TIER II Plus airborne EO sensor LOS control and image geolocation

TIER II Plus is a high altitude unmanned reconnaissance aircraft carrying a synthetic aperture radar (SAR) and electro-optical/infrared (EOIR) sensor that will provide all-weather, day and night, high resolution imagery of ground targets for joint armed forces users. Its high area coverage rate is achieved in near real-time by transmitting the collected imagery while the vehicle is airborne and relaying that imagery via satellite to ground stations for processing and dissemination. The electro-optical sensor assembly consists of a mid-wave infra-red (MWIR) staring array built by Hughes Aircraft Company and a CCD visible staring array from Kodak that share common reflective optics. The telescope/sensor subassembly is mounted on the inner gimbal of a two axis gimbal set that directs the sensor line-of-sight (LOS) to designated earth-fixed locations. An on-gimbal inertial rate sensor provides the 2-degree-of-freedom (2DOF) inertial reference to stabilize the sensor LOS. An off-gimbal GPS-aided inertial navigation system (INS) provides aircraft navigation data to the control system for inertial position stabilization and for determining the target image geolocation. Fine stabilization and step/stare requirement is jointly achieved with two-axis image motion compensation (IMC) mirror mechanisms mounted internally in the telescope optical train. This paper describes the salient features of the TIER II Plus control system design with emphasis on the algorithms used for LOS control, command generation, and target image geolocation. Computer simulation results will be presented to support the design