# Patent

## Title
Disposable, miniature internal optical ignition source for ammunition application

## Abstract

An ammunition cartridge for a gun is optically initiated by a mechanism wholly within the cartridge case itself. The case has as optical primer initiation means producing light fluence to ignite a primer, which ignited primer may in turn ignite into a flashtube, and which ignited flashtube may in turn ignite a bed of propellant in said cartridge. The optical primer initiation means may be an LED, a laser diode, a VCSEL, or some other light emitting device in general. The cartridge optically initiated primer package is so sized and made electrically and mechanically seamlessly physically compatible with current ammunition cartridges such that these new cartridges are completely interchangeable. If the cartridge primer initiation means is of a percussion type, the cartridge is adapted to include an in-line piezoelectric crystal so that electrical power will be generated when the cartridge assembly is struck by a firing pin during percussion type operations; the power is then used to initiate the light emitting device.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application claims benefit of provisional application 61/806,086 filed Mar. 28, 2013, the entire file wrapper contents of which application are hereby incorporated by reference as if set forth at length.


FEDERAL INTEREST STATEMENT
The inventions described herein may be manufactured, used and licensed by or for the United States Government for United States Government purposes.


BACKGROUND AND FIELD OF THE INVENTION
This invention relates generally to the field of the ignition of small, medium and large caliber munitions and specifically to the use of an optical source (laser or other light emitting source) contained within the base of each cartridge case in place of the traditional chemical primer. Most conventional cartridge systems are initiated by use of a center fire based primer within a metal casing. Such primers are typically initiated through electrical, mechanical or optical means. These systems in particular are used in many small, medium and large caliber gun systems. Recently, advanced artillery systems have explored the use of laser ignition systems wherein the propelling charge is ignited by a laser emitter located in the breech of the artillery system.
As can be appreciated, locating a laser ignition system in the breech of an artillery system presents numerous challenges. Among the most difficult of these challenges are those related to making the laser ignition system sufficiently robust to endure the continuous extreme vibration, shock and thermal excursions produced by the weapon system when fired, as well as the extreme environmental conditions such as long term storage and operation in hot or cold and wet or dry weather conditions.
SUMMARY OF THE INVENTION
The above problems are solved and an advance is made in the art according to the principles of the present invention. The availability of low cost optical emission sources such as laser diodes, vertical cavity surface emitting lasers (VCSEL's) and light emitting diodes (LED's) allow for the insertion of an active optical source directly within the body of the cartridge. This technology approach is diametrically opposed to current and past efforts of using a single, external laser to initiate the propelling charge and/or cartridge.
Viewed from a first aspect—the present invention is directed to the use of a light emitting source. For technical clarity, the term ‘laser diode’ will be used, though, any optical source with sufficient output energy could be substituted. Laser diodes are inherently robust, compact and readily available from multiple sources.
Viewed from another aspect—the present invention is directed to the use of a traditional metallic cartridge made of brass, steel or aluminum. This cartridge currently consists of three major components: a primer used to initiate the propellant either directly or via a booster charge, a propelling charge whose products of combustion are used to accelerate a projectile, and the projectile which is the mass discharged by the weapon. Advantageously—and in sharp contrast to previous laser ignition based systems, the proposed invention incorporates an optical based ignition source into and within the confines of cartridge case of munitions similar to present electrical or percussion-based system.
The incorporation of a diode laser within the physical confines of the primer geometry permits a seamless interchangeability and dynamic substitution of both optical and electrical based cartridges with no modification to existing weapon platforms. For systems using electrical ignition sources, a power source is already available, and the laser diode located within the cartridge casing will make use of this source. Alternatively, for weapon systems which use a mechanical firing pin, a diode laser would be coupled with a piezoelectric cell to convert mechanical energy into electrical energy to drive the optical source.
In addition, an optically based igniter integrated within the individual cartridge can be used with environmentally friendly based ‘green’ primary energetic compounds and would eliminate the need for lead styphnate based mixes with these cartridges.
Of principal relevance is the inherent dual protection by the principle of a Faraday cage which is provided by both the primary exterior metallic cartridge case in combination with the secondary metallic primer housing.
The primary Faraday cage is provided by the exterior case and projectile provides significant protection from electromagnetic environmental effect or E3. A secondary Faraday cage is provided by the primer assembly which completely surrounds the light emitting source. These two features effectively shield the laser diode from electrostatic discharge (ESD) which significantly reduces risk of inadvertent initiation.
Of further advantage is reduction of the threat of inadvertent ignition of the munitions from stray or directed energy fields. Laser diodes, by nature, do not emit optical energy when exposed to high intensity radio frequency fields (RFF). The reduction of sensitivity being primarily the result of the nature of laser diodes to not lase under exposure to high intensity radio frequency fields (RFI). This protection is further enhanced through the reduction and/or elimination of wire leads from the assembly. The principal role of the micro electric circuit design would feature to also provide protection to prevent such damage. Should a laser diode fail, it would fail ‘safe’, rendering the cartridge inoperable and would be safely ejected with no damage to the weapon platform.
Of further advantage is the reduction of the threat of inadvertent ignition of the munitions from an electro-magnetic pulse (EMP). This reduction in sensitivity is primarily the result of the optical source being contained within multiple Faraday cages and the lack of a suitable antenna.
The insertion of a laser diode based primer assembly/ignition system into the cartridge case presents minimal technical challenges and can be inserted with only minor modification to fabrication and assembly equipment. The elimination of inadvertent ignition by ESD would reduce the risk to manufacturing, transportation, storage and use of munitions of this type. The substitution does not affect the weight, performance, form, fit or function of existing weapon hardware.



BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention may be understood from the drawings in which:
FIG. 1 is a sectional perspective view of a standard primer sans energetics.
FIG. 2A is a sectional perspective view of a diode laser assembly as proposed mounted within the confines of the standard primer cup from FIG. 1 according to the present invention. FIG. 2B is a sectional perspective view of a diode laser assembly when percussion by a firing pin, e.g., starts the ignition process, as proposed mounted within the confines of the standard primer cup from FIG. 1 according to the present invention.
FIG. 3a is a cut away of a fully assembled optically based igniter according to the present invention located within a standard cartridge munitions without a booster mechanism, i.e. flash tube.
FIG. 3b is a cut away of a fully assembled optically based primer according to the present invention located within a standard cartridge munition which utilizes a booster mechanism, i.e. a flash tube.
FIG. 4a is a cross sectional view of a fully assembled optical primer based cartridge case containing the exterior case, projectile, propellant, and optical igniter assembly.
FIG. 4b is a cross sectional view of a fully assembled optical primer based cartridge case containing the exterior case, projectile, propellant, optical primer assembly and flash tube assembly.



DETAILED DESCRIPTION
The following merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.
Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions.
Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.
In accordance with one preferred embodiment of this invention reference is made to FIG. 1, which shows an external view of a standard primer cup usually made of brass or other conductive material. More particularly, one may observe the brass primer cup 1-001, a generally hollow tube structure, the insulator/seal 1-002 and the conductive button, usually made of brass or other conductive material 1-003. The reader will note that these are assembled in a conventional manner by pressing the various components together.
FIG. 2A depicts an artistic conception of the installation of the laser diode, microelectronics package, and dielectric materials within the embodiments as described in FIG. 1. The laser diode 2-004 is mounted and positioned above the microelectronics assembly 2-005, both of which rest on top of the conductive button. The microelectronics package may be soldered directly to the conductive button. FIG. 2B shows a cup assembly for a percussion type round, where 2-030 is struck by a firing pin, e.g., and causes a piezoelectric crystal type device 2-010 to generate an electrical signal, thereafter to power the microelectronics 2-005 and etc., thence in turn to power the laser diode 2-004, and so forth.
Upon detailed inspection of FIGS. 2A and 2B, the reader will note that the laser diode 2-004, microelectronics assembly 2-005 with ESD mitigation microelectronics added too, and dielectric insulators 2-031/and spacers 2-009 (either or both where required) are hermetically potted within a dielectric agent such as epoxy 2-006. This feature may be extended in FIG. 2A to particularly encapsulate the conductive button 1-003; thereby eliminating the need for a separate insulator 1-002 in FIG. 2A.
Continuing in FIGS. 2A and 2B, the reader will note the two electrical leads 2-007 and 2-008 connecting the laser diode to the primer cup 1-001 and the microelectronics package 2-005 to the laser diode 2-004 respectively. Dielectric insulators 2-031/and spacers 2-009 as shown may either or both be required.
FIG. 3a depicts a complete optical igniter assembly which includes all of the embodiments of FIG. 2A as well as illustrates its location within a cartridge case 3-010. This demonstrates an example where the optical igniter directly ignites the propellant, and sometimes it is done through a channel 3-013.
FIG. 3b depicts a complete optical primer assembly which includes the embodiment(s) of FIG. 2A and illustrates a potential location (cartoon) for various energetic materials within a cartridge case 3-010, where energetic pellets or gas generators 3-011 are used with a flash tube 3-012 to ignite the propellant.
FIG. 4a depicts the complete assembly from FIG. 3a complete with propellant 4-013 and a projectile 4-014 in place.
FIG. 4b depicts the complete assembly from FIG. 3b complete with propellant 4-013 and a projectile 4-014 in place.
For fabrication, assembly and transportation, all energetic materials will be external to the optical igniter assembly. The separation of the energetics from the optical igniter assembly allows safe physical assembly and unrestricted commercial transportation of the optical igniter assembly. Where a separate igniter compound (s) is needed, the flashtube with all energetics will be coupled to the optical igniter assembly within a controlled ammunition assembly facility.
At this point, while we have discussed and described the invention using some specific examples, those skilled in the art will recognize that our teachings are not so limited. For example, the preferred embodiments of the invention have been provided for the purpose of explaining the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention. Various embodiments and various modifications are contemplated. Accordingly, the invention should be only limited by the scope of the claims attached hereto.

## Claims

1. An optically initiated ammunition cartridge for a gun, comprising: a brass cartridge case comprising a projectile element, a bed of propellant, a flashtube embedded in said bed of propellant, and a primer assembly to initiate said propellant, said primer assembly comprising a primer, a primer button and a brass cup, and having an optical primer initiation means producing light fluence to ignite said primer, which ignited primer in turn ignites into said flashtube, and which ignited flashtube in turn ignites said bed of propellant.

2. The cartridge of claim 1 wherein said optical primer initiation means is selected from the group of: an LED, a laser diode, a VCSEL, or a light emitting device in general.

3. The cartridge of claim 2 wherein the optical primer initiation means has a positive and negative electrical lead one of which leads may be electrically connected to the exterior case of the cartridge and the other lead of which may then be mounted in the center of said primer button.

4. The cartridge of claim 3 wherein the optically initiated primer package is sized and made electrically and mechanically seamlessly compatible with current ammunition cartridges so as to be completely interchangeable in said cartridges.

5. The cartridge of claim 4 wherein said cartridges exhibit the same gun mechanical operation, electrical and electronic fire control system operation, and exhibit identical ballistic results, as current cartridges.

6. The cartridge of claim 1 wherein said primer initiation means is a percussion type device, and wherein the percussion initiated primer assembly is adapted to comprise an in-line piezoelectric crystal so that electrical power will be generated when the cartridge assembly is struck by a firing pin during percussion type operations, and said electrical power is adapted to be fed to a microelectronics package to serve as the optical primer initiation power source.

7. The cartridge of claim 1 further including an ESD mitigation control micro-electronic subsystem within the primer assembly to minimize potential damage from ESD.