1. A passive ranging/tracking method for tracking a target, comprising the steps of: (a) producing at least a first and a second sets of direction measurements of the target with respect to a carrier from at least a first and second passive sensors through at least a first and second tracking control devices respectively, wherein said two passive sensors are installed on said carrier and each of said passive sensors is controlled by said respective tracking control device to keep pointing to said target; (b) producing navigation data of said carrier, including position, velocity, and attitude data, using an onboard navigation system; (c) computing a target range vector measurement of said target with respect to said carrier using said two sets of direction measurements; and (d) extracting three-dimensional position and velocity information of said target at a current epoch using said target range vector measurement.