermal trigger device  100  includes a first stage  110 , a second stage  140  and an arming assembly  120 . An output assembly  150  may optionally be included as a part of the thermal trigger device  100 , or output assembly  150  may be a separate assembly. 
     In  FIG.  1   , the first stage  110  may be activated when a first temperature  101  is reached. In response to first temperature  101 , the first stage  110  may reposition  125  the arming assembly  120  from a disarmed position  121  to an armed position  122 . The second stage  140  may be activated when a second temperature  131  is reached. In response to second temperature  131 , the second stage  140  may activate  145  the arming assembly  120 . In response to activation  145  of the second stage  140 , and when the arming assembly  120  is in the armed position  122 , the arming assembly  120  may activate  155  the output assembly  150 . In response to activation  155 , output assembly  150  may activate  165  the application  160 . Thus the thermal trigger device  100  and output assembly  150  may be used to activate  165  the application  160  after both the first temperature  101  and the second temperature  131  are reached. 
       FIG.  2    is a block diagram illustrating an example output assembly and application, in accordance with at least some embodiments of this disclosure. As illustrated in  FIG.  2   , in some embodiments, output assembly  150  may comprise, e.g., an explosive or detonation transfer line or assembly  201  and linear shaped charge  202 . In some embodiments, explosive or detonation transfer line or assembly  201  may comprise, e.g., confined or flexible detonating cords or assemblies, or confined energy transfer lines. In some embodiments, output assembly  150  may comprise an assembly containing a primary or deflagrating propellant. Application  160  may comprise, e.g., a venting system  230  for a solid rocket motor or munition. 
     In  FIG.  2   , detonation transfer line  201  may be activated  155  by the thermal trigger device  100  illustrated in  FIG.  1   . In response to activation  155 , detonation transfer line  201  may activate linear shaped charge  202 . In response to activation of linear shaped charge  202 , linear shaped charge  202  may in turn activate  165  venting system  230 . 
       FIG.  2    illustrates one example output assembly  150  and application  160 , however, it will be appreciated that thermal trigger devices disclosed herein may be used with a wide number of different output assemblies and applications. In general, output assemblies may comprise any structures operable to transfer activation outputs of thermal trigger devices to applications. Output assemblies may also comprise detonative or deflagration materials, or primary or secondary explosives or propellants. In general, applications may comprise any devices or systems which are advantageously activated in response to thermal conditions, such as second temperature  131 , to which thermal trigger devices are adapted to respond. 
     In some embodiments, application  160  may comprise an electronic thermally initiated venting system, and the output assembly  150  may comprise, for example, a thermal battery and electronic or electromechanical safety and arming system, or a mechanical safety and arming system adapted to mechanically initiate the application  160 . As noted herein, the output assembly  150  may optionally be integrated into the thermal trigger device  100 . 
       FIG.  3    and  FIG.  4    provide side cross sectional views of an example multistage thermal trigger device  300 , showing internal components thereof, in accordance with at least some embodiments of this disclosure. The example multistage thermal trigger device  300  includes a housing  301 , a thermal actuator  310 , a return spring  311 , a slider  312 , a selector/indicator  330 , an AIM capsule  340 , a rotor assembly  320 , a return spring  321 , a booster  322 , an install interlock pin  331 , and a detonation transfer line interface  351 .  FIG.  3    furthermore illustrates an output assembly comprising a detonation transfer line  350 , which is plugged into the detonation transfer line interface  351 . 
     In  FIG.  3    and  FIG.  4   , thermal actuator  310  implements the first stage  110  illustrated in  FIG.  1   . Rotor assembly  320  and booster  322  implement the arming assembly  120  illustrated in  FIG.  1   . AIM capsule  340  implements the second stage  140  illustrated in  FIG.  1   . 
     In  FIG.  3    and  FIG.  4   , the rotor assembly  320  has a disarmed position in which booster  322  comprising a detonator material is rotated out of line from the AIM capsule  340  and the detonation transfer line  350 . The rotor assembly  320  has an armed position in which the booster  322  is rotated in line with the AIM capsule  340  and the detonation transfer line  350 . The thermal actuator  310  is coupled via an arming slider  312  with the rotor assembly  320 , in order to rotate the booster  322  from the disarmed position to the armed position, in response to activation of the thermal actuator  310 . 
     Initiation of the detonation transfer line  350  by the multistage thermal trigger device  300  illustrated in  FIG.  3    and  FIG.  4    may involve the following steps: The multistage thermal trigger device  300  may be installed, thereby depressing the install interlock pin  331 . The selector/indicator  330  may be manually set to an “enable” position, which is discussed further in connection with  FIG.  5    and  FIG.  6   . Thermal stimuli at first temperature  101  may activate the first stage thermal actuator  310  to thereby arm the multistage thermal trigger device  300 . Thermal stimuli at second temperature  131  may initiate the second stage AIM capsule  340 . The second stage AIM capsule  340  may in turn initiate the booster  322  in the rotor assembly  320 . The booster  322  may in turn initiate the detonation transfer line  350 . 
       FIG.  3    illustrates an uninstalled thermal trigger device  300 , while  FIG.  4    illustrates an installed thermal trigger device  300 , with an arming assembly in an armed position. The install interlock pin  331  provides an example interlock which prevents the thermal trigger device  300  from entering the enable mode unless the thermal trigger device  300  is installed. Those of skill in the art will appreciate that other interlock structures may be employed in some embodiments. Interlocks may be engaged when the thermal trigger device  300  is installed, and disengaged when the thermal trigger device  300  is not installed. 
     In the uninstalled thermal trigger device  300  illustrated in  FIG.  3   , the install interlock pin  331  remains in an extended position relative to housing  301 . The install interlock pin  331  is coupled with the rotor assembly  320  so that, when the install interlock pin  331  is in the extended position, the booster  322  is positioned out of line, in a different plane, from the output of the AIM capsule  340  and detonation transfer line  350 , as illustrated in  FIG.  3   . If the AIM capsule  340  were to fire in an uninstalled thermal trigger device  300  such as illustrated in  FIG.  3   , the rotor assembly  320  would block the output of the AIM capsule  340  and/or output of the booster  322  in the rotor assembly  320  so that detonation transfer line  350  would not be successfully activated. 
     In the installed thermal trigger device  300  illustrated in  FIG.  4   , the install interlock pin  331  is depressed into an engaged position relative to housing  301 . The install interlock pin  331  is coupled with the rotor assembly  320  so that, when the install interlock pin  331  is in the engaged position, the booster  322  is in a same plane as the output of the AIM capsule  340 , as illustrated in  FIG.  4   . However, the booster  322  is still out-of-line with the AIM capsule  340  and detonation transfer line  350 . 
     If the AIM capsule  340  were to fire in an installed thermal trigger device  300  such as illustrated in  FIG.  4   , the rotor assembly  320  may or may not block the output of the AIM capsule  340  to prevent activation of the booster  322  and the detonation transfer line  350  from successfully activating, depending on whether and booster  322  is rotated into an armed or disarmed position by rotor assembly  320 .  FIG.  4    illustrates booster  322  in an armed position, indicating that thermal actuator  310  has been activated at first temperature  101 , and thermal actuator  310  has therefor repositioned the rotor assembly  320  into the armed position. If the AIM capsule  340  were to fire with booster  322  in the armed position as illustrated in  FIG.  4   , the output of the AIM capsule  340  would activate booster  322  and the booster  322  would in turn activate the detonation transfer line  350 . 
     In some embodiments, the install interlock pin  331  may be replaced by, or supplemental to, a lock-out mechanism. Example lock-out mechanisms may generally prevent the thermal trigger device  300  from entering certain modes. For example, in some embodiments, a lock-out mechanism may prevent manual engagement of install interlock pin  331 . In some embodiments, a lock-out mechanism may prevent rotation or translation of the rotor assembly  320  or equivalent functionality. In some embodiments, a lock-out mechanism may prevent manual switching of thermal trigger device  300  into an enable mode, which is discussed in further detail in connection with  FIG.  5    and  FIG.  6   . Lock-out mechanisms may be disabled, e.g., by use of a special tool, key, or electronic signal, in order to install and enable thermal trigger device  300 . 
     When the thermal trigger device  300  is installed, the selector/indicator  330  may indicate when the arming assembly  320  is in a “safe” mode, an “enabled” mode, or an “armed” mode. In some embodiments, the selector/indicator  330  may be manually set to an “enable” position, which is discussed further in connection with  FIG.  5    and  FIG.  6   . When enabled, the multistage thermal trigger device  300  arms at the desired first temperature  101 . The thermal actuator  310  moves the arming slider  312 , which rotates the rotor assembly  320 . The mechanical barrier of a rotor assembly  320  sidewall rotates out of line, while the booster  322  in the rotor assembly  320  rotates in-line with the AIM capsule  340  and detonation transfer line  350 , as illustrated in  FIG.  4   . 
     In some embodiments, the thermal actuator  310  may contain, e.g., any thermal expansion or contraction material which expands or contracts when heated. In some embodiments, the thermal actuator  310  may contain a melt plug, eutectic material, or other thermally responsive material. In some embodiments, the thermal actuator  310  may contain a paraffin blend which may be customized to activate at a desired first temperature  101 . The paraffin blend may expand and contract to move thermal actuator  310  and arming slider  312 . Paraffin blend thermal actuators can be customized to actuate at desired arming temperatures up to, e.g., approximately 300° F. or higher. If the thermal stimuli is removed before reaching the critical temperature to activate AIM capsule  340 , the paraffin in the thermal actuator  310  may retract, returning the booster  322  in the rotor assembly  320  out of line with the AIM capsule  340 , and returning the mechanical barrier of a rotor assembly  320  sidewall back in line with the AIM capsule  340 , so the thermal trigger device  300  is again disarmed and re-safed. 
       FIG.  3    and  FIG.  4    illustrate various springs, including actuator return spring  311  and rotor assembly return spring  321 . Return springs  311  and  321  may return the thermal actuator  310  and rotor assembly  320  from the armed position to the disarmed position when the thermal actuator  310  is deactivated. The thermal actuator  310  may deactivate, for example, when the temperature drops below the first temperature  101  and the paraffin wax blend in the thermal actuator  310  contracts. The illustrated return springs  311  and  321  are one example means to return the rotor assembly  320  from the armed position to the disarmed position when the thermal actuator is  310  deactivated, however it will be appreciated that other means, such as magnets, compressible foam, electronic motors or otherwise, may replace or supplement the illustrated springs  311  and  321 .  FIG.  2    also illustrates a variety of other features which will be understood by those of skill in the art with the benefit of this disclosure. 
     The illustrated rotor assembly  320  is one embodiment of an arming assembly  120 , however it will be appreciated that other arrangements, such as slider assemblies, linear motion assemblies, piston assemblies, electrically activated assemblies, magnet assemblies, pivot assemblies and any number of other arrangements may be employed as an arming assembly  120 , with the benefit of this disclosure. When the illustrated rotor assembly  320  is in the disarmed position, the multistage thermal trigger device  300  has a mechanical barrier, in the form of a rotor assembly  320  sidewall, between the AIM capsule  340  and the detonation transfer line  350 . Furthermore, there is a mechanical barrier (a rotor assembly  320  sidewall) between the booster  322  and the detonation transfer line  350 . 
     In some embodiments, the AIM capsule  340  and booster  322  may contain “primary” explosives while the detonation transfer line  350  may comprise a “secondary” explosive. The illustrated example multistage thermal trigger device  300  includes a mechanical barrier between the primary and the secondary explosives. Such arrangements are particularly useful for scenarios in which certain primary explosives are not approved for use which is “in-line” with secondary explosives. In  FIG.  3   , the AIM capsule  340  and booster  322  are out of line with the detonation transfer line  350  due to the mechanical barrier of the rotor assembly  320  sidewall. 
     Booster  322  may be employed to boost the output of AIM capsule  340 . In some embodiments, the booster  322  may comprise a deflagrating or detonating propellant or explosive, e.g., boron potassium nitrate (BKNO 3 ), lead azide and/or hexanitrostilbene (HNS) or similar type propellants. When the rotor assembly  320  is repositioned into the armed position, the booster  322  is repositioned between the AIM capsule  340  and the detonation transfer line  350 . When the AIM capsule  340  fires, it activates the booster  322  which in turn activates the detonation transfer line  350  inserted in the detonation transfer line interface  351 . 
     It will be appreciated that booster  322  need not be included in some embodiments. For example, in an “inert barrier” embodiment, rotor assembly  320  may omit booster  322 , and rotor assembly  320  may instead simply remove an inert mechanical barrier between AIM capsule  340  and detonation transfer line  350 , so that AIM capsule  340  activates detonation transfer line  350  without the added benefit of booster  322 . In a “deflagration output” embodiments, booster  322  may comprise a material designed to burn rather than detonate. In another embodiment, the AIM capsule  340  output may activate a propellant or other type output assembly. 
     AIM capsule  340  may comprise an autoignition material or propellant that automatically ignites at a specified second temperature  131 . The second temperature  131  may comprise any temperature which is higher than the first temperature  101 . After the multistage thermal trigger device  300  is armed at the first temperature  101  as described herein, and as the temperature of the multistage thermal trigger device  300  increases past second temperature  131 , the autoignition material in the AIM capsule  340  ignites and triggers a pyrotechnic train to initiate the detonation transfer line  350  and ultimately to activate the application  160 . The AIM capsule  340  is described in further detail in connection with  FIGS.  7 - 10   . 
     While  FIGS.  3  and  4    illustrate a thermal actuator  310  and AIM capsule  340  as a first stage  110  and second stage  140 , respectively, this is only one example implementation and those of skill in the art will appreciate that other implementations are possible. For example, an electronic embodiment may use a thermometer and a computing device or electronic logic circuits to implement the first stage  110  and second stage  140 . The computing device may be adapted to activate an electronic motor to reposition arming assembly  120  when first temperature  101  is reached, and the computing device may be adapted to electronically activate an explosive or other output when second temperature  131  is reached. 
     While  FIGS.  3  and  4    illustrate a thermal actuator  310  and AIM capsule  340  as a first stage  110  and second stage  140 , respectively, this is only one example implementation and those of skill in the art will appreciate that other implementations are possible. For example, the AIM capsule output may be used to pressurize a cavity to activate an actuator, piston or stabber mechanism that in-turn activates the booster or detonator in the rotor assembly or output assembly. 
       FIGS.  3  and  4    illustrate an output assembly  150  implemented as the detonation transfer line  350 . The detonation transfer line  350  comprises an end tip which fits into detonation transfer line interface  351  in the thermal trigger device  300 . Detonation transfer lines may also be referred to as detonation cords, and include Flexible Confined Detonation Cord Assemblies (FCDCAs) and FCDCs, explosive transfer lines or assemblies, confined or flexible detonating cords or assemblies, and confined energy transfer lines. The detonation transfer line  150  may be activated by the AIM capsule  340  or booster  322 , via the rotor assembly  320 , when the AIM capsule  340  activates and the rotor assembly  320  is in the armed position and the booster  322  is activated. The detonation transfer line  350  cannot be activated by the AIM capsule  340  or the booster  322  when the rotor assembly  320  is in the disarmed position. 
     In some embodiments, multistage thermal trigger devices disclosed herein may respond within suitable temperature ranges in slow cook-off (SCO) and fast cook-off (FCO) environments, and may initiate thermally initiated venting systems to prevent catastrophic failure of solid rocket motors. An insensitive munition thermal sensor design, such as illustrated in  FIGS.  3  and  4   , may use autoignition material in a safe-and-arm assembly to self-initiate a pyrotechnic train to initiate a linear shaped charge. This approach decreases venting system complexity by decreasing the number of system and subsystem components, and can also provide fast and effective response times. Furthermore, example thermal trigger devices may optionally respond solely to thermal stimuli from the SCO/FCO event and need not require batteries or electrical input. Example trigger safe/arm assemblies may isolate the thermal sensing mechanisms from the linear shaped charge and prevent unintended initiation of the solid rocket motor venting system. This technology can be tailored for various solid rocket motor propellants with varying cook-off temperatures and is adaptable for thermally initiated venting systems, other venting mechanisms, and rocket motor safe-and-arm ignition systems. 
     Embodiments of this disclosure may implement any desired event sequencing within a multistage thermal trigger device, as a function of temperature. For example, in some embodiments, multistage thermal trigger devices may be designed activate the first stage  110  at a first temperature  101  around 100° C.-120° C., and to activate the second stage  140  at a second temperature  131  around 120° C.-140° C. Other examples may activate the first stage  110  and/or second stage  140  at higher or lower temperatures, with the proper event sequencing for the first and second stages  110 ,  140 , such that the first stage  110  is activated prior to the second stage  140  at all heating rates and in FCO. Multistage thermal trigger devices may arm at a first temperature  101  which is below the second temperature  131  at which the second stage  140  activates, in order to provide a desired margin below the second temperature  131  at which the AIM in the second stage  140  ignites, while also delaying arming as long as possible to maximize time for firefighter response. In FCO conditions, this margin may allow for proper event sequencing and a fast response time, e.g., within less than 1 minute, or within an amount of time otherwise shorter than cook off of a solid rocket motor. 
     In some embodiments, features of example multistage thermal trigger devices may include, inter alia: (1) thermal trigger device can be tuned to desired second temperature  131  by modifying AIM blend in AIM capsule  340 , (2) AIM capsule  340  may contain autoignition material or propellant in a hermetically sealable capsule to ensure stability, shelf life, and performance, and (3) thermal trigger device response temperature may be consistent or variable over SCO heating rates of 6° F./h, 45° F./h, 100° F./h and FCO 
       FIG.  5    and  FIG.  6    provide perspective views and top cross sectional views of an example multistage thermal trigger device, in accordance with at least some embodiments of the present disclosure. In  FIG.  5    and  FIG.  6   , like elements introduced in  FIG.  3    are assigned like identifiers.  FIG.  5    and  FIG.  6    illustrate, inter alia, housing  301 , selector/indicator  330 , rotor assembly  320 , detonation transfer line  350 , and AIM capsule  340 .  FIG.  5    and  FIG.  6    also illustrate a poppet  501 . 
     In  FIG.  5    and  FIG.  6   , the selector/indicator  330  comprises a safe mode, an enable mode, and an arm mode. In  FIG.  5   , the selector/indicator  330  is in safe mode, and the rotor assembly  320  is correspondingly in a disarmed orientation. In  FIG.  6   , the selector/indicator  330  is in armed mode, and the rotor assembly  320  is correspondingly in an armed orientation. 
     In the safe mode, the thermal actuator  310  may be decoupled from the rotor assembly  320 , or the rotor assembly  320  may be disabled or locked, so that the thermal actuator  310  does not move the rotor assembly  320  from the disarmed position to the armed position, even if the thermal actuator  310  is activated at the first temperature  101 . In some embodiments, the selector/indicator  330  may be manually switched from the safe mode to the enable mode. In some embodiments, the selector/indicator  330  may be mechanically switched from the safe mode to the enable mode, e.g., in response to engaging the install interlock pin  331 . 
     In the enable mode, the thermal actuator  310  is coupled with the rotor assembly  320 , or the rotor assembly  320  is otherwise enabled, so that the thermal actuator  310  does move the rotor assembly  320  from the disarmed position to the armed position when the thermal actuator  310  is activated at the first temperature  101 . However, the rotor assembly  320  remains in the disarmed position in enable mode, until rotor assembly  320  is repositioned into the armed position by thermal actuator  310 . Thus in the enable mode, the selector/indicator  330  may point to enable, while the rotor assembly  320  remains in the disarmed orientation shown at the right side of  FIG.  5   . 
     The selector/indicator  330  may indicate arming assembly status. In the arm mode, the selector/indicator  330  may point to arm as illustrated in  FIG.  6   , while the rotor assembly  320  has been repositioned into the armed orientation shown at the right side of  FIG.  6   , by operation of thermal actuator  310 . 
     In some embodiments, the multistage thermal trigger device  100  may include a selector for selecting between safe and enable modes, and a separate indicator for indicating whether the thermal trigger device  100  is disarmed or armed. In the illustrated embodiment, the “safe” and “enable” modes may be manually selected, and the multistage thermal trigger device enters indicates “arm” when the thermal actuator  310  arms the thermal trigger device  100 . Thus, unlike “safe” and “enable”, “arm” is not human selectable in such embodiments. Instead, “arm” is indicated responsive to activation of the thermal actuator  310 . Of course, embodiments are also possible in which the thermal trigger device  100  may be manually armed, e.g., by moving selector/indicator  330  into arm mode. 
       FIG.  5    and  FIG.  6    also illustrate a poppet  501 . In  FIG.  5   , the poppet  501  remains unpopped, while in  FIG.  6   , the poppet  501  has popped. Poppet  501  may be adapted to have sufficient friction with housing  301  or a locking feature to generally hold poppet  501  in place once extended, while allowing poppet to move between the unpopped and popped positions under sufficient force. Poppet  501  indicates if any of the propellant or explosive components, such as AIM capsule  340  or booster  322 , have initiated and/or if the thermal trigger device  100  has functioned. The initiation of any of the propellant or explosive components will force poppet  501  outward into the popped position illustrated in  FIG.  6   . In some embodiments, one or more additional poppets may be incorporated into thermal trigger device  100 , e.g., to indicate whether thermal trigger device  100  is armed or has been previously armed. It will be appreciated that poppets are one structure for achieving desired indications, and that other structures, such as other expanding, extendable, or deformable structures, may provide similar indication functions. 
       FIG.  7    illustrates an example AIM capsule which may be included in a multistage thermal trigger device, and  FIG.  8    illustrates a side cross sectional view the example AIM capsule illustrated in  FIG.  7   , in accordance with at least some embodiments of the present disclosure. AIM capsule  700  may be included in a multistage thermal trigger device  300 , e.g., as AIM capsule  340 . The illustrated AIM capsule  700  includes a hermetically or environmentally sealed capsule formed by the illustrated capsule body  701  and capsule closure assembly  702 . The illustrated AIM capsule  700  further includes an AIM mixture  703  or propellant disposed inside the AIM capsule  700 ; an AIM capture assembly  704  comprising, e.g., a gas permeable retainer system which retains the AIM mixture  703  in position; a stabilizer  705  such as a desiccant to remove moisture or a molecular sieve to trap gases formed during storage, aging, or use of AIM capsule  700 ; a burst orifice  706  for gas output upon activation of the AIM mixture  703 , and an orifice disc retainer  707 . The illustrated AIM capsule  700  may further include a port interface  708 , e.g., threads or a particular interface shape for screwing or otherwise engaging the AIM capsule  700  in a thermal trigger device  300 . 
     In  FIG.  7    and  FIG.  8   , the AIM mixture  703  may include, e.g., an off-the-shelf autoignition material or propellant that is blended with a propellant booster such as boron potassium nitrate (BKNO 3 ). The AIM mixture  703  selection determines the response temperature (the second temperature), which may be adapted to suit desired temperature response requirements. The AIM mixture  703  may be blended with a booster selected based on the thermal output or pressure output needs for the pyrotechnic train or percussion primer to the detonation transfer line  350  or other output assembly. 
     In  FIG.  7    and  FIG.  8   , the AIM capture assembly  704  may comprise a breathable filter that retains the AIM mixture  703  having particle sizes as low as &lt;10 μm while allowing penetration of gases that form during storage and/or use of the AIM capsule  700 . Any of a variety of materials may be used for the breathable filter. For example, in some designs, the breathable filter may comprise a cellulose material, e.g., a filter paper. In some designs, the breathable filter may comprise a metal mesh. 
     In  FIG.  7    and  FIG.  8   , the orifice disc retainer  707  may provide a hermetic or environmental seal which may meter the gases and pressure inside the AIM capsule  700  during operation. 
       FIG.  9    illustrates a side cross sectional view of another example AIM capsule, prior to activation of the AIM capsule, which may be included in a multistage thermal trigger device; and  FIG.  10    illustrates a side cross sectional view the example AIM capsule illustrated in  FIG.  9   , after activation of the AIM capsule, in accordance with at least some embodiments of the present disclosure.  FIG.  9    and  FIG.  10    include a capsule body  901  and capsule closure assembly  902 ; an AIM mixture  903 ; an AIM capture assembly  904 ; a stabilizer  905 ; a burst orifice  906 , an orifice disc retainer  907 ; and a port interface  908 . 
     In embodiments according to  FIG.  9    and  FIG.  10   , the AIM capsule  900  may comprise two main parts: a slidable capsule body  901  inside a capsule closure assembly  902 , wherein the slidable capsule body  901  slides outward from the capsule closure assembly  902  upon activation of the AIM mixture  903 .  FIG.  9    illustrates the AIM capsule  900  prior to activation, while  FIG.  10    illustrates AIM capsule  900  after activation. In  FIG.  10   , the AIM capsule  900  has functioned and activated an integral extendable feature so that the AIM capsule  900  is in an extended position to indicate that it has functioned. The AIM capsule  900  may expand upon pressurization and serve as an indication that the AIM capsule  900  has been fired or is used or spent (inert). Various other elements such as a housing cap, sealing o-rings, hoopster snap ring, and dampening o-ring may stabilize and retain the slidable capsule body  901  inside the capsule closure assembly  902 . 
     In  FIGS.  7 - 10   , the stabilizer  705 ,  905  may be disposed inside a holder assembly. The stabilizer and holder assembly do not obstruct gas flow out of the AIM capsules  700 ,  900  when the AIM mixture  703 ,  903  is activated. For example, the stabilizer  705 ,  905  may comprise a molecular sieve which may be sufficiently loose, permeable, and weakly bonded so that it is displaced when the AIM mixture  703 ,  903  is activated. The stabilizer  705 ,  905  may absorb any AIM mixture  703 ,  903  gaseous constituents or products or water which may evaporate out of the AIM mixture  703 ,  903  or may otherwise be trapped in the AIM capsules  700 ,  900 . The stabilizer  705 ,  905  may include, e.g., a gas absorbing material such as a zeolite or silica. This serves to trap gases or water vapor that are formed or present during storage, aging or use of the AIM mixture  703 ,  903 . 
     While a variety of dimensions, volumes, and materials may be used in different embodiments, a weight of the AIM mixture  703 ,  903  may be, e.g., between 0.001 milligrams and 100,000 milligrams. A volume ratio of headspace volume to AIM mixture  703 ,  903  ullage volume may be, e.g., less than 50:1. In some embodiments, the volume ratio of headspace volume to AIM mixture  703 ,  903  ullage volume may be less than 20:1. The AIM capture assembly  704 ,  904  may comprise, e.g., a cellulosic fabric, a filter paper, or a metal mesh as noted herein. In some embodiments, the AIM capture assembly  704 ,  904  may comprise a Teflon or Polytetrafluoroethylene (PTFE) seal, e.g., in combination with the cellulosic fabric, filter paper, or metal mesh. The AIM mixture  703 ,  903  may comprise an autoignition composition designed to initiate combustion of a main pyrotechnic charge in a gas generator, pyrotechnic device, pyrotechnic train, or explosive train exposed to flame or a high temperature environment. The autoignition composition may include a mixture of an oxidizer and a metal or organic fuel. As an example, the autoignition composition may comprise a metal nitrate salt, metal chlorate, metal perchlorate, ammonium perchlorate, a salt nitrite, organic nitrate, organic nitrite, or a solid organic amine, and the fuel and oxidizer may be present in amounts sufficient to provide a desired autoignition temperature. One example is disclosed in U.S. Pat. No. 5,959,242. Any propellant, autoignition material, co-melt, eutectic material, thermite material, or material that is thermally responsive at a specific temperature range and provides a heat, deflagration or explosive output may be used in AIM mixture  703 ,  903 . The autoignition material may optionally be blended with a propellant booster material such as BKNO 3  or other propellant or explosive booster. For example, the autoignition material to propellant booster weight ratio may range from: autoignition material:propellant booster=1:99 (wt:wt) to an autoignition material:propellant booster=99:1(wt:wt). In some embodiments, the booster may optionally be separated from the AIM mixture  703 ,  903  within the AIM capsules  700 ,  900 . 
     In some AIM capsule embodiments, the AIM mixture  703 ,  903  may be packaged in a configuration that allows for a hermetic seal to provide a minimum shelf life of 5 or more years and is compact to minimize the trigger weight and volume. Both the stability and performance of the AIM mixture  703 ,  903  may be dependent on the packaging configuration. Relevant AIM capsule parameters which affect AIM performance include but are not limited to: (i) ullage volume ratio, (ii) AIM blend, (iii) gas and moisture traps, and (iv) capsule (packaging) materials. Adjustment of these parameters may allow tuning of the trigger response temperature in small increments over a wide temperature range from about 90° C. to above 170° C. 
     Finally, all of the components of an AIM capsule such as illustrated in  FIGS.  7 - 10    may optionally be made of materials that are compatible with the AIM mixture  703 ,  903 . For some applications, the materials may be compatible with acidic components or oxidizing components such as nitric acid or nitrate salts, and transition metals such as molybdenum or nickel, platinum group metals such as silver. All components of the AIM capsule may for example be made from titanium, PTFE, Teflon©, stainless steel, silica-alumina, 4 A zeolite, or cellulosic material. 
     While certain example techniques have been described and shown herein using various methods, devices and systems, it should be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from claimed subject matter. Additionally, many modifications may be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular examples disclosed, but that such claimed subject matter also may include all implementations falling within the scope of the appended claims, and equivalents thereof.