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Current targeting approaches involve guiding to a spatially derived guidepoint of a group of objects likely to be the preferred object. This method may not allow the intercepting missile to contain the preferred, or other probable object(s), within its divert capability. The guidepoint is shifted cl

Current targeting approaches involve guiding to a spatially derived guidepoint of a group of objects likely to be the preferred object. This method may not allow the intercepting missile to contain the preferred, or other probable object(s), within its divert capability. The guidepoint is shifted closer to the preferred object using specific energy and angular momentum, constants of orbital motion, which describe properties of an object's trajectory. Guiding to the specific energy derived guidepoint does not offer significant benefit over guiding to the spatially derived guidance point. However, computing the spatial rate of change of specific energy within the plane formed by the guidance objects establishes a vector pointing close to the preferred object. This is the direction to shift the guidepoint in order to contain the preferred object within the interceptor's divert capability.

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1. A method for targeting a preferred object from among a plurality of ballistic objects in an associated group of objects, said method comprising the steps of: sensing a group of potential target objects which includes a preferred object and an associated group of non-preferred objects to produce p

1. A method for targeting a preferred object from among a plurality of ballistic objects in an associated group of objects, said method comprising the steps of: sensing a group of potential target objects which includes a preferred object and an associated group of non-preferred objects to produce position and velocity vectors for each potential target object;computing from said position and velocity vectors at least one of specific energy and specific angular momentum for each of said potential target objects, to produce constants of orbital motion;from said constants of orbital motion, identifying three target objects having values of said one of said specific energy and specific angular momentum above a threshold, to identify a group of the three most likely target objects;calculating a spatially derived guidance point of said group of three most likely target objects;calculating a spatial rate of change of said constants of orbital motion, to produce a guidance direction increment;combining said spatially derived guidance point with said guidance direction increment to produce a target point which is closer to a location of said preferred object than is said spatially derived guidance point; andcontrolling thrust of an interceptor vehicle to guide said interceptor vehicle toward said target point. 2. A method according to claim 1, wherein said step of computing from said position and velocity vectors at least one of specific energy and specific angular momentum for each of said potential target objects, to produce constants of orbital motion, includes the steps of, for each of said potential target objects, calculating one of (a) the specific energy E of the potential target object as E=V22-μerwhere:V is the velocity of the potential target object;r is the radius to the center of the Earth; and μe=3.986×1014⁢m3s2and(b) the specific angular momentum H as H=rV cos φwhere:φ is the angle between the velocity vector and the local horizon. 3. A method according to claim 1, wherein said step of identifying three target objects having values of said one of said specific energy and specific angular momentum above a threshold value, to identify a group of the three most likely target objects, includes the step of: ranking a value of said one of said specific energy and specific angular momentum for each of said potential target objects; anddeeming those three objects having values above a threshold as being the group. 4. A method according to claim 1, wherein said step of calculating a spatially derived guidance point includes the step of calculating: r→c=13⁢∑i=13⁢⁢r→iwhere:the number of objects is three;{right arrow over (r)}i is a position vector of the ith object; andi is an index representing the ith object. 5. A method according to claim 1, wherein said step of calculating a spatial rate of change of said constants of orbital motion, to produce a guidance direction increment includes the step of calculating the specific energy gradient as: ∇→⁢E=∂E⁡(x,y)∂x⁢i^+∂E⁡(x,y)∂y⁢j^. 6. A method according to claim 1, wherein said step of combining said spatially derived guidance point with said guidance direction increment to produce a target point includes the steps of: identifying a line extending between two of said three target objects having values of said one of said specific energy and specific angular momentum above a certain threshold; andidentifying as said target point an intersection of said line and a projection of said spatially derived guidance point that is parallel with said direction increment. 7. A method according to claim 1, wherein said step of combining said spatially derived guidance point with said guidance direction increment to produce a target point includes the steps of: shifting a guide point from the spatially derived guidance point in a direction parallel to a direction of the specific energy gradient; andcontinuing said shifting of the guide point from the spatially derived guidance point until the guide point intersects a line connecting the two objects having values of specific energy above a certain threshold. 8. A method according to claim 1, wherein said method includes the step, after said step of controlling the thrust of said interceptor vehicle toward said target point, of: determining which of said potential target objects is the preferred object; andtransitioning control of said interceptor vehicle to guidance toward said preferred object. 9. An engagement system for targeting and engaging a preferred object among a group of non-preferred objects, said system comprising: at least one sensor for sensing a group of potential target objects which includes a preferred object and an associated group of non-preferred objects to produce position and velocity vectors for each potential target object;a computer for computing from said position and velocity vectors at least one of specific energy and specific angular momentum for each of said potential target objects, to produce constants of orbital motion;a computer for ranking the constants of orbital motion for each of the potential target objects, and for determining three target objects having values of said one of said specific energy and specific angular momentum above a threshold value as a group of the three most likely target objects;a computer for calculating a spatially derived guidance point of said group of three most likely target objects;a computer for calculating a spatial rate of change of said constants of orbital motion, to produce a guidance direction increment;a computer for combining said spatially derived guidance point with said guidance direction increment, to produce an interceptor vehicle target point which is closer to a location of said preferred object than is said spatially derived guidance point; anda controllable thrust controller coupled to receive said interceptor vehicle target point, and coupled to said interceptor vehicle, for controlling thrust of said interceptor vehicle to guide said interceptor vehicle toward said interceptor vehicle target point. 10. A system according to claim 9, further comprising: a computer coupled for receiving at least said constants of orbital motion, for determining which of said potential target objects is the preferred object, and for commanding a transition from guidance toward said interceptor vehicle target point to guidance toward said preferred object; anda computer coupled to said interceptor vehicle for receiving said command for transition from guidance toward said target point to guidance toward said preferred object, and for effectuating said transition from guidance toward said target point to guidance toward said preferred object. 11. A system for targeting a preferred object from among a plurality of ballistic objects in an associated group of objects, said system comprising: a processor executing instructions for performing the steps of: sensing a group of potential target objects which includes a preferred object and an associated group of non-preferred objects to produce position and velocity vectors for each potential target object;computing from said position and velocity vectors at least one of specific energy and specific angular momentum for each of said potential target objects, to produce constants of orbital motion;from said constants of orbital motion, identifying a plurality of target objects having values of said one of said specific energy and specific angular momentum above a threshold, to identify a group of the most likely target objects;calculating a spatially derived guidance point of said group;calculating a spatial rate of change of said constants of orbital motion, to produce a guidance direction increment;combining said spatially derived guidance point with said guidance direction increment to produce a target point which is closer to a location of said preferred object than is said spatially derived guidance point; andcontrolling thrust of an interceptor vehicle to guide said interceptor vehicle toward said target point. 12. A system according to claim 11, wherein said step of computing from said position and velocity vectors at least one of specific energy and specific angular momentum for each of said potential target objects, to produce constants of orbital motion, includes the steps of, for each of said potential target objects, calculating one of: (a) the specific energy of the potential target object, and (b) the specific angular momentum of the potential target object. 13. A system according to claim 11, wherein said step of identifying three target objects having values of said one of said specific energy and specific angular momentum above a threshold value, to identify a group of the most likely target objects, includes the steps of: ranking a value of said one of said specific energy and specific angular momentum for each of said potential target objects; anddeeming those objects having values above a threshold as being the group. 14. A system according to claim 11, wherein said step of calculating a spatial rate of change of said constants of orbital motion, to produce a guidance direction increment includes the step of calculating a specific energy gradient. 15. A system according to claim 11, wherein said step of combining said spatially derived guidance point with said guidance direction increment to produce a target point includes the steps of: identifying a line extending between two objects of said group having values of said one of said specific energy and specific angular momentum above a certain threshold; andidentifying as said target point an intersection of said line and a projection of said spatially derived guidance point that is parallel with said direction increment. 16. A system according to claim 11, wherein said step of combining said spatially derived guidance point with said guidance direction increment to produce a target point includes the steps of: shifting a guide point from the spatially derived guidance point in a direction parallel to a direction of the specific energy gradient; andcontinuing said shifting of the guide point from the spatially derived guidance point until the guide point intersects a line connecting the two objects having values of specific energy above a certain threshold. 17. A system according to claim 11, wherein said processor executes instructions for performing the additional steps, after said step of controlling the thrust of said interceptor vehicle toward said target point, of: determining which of said potential target objects is the preferred object; andtransitioning control of said interceptor vehicle to guidance toward said preferred object.