Abstract:
An interface connector is provided for connecting homogenous spacecraft cells. The interface connector includes at least one male valve assembly and at least one female valve assembly. The male valve assembly includes an extendable and retractable piston having a central conduit. The female valve assembly has a central bore closed by a ball valve. Preferably, the male and female valves are positioned so that extension of the piston engages the ball valve so as to create a fluid pathway. Various components in the male and female valve assemblies are electrically conductive to allow the transmission of power and data. Further, the male valve assembly is constructed to function as a propulsion thruster when not mated to a female valve assembly.

Description:
[0001]    This invention was made with government support under contract no. HR0011-14-C-0023 awarded by the Defense Advanced Research Projects Agency. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to spacecraft engineering and design. More particularly, the present invention relates to structural, fluid, and electrical connectors for interconnection of spacecraft modules. Furthermore, the present invention relates to spacecraft docking and separation systems for providing structural, fluid, and electrical connection between components. 
         [0003]    There is an enormous benefit to docking or connecting spacecraft and spacecraft components. The many applications include launching a spacecraft for rendezvous in orbit with another spacecraft. Furthermore, the ability to connect or disconnect spacecraft modules has application where a broken module can be jettisoned and replaced. Electronic and structural components are also connected prior to launch to form a spacecraft. 
         [0004]    Structural, fluid and electrical connectors are often combined to create an “interface” connection which is employed in a wide variety of applications. Current spacecraft and launch vehicle interfaces employ various electrical connectors and separation systems including pyrotechnically actuated clamp bands, separation nuts, and separation bolts. The interface must be capable of transferring loads between the two structures. The loads may include vibration, acceleration, thermal conduction, and static loads. For example, U.S. Patent Application Publication No. 2002/0164204 describes a spacecraft interface structure for mechanically connecting various spacecraft components including a spacecraft to a launch vehicle. 
         [0005]    Structural, fluid and electrical interface connectors have been developed for in-space docking and separation. For example, U.S. Pat. No. 8,006,937 describes a docking interface in which alignment cups are heated to an austenitic temperature to form a mechanical connection. Power and fluids may be transferred between the two spacecrafts. Fluid, such as a propulsion fluid, is transferred through a central conduit, and data and power can be transferred through the mechanical coupling. Similarly, U.S. Patent Application Publication No. 2012/0000575 describes a docking interface for refueling satellites in space. The docking assembly includes a connector including male and female components for providing fluid transfer. The connector provides electrical power and data transfer as well. 
         [0006]    Past spacecraft have been custom designed and optimized for a particular mission or payload wherein electronic components are mounted inside box-like modules. The spacecraft electronic components provide a single spacecraft function, such as power, thermal, structural, telemetry, tracking, control or processing, or a specific payload function, such as communications or surveillance. The modules are mounted to a spacecraft frame and interconnected with extremely complex wiring harnesses. Unfortunately, the designs cannot be adapted to accomplish different missions as changing any part or sub-system typically has required significant rework of the design. 
         [0007]    Modular spacecraft are attempts to transition away from custom designed spacecraft toward multi-use designs and mass production in an effort to reduce the cost of spacecraft development. The modular spacecraft include a bus which provides a general purpose spacecraft platform. Various payloads can be mounted to the spacecraft platform utilizing a standard structural, fuel and electric interface. Again, the interface connector is of paramount importance. 
         [0008]    Even more recently, spacecraft have been designed by combing homogeneous cells. Each cell possesses the traditional architecture of a spacecraft including structure, power, fuel, attitude control and determination, satellite processing, etc. Each cell is substantially identical so as to be manufactured inexpensively and quickly. These cells are combined to create larger and larger platforms to support payload functions such as communications and surveillance. Though there is substantial redundancy by each cell incorporating all spacecraft sub-system capabilities, the extra costs are more than made up for by mass production savings and rapid assembly. Of course, the satellite reconfigurable cell concept also requires that cells be interconnected by a structural, fluid and electrical interface. 
         [0009]    Unfortunately, previous structural, fluid and electrical interface connectors have suffered from various drawbacks. 
         [0010]    Thus, there is a need for an improved structural, fluid and electrical connector. 
         [0011]    There is also a need for an improved spacecraft connector which can be docked and separated in space. 
         [0012]    Additionally, it would be advantageous to provide a connector that can be utilized as a launch lock for affixing a spacecraft to a launch vehicle. 
         [0013]    Also desirable would be a spacecraft connector that can be utilized to connect and function as an interface between homogeneous cells of a spacecraft. 
         [0014]    Furthermore, it would be desirable to provide a spacecraft connector which is capable of functioning as a propulsion thruster when not functioning as a spacecraft interface connector. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention addresses the aforementioned disadvantages by providing an improved interface connector which has broad application throughout various industries wherever a connector is required to provide a structural, fluid and electrical connection. The interface connector of the present invention is believed to have particular application for use with vehicles, and particularly spacecraft. 
         [0016]    The connector interface of the present invention includes at least one male valve assembly and at least one female valve assembly. The male valve assembly includes a hollow housing forming a central cylindrical bore. The central bore has a proximal end which connects to a fuel supply, such as a fuel supply line or hose. The male valve further includes a piston within the central bore. The piston is retractable into the central bore and extendable from the central bore&#39;s distal end. Preferably, the male valve assembly includes one or more  0 -rings positioned around the piston for forming a fluid tight seal within the central bore&#39;s cylindrical surface. Each piston has a central conduit having a proximal end which is in fluid communication with the male valve&#39;s central bore. Meanwhile, the distal end of the piston&#39;s central conduit projects distally from the central bore&#39;s distal end. Further, the piston conduit&#39;s distal end is preferably formed to provide a divergent nozzle. The extension and retraction of the piston can be controlled by various mechanical apparatus as can be determined by those skilled in the art. However, in a preferred embodiment, the position of the piston is controlled by a helical spring, pneumatic extension and electromagnetic retraction. 
         [0017]    The connector interface&#39;s female valve assembly includes a hollow housing having its own central bore which includes a proximal end connected to a fuel tank, such as by a fuel line. A female valve assembly&#39;s central bore&#39;s distal end forms a receptacle sized for receipt of the male valve assembly&#39;s piston. To this end, preferably the piston&#39;s distal end has a substantially hemispherical shape sized for engaging an O-ring located within the female valve assembly&#39;s receptacle. 
         [0018]    Preferably, both the male valve assembly and female valve assembly include a valve for controlling the flow of fluid through their respective valve assemblies. Preferably, the male valve assembly&#39;s valve is simply a traditional open and closeable valve situated between a fuel source and the male valve assembly&#39;s central bore. Preferably the valve can be controlled by a central processor or the like. Meanwhile, the female valve assembly is preferably provided in the form of a ball valve within the female valve assembly&#39;s central bore. The ball valve includes a ball and a spring for biasing the ball towards and against the distally positioned O-ring. To open the ball valve, preferably the movement of the male valve assembly&#39;s piston to a distal position causes the piston to engage the ball to retract the ball proximally so as to disengage the O-ring to allow the flow of fluid through the female valve assembly. 
         [0019]    The interface connector of the present invention with its male and female valve assemblies is acceptable for use wherever structural, fluid and electrical (power and data) connection is required. For each instance, it is anticipated that the male valve assembly will be mounted to a first apparatus which will be referred to generally as a first frame. Meanwhile, the female valve assembly will be mounted to a second frame. The term “frame” is intended to be interpreted broadly to include any structure or housing of two units to be connected. 
         [0020]    In a preferred embodiment, the male valve assembly mounts to a first homogenous satellite cell having a first frame and the female valve assembly mounts to a second homogenous satellite cell having a second frame. Preferably more and more satellite cells are combined utilizing the interface connectors of the present invention to create a larger spacecraft. 
         [0021]    In a preferred embodiment, two spacecraft homogeneous cells are connected by a connector interface including two male valve assemblies and two female valve assemblies. The first and second male valve assemblies are mounted to a first spacecraft housing in an outwardly facing coaxially aligned relation to one another. More specifically, each male valve assembly&#39;s central bore and piston have the same central axis and the male valve assemblies are mounted in an opposing relation to one another such that extension of the pistons causes the pistons to move axially outward from one another, and retraction of the piston causes them to move axially inward toward each other. 
         [0022]    Meanwhile, the first and second female valve assemblies are mounted to a second spacecraft housing. Like the male valve assemblies, the female valve assemblies are mounted to the spacecraft in a manner wherein their central bores are coaxially aligned. However, instead of facing outward, the female valve assemblies are mounted to the second spacecraft in an inwardly facing relationship to one another. Furthermore, the female valve assemblies are mounted so as to be spaced so as to receive the two male valve assemblies, mounted to the first spacecraft, between the female valve assemblies when the male valve assembly pistons are in a retracted condition. However, the female valve assemblies are mounted to the second spacecraft so as to be sufficiently close together that the male valve assemblies and female valve assemblies will lock together when the male valve assembly pistons have projected into an extended position with the pistons projecting into the female valve assembly receptacles. More specifically, the male and female valve assemblies form interface connectors when the male valve assembly pistons are extended into the female valve assembly receptacles so as to engage the O-ring concentrically positioned within the female valve assemblies central bores. 
         [0023]    Advantageously, the pair of connectors, each with its own male and female valve assembly, forms a structural connection as the respective connectors, and spacecraft, cannot disengage without the connector pistons retracting. Moreover, the connectors form a fluid connection as a fluid flow path is provided from a first fuel tank in the first spacecraft through the male assembly&#39;s central bore, piston conduit, and through the female assembly&#39;s central bore to the second fuel tank in the second spacecraft. Moreover, preferably the connectors provide an electrical connection between spacecraft. Specifically, preferably the male valve assemblies helical springs and pistons are electrically conductive, and the female valve assemblies ball valve balls and helical springs are electrically conductive to allow the transmission of power and data. 
         [0024]    In addition, it is preferred that the male valve assembly be constructed so as to allow the piston to function as a propulsion thruster when not mated to a female valve assembly. To this end, it is preferred that the piston&#39;s distal opening be constructed in the form of a divergent propulsion nozzle. When not mated to a female valve assembly, propellant from a fuel storage tank can be made to flow through the male valve assembly and ejected from the piston&#39;s divergent nozzle by opening the male valve assembly&#39;s controllable valve. A preferred propellant is R134 tetrafluoroethane, though another cold gas, warm gas, or mono-propellant such as hydrazine would also be acceptable. 
         [0025]    Advantageously, it is an object of the present invention to provide a connector that provides improved structural integrity, such as for spacecraft docking applications. Unlike previous connectors, the present connectors utilize its mechanical properties of transferring force primarily in sheer and not normal. 
         [0026]    It is an additional object of the present invention to provide a connector that can be docked and separated in space. 
         [0027]    Still another object of the present invention is to provide an improved connector which provides structural, fluid and electrical (power and data) connectivity. 
         [0028]    Furthermore, it is an object of the present invention to provide a spacecraft connector which is capable of functioning as a propulsion thruster when not mated. 
         [0029]    Other features and advantages of the present invention will be appreciated by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a perspective view of a spacecraft homogenous cell incorporating traditional spacecraft architecture with a plurality of unmated male and female valve assemblies of the present invention; 
           [0031]      FIG. 2  is a perspective view illustrating three (3) homogenous spacecraft cells connected in a stacked condition utilizing the interface connectors of the present invention; 
           [0032]      FIG. 3  is a top perspective view illustrating six (6) homogenous spacecraft cells connected side-by-side utilizing the interface connectors of the present invention; 
           [0033]      FIG. 4  is a side cut-away view of the male and female valve assemblies of the interface connector of the present invention wherein the male valve assembly piston is being actuated from a soft dock condition to an extended locking condition; 
           [0034]      FIG. 5  is a side cut-away view of the male and female valve assemblies of the interface connector of the present invention wherein the male valve assembly piston has been extended so as to lock male and female valve assemblies together; 
           [0035]      FIG. 6  is a side cut-away view of a male valve assembly wherein the piston has been extended and propellant is being ejected from the piston&#39;s distal nozzle; 
           [0036]      FIG. 7  is a side cut-away view of a male valve assembly of the present invention wherein the male valve assembly&#39;s piston is being actuated from a soft dock condition to an extended condition; and 
           [0037]      FIG. 8  is a side cut-away view of the male valve assembly wherein the male valve assembly&#39;s piston has been retracted. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    While the present invention is susceptible of embodiment in various forms, as shown in the drawings, hereinafter will be described the presently preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the invention, and it is not intended to limit the invention to the specific embodiments illustrated. 
         [0039]    With reference to the figures, the present invention is an interface connector  21  having particular usefulness in connecting homogeneous spacecraft cells  1 . As illustrated in  FIGS. 1-3  a preferred homogenous spacecraft cell  1  has a top  3  a bottom  5 , and four sides  7 . The homogenous cell may include one more solar panels  9  and one or more momentum wheels  11 . In addition, the spacecraft cell  1  has a housing  13  forming a frame upon which the interface connectors  21  are mounted. 
         [0040]    The interface connector  21  includes a male valve assembly  23  and a female valve assembly  71 . As best illustrated in  FIGS. 1-3 , the male valve assembly  23  has a tapered housing  25 . The housing&#39;s tapered shape is considered ideal for in-space rendezvous and docking so as to self align when received by correspondingly shaped beveled recesses  15  formed upon another homogenous spacecraft cell. As illustrated in  FIGS. 4-8 , the male valve assembly&#39;s housing  25  may include a removable insert  26  for allowing the installation and removal of the remaining valve assembly components from within the male valve assembly&#39;s housing. O-rings  57  may be provided between the housing&#39;s insert  26  and exterior tapered portion of the housing so as to affix the insert  26  in place. 
         [0041]    As illustrated in  FIGS. 4-8 , the male valve assembly  23  includes a central bore  27 . Preferably, the cylindrical bore has a circular cross-section. As illustrated in the figures, the central bore has a smaller diameter towards its proximal end  29  and a larger diameter at its distal end  31 . Furthermore, the male valve assembly&#39;s central bore is connected to a fuel source such as by a fuel line  33  which radially projects through the valve assembly&#39;s housing towards the central bore&#39;s proximal end. 
         [0042]    The male valve assembly  23  also includes a piston  37 . As illustrated in the figures, a preferred piston is manufactured to include two components including a smaller diameter shaft  38  and a larger diameter piston head  39 . Preferably, the piston head  39  has a diameter sufficiently large to form a substantially gaseous tight seal within the central bore  27 . Furthermore, the piston may include an O-ring concentrically positioned around the piston head to form a gaseous tight seal between the piston head and the cylindrical surface of the central bore  27 . Advantageously, the difference in diameter between the piston&#39;s shaft  38  and piston head  39  provides the piston head with a circular collar region  47 . The smaller diameter shaft  38  slidably resides within the smaller proximal end  29  of the central bore  27 . Meanwhile, the larger diameter piston head  39  slidably resides in the larger distal end  31  of the central bore  27 . The piston  37  includes a central conduit  40  which extends the entire length of the piston through the shaft  38  and piston head  39 . Preferably, the piston head  39  includes a divergent nozzle  43  forming the distal end of the central conduit  40 . 
         [0043]    The male valve assembly&#39;s piston  37  is capable of moving proximally and distally within the central bore  27 . Movement of the piston can be actuated by various electrical or mechanical apparatus known to those skilled in the art. Applicant&#39;s preferred interface connector  21  includes a piston which is projected distally using pneumatic actuation, but moved proximally using an electromagnetic actuator. Moreover, it is preferred that the piston be maintained in a neutral central position by a helical spring  35  when not actuated proximally or distally. 
         [0044]    To enable the piston  37  to be pneumatically extended, the piston shaft  38  has a first channel  51  which extends from the fuel line  33  into a chamber  49  formed behind the piston&#39;s collar  47  when the piston is in a neutral “soft dock” position. As illustrated in  FIG. 4 , the release of propellant through the fuel line  33 , such as by opening a fuel valve (not shown), allows propellant to flow through the first channel  51  into chamber  49  so as to pneumatically force the piston distally. As illustrated in  FIG. 5 , the piston is forced distally until the first channel  51  is no longer in fluid communication with the fuel line  33 . Preferably an O-ring  57  is provided to provide a fluid tight seal so as to prevent further propellant passing through the first channel  51  into chamber  49 . 
         [0045]    As illustrated in  FIGS. 4-8 , preferably the piston shaft  38  further includes a second channel  53  which comes into fluid communication with the fuel line  33  when the piston has been extended to a distal position. As illustrated in  FIG. 5 , the second channel  53  connects the fuel line  33  with the male valve assembly&#39;s central bore  27  at the central bore&#39;s proximal end  29  so as to allow propellant to flow through the fuel line into the central bore  27 , and thereafter through the piston&#39;s central conduit  40 , so as to be ejected from the piston&#39;s distal end  43 . 
         [0046]    To move the piston  37  in the proximal direction, the male valve assembly  23  includes a magnetic actuator including an electrical magnetic field generator, such as a coil winding  59  concentrically positioned around the piston&#39;s shaft  38 . As understood by those skilled in the art, incorporating magnetic properties into the shaft  38  in cooperation with a controllable electromagnetic field provided by the magnetic field actuator  59  will cause the piston  37  to move in the proximal direction such as illustrated in  FIG. 7 . 
         [0047]    As illustrated in each of the figures, the interface connector  21  also includes a female valve assembly  71  intended to connect with the male valve assembly  23 . The female valve assembly  71  includes a tapered housing  73  which is also sized to be received and aligned within beveled recesses  15  formed within a homogenous spacecraft cell&#39;s housing  13 . Preferably the female valve assembly&#39;s housing also includes an insert  75  for allowing the valve assembly components to be easily installed and removed. 
         [0048]    As illustrated in  FIGS. 4 and 5 , the female valve assembly includes a central bore  77  having a proximal end  79  and a distal end  81 . The distal end is closeable by a ball valve  83 . The ball valve includes a ball  87 , an O-ring  89  having an inner diameter smaller than the diameter of the ball, and a helical spring  85  for biasing the ball distally into the O-ring for creating a fluid tight seal. As understood by those skilled in the art, the helical spring  85  maintains the ball valve in a normally closed condition. However, movement of the ball  87  in the proximal direction, such as by engagement by a male valve assembly piston  37 , will cause the ball valve to open. The female valve assembly further includes a fuel line  91  so that the female valve assembly&#39;s central bore  77  is connected to a fuel source (not shown). 
         [0049]    As illustrated in  FIGS. 4-8 , a connector  21  of the present invention includes both a male valve assembly  23  connected to a female valve assembly  71 . In a preferred embodiment, the interface connector  21  includes two sets of male and female valve assemblies. As illustrated in  FIGS. 1-3 , for this embodiment, the first and second male valve assemblies  23  are mounted, for example to a first spacecraft housing  13 , in an outwardly facing coaxially aligned relationship to one another. More specifically, each male valve assembly&#39;s central bore  27  and piston  37  share the same axis and the male valve assemblies are mounted so that each piston extends outward from one another and each piston retracts toward each other. Meanwhile, the female valve assemblies are mounted to a second spacecraft housing in a manner wherein the female valve assemblies central bores are also coaxially aligned. However, the female valve assemblies are positioned to be inwardly facing, and aligned and spaced so as to connect with two male valve assemblies. 
         [0050]      FIG. 4  illustrates a soft dock connection between a male valve assembly  23  and a female valve assembly  71 . The male valve assembly&#39;s piston is maintained in a neutral condition by the spring  35 . The male piston  37  projects partially into the female valve assembly&#39;s receptacle  62 , but the piston is not extended so far as to engage the female valve assembly&#39;s O-ring  89  so as to form a fluid tight seal. Without introduction of a gas, such as a propellant, into the male valve assembly&#39;s chamber  49 , the piston  37  can be displaced proximally relatively easily so as to allow engagement or disengagement of the male valve assembly to the female valve assembly. However, as illustrated in  FIGS. 5 and 7 , the introduction of propellant from fuel line  33  through first channel  51  into the male valve assembly&#39;s chamber  49  causes the piston  37  to move distally into the female valve assembly&#39;s receptacle  62  so as to engage and form a fluid tight seal with the female valve assembly&#39;s O-ring  89 . Though not illustrated in the figures, the piston conduit&#39;s distal end has a lateral slit across the divergent nozzle  43  so as to prevent a fluid tight seal between the piston&#39;s conduit  40  and the female valve assembly&#39;s ball  87 . Thus, as illustrated in  FIG. 5 , when the male valve assembly piston has been moved to a distal “hard dock” position, gas is freely capable of flowing through the male and female valve assemblies, as controlled by a valve connected to the male valve assembly&#39;s fuel line  33 . As would be understood by those skilled in the art, the opening of this valve causes propellant to flow from the high pressure region in either the first or second spacecraft, to the low pressure region in the first or second spacecraft. Disconnection of the male valve to the female valve and a resulting undocking of spacecraft can be accomplished by energizing the male valve assembly&#39;s magnetic coil winding  59  so as to retract the piston  37 . 
         [0051]    The interface connector  21  provides a structural-mechanical connection between two objects, such as affixing a spacecraft to a launch vehicle or connecting two homogenous spacecraft cells  1 . For example, as illustrated in  FIG. 2 , the interface connector  2  can connect a spacecraft comprised of plurality of homogenous cells  1  to a vehicle launch support structure  95 . Meanwhile as illustrated in  FIGS. 1-4 , preferably four sets of male and female valve assemblies are used to structurally connect two homogeneous spacecraft cells. Two male valve assemblies  23  and two female valve assemblies  71  are mounted to the side of a first spacecraft. As illustrated, these respective valve assemblies are affixed to opening edges of one side of the spacecraft. Meanwhile, the second homogenous spacecraft cell  1  also includes two male valve assemblies  23  and two female valve assemblies  71  mounted to opposing edges of a spacecraft side. The male valve assemblies are aligned to be outwardly facing and positioned between the female valve assemblies which are inwardly facing. The homogenous cells can be stacked as illustrated in  FIG. 2  or positioned side-by-side as illustrated in  FIG. 3 . Moreover, preferably the homogeneous cells include a carrousel  11  which incorporates reaction wheel, momentum wheel, control moment gyroscope, and/or gimbal capabilities. Preferably, the carousels  11  of adjoining cells can also be externally connected utilized four sets of male and female valve assemblies. 
         [0052]    In addition to providing a structural connection, the interface connector  21  of the present invention provides a fluid connector so as to allow propulsion fluids to flow from one spacecraft to another as illustrated in  FIG. 5 . Finally, the interface connector is capable of transmitting power and data. For this embodiment, preferably the female valve assembly&#39;s insert portion  75  of housing  73 , helical spring  85 , and ball  87  are electrically conductive. Conversely, it is preferred that the male valve assembly&#39;s insert portion  26  of housing  25 , piston  37  and helical spring  35  be electrically conductive. Movement of the piston  37  to a distal position to engage ball  87  provides an electrical connection through the male and female valve assemblies so as to permit the transmission of power and data. 
         [0053]    As illustrated in  FIG. 6 , the male valve assembly  23  is capable of functioning as a propulsion thruster when not mated to a female valve assembly. By opening the valve restricting the flow of propellant through fuel line  33  causes the piston to move distally so as to allow the passage of propellant into second channel  53  to the male valve assembly&#39;s central bore  27 . Propellant is then ejected from the piston&#39;s divergent nozzle  43  to provide station keeping or propulsion. 
         [0054]    As would be understood by those skilled in the art, the opening or closing of the valve supplying fuel to the male valve assembly&#39;s fuel line  33  is preferably controlled by one or more control processors, referred to herein as a controller. The controller may be a general purpose computer or microprocessor including hardware and software as can be determined by those skilled in the art to provide automated or directed control of the fuel valve so as to open and close the valve to thereby control the flow of fuel through the male valve assembly and the female valve assembly when a connector is in a mated condition. Similarly, the same controller, or a separate controller, is connected to the electromagnetic actuator  59  to control the retraction of a piston  37 . In addition the same controller, or a separate controller, controls the expulsion of the propellant from the male valve assembly&#39;s nozzle  43  when the male valve assembly  23  is not connected to a female valve assembly  71 . Furthermore, one or more controllers may control the transmission of power and data through the male and female valve assemblies from the one connected. 
         [0055]    While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Therefore, it is not intended that the invention be limited except by the following claims. Having described my invention in such terms so as to enable person skilled in the art to understand the invention, recreate the invention and practice it, and having presently identified the presently preferred embodiments thereof I claim: