1. A method for estimating range of an object of interest in a cloud of objects of lesser interest and travelling in a ballistic manner within the field of view of an IR sensor, the method comprising: (a) receiving in an object selection and discrimination processor, RF sensor data associated with an object, the RF data including position and velocity data in a given coordinate frame; (b) transforming in said object selection and discrimination processor, the RF sensor data from the given coordinate frame to an IR coordinate frame and subtracting the sensor location in the IR coordinate frame to generate an initial range measurement perpendicular to the IR sensor focal plane; (c) receiving IR sensor data in said object selection and discrimination processor, associated with an object and generating an initial line of sight (LOS) vector in the IR coordinate frame; (d) combining in said object selection and discrimination processor, the initial range measurement represented in the IR sensor focal plane with the initial line of sight (LOS) vector in the IR sensor coordinate frame to form an initial IR 3-D state estimate; (e) initializing at least a 6-state estimation filter for providing a position estimate using the initial IR 3-D measurement represented in the IR sensor focal plane; (f) receiving IR sensor data including IR angular measurements associated with an object and generating in said object selection and discrimination processor a line of sight (LOS) vector in the IR sensor coordinate frame; (g) filtering using the at least 6-state estimation filter 3-D position and velocity estimates using the IR LOS measurements as inputs to generate in said object selection and discrimination processor, updated 3-D position and velocity state estimates; and (h) comparing in said selection discrimination processor, said updated 3-D position and velocity state estimates with a threshold value, and repeating steps (f) and (g) over a given time interval until said threshold value is reached.