Tracking is accomplished either by way of an optical tracker or by providing the control program azimuth and elevation coordinates. MATrIS currently uses differential GPS in addition to optical tracking. A GPS located on the system combined with radiated GPS data from targets can provide a very accurate means of tracking. The information from both GPSs is processed by a MATLAB (The Math Works, Natick, Massachusetts) program to obtain relative azimuth and elevation to the target and is sent to the gimbal control. GPS tracking has the ability to be very accurate but delays and dropouts can cause tracking errors. The data delays and dropouts in the GPS tracking require extrapolation of the target velocity vector, which can cause problems with tracking aggressively-maneuvering vehicles. GPS coordinates and pre-programmed or other knowledge of the trajectory is almost a necessity for initial acquisition of many targets. Optical tracking is not as inherently accurate, can be jittery, and can loose-lock on the target if another object enters the field (for example, clouds). Optical tracking does not offer any benefit for initial target acquisition. The ability to blend optical and GPS tracking offers a possible method to overcome many of the combined limitations and is being pursued.
A mobile, rapidly deployable ground-based system has been developed to track and image targets of aeronautical interest. The MATrIS (Mobile Aerial Tracking and Imaging System) was conceived through a study of ground-based imaging to obtain global aerothermal characteristics of reusable launch vehicles (RLVs). This study was conducted jointly with NASA and the Missile Defense Agency/Innovative Science and Technology Experimentation Facility (MDA/ISTEF). The favorable results indicated the desire to have a relatively inexpensive, mobile, and rapidly deployable system to obtain these measurements. Further, such a system can be adapted for use with other aeronautical targets in addition to reentry vehicles.
Many challenges in developing this system persist. Although high spatial resolution is desired the resultant long-focal-length, high-f/number systems require very precise tracking because of the high sensor integration time necessary for the small relative aperture and the narrow field of view. Larger optics and more precise trackers were cost prohibitive, so shorter focal length systems are necessary for imaging lower contrast, fast angular rate targets. Acquiring, and more so re-acquiring, a target is extremely difficult without near-real-time trajectory data (known trajectory, GPS or radar). GPS tracking and optical tracking each have benefits and limitations. Blended GPS and optical tracking may alleviate many of these limitations and is being pursued.
Future plans include demonstrating this system on the next practical reentry event and expanding the range of vehicles and flows that can be visualized with long range IR thermography.