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CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority from U.S. Provisional Patent Application “The Archimedes Javelin” Ser. No. 60/666,970 filed Mar. 31, 2005 by Wojciech Andrew Berger, Robert A. Spalletta, Jerry A. Carter, Marian Mazurkiewicz, Richard M. Pell, Christopher Davey. The present Patent Application is also related to U.S. patent application Ser. No. 11/886,374 (U.S. Pat. No. 7,584,807) entitled “System for Rapidly Boring Through Materials” and U.S. patent application Ser. No. 11/886,372 “Multiple Pulsejet Boring Device” both filed on Sep. 15, 2007 by Wojciech Andrew Berger, Robert A. Spalletta, Jerry A. Carter, Richard M. Pell, Marian Mazurkiewicz. All above applications are hereby incorporated by reference as if set forth in its entirety herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a valveless cryogenic system for boring through materials. 
   2. Discussion of Related Art 
   There currently are prior art boring devices and other machinery which are designed to drill through materials, such as rock and earth. Many of these employ mechanical rotary drills. Which require strong structures to anchor the drill and counter the rotational forces. 
   Other drills exist which employ forcing a high pressure liquid at the material to bore through it. These require a great deal of pressure to be passed to the cutting end of the drill. 
   Since many of the materials being bored are brittle, prior art cryogenic drills have been used. These use high pressure (but not as high as the liquid cutting drills) to force cryogenic liquid at a brittle object, freezing it and impacting it with the cryogenic liquid. The frozen material is more brittle and fractures when impacted by the cryogenic liquid. 
   Since these apply high pressure to the cutting tip, which may be some distance away, it has structural requirements not only to contain the pressure and pass it to the tip, but also to keep the cryogen cool. These tend to make the drill bulky and hard to manage. 
   In addition, these require a valved system to intermittently allow and stop the fluid to create a stream of pulsed liquid slugs which impact the target. 
   These valves are acting under extreme conditions and tend to freeze and fail. 
   Currently, there is a need for a low pressure drilling device which is more effective than prior art devices. 
   SUMMARY OF THE INVENTION 
   One embodiment of the present invention is a cryogenic rapid boring system for rapidly boring a hole in a material ( 1 ) comprising:
         a) A borehead ( 3000 ) having at least one pulsejet ( 3100 ) with a proximal end ( 3001 ) and a distal end ( 3003 ) located adjacent said material ( 1 ) intended to be bored;   b) A cryogen supply unit ( 1010 ) for providing a cryogenic liquid ( 7 ) to fill the pulsejet ( 3100 );   c) The pulsejet ( 3100 ) having an expansion section ( 3120 ) located adjacent to the distal end ( 3003 );   d) The tube having a freeze section ( 3110 ) located just proximal to the expansion section ( 3120 );   e) At least one thermal unit ( 3410 ) capable of freezing cryogenic liquid ( 7 ) into a plug ( 8 ) and capable of melting frozen plug ( 8 ) located adjacent to the freeze section ( 3110 );   f) At least one thermal unit ( 3510 ) capable of vaporizing cryogenic liquid ( 7 ) into a gas, and capable of cooling the expansion section ( 3120 );   g) A controller ( 1020 ) coupled to the cryogen supply unit ( 1010 ), the thermal units ( 3410 ,  3430 ,  3510 ,  3530 ), operating to activate:
           i. the cryogen supply unit ( 1010 ) to fill the pulsejet ( 3100 ) with cryogenic liquid ( 7 );   ii. thermal units ( 3410 ,  3430 ) to freeze a plug ( 8 ) at the freeze section ( 3110 );   iii. thermal units ( 3510 ,  3530 ) to rapidly vaporize cryogenic liquid ( 7 ), into a gas just distal to the frozen plug ( 8 ) thereby causing it to force cryogenic liquid ( 7 ) distal to the gas, out of the distal end ( 3003 ) of pulsejet ( 3100 ) at a high velocity impacting said material ( 1 ) thereby ‘firing’ the pulsejet ( 3100 ).   
               

   The present invention may also be embodied as a method of boring through solid material ( 1 ) with a cryogenic liquid ( 7 ) comprising the steps of:
         a. providing a borehead ( 3000 ) having at least one pulsejet ( 3100 ) capable of holding a liquid, having a distal end ( 3003 ) and an opposite proximal end, the distal end being positioned near, and pointing toward said material;   b. providing cryogenic liquid ( 7 ) to the proximal end of the pulsejet ( 3100 );   c. freezing the cryogenic liquid ( 7 ) near the distal end of the pulsejet ( 3100 ) into a plug ( 8 ) at a location such that there is cryogenic liquid ( 7 ) distal to the plug ( 8 );   d. rapidly heating the cryogenic liquid ( 7 ) distal to the plug ( 8 ) causing it to be converted into rapidly-expanding gas ( 9 ) rapidly forcing the cryogenic liquid ( 7 ) distal to the gas ( 8 ) out of the distal end of the pulsejet ( 3100 ) as a slug ( 10 ) which impacts said material ( 1 );   e. repeating steps “b”-“d” to cause multiple slugs ( 10 ) to be forced out of the pulsejet ( 3100 ) thereby boring a hole through said material ( 1 ).       

   OBJECTS OF THE INVENTION 
   It is an object of the present invention to provide a system which bores through materials more efficiently than the prior art devices. 
   It is another object of the present invention to provide a simpler system for boring through materials than the prior art devices. 
   It is another object of the present invention to provide a more reliable system for boring through materials than the prior art devices. 
   It is another object of the present invention to provide a valveless cryogenic system for boring through materials. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages of the instant disclosure will become more apparent when read with the specification and the drawings, wherein: 
       FIG. 1  is a perspective view of a cryogenic boring system according to one embodiment of the present invention. 
       FIGS. 2   a - 2   f  are enlarged views of a portion of the cryogenic boring device of  FIG. 1 , showing the operation of the pulsejets. 
       FIG. 3  is a flowchart illustrating the functioning of the present invention. 
       FIG. 4  shows an embodiment of the present invention employing multiple cryogenic pulsejets in a single borehead. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   One embodiment of the present invention is shown in perspective view in  FIG. 1 . A number of ground units  100 ,  4000 ,  5000  are delivered to the ground. Unit  100  is positioned just above a target  1  which may be an underground void or object. Ground unit  100  may be delivered there by a number of different conventional known methods including an air-drop for inaccessible locations. 
   Ground unit  100  employs a platform subsystem  1000  having retention and orientation devices  1500  which secure ground unit  100  to the ground and tilts platform  1000  to an optimum orientation for boring to target  1 . Platform subsystem  1000  is designed to hold, store and carry all the equipment during deployment, initiate boring of an access hole, hold materials to be used in a fuel reservoir, stabilize ground unit  100  for boring, and communicate with other units. 
   A boring subsystem  3000  bores down through the ground toward target  1 , creating an access hole  5 . Boring subsystem  3000  is designed to force the excavated materials out of the access hole  5  and to the surface. 
   Boring subsystem  3000  is connected to platform subsystem  1000  by an umbilical subsystem  2000 . 
   Umbilical subsystem  2000  connects the Platform  1000  and Boring  3000  subsystems. It acts to pass materials, electricity, and control signals between platform  1000  and boring  3000  subsystems. 
   Umbilical subsystem  2000  also employs mechanical actuators to absorb much of the forces produced during boring, as well as for steering and advancing umbilical subsystem  2000  and boring  3000  subsystems deeper into the access hole  5 . 
   The boring subsystem  3000  employs pulsejets shown in greater detail in  FIGS. 2   a - 2   f.    
     FIGS. 2   a - 2   f  are a time sequence of enlarged views of a pulsejet  3100  of the cryogenic borehead ( 3000  of  FIG. 1 ), showing the operation of the pulsejet  3100 . 
   In  FIG. 2   a , a pulsejet  3100  is shown in an enlarged view. A cryogenic fluid  7  passes through umbilical  2000  to pulsejet  3100 . Pulsejet  3100  employs a freezing section  3110  near the distal end of pulsejet  3100 . Just distal to the freezing section  3110  is an expansion section  3120 . Just distal to the expansion section is an exit section  3300 . 
   In  FIG. 2   a , cryogenic fluid  7  has passed down umbilical  2000  and has filled freeze section  3110 , expansion section  3120  and exit section  3300 . Adjacent to freeze section  3110  is at least one thermal unit  3410 ,  3430 . In  FIG. 2   a  both thermal units  3410 ,  3430  are inactive. Adjacent to expansion section  3120  is at least one thermal unit  3510 ,  3530 . In  FIG. 2   a  both thermal units  3510 ,  3530  are inactive. 
     FIG. 2   b  shows the system at some time after that of  FIG. 2   a , thermal units  3410 ,  3430  are activated to cause cryogenic fluid  7  in freeze section  3110  to solidify. Preferably, freeze section  3110  is narrower than the remainder of the system allowing quick freezing. At this time thermal units  3510 ,  3530  are inactive. 
   In  FIG. 2   c , thermal units  3510 ,  3530  are activated to provide heat to the cryogenic fluid  7  in expansion region  3120 . Fluid  7  rapidly changes into a gas producing a rapidly-expanding gas bubble  9  pushing fluid  7  in exit section  3300  out as a liquid slug  10 . 
   An efficient method of supplying electric energy to thermal units  3410 ,  3430  first, then to thermal units  3510 ,  3530  is to use the Peltier effect 
   In the Peltier effect, an electric current of magnitude J across the junction of two different conductors A and R with Peltier coefficients Π A  and Π B  produces heat at the rate            −(Π A −Π B )·J
   The sign of             can be positive as well as negative. A negative sign means cooling of the junction. Contrary to Joule heating, the Peltier effect is reversible and depends on the direction of the current. In this effect, thermal units  3410 ,  3510  are coupled. Thermal units  3430  and  3530  are also coupled. Energy is first provided to thermal units  3410 ,  3430 , then by the Peltier effect, the energy is then passed through thermal units  3510  from  3410 ; and through thermal unit  3530  from thermal unit  3430 .
   In  FIG. 2   d  thermal units  3510 ,  3530  have stopped providing heat to fluid  7 . It can be seen here that expansion section  3120  and exit section  3300  are filled with the gas. The liquid slug  10  has been expelled from the exit section at a high velocity. Slug  10  is typically directed to the material which is intended to be bored. Slug  10  freezes and shatters the frozen material, thereby boring through the material. 
   In  FIG. 2   e  thermal units  3410 ,  3430  heat frozen plug  8 , melting it. At the same time, thermal units  3510 ,  3530  cool expansion section  3120 , getting it ready to receive more cryogenic fluid  7 . 
   In  FIG. 2   f , fluid  7  fills freeze section  3110 , expansion section  3120  and exit section  3300 , putting the system in the state it was in as shown in  FIG. 2   a . The cycle may now be repeated. 
   By controlling when thermal units  3410  and  3430  freeze the liquid  7 , one can adjust the amount of liquid distal to the plug  8 . This thereby adjusts the size of the slug  10 . 
   By controlling how much energy is provided to thermal units  3510  and  3530 , one may adjust the intensity in which the pulsejet  3100  is ‘fired’. 
   The present invention may also be viewed as a novel method of boring through a material. 
     FIG. 3  is a flowchart illustrating the functioning of the present invention. This invention is a method of drilling through solid materials employing pumping a cryogenic fluid through a pipe into the target material. The process begins at step  301 . 
   In step  303  a tube extending in a proximal direction and a distal direction is filled with cryogenic fluid. 
   In step  305 , at a location within the material, a refrigeration section freezes the cryogen in the pipe into a solid “plug”. 
   The cryogenic liquid near the distal end of the tube is frozen into a plug by applying current to freezing coils. This plug is positioned such that there is cryogenic liquid distal to the plug in the tube. The plug at least partially blocks the tube. 
   In step  307 , the cryogenic liquid distal to the plug is heated, causing a rapidly-expanding gas bubble to form. The rapidly-expanding gas bubble pushes the cryogenic liquid distal to the bubble as a slug out of the end of the distal end of the tube at a high velocity. The frozen cryogen is used as a ‘backstop’ to bounce against causing the force to cause the liquid to pass outward through the distal end of the tube against the material to be bored. 
   In step  309 , the plug is rapidly heated to melt it allowing cryogenic fluid again to fill the tube. 
   In step  311  it is determined if the boring has been completed. If boring has been completed (“yes”), then the process stops at step  313 . 
   If not (“no”), then steps  303  through  311  are repeated. Repeating the sequence causes a plurality of slugs to be rapidly forced out of the tube. The repeated slug impacts destroy and cut through the target material, thereby boring a hole through the material. 
   The tip may also employ small reverse nozzles which point away from the material to be bored. Some of the escaping gases fire through these reverse nozzles propelling the tip further into the material to be bored. 
     FIG. 4  shows an embodiment of the present invention employing multiple cryogenic pulsejets in a single borehead. The distal ends of several pulsejets  3101 ,  3103 ,  3105 ,  3107  and  3109  are shown. These pulsejets may be fired in different sequences and intensities to simulate rotary boring and also cause steering. 
   In one embodiment, slugs  10  are fired in sequence to create the effects of rotary boring and maximize boring efficiency. Here, pulsejets  3101 ,  3103 ,  3105 ,  3107  and  3109  around the periphery of the borehead  3000  are fired in this order creating slugs  10 , shown at various distances from the pulsejets. A controller ( 1020  of  FIGS. 2   a - 2   f ) activates thermal units ( 3510 ,  3530  of  FIGS. 2   a - 2   f ) at the proper times to create the sequence as shown. This simulates the effect of a rotary drilling in the direction by the arrows marked “A”. 
   Steering is more fully discussed in “Steerable Boring Device” incorporated by reference in the Cross Reference to Related applications above. 
   In another embodiment of the present invention, the boring subsystem may be used above ground to cut or shape materials. It works best with materials which become brittle when cooled. 
   The present invention provides a cryogenic pulse jet source which cuts through hardened materials much more quickly than a steady flow cryogenic jet. 
   The present invention provides a cryogenic pulse jet that does not require valves which tend to freeze and malfunction. This results in a more reliable system. 
   The present invention does not require the use of high pressure liquids as do other prior art devices, therefore resulting in a simpler, less bulky system. 
   The present invention employs the ambient energy of the ground as a heat source to provide a temperature differential used to fracture hard materials in the ground. 
   Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for the purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention.

Summary:
A cryogenic system is described for boring a small-diameter hole through various materials including rock, soil and stone. It employs a valveless technique in a borehead [ 3000]  where cryogenic fluid [ 7]  fills at least one pulsejet [ 3100]  which has proximal [ 3001]  and distal [ 3003]  ends. The cryogenic fluid [ 7]  is frozen into a plug [ 8]  near the distal end [ 3003] , acting as a valve. Cryogenic fluid [ 7]  just distal to the frozen plug [ 8]  is rapidly heated by thermal units [ 3510, 3530]  causing it to become a rapidly-expanding gas bubble. The rapidly-expanding gas bubble forces any liquid [ 7]  distal to the expanding gas out of the distal end [ 3003]  of each pulsejet [ 3100]  causing it to impact the material [I]. Rapidly repeating this process causes the system to bore a hole through the material [I].