Active tracking at optical wavelengths through a long atmospheric path

This paper presents an overview and the results of a scaled experiment in the active tracking of theater missiles. The objective of the experiment was to explore the use of optical wavelengths in the tracking of theater missiles from an airborne platform. The experiment adjusted the wavelength, aperture size, and path length so that measured results of the short-path, scaled experiment would infer the performance of an airborne platform tracking a missile through a near-horizontal atmospheric path hundreds of kilometers long. The tracking stabilized the line-of-sight to target to allow the subsequent pointing of a scoring beam. The scoring beam is used as a surrogate for the high energy laser planned for the actual mission. In the experiment, the scoring beam had to be pointed with enough precision to hit a designated aimpoint on the missile. This goal and the operational environment generated requirements for precision tracking and pointing which previously have not been achieved. The paper addresses the two major issues in actively tracking missiles over a long, atmospheric path. The first issue is to provide uniform illumination of the missile's body for the active tracker. The second issue is the stabilization of the line-of-sight (LOS) from the missile's illuminated nose to the receiving aperture of the tracker. Two kinds of classical track algorithms were examined for this purpose. The paper includes the method for track illumination and the performance of these two classes of optical track algorithms tested.