Abstract:
The present invention provides a fast, low-cost, small diverter capable of generating a relatively high impulse (1-5 N-sec) over a short time period. The diverter is adapted for installation in a projectile for steering the projectile in flight by ejecting an end cap or hot burning gases in response to control signals from a guidance system. In one embodiment, multiple diverters are arranged in one or more bands about a flying projectile such as a rocket. Each diverter includes a header assembly providing support for a plurality of electrical leads, a mounting surface either on the header assembly or on a sealing assembly, a reactive semiconductor bridge mounted on the mounting surface and providing an electrical path for the electrical leads at a certain voltage across the bridge, a diverter body supporting the header assembly and containing a prime, wherein the reactive semiconductor bridge and the prime permit a gap, and an end cap or a sealing assembly attached to the diverter body containing the propellant.

Description:
This application is a continuation of U.S. application No. 09/782,198, filed on Feb. 8, 2001, now abandoned, which is a continuation-in-part of U.S. application No. 09/502,119, now U.S. Pat. No. 6,367,735 B1, filed on Feb. 10, 2000, which are hereby incorporated by reference. The present invention relates to controlling the flight path of rockets, missiles, and other flying projectiles. In particular, the invention relates to a small fast diverter for use with a projectile for steering the projectile in flight. 

   BACKGROUND OF THE INVENTION 
   In general, a diverter generates lateral reaction force to steer a rocket, missile, and other projectile in flight. The amount of impulse generated by the diverter will determine how much the flight path is diverted. Impulse is the product of the average reaction force over the time exerted. 
   Recent applications for diverters include steering 2.75-inch diameter rockets, artillery, and gun projectiles, e.g., 30 mm projectiles. In such applications, we need small diverters that can generate relative high impulse (e.g., 1 to 5 N-sec) in short time periods. Because rockets, missiles, and projectiles often spin at high rates, the impulses must be made in a short time period, e.g., on the order of 1 ms. If, for example, a projectile is spinning at 3600 RPM, it is spinning at 60 revolutions per second or 21.6 degrees per millisecond. If the diverter provides a reaction force for 10 ms, this will provide force over 216 degrees. Providing the force over this time period is not efficient. Instead, we would like to provide the force for 1-ms or less. If the diverter can provide the force over this shorter period, the guidance system can make multiple steering corrections when needed as a projectile flies through space by igniting the multiple diverters arranged around it. 
   One might consider using small rocket motors for diverters having small volume, but this has proven ineffective when a relatively high impulse is required over a short time. It is too difficult for a rocket motor with loose loaded propellant to burn all of its propellant in a short time without ejecting a large percentage of the propellant unburned. Further, the relatively low packing density of propellant results in the rocket motor ejecting a considerable volume of propellant. Additionally, the rocket propellant container cannot be manufactured that small. Providing the propellant in a higher density form, e.g., cast propellant grain, might appear helpful, but a compact single grain is unlikely to have a thin enough web to operate in the required time period due to propellant burn rate limitations. Where low cost is required, such as less than $5.00 per diverter, without large capital investment, it is difficult to envision good results with rocket motors. Small rocket motors can provide impulses of 1-5 N-sec, but for longer time periods on the order of 10 milliseconds. Additionally, rocket motors are not volume efficient for another reason. To fully use the energy in a rocket propellant, a converging/diverging nozzle with significant mass and volume is needed to fully expand and accelerate the propellant gas. 
   Another approach might be to use conventional bridgewire pyrotechnic devices for small diverters, but there are unsolved problems. One problem is how to ignite them quickly and reliably. Conventional semiconductor bridge technology provides very fast hot ignition, but it is also only low energy ignition lasting for microseconds. The energy output is dependent on energy input; when only low input energy is available, only small output energy can be produced, which may not be sufficient to provide reliable ignition. Further, conventional pyrotechnic devices and semiconductor bridges require tight coupling between the ignition element and the pyrotechnic material. Up to now it has been critical for reliable ignition with semiconductor bridges that the ordnance or pyrotechnic material to be ignited be in close contact with the semiconductor bridge during ignition. This means lower ignition energy can be used, but it requires intimate contact between the bridge and prime, adding to manufacturing costs. The applications mentioned earlier can subject diverters to very high accelerations and shocks, e.g., on the order of 100,000 g&#39;s. During such events the prime may separate from the ignition element and reduce the reliability of the diverter. Bridgewires require high firing energies or very small and unsafe bridgewires for fast response. Thus, attempts to produce small low cost diverters generating relatively high impulse over brief periods of time have not been successful. 
   SUMMARY OF THE INVENTION 
   The present invention provides a small, fast, low cost diverter for steering a rocket, missile, or other projectile. 
   One embodiment of the diverter uses a reactive semiconductor bridge for the ignition source and ejects an end cap from a diverter body to generate a fast relatively high impulse. A header assembly extends into the diverter body and supports the reactive semiconductor bridge and provides electrical contact to a fireset. When desired, the reactive semiconductor bridge provides fast ignition of the prime and allows for a gap between the semiconductor bridge and the prime. The ignited prime in turn ignites the propellant. The burning propellant produces gases, which are confined in the diverter until the pressure builds to the point when the end cap of the diverter is ejected. Requiring the propellant to generate high pressures to eject a solid mass such as an end cap is a much more efficient method of retrieving the energy from the propellant than ejecting hot gases from a rocket motor. 
   One advantage of the present invention is a relatively low cost, high impulse compact, and fast functioning diverter results compared to what can be provided with a small rocket motor. The use of the reactive semiconductor bridge allows very fast firings since ignition occurs in microseconds. The reactive semiconductor bridge allows reliable operation at low input energies since the reactive semiconductor bridge provides a large energy output to ignite the prime. The reactive semiconductor bridge can ignite prime across a gap and this provides a safety margin in case the shock or acceleration of projectile launch would cause the prime to become separated from the bridge. Reliable diverters can be therefore built at relatively low cost using this technology. 
   Thus, in one embodiment, the invention relates to a small fast diverter for use with a projectile for steering the projectile in flight by ejecting an end cap of the diverter in response to a signal from a guidance system. In another embodiment, the invention relates to a diverter and other impulse type of cartridges capable of high impulse, such as less than 1 ms, without throwing a mass such as the end cap, but instead using the ejection of the hot high-pressure velocity gases out of the diverter body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a cross-sectional view of a rocket with a single diverter installed on the right hand side. 
       FIG. 2  illustrates a perspective view of the rocket with three bands of diverters. Each band may include eight diverters like those shown in  FIGS. 1 and 3B . The view includes a partial cross-section through the first of the three bands of diverters. 
       FIG. 3A  is an end view of the diverter shown in FIG.  1 . 
       FIG. 3B  is a detailed cross-section of the diverter shown in FIG.  1 . 
       FIG. 4A  is an electrical lead end view of the header assembly shown in FIG.  4 B. 
       FIG. 4B  is a cross-section of the header assembly shown in FIG.  3 B. 
       FIG. 4C  is a semiconductor bridge end view of the header assembly shown in FIG.  4 B. 
       FIG. 5A  is a detailed cross-section of the semiconductor bridge shown in FIG.  3 B. 
       FIG. 5B  is a view of the semiconductor bridge mounted on the header assembly shown in  FIGS. 3B and 4C . 
       FIG. 6  is a detailed cross-section of an alternative embodiment of the diverter shown in FIG.  3 B. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a cross-sectional view of a rocket  10  with a single diverter  12  on the right side. In this embodiment, the rocket  10  is a 2.75-inch diameter rocket. It should be apparent from the specification, however, that the diverter would be useful on many types of projectiles. As shown in  FIG. 1 , the core of rocket  10  has eight barrels  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 , and  8  for installing eight diverters, just like diverter  12 , in a band about the rocket  10 . The rocket  10  includes a free passage  9  to allow connection of each of the diverters  12  to the fireset (not shown). 
   The diverters can be arranged in several bands about the rocket  10  as shown in FIG.  2 .  FIG. 2  illustrates a perspective view of the rocket  10  with three bands of diverters  12 . Each band includes eight diverters, but other amounts are possible besides those shown in  FIGS. 1-2 .  FIG. 2  shows a partial cross-section through the first of three bands of diverters. 
   As shown in  FIGS. 1-2 , the diverters have axes perpendicular to the axis of rocket  10 , such that the ejection of an end cap  16  from a diverter body  22  will produce a lateral reaction force. It may be desirable to have from 1 to 64 diverters on the rocket  10 . It is preferred that the diverter axes be perpendicular to the rocket axis and arranged at equal angles apart to simplify guidance system calculations. 
     FIG. 3B  shows additional details of the diverter  12  shown in FIG.  1 . As shown in  FIG. 3B , the diverter  12  includes an end cap  16 , made of strong steel, preferably of 17-4 PH CRES, condition H-1025, with a clean passivated finish. The end cap  16  is attached to the diverter body  22 , and made of the same material and finish as the end cap  16 . A conventional adhesive bonding material  26 , such as a cyano acrylate adhesive, a suitable conventional structural epoxy, or a conventional urethane adhesive, is applied on the contacting surfaces between the end cap  16  and the diverter body  22  to bond the end cap  16  to the diverter body  22  until the time that the end cap  16  is elected. One of ordinary skill would also understand that the end cap  16  and the diverter body  22  could be also attached by other techniques such as crimping. The end cap  16  is filled with a loosely loaded propellant  14 , preferably 50 wt.% Bullseye (pistol powder) and 50 wt.% HMX (an explosive ordnance material), shotgun powder or the like. In an optional feature, the invention provides a conventional adhesive backed paper closure, which acts as a thermal closure  24 , to seal and hold the propellant  14  in place for handling during assembly of the diverter  12 . 
   The diverter body  22  contains the prime  18 , preferably zirconium potassium perchlorate, or a similar ordnance material. The diverter body  22  has an aperture for housing the header assembly  20 . The header assembly  20  includes a glass substrate  44  from which two electrical leads  30  and  32  protrude to provide electrical contact from a fireset (not shown) to a reactive semiconductor bridge  40  mounted on the other end of the header assembly  20 . Electrical leads  30  and  32  are made of stainless steel or KOVAR. Conventional shrink tubing  34  and  36  insulates the electrical leads  30  and  32  from contacting and shorting to the diverter body  22 . Conventional potting material  28  retains the shrink tubing  34  and  36  and fills the gap between the shrink tubing  34  and  36  and the diverter body  22 . A conventional shunt  38  provides an electrical short when attached to the electrical leads  30  and  32  for safe handling of the diverter  12 , and which shunt is removed when the diverter  12  is attached to the fireset.  FIG. 3A  is an electrical lead end view of the diverter  12  shown in FIG.  3 B. 
     FIG. 4A  shows the end of header assembly  20  from which electrical leads  30  and  32  protrude.  FIG. 4B  shows a cross-section through the header assembly  20 , including the glass substrate  44 , the stainless steel sleeve or eyelet  42 , and the electrical leads  30  and  32 , and also through the semiconductor bridge  40 .  FIG. 4B  includes detail A shown as  FIG. 5A , and a view B—B shown as FIG.  5 B.  FIG. 4C  shows the end of the header assembly  20  on which the semiconductor bridge  40  is mounted. 
     FIG. 5A  is a close up and a cross-section of the semiconductor bridge  40  mounted on the header assembly  20 , labeled detail A in FIG.  4 B.  FIG. 5B  is an end view. The reactive semiconductor bridge  40  is shown as mechanically attached on the header assembly  20  by a non-conductive epoxy  47  such as Able Bond 84-3. Electrical leads  30  and  32  provide an electrical contact point on the header assembly  20 . Electrically conductive epoxy  46  and  45  such as Able Bond 84-1 electrically connect each of the contact pads of the semiconductor bridge  40  to the electrical leads  30  and  32 . 
   In operation, the reactive semiconductor bridge  40  provides fast ignition of the prime  18  even when there is a gap between the semiconductor bridge  40  and the prime  18 . A suitable reactive semiconductor bridge  40  and the associated structures are described in detail in U.S. Pat. No. 5,847,309 and U.S. Pat. No. 5,905,226, which patents are hereby incorporated by reference. 
   After the semiconductor bridge  40  is triggered based on electrical signals from the fireset, hot plasma forms, igniting the prime  18 , which in turn ignites the propellant  14 . Burning propellant  14  produces gases, which are confined in the diverter  12  until the pressure builds to the point where the end cap  16  is ejected. Ejecting the end cap  16  is more efficient than generating an impulse by rocket propellant. The ability of the reactive semiconductor bridge  40  to ignite the prime  18  across the gap provides a margin of safety in case the shock or acceleration of the launch causes the prime  18  to separate from the semiconductor bridge  40 . Diverters  12  can be built at low cost using this technology. 
   In a preferred embodiment, the diverter body  22  has an undercut  48  such that the mouth of the diverter body  22  is smaller than the base as shown in  FIG. 3B  to hold the prime  18  in place during high shock conditions and during ignition. When fired a semiconductor bridge  40  tends to throw off the prime  18  rather than ignite it unless the prime  18  is retained. The undercut  48  retains the prime  18  in place during firing. The reactive semiconductor bridge  40  allows a gap between the semiconductor bridge  40  and the prime  18 . It should be noted that the reactive semiconductor bridge  40  ignites the prime  18  across a gap, but not necessarily if the prime  18  is allowed to dynamically shift away from the semiconductor bridge  40  during the firing process. 
   Methods of the present invention provide the following steps: a firing signal from the fireset is transmitted to the electrical leads  30  and  32  of the diverter  12  when the shunt  38  is removed. The voltage level of fire signal required depends upon the type of the semiconductor bridge  40  mounted on the header assembly  20 . The firing signal can be supplied by many methods including applying one of the following:
         1) A constant current of 1 to 10 amps for less than 1 ms. The actual current will depend on the sensitivity and type of semiconductor bridge used.   2) A capacitive discharge of, e.g., approximately 25 volts from a 40-microfarad capacitor would be typical for driving a semiconductor bridge, but values down to 3 volts and capacitor values down to less than 1 microfarad are possible when highly sensitive semiconductor bridges are used. Higher voltages, voltages up and greater than 500 volts can be used with junction semiconductor bridges that have DC blocking.   3) A voltage signal whose value depends on the semiconductor bridge type, properties, and characteristics.       

   The firing signal causes the semiconductor bridge  40  to generate hot plasma (&gt;2000 F) that ignites the prime  18 . The prime  18  is designed to ignite promptly when driven by the semiconductor bridge  40  and generate in less than 100 microseconds hot particles and heat. The hot particles and heat from the ignited prime ignite the propellant  14 . The propellant  14  is designed to rapidly bum resulting in a rapid pressure rise in the volume confined by the end cap  16  and the diverter body  22 . Each diverter  12  is contained within a barrel as shown in  FIGS. 1-2 . The electrical lead end of the barrel is closed to match the taper at the back of the diverter  12 . The taper is provided on the diverter  12  so the diverters can be placed close together. A slot, not shown, is cut in the side of the back of the barrel to allow the electrical wires to exit and make connection to the fireset. The opposite end of the barrel is open as shown in  FIGS. 1-2 . As the pressure builds inside the diverter  12  produced by the burning of the prime  18  and the propellant  14 , the end cap  16  outer diameter swells and seals against the inner diameter of the barrel defined by the rocket  10 . Also the pressure forces the diverter body  22  back against the taper sealing this potential exit path for hot gas. The header assembly  20  is mounted on the diverter body  22 . As the pressure within the diverter  12  continues to increase from the burning of prime  18  and propellant  14 , the force on the end cap  16  reaches a point where the end cap  16  separates from the diverter body  22  and is accelerated down the barrel and ejected. Ejecting the end cap  16  results in a reaction force, that is, the diverting force. Additionally, diverting force is created by the reactive forces from the ejection of the hot gases from the burning of the prime  18  and the propellant  14  out of the barrel similar to the operation of a rocket. 
     FIG. 6  illustrates an alternative embodiment of the diverter, which does not throw a solid mass. As in the previous embodiment, the diverter  50  includes a diverter body  52  having a glass substrate  54  joined to a set of pins or leads  56  and  58 . This produces a glass-to-metal seal header assembly  60  where the leads  56  and  58  enter the header assembly  60 . A suitable ignition element such as a semiconductor bridge  40  is electrically attached to the leads  56  and  58  that exit the glass substrate  54 . Preferably, the leads  56  and  58  extend to the exit end of the diverter body  52 , for example, near the solder connection  64 . The semiconductor bridge  40  mounts on a mounting surface of an assembly, which seals off the exit end of the diverter body  52 . One suitable mounting surface is a glass laminate printed circuit board (PCB)  62 , which includes conductive paths to connect opposite ends of the semiconductor bridge  40  to the respective leads  56  and  58 . A solder connection  64  connects the electrical lead  58  to one conductive path associated with the PCB  62 . Solder connection  76  connects electrical lead  56  to the other conductive path leading to the other end of the semiconductor bridge  40 . Any suitable connection method can replace the solder connections, for example, either crimping or conductive epoxy. Conductive epoxy may be preferred over solder connections  64  and  76 , because the propellant  66  is typically loaded in the diverter body  52 , the prime  18  is applied to the semiconductor bridge  40 , and they may ignite from a hot solder connection or from mechanically pinching the prime  18  or the propellant  66 . 
   In the embodiment shown in  FIG. 6 , the insulating sleeves  68  and  70  cover the leads  56  and  58  to minimize the danger of an electrostatic discharge (ESD) igniting the prime  18  or shorting to the diverter body  52 . Either lead  56  or lead  58  can be tied to diverter body  52  to minimize the risk of lead-to-lead ESD ignition from the diverter body  52 . That tied lead can be closed with crimp or any other standard closing process. The sealing assembly of the embodiment shown in  FIG. 6  also includes a metal end closure  72  sealed with a crimp  74  and with epoxy adhesive (not shown). 
   In operation, the control system applies power to the leads  56  and  58  that applies power to the conductive paths to the semiconductor bridge  40 . The semiconductor bridge  40  ignites the prime  18 , which ignites the propellant  66  at the interface between the prime  18  and the propellant  66 . The propellant  66  starts to burn, exerting restraining force on the unburned propellant  66  until the propellant  66  is consumed. 
   A reactive semiconductor bridge  40  can provide fast ignition of the prime  18 . The ignited prime  18  ignites propellant  66 , namely, compacted energetic ordnance materials that burn rapidly, such as zirconium potassium perchlorate. The gases created by the burning or rapid deflagration of this energetic material serve to restrain the un-reacted propellant  66  until it is consumed. 
   Accordingly, the diverter  50  functions like an initiator, but the semiconductor bridge  40  is preferably at the exit end of the diverter body  52  so that the energetic column of the propellant  66  is ignited at the exit end rather than at the bottom. Another approach is to ignite the propellant  66  at the bottom of the diverter  50 , but it is believed to expel the propellant  66  out of the diverter  50  before its completely burned. Thus, we prefer to ignite the propellant  66  at the exit end to keep unburned propellant  66  in place until it is completely consumed, resulting in more efficient use of the energy stored in the propellant  66 . 
   A reactive semiconductor bridge  40  is also preferred, because it allows a gap between the semiconductor bridge  40  and the prime  18 , which permits the semiconductor bridge  40  to fire even if the prime  18  moves away from the semiconductor bridge  40 . As before, the reactive semiconductor bridge  40  will ignite the prime  18  across a gap, but not always when the prime  18  dynamically moves away during the firing process. With the semiconductor bridge  40  firing into the prime  18 , the prime  18  is retained by the exit end of the diverter  50  holding the propellant  66  in the diverter body  52 . 
   The operation of the alternative embodiment is identical with that of the previous embodiment, except that as follows:
         1) The hot particles and heat from the ignited prime  18  ignites the propellant  66  from the exit end of the diverter  50 .   2) The propellant  66  is formulated and configured in such a manner as to burn very rapidly, preferably, e.g., less than one millisecond.   3) The reaction from the burning of the propellant  66  results in the diverting force rather than reaction from throwing the end cap  16 . The diverting force is created by the ejection of the hot high-pressure high velocity gases from the burning of the prime  18  and the propellant  66  out of the diverter body  52  similar to the operation of a rocket.       

   There are other advantages to this alternative embodiment. First, it provides high impulse in a small package. Second, it does not throw a solid mass, which can cause fratricide to adjacent missiles and rockets and pose to risk to personnel on the flight path, e.g., friendly troops. The use of the reactive semiconductor bridge  40  allows very fast firings, since the ignition occurs in microseconds. It also allows reliable operation at low input energies, since the reactive semiconductor bridge  40  provides a large energy output to ignite the prime  18 . The reactive semiconductor bridge  40  can ignite across a gap, providing a margin of safety against the shock or acceleration of a launch, which can cause the prime  18  to separate from the semiconductor bridge  40 . The diverter  50  can be built at low cost using well known impulse cartridge technology. This will be cost effective compared to a rocket motor with a nozzle and use of a solid grain. Thus, the alternative embodiment provides an inverted ignition structure does not need to throw a solid mass, and achieves a relatively high impulse in very short time periods at low cost. The reactive semiconductor bridge provides for shock insensitivity, and the propellant and the prime can be different ratios to provide the desired impulse. Finally, a nozzle can be attached to the diverter  50  to increase the impulse, and make the impulse cartridge function like a rocket motor.