Reentry Tracking Improvements for the Tradex Radar

The Tradex radar at Kwajalein gathers both signature and metric data on reentry objects. Accurate real-time tracking is essential to: (1) keep the target in the center of the antenna beam for highest possible signal-to-noise, (2) place a limited number of data samples about the target, end (3) to provide accurate real-time pointing data for other sensors. For tracking well-behaved ballistic reentry objects, the Tradex radar employs a 6-state Kalman ballistic filter which is based on ballistic equations of motion and nominal drag profiles. The perfomance of this filter depends on the validity of the a priori drag infomation. Unfortunately, the drag profiles of Tactical Ballistic Missiles to be tested in upcoming missions are variable or unknown. Although Tradex could use its 9-state Kalman polynomial filter for these targets, the performance of the filter is severely limited by simplifying assumptions embedded in its formulation. Recent increases in processor speeds allow for more complex filters with fewer limitations. We propose to use a 7-state Kalman ballistic filter with drag as the seventh state and hence, does not depend on a priori drag information. Three and four measurement versions will be implemented. To improve track perfomance these filters use few simplifying assumptions, yet maintain sufficient computational efficiency to be implemented on existing Tradex equipment. An improved track filter will permit Tradex to maintain track of targets which would have otherwise been lost. By maintaining track of errant vehicles, data will be collected without expanding scarce resources for additional testing. Since it is implemented in software, the filter will be readily transferable to other test range radars, military defense systems, as well as commercial tracking facilities.