Abstract:
A rocket tube for housing a reloadable rocket motor is connected to a spacer element and a wire-rider element. A sensor target for reflecting radar signals is screwably attached to the rocket tube. The sensor target is provided with a plug for effectively sealing one end of the rocket tube with the other end of the rocket tube being utilized to reload a rocket motor upon completion of a test firing. A guide wire is threaded through the wire-rider element with the guide wire serving as a travel path. The rocket tube, spacer element, and wire-rider element are connected in an easily assembled, aerodynamic manner that allows for multiple radar tests using the same components within a brief time period.

Description:
The invention described herein may be manufactured, used and licensed by or for the U.S. Government for governmental purposes without payment of any royalties thereon. 
   BACKGROUND OF THE INVENTION 
   I. Field of the Invention 
   The present invention relates to the field of radar reflector devices for radar testing. More particularly, the present invention pertains to a wire-guided, reusable, low cost, variable velocity, low mass rocket assembly for use in ground truthing tests for radar tracking and ranging systems 
   II. Discussion of the Background 
   An often used prior art method of radar testing requires the simultaneous use of multiple rocket motors mounted concentrically around a guide wire which necessitated the fabrication and use of elaborate wire riders. Very lengthy reload times were experienced with these heavy and relatively complicated prior art systems. Further, the prior art rocket models were difficult to stop on a guide cable. The significant weight or mass of these prior art models resulted in relatively high amounts of kinetic energy being realized at peak velocities which necessitated the construction of elaborate bungie-type stop mechanisms. Still further, the quantity of parts required for prior art systems resulted in significant material costs. 
   Thus, a clear need was present for a low-cost, time efficient, high velocity high-radar return rocket powered sensor target assembly. 
   SUMMARY OF THE INVENTION 
   Accordingly, one object of the present invention is to provide a low cost, re-usable rocket-powered, sensor target assembly. 
   Yet another object of the present invention is to realize a rocket-powered, sensor target assembly having a high radar return. 
   These and other valuable objects are realized by a radar sensor target assembly that includes a rocket tube, a spacer element, and a wire-rider element that are connected together. A sensor target is connected to the rocket tube. A guide wire is inserted through the wire-rider element to provide a travel path for the radar sensor target assembly. The assembly is propelled along the guide wire by a reloadable rocket motor that is easily inserted into the rocket tube. 
   The sensor target has a base plug region for sealing an end of said rocket tube. The base plug region is connecting to a threaded portion of the sensor target, the threaded portion allowing the sensor target to be screwably secured to the rocket tube. The plug region and threaded portion of the sensor target are integrally connected. 
   The present invention allows many radar tests to be conducted over a short period of time. Further, the present invention may be utilized in acoustic tests, infrared tests and other type tests where waves of a specific wave-length are reflected off the sensor element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of the rocket-powered, sensor target assembly according to the present invention. 
       FIG. 2  is a perspective view of a corner reflector sensor as used with the assembly of  FIG. 1 . 
       FIG. 3  is a side view of the corner reflector sensor as used with the assembly of  FIG. 1 . 
       FIG. 4  is a frontal or top view of the corner reflector sensor as used with the assembly of  FIG. 1 . 
       FIG. 5  is a perspective view of a rocket-powered, sensor target assembly according to another embodiment of the present invention. 
       FIG. 6  is a frontal view of the target sensor element according to the embodiment of  FIG. 5 . 
       FIG. 7  is a side view of the target sensor element according to the embodiment of  FIG. 5 . 
       FIG. 8  is a frontal view of the target sensor element and wire rider tube according to the embodiment of  FIG. 5 . 
       FIG. 9  is a side view of the embodiment of the invention of  FIG. 5 . 
       FIG. 10  is a frontal view of the corner reflector sensor and wire rider tube used in the embodiment of the invention in  FIG. 1 . 
       FIG. 11  is a side-view of the embodiment of the invention of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   With reference to  FIG. 1 , a rocket-powered, sensor target assembly  10  according to the present invention has a rocket tube  12  for accommodating a reloadable rocket motor such as the type disclosed in U.S. Pat. No. 5,212,946 to Hans et al. which issued on May 25, 1993 for a “Reloadable/Modular Solid Propellant Rocket Motor” and which is herein incorporated by reference. 
   In the prototype of the present invention, the rocket tube used was a one-inch diameter aluminum tube having a length of approximately eight and one-half inches. The opening  24 A at the front of the tube is bordered by an inner threaded circumferential portion on the inside wall of the tube (not shown) which allows the tube  12  to be securely and screwably attached to the sensor target  16 . The rear opening  24 B provides access to the interior of tube  12  so as to provide for the easy reloading of a propellant rocket motor. 
   A spacer element  14  lies over tube  12  and extends over the tube&#39;s length. Spacer element  14  has a prism-type shape except that an arc-shaped surface  20  extends along its top and an arc-shaped surface  22  extends along its bottom. Arc-shaped surface  20  accommodates a wire-rider tube  18  and arc-shaped surface  22  allows for flush contact with an outer circumferential region of the rocket tube  12 . In the prototype of the present invention spacer  14  was made of molded plastic and the wire-rider tube  18  was a ¼ inch copper tube. 
   The rocket tube  12 , the spacer  14  and the wire-rider tube  18  are secured to each other by tubing spacer clamps  26 A,  26 B. Alternatively, the rocket tube  12 , spacer  14  and wire-rider tube  18  could be glued, epoxied, or welded together or molded as an integral unit. (The wire-rider tube could be replaced with rings or eyelets connecting to a spacer element. The eyelets can be provided with a spring-loaded quick attachment/detachment mechanism similar to the locking/securing mechanisms used in a jewelry necklace, i.e., a clasp securing mechanism. Also, the spacer can be a two-pieced hinged element that is opened and closed by locking and unlocking a hinged cap by a hasp with the guide wire being positioned between the two pieces of the spacer; thus the spacer would include a wire-riding means.) 
   With reference to  FIGS. 2 ,  3  and  4 , the sensor target  16  is a corner-reflector type sensor target. The well  30  of the sensor target has a bottom  32  or vertex that may be viewed as the connecting point of three isosceles triangle-shaped surfaces  34 A,  34 B,  34 C. A threaded portion  28  of the target sensor  16  allows a secure connection to the rocket tube  12  and a plug portion  29  at the base of the sensor target serves as a forward plug seal that restricts out-gassing and encourages proper burning of the rocket motor propellant. 
   The rider tube  18  allows the rocket-powered, sensor target assembly  10  to be propelled along the path of a guide wire  80  which is inserted through the rider tube  18 . 
   When the sensor target  16  is used with a reloadable solid propellant rocket motor such as disclosed in the aforementioned U.S. Pat. No. 5,212,946, the forward plug assembly elements are simply removed from the cylindrical housing or rocket tube and replaced with the sensor target  16 . (In U.S. Pat. No. 5,212,946, the forward plug assembly elements are those elements which lie above O-ring  37  in  FIG. 3  thereof). 
   In  FIGS. 5 and 9 , the rocket-powered, sensor target assembly  40  according to another embodiment of the invention has a rocket tube  12  that is secured to offset spacers  50 A and  50 B and to wire-rider tube  18  by clamps  60 A and  60 B. Offset spacer  50 A has a tapered region  52 A that extends laterally inward from opposing sides of offset spacer  50 A. Point A can be viewed as extending on a line formed by the opposing tapered sides of offset spacer  50 A which line is normal to a centerline that extends through the entire length of rocket tube  12 . 
   In a like manner, offset spacer  50 B has a tapered region  52 B that extends laterally inward from opposing sides of offset spacer  50 B. Point B can be viewed as extending on a line formed by the opposing tapered sides of offset spacer  50 B which line is normal to a centerline that extends through the entire length of rocket tube  12 . 
   A line drawn through points A and B would be parallel to a centerline extending through the rocket tube  12 . The top and bottom of offset spacer  50 A and the top and bottom of offset spacer  50 B are formed to accommodate the wire-rider tube  18  and the rocket tube  12 , respectively. An open space  54  is formed between the offset spacers  50 A,  50 B and the rocket tube  12  and the wire-rider tube  18 . 
   Still with reference to  FIGS. 5 and 9 , the sensor target  42  is in the shape of a rocket propelled grenade (RPG) so that radar testing can be performed on an object having the actual shape and velocity of an RPG. 
   In a similar fashion, sensor targets could be molded to conform to any number of desired shapes, etc. The target sensor  42  is made of aluminum and has a nose section  46  that is positioned in front of a conical section that is attached to an end plate region  44 . End plate region  44  is attached to threaded portion  48  and plug portion  49 . Like the sensor reflector target  16 , the sensor target  42  is threadably attached to the rocket tube  12 . 
   With reference to  FIGS. 8 and 9 , the frontal view of the rocket-powered sensor target assembly  40  demonstrates that the wire-rider tube  18  is positioned just above and behind the top of the end plate region of the sensor target  42 . This positioning ensures that a guide wire inserted into the wire-rider tube will not contact or be impeded by other elements of the assembly. This positioning in conjunction with the lightweight, and aerodynamic design of the rocket-powered sensor target assembly provides for improved acceleration capability and velocity over the prior art. 
   Likewise, with reference to  FIGS. 10 and 11 , the wire-rider tube is positioned just above and behind the sensor target  16  so as to ensure that a guide wire inserted into the wire-rider tube  18  will not contact or by impeded by other elements of the rocket-powered, sensor target assembly  10 . 
   In a preferred operation of the assembly, wire-rider tubes  18  would be threaded to guide wire cables of sufficient length for the rocket assembly to come to a stop after burnout while still on the guide wire. When the wire-rider tube is on the guide-wire, the remaining elements of the rocket-powered, sensor target assembly are assembled to the wire-rider tube. 
   The rocket is armed by inserting an electric ignition match into the motor assembly. The operator can then move a safe distance away and fire the rocket at a desired time. After motor burnout and flight, the empty motor is replaced with a replacement motor. The rocket-powered, sensor target assembly is then ready for a new test within a span of about five minutes. The hardware of the present invention is re-usable and interchangeable, with the only consumable item being the rocket motor reload. 
   The corner reflector sensor target threads directly into a reloadable rocket motor assembly without having to use any interfacing hardware. The corner reflector sensor target utilizes the high radar reflectivity properties of a corner cube such that the relatively small reflector area provides a large radar cross-sectional return. The velocity profile of the model can be changed by varying the load of the reloadable rocket motor. The small area of the rocket assembly of the present invention reduces drag forces and allows the model to approach speeds of Mach 1. The unique characteristics of the device allow it to be reloaded and reused in roughly five minutes. In the present invention only one reloadable rocket motor is utilized per firing; thus, both the time and cost of radar testing is reduced significantly. 
   The light weight of the present invention makes it possible for a copper-tube wire guide (the type available at hardware stores) to be used to guide the rocket powered sensor target assembly down a rocket path that is provided by a steel cable or guide wire. 
   The light weight and low inertial design of the present invention allows it to be accelerated to higher velocities while realizing shorter stopping distances. The invention allows for more testing in less time with fewer parts that require less maintenance. Accordingly, significant cost savings are achieved. Further, since the present invention is lightweight and can be easily contained on a steel cable, radar testing laboratories can conduct tests at their own facilities without need of traveling to a rocket test range. 
   Various modifications are possible without deviating from the spirit of the present invention. Accordingly the scope of the invention is limited only by the claim language which follows hereafter.