Patent Application
20090114110
The invention is related generally to safe and arm devices, adaptive structures therewith and reliability features therefor. More particularly, embodiments of the invention are related to electromechanical safe and arm devices, such as a booster assembly, having dual fault tolerant safety and reliability features that may be used individually or as part of a system requiring maximum degrees of safety and reliability desirable for connection to solid propellant or igniter engines.
Reusable solid rocket motors (RSRM) used for launching and controlling spacecraft for human and non-human rated flight utilize safe and arm devices to control unwanted ignition of the rocket motor. These conventional safe and arm devices include a mechanical barrier, an initiator and a so-called “booster charge” or ignitable composition. The mechanical barrier may be positioned between a so-called “safe” position and a so-called “arm and fire” position. The safe position prevents an inadvertent so-called “firing” or detonation action of the initiator from being propagated along a so-called “fire path” to the booster charge. The arm and fire position allows firing of the initiator upon receipt of a proper mechanical or electrical impulse to be propagated along the fire path to ignite the booster charge. The safe and arm device is conventionally flanged mounted into an end of the RSRM and sealed thereto with a flange gasket made from leather or other suitable material for flange gaskets. In other applications, the safe and arm device may also be directly mounted into a housing of an igniter, which is also mounted in the RSRM.
A conventional safe and arm device 900 as shown in
The barrier base assembly 904 also includes leak test ports 922 for testing or monitoring redundant shaft seals 924 located on a shaft of the mechanical barrier 906 and redundant initiator seals 926 located between each initiator 908 and 928 and the barrier base assembly 904. The seals 924, 926 help to prevent energy coming from the motor of the RSRM (not shown) from escaping through the barrier base assembly 904 during combustion, to contain energy within the barrier base assembly 904 in the event of inadvertent initiator firing and to protect the internal compartments of the barrier base assembly 904 from corrosion. The flange gasket 930 in broken lines provides a seal between the motor of the RSRM and the flange 931 of the safe and arm device 900. The flange gasket 931 also helps prevent energy from escaping from the motor of the RSRM during combustion. While the flange gasket 930 is highly reliable, it is desirable to monitor or verify the adequacy of the seal between the RSRM and the safe and arm device.
In addition to being used with the motor of an RSRM, the safe and arm device 900 may be used with a jettison motor (not shown) of an aircraft or other vehicle in flight. Conventional safe and arm device 900 includes two initiators 908, 928, one of which provides single redundancy should one of the initiators fail to fire when receiving the proper mechanical or electrical impulse. Accordingly, it is also desirable to provide a safe and arm device 900 that provides further redundancy should both initiators fail to fire, especially when the safe and arm device 900 is used with jettison motors or other motors that necessitate increased reliability.
Further, the manual safing mechanism 918 of the actuation and monitoring assembly 902 allows a safing pin (not shown) to be installed into the manual safing mechanism 918 by rotating the mechanical barrier 906 to the safe position and then locking the safing pin into the manual safing mechanism 918. The safing pin physically prevents the mechanical barrier from positioning (rotating) into the arm and fire position beyond, i.e., out of, the so-called “sure-safe” region. The sure-safe region also includes the safe position. The “sure-safe” region is determined by the required degrees of safety and reliability as may be defined in Naval Ordnance (NAVORD) report 2101 and the Bruceton testing procedure. Conventional wisdom with respect safety concerns and avoidance of unintentional firing by a conventional safe and arm devices, such as conventional safe and arm device 900, may require greater than five degrees of safety and reliability when the mechanical barrier 906 is positioned in the so called “sure-safe” region. For the conventional safe and arm device 900, six degrees of safety and reliability is achieved when the mechanical barrier is rotated at least 26.3 degrees away from the fire and arm position toward thesafe position. In this respect, when the mechanical barrier 906 is positioned between 0 and 66 degrees, 66 and 74 degrees or 74 and 90 degrees, the safe and arm device 900 is respectively in the safe position, an unknown position or the fire and arm position. When installed properly, the safing pin ensures that the mechanical barrier 906 cannot be rotated out of the “sure-safe” region. However, because of tolerance between gears and mechanical engagement requirements of the manual safing mechanism 918, the mechanical barrier 906 may be rotated toward the fire and arm position approximately 30 degrees by the electromotive drive 914 of the actuation and monitoring assembly 902. While the manual safing mechanism 918 physically ensures that the mechanical barrier 906 is secured within the “sure-safe” region of the safe position thereby allowing the degrees of safety and reliability to be adequately maintained until the safing pin is removed, indication by sensor signal may be lost because the mechanical barrier 906 is rotated beyond the indication limits of the electrical position switches 910, 916. (conventionally set for indicating approximately 10 degrees of rotation from either the arm and fire position or the safe position). In this regard, while the safing pin is installed, the mechanical barrier 906 may be in the “sure-safe” region, but rotated beyond the indication capabilities of the position switches 910, 916. Accordingly, it would also be of advantage to provide a safing pin and safing assembly 918 (with an accompanying gear arrangement) that limits rotation of the mechanical barrier 906 to within the rotational limits of the electrical position switches 910, 916 in order to provide positive indication (physical indication and electrical indication) of the safe position when the mechanical barrier 906 is within the “sure-safe” region while providing a so-called “lock” to prevent the mechanical barrier 906 from rotating into the arm and fire position even when commanded by the electromotive drive 914 of the actuation and monitoring assembly 902.
The ignitable composition of the so called “booster charge” of the safe and arm device 900 is contained between the pellet basket 912 and barrier base assembly 904. The ignitable composition may be a packet of boron potassium nitrate (BKNO3) pellets, such as a Velostate™ bag with BKNO3 therein. The pellet basket 912 includes a cylindrical housing having two open ends and fastener ports for receiving retaining bolts 932 therethrough. The packet of BKNO3 pellets is received into the cylindrical housing at one open end and a diffuser plate is coupled to the other open end. The open end of the pellet basket 912 is coupled to the barrier base assembly with the bolts 932. The diffuser plate allows energy from the ignitable composition when combusting to be axially expelled from the pellet basket 912. It is necessary to use care in properly assembly the pellet basket 912 so as to avoid loss of ignitable material. Further, to ensure that the “fire-path” through the mechanical barrier 906 is correct when positioned in the arm and fire position, the pellet basket must be adequately located, aligned and secured to the booster base assembly 904. Accordingly, it would be of additional advantage to provide a safe and arm device that includes a pellet basket that is modular in design and self-contained, enabling attachment of pellet baskets containing different amounts of the ignitable composition to the booster base assembly. Moreover, it is also desirable to provide a pellet basket that includes a self-locating feature for ensuring proper, i.e., determinate, alignment of the “fire-path” between the initiator, mechanical barrier and the pellet basket. Furthermore, it is desirable to provide a pellet basket that includes a modular or standardized housing that enables coupling with the booster base while allowing different amounts of ignitable composition to be inserted therein. Still, it is desirable to provide a modular housing that self contains an ignitable composition for ready attachment to the booster base and the modular housing may be designed to further enhance directed diffusion of energy therefrom when the ignitable material is combusted.
An embodiment of a safe and arm device includes the ability to verify and monitor the adequacy of a seal between the safe and arm device and its mounting upon a rocket motor, double redundancy (dual fault tolerant initiation) using at least three initiators in the safe and arm device, positive indication of safe position within the limits of switch contacts when a safing pin is installed in to a safing assembly, and a standardized unitary booster basket assembly allowing for a modular ignitable composition.
Embodiments of the safe and arm device includes a booster base assembly having a booster base housing and a barrier. The booster base housing includes an axis, a shaft port extending substantially in line with the axis, at least three initiator ports located about the axis, and a matching number of explosive transfer paths in respective communication with the at least three initiator ports. The barrier includes a matching number of like-spaced fire-train transfer ports and an axially aligned drive shaft. The drive shaft of the barrier is coupled within the shaft port of the booster base housing allowing the barrier to be rotationally positioned about the axis into at least one of a safe position and an arm and fire position and, in the latter position, allowing the fire-train transfer ports to be substantially aligned with the matching number of explosive transfer paths.
Embodiments of a safe and arm device include booster basket assemblies comprising structures including a modular interface structure for connection to the booster base assembly for containing and burning varying quantities of a combustible material without modification to the booster base assembly. The booster basket assemblies may be preloaded with the combustible material prior to connection to the booster base assembly.
The features of the safe and arm device will become apparent when viewed in light of the detailed description of the various embodiments of the safe and arm device when taken in conjunction with the attached drawings and appended claims.
Reference will now be made to the Figures, wherein like numerals refer to like features and elements throughout. It will be appreciated that these Figures are not necessarily drawn to scale.
One embodiment of the invention comprises a safe and arm device offering double redundancy in a firing and safety system particularly suited for applications of critical motor initiation, such as igniting a reuseable solid rocket motor (RSRM) or providing for flight crew evacuation with a jettison motor abort or attitude control motors. The safe and arm device provides three independent initiators that may be fired concurrently to initiate burning the fuel in a motor. Where general requirements for conventional safe and arm devices have assumed the need for 90 degree of physical rotation of a mechanical barrier between a safe position and an arm and fire position for a safe and arm device in order to meet the required degrees of safety and reliability as defined in Naval Ordnance (NAVORD) report 2101 and the Bruceton testing procedure limiting the rotation of the blocking device to 90 degree rotation and the number of initiators to two separated by 180 rotational degrees, embodiments of the safe and arm device of the invention achieve the required safety and reliability by providing a barrier requiring only about 60 degrees of physical rotation while also advantageously providing three initiators rotational separated by 120 degrees. The three initiators advantageously increase the reliability for successfully “firing” the safe and arm device by providing dual backup, should one or two of the initiators fail to fire, with the second and third initiators. In this respect, the safe and arm device of the invention may tolerate two defective initiators without loss of “firing” capability thereby achieving a device having dual fault tolerance. The safe and arm design of embodiments of the invention also provides redundant monitoring of barrier position and provides a safing assembly to lock the barrier in the safe position in a manner monitorable by position switches. Further, the safe and arm device of embodiments of the invention comprises, in combination, a booster base assembly and an arm and motor assembly which enables the arm and motor assembly to be reused after certification to save expense, while enabling design of the booster base assembly to handle the most severe expected operating conditions for a single use. Advantageously, by designing the booster base assembly for single use while providing a separate, reusable assembly for the arm and motor assembly, the total cost of manufacturing is significantly reduced, as is overall device weight of the safe and arm device.
Embodiments of the safe and arm device of the invention offer improved mounting and sealing with associated rocket motors to contain motor gases under expected operational pressure. The safe and arm device utilizes cylindrical seals to provide sealing contact with a rocket motor that deviates from conventional rocket motor designs, such as a flange and gasket of the conventional RSRM. In this regard, a collar protrudes from the bottom of a flange of a booster base housing and includes redundant seal grooves on the outer cylindrical surface of the collar for receiving redundant O-ring seals therein to seal against an inside cylindrical surface of the rock motor mounting. Use of the collar in the booster base housing enables configuration of a booster basket assembly that fits into an inner port of the collar and abuts against a barrier of the booster base assembly to enable standardized attachment of the booster basket assembly while providing unitary assembly thereof In this regard the booster basket assembly, together with a contained ignitable composition, provides a modular component that may include determinant assembly features for increasing the safety and reliability of assembling the booster basket assembly with the booster base. The booster basket assembly according to embodiments of the invention may be sized and shaped to accommodate various combustible compositions while providing a standardized attachment structure for engagement with the collar of the booster base assembly.
In the safe position (not shown), the barrier 20 is rotationally positioned to block propagation of an energy wave between the explosive transfer path 24 and the cavity 42 of the booster basket 40 should an inadvertent firing occur of one or more of the initiators 30. In this respect, the barrier 20 may includes ullage cavities 26 providing additional expansion volume for receiving and containing the inadvertent energy wave propagated from the explosive transfer path 24, while preventing the energy wave from communicating with the cavity 42 of the booster basket 40. In this regard, while not shown in the figures, as the barrier 20 is rotationally positioned into the safe position, each of the ullage cavities of the barrier 20 align with respective explosive transfer paths 24, while the fire-train transfer ports 22 in the barrier 20 are made non-communicative with the explosive transfer paths 24. Each ullage cavity 26 allows absorption of the energy wave if released from one or all of the initiators 30. Also, the safe and arm device 10 includes ullage chambers 28 in communication with the ullage cavities 26 when the barrier 20 is rotationally positioned into the safe position which provides additional expansion volume to further absorb energy. The ullage cavities 26 and the ullage chambers 28 allow expanding gas, and other energy, to be contained during an inadvertent charging of the initiators 30 when the harrier 20 is not in the arm and fire position.
The safe and arm device 10 is configured to position the barrier 20 through a range of rotation from the arm and fire position to the safe position in order to provide a margin of safety sufficient to comply with or exceed requirements of National Aeronautics and Space Administration (NASA) human rated flight systems. The safe and arm device 10 advantageously includes three initiators 30 providing dual redundancy as described above. Where the conventional safe and arm devices provide single redundant initiation by providing two initiators that require a barrier to be rotationally positioned through a range of 90 degrees motion in order to meet NASA requirements, the safe and arm device 10 advantageously provides dual fault initiation by providing at least three initiators 30 requiring the barrier 20 to be rotationally moved through only approximately 60 degrees of motion while exceeding NASA minimum degrees of safety and reliability requirements.
The safe and arm device 10 comprises an arm and motor assembly 12 and a booster base assembly 14. The arm and motor assembly 12 is coupled axially to the booster base assembly 14 by fasteners 16, allowing an output shaft 13 of arm and motor assembly 12 to be directly aligned with and coupled to a harrier drive shaft 21 of the barrier 20. Advantageously, space is conserved and optimized by having the safe and arm device 10 comprised of two assemblies 12 and 14, where the two assemblies allow alignment of the drive train directly or at 90 degree mounting.
Before describing the booster base assembly 14, the arm and motor assembly 12 are described both with continued reference to
The arm and motor assembly 12 provides an electro-mechanical drive system 220 for rotationally positioning the barrier 20 about the axis 18 as described above. The electro-mechanical drive system 220 includes a conventional gear motor 224 to drive a conventional gear and transmission system 226 that applies torque to the output shaft 13 and through barrier drive shaft 21 to rotationally move the barrier 20 from the safe position to the arm and fire position as shown in
The clutch assembly 228 is conventional in that it comprises a clutch plate, made from a material, such as a polymeric material or ceramic, compressively retained between the gear 72 and a pressure disk. The pressure disk supplies force, i.e., to generate torque, upon the clutch plate from a Belleville spring, or washer, that is compressively loaded by a clamping collar that is threaded onto the arbor of the intermediate shaft 230. The clamping collar may be rotated on and then secured to the arbor to achieve an appropriate release torque in the clutch assembly. The clamping collar may be secured to the arbor with a fastener once the desired torque level is set. The fastener may include, but is not limited to, a locking pin, set screw, jam nut, Locktite®, and epoxy, for example, and without limitation. The intermediate shaft 230 is coupled to the arm and motor housing 70 by bearing assemblies (not shown).
The intermediate shaft 230 includes a gear 234, such as a helical gear, bevel gear and spiral bevel gear for example, and without limitation, that rotationally engages a corresponding gear 76 on the output shaft 13 to provide a perpendicular oriented drive train 220 for improved utilization of space and utility for coupling with the booster base assembly 14. The output shaft 13 is rotationally supported and coupled to the arm and motor housing 70 by bearing assemblies 78 and axially secured therein by a fastener (not shown), such as a snap ring. The gear 76 transfers torque from the gear motor through the intermediate shaft 230 to directly drive the output shaft 13. The output shaft 13 is oriented at 90 degrees to the intermediate shaft with a gear ratio of 1:1. This gear ratio of 1:1 advantageously provides an equivalent rotational motion for the stop arms 74 as for the barrier 20. It is recognized that the gear ratio may be increased or decreased in order to change the fidelity of the switch mechanism. Optionally, the stop arms 74 and intermediate shaft may have greater or lesser rotational travel than the 60 degrees provided, particularly when the gears include a gear ratio compensating for rotationally positioning the barrier 20 between the safe position and the arm and fire position. The rotational motion allowed for the stop arms 74 and intermediate shaft may also be affected by the rotational spacing between all initiators 30 provided upon the booster base assembly 14.
The intermediate shaft 230 also rotates switch or rotor contacts (not shown) of a double stacked switch 80 that is coupled to the arm and motor housing 70. The double stacked switch 80 provides electrical sensing of the position of the barrier 20, particularly when either in the safe position and the arm and fire position. One of the rotor contacts provides contact closure when the intermediate shaft 230 has rotated the barrier 20 approximately between 0 and 10 degrees from the safe position, and provides an open, i.e, no contact closure when the intermediate shaft 230 has rotated the barrier 20 beyond 10 degrees from the safe position. The other rotor contact provides contact closure when the intermediate shaft 230 has rotated the barrier to within approximately 10 degrees (substantially between 50 to 60 degrees rotation from the safe position) of the arm and fire position. Optionally, the rotor contacts may be configured for contact closures or opens over a greater or lesser extent than the 10 degree ranges indicated herein. The double stack switch 80 may also provide an electrical current path from a command control system (not shown) to power the gear motor when positioning the barrier 20 between the safe position and the arm and fire position. Desirably under normal operational conditions, the electrical continuity may be interrupted to the gear motor 224 when the barrier 20 is within 3-6 degrees of the desired rotational position to prevent a “stall” condition in the gear motor or to prevent unnecessary slipping of the clutch assembly 228. However, the arm and motor assembly 12 may drive the gear motor 224 to the maximum rotational extent in either direction by allowing the clutch assembly 228 to slip when the stop arms 74 engage end stops (not shown) within the arm and motor housing 70. It is recognized that other switches or position indicators may be used to in arrangements different from the double stacked switch 80 as illustrated, and may further include a single switch or multiple switches. It is also recognized that the double staked switch 80 may include additional functions or monitoring positions utilizable to advantage in or to resolve rotation angle or control motor speed, such as with an encoder.
Further, a locking gear 82 and a visual position indicator 84 are coupled to the intermediate shaft. The visual position indicator 84 is mounted inside of a cover 85 coupled to the arm and motor housing 70. The cover 85 includes a lens 86, such as a mineral glass window, to allow personnel working on or near the device to ascertain by direct observation whether the safe and arm device 10 is in the safe position or in the arm and fire position. Typically, the visual position indicator 84 includes a surface (not shown) that rotationally transitions directly with the intermediate shaft 230 to provide a visual indicia of position. The visual indicia may include red color and or the letter “A” to indicate the arm and fire position, and green color and or the letter “S” to indicate the safe position.
The locking gear 82 actuates a safing pin assembly 90. Reference may also be made to
A safing pin 98 may be inserted into or removed from the safe pin adapter housing 96 on the opposite side thereof from the rack shaft 94 when the locking gear 82 is rotationally positioned in the direction of the safe position. The safing pin 98 includes an “L” shaped slot 99 that engages the pin 97 of the safe pin adapter housing 96 when removing and inserting the safing pin 98 into the safe pin adapter housing 96. The slot 99 allows the safing pin 98 to be rotated approximately a quarter turn at the base of the “L” when fully inserted into the safe pin adapter housing 96 and engaged against a biasing spring (not shown) to bring the pin 97 longitudinally into retaining contact with a retention slot 95 of the safing pin 98 at the end of retention slot 95. The biasing spring is coupled within the safe pin adapter housing 96 to provide a retention force against the safing pin 98. When the safing pin 98 is installed, engagement between the retention slot 95 and the pin 97 prevents removal of the safe pin 98 from the safe pin adapter housing 96 when an arm and fire position is commanded to the gear motor. The safing pin 98 thus prevents the locking gear 82, by way of the rack gear 92, from rotating the intermediate shaft and moving the barrier 20 out of the safe position. Also, the biasing spring supplies a retention force upon the safing pin 98 in order to hold the pin 97 in contact with the retention slot 95, which help prevents the safing pin 98 from being removed accidentally from the safe pin adapter housing 96. The safing pin 98 may only be removed when a safe signal is applied to the gear motor or when the barrier 20 is in the safe position. The safing pin 98 cannot be removed from the safe pin adapter housing 96 when an arm signal is commanded to the gear motor 224 which supplies torque to the rack gear 92, causing force to be applied to the rack shaft that forces the retention slot 95 against the pin 97.
An arm signal command may be given to the gear motor 224 after insertion of the safing pin 98 into the safe pin adapter housing 96 causing the rack gear 92 to rotate and provide additional locking force upon the pin 97 by way of the retention slot 95, which helps to prevent the intentional or unintentional removal of the safing pin 98. In supplying the arm signal command, the rack gear 92 supplies the necessary locking force while only allowing the barrier shaft 21 to be rotated about 4 degrees within the safe position in order to maintain the barrier 20 in a safe position that is well within NASA minimum degrees of safety and reliability requirements. As described above, conventional safing pins and saying pin assemblies require the shaft of a barrier to be rotated up to 30 degrees to lock the sating pin into the housing of the safing pin assembly, a degree of rotation which provides no indication of barrier position from the switch or switch stack assemblies employed in the safe and arm device because the switch stack assemblies are rotated beyond the contact closure limits when in the safe position and are yet within the contact closure limits of the arm and fire position. Advantageously, the rack gear 92 may be sized to provide necessary locking force upon the safing pin 98 by allowing the barrier 20 to be rotated to a greater or lesser extent than the 4 degrees indicated. However, it is desirable to size the rack gear 92 to prevent rotation of the barrier 20 beyond about 10 degrees of the safe position in order to receive positive indication that the contacts of the double stacked switch 80 are closed, allowing independent, remote verification that the barrier 20 is still within the safe position.
The arm and motor assembly 12 also includes between its various components o-ring seals (not shown) to help provide protection from atmospheric corrosion during storage and operation of the safe and arm device 10. To further protect the arm and motor assembly 12 from internal corrosion, a dill valve 88 is provided in the arm and motor housing 70. The dill valve 88 may be used to evacuate and pressurize internal spaces of the arm and motor housing 70 with a gas such as nitrogen gas, which is inert and helps to prevent atmospheric and galvanic corrosion.
Referring to
Referring to
Further to the description given above, referring to
As shown in
Initiators 30 may comprise a NASA standard initiator (NSI) or any other suitable initiator. An example of an initiator suitable for use with the safe and arm device 30 is disclosed in U.S. Pat. No. 6,992,877, titled “Electronic switching system for a detonation device,” the entire disclosure of which is incorporated herein by reference.
Redundant seals 32, such as o-ring seals, are provided between each initiator 30 and its initiator port 31 to help minimize or prevent pressure and hot gases coming from combusting fuel in the rocket motor from escaping through the booster base assembly 14. As in the case of collar 52, a leak check port 34 is provided for testing and verifying the integrity of the seals 32.
As mentioned above, the barrier 20 is rotationally positioned about the axis 18 by the barrier shaft 21. The barrier shaft 21 and barrier 20 as illustrated are made from a unitary piece of material, but may also be made from multiple pieces of material that are coupled together. The barrier shaft 21 is closely slidably contained by the bearing surface of the shaft port 60 in the booster base housing 15. The shaft port 60 is centered substantially symmetrical about the axis 18.
The drive shaft 21 may include grooves 62 and 63 that each include a seal 64, such as an O-ring, and a backing ring 65, such as a high-temperature V-rings disposed between the wall of the shaft port 60 and drive shaft 21 to help minimize or prevent pressurized, combusting fuel in the rocket motor from escaping through the booster base assembly 14. As in the case of collar 52, a leak check port 66 is provided between grooves 62 and 63 for testing and verifying the integrity of the seals 64.
A rotor stop arm 58 directly coupled to the barrier shaft 21 limits the rotation of the barrier 20 to approximately 60 degrees by being physically limited to rotationally travel within a slotted channel within a cover 59 securely fastened to the booster base housing 15. However, the rotor stop arm 58 may limit rotation of the barrier 20 to a greater or lesser extent than the 60 degrees described in the case of other designs within the scope of the invention. In this respect, the rotor stop arm 58 is held in position with the cover 59 and restrains the limited motion of the barrier 20 about the axis 18 by limiting the extent of rotational travel by the rotor stop arm 58. The cover 59 is coupled to the booster base housing 15 by fasteners (unnumbered).
The drive shaft 21 also rotates rotor contacts of a switch 67. The switch 67 is coupled to an inside cavity 17 of the booster base housing 70. The switch 67 provides electrical sensing of the position of the barrier 20, particularly when positioned in the safe position and the arm and fire position. The switch 67 may be a single switch or a double stacked switch, but includes at least two rotor contacts. One of the rotor contacts provides a contact closure when the drive shaft 21 has rotated the barrier 20 between 0 and 10 degrees from the safe position, and provides an open connection when the intermediate shaft has rotated the barrier 20 beyond 10 degrees from the safe position. The other rotor contact provides a separate signal indicating contact closure when the barrier shaft 21 has rotated the barrier 20 to within 10 degrees (50 to 60 degrees rotation from the safe position) of the arm and fire position. Optionally, the rotor contacts may be configured to have contact closures or opens to a greater or lesser extent than the 10 degrees indicated herein. It is recognized that other switches or position indicators different from the switch 67 as illustrated may be used.
A cover 19 coupled to the booster base housing 15 contains the inside cavity 17 and allows a seal (not shown) to be maintained between the arm and motor housing 70 and the booster base housing 15 when the arm and motor assembly 12 is coupled to the booster base assembly 14, respectively. A dill valve 89 may also be coupled to the booster base housing 15 to allow the inside cavity 17 to be charged with a gas, such as nitrogen, to protect the internal components from corrosion during storage and operation of the safe and arm device 10.
Electrical ports (not shown) are provided in the arm and motor housing 70 and the booster base housing 15 for mounting electrical connectors (not shown) that are respectively electrically coupled to the contacts (not shown) of the switches 67 and 80, and supply power to the gear motor.
To facilitate positioning of the barrier 20 as described above, the barrier 20 may include a series of detents (see reference numeral 950 as shown in
While many of the components mentioned herein may be made from stainless steel, including other metallic materials for example, it is desirable to make the booster base housing 15, the booster basket assembly 40 and the arm and motor housing 70 out of an aluminum, such as 2024-T351 aluminum alloy, in order to decrease the weight. The material of all components mentioned herein may be made from materials that are generally suitable for safe and arm devices and, particularly, those materials that are generally known to a person having ordinary skill in the art.
Reference may now be made to
Optionally, a seal 47 may be provided between the flange surface 49 of the collar 52 and the flange 43 of the basket housing 41 to help with containment of expanding gas should one of the initiators 30 be inadvertently ignited when the barrier 20 is not in the arm and fire position.
Further, an alignment feature 46, such as a pin, may optionally be provided that extends from the flange surface 49 of the collar 52. The alignment feature, or pin 46 engages a strategically placed alignment feature in the form of port 39 located in the basket housing 41 to ensure that explosive transfer path ports 25 within the basket housing 41 will be aligned with the fire-train transfer ports 24 of the barrier 20 when the latter is positioned in the arm and fire position.
Also, the explosive transfer path ports 25 may each optionally include a rupture disc 29 seal-welded therein. The rupture discs 29 are designed to burst, allowing an energy wave to be propagated through the explosive transfer path port 25 from the explosive transfer path 24 and fire-train transfer port 22, when the initiators 30 are fired and the barrier 20 is positioned in the arm and fire position. Otherwise, the rupture discs 29 are designed to help contain an inadvertent firing of the initiators 30 when the barrier 20 is not in the arm and fire position.
The volume of cavity 42 of the booster basket assembly 40 may be adapted to contain the quantity of ignitable composition required for igniting a particular igniter or rocket motor. Particularly, the basket cover 44 may be designed or adapted for use with various sized igniters or rocket motors and may also be configured to help direct the burn of the ignitable composition. As shown in
Optionally, a polymeric film (not shown) may be attached to the inner or outer side of the basket cover 44 to provide an environmental seal over the ports 38. The polymeric film may also be removably attached in order to facilitate selective removal before use of the booster basket assembly with a booster base; or may be made from a pressure sensitive material that includes a frangible or friable quality suitable during use with a booster base. The polymeric film may include a material that dissipates static energy.
Optionally, the basket cover 44 may have any other suitable shape than the plate shape as illustrated in
Advantageously, the booster basket assemblies 40, 140, 240 may be pre-assembled and ready for assembly into the collar 52. Pre-assembly of the booster basket assemblies 40, 140, 240 is accomplished by containing an ignitable composition within the cavity created between the basket cover 44, 144, 244 and the basket housing 41 and then securing the basket cover 44, 144, 244 to the basket housing 41 with fasteners, such as with hex-headed bolts 45, respectively. As is depicted in each of
Advantages provided by embodiments of this invention are: the ability to verify and monitor the adequacy of a seal between the safe and arm device and its mounting upon a rocket motor; double redundancy (dual fault tolerant initiation) by including at least three initiators in the safe and arm device; positive indication of safe position within the limits of switch contacts when a safing pin is installed in to a safing assembly; and standardized unitary booster basket assembly allowing for modular and robust containment of an ignitable composition for ready installation with the safe and arm device. Other advantages provided by embodiments of this invention are provided herein.
Generally in embodiments of the invention, the safe and arm device provides for increased motor maximum expected operating pressure (MEOP) particularly for use with an RSRM, because the booster base assembly 14 may be designed for man-rated single use while preserving the arm and motor assembly 12 for subsequent reuse after refurbishment and certification. By providing a device having the booster base assembly designed with increased MEOP that is man-rated and for single use, the safe and arm device is resultantly of lighter weight than conventional devices designed for the same criterion and for multiple reuses.
While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the language of the appended claims and their legal equivalents.
