Infrared Window Aerothermal Response Model for Hardware-in-the-Loop

The U.S. Air Force Research Laboratory (AFRL) continues to advance the state-of-the-art in high-speed, low-altitude flight guided by electro-optic / infrared (EO/IR) seekers. Hardware-in-the loop (HWIL) test facilities provide a low-cost, repeatable, low-risk alternative prior to flight testing or operational deployment to support more complete exploration of the potential flight envelope, and early testing of hardware or software modifications. This capability reduces development risk, reduces acquisition life-cycle costs, and increases government insight into system performance by identifying issues earlier in the acquisition life-cycle. With expanding flight envelopes, HWIL technologies must be developed for testing in relevant flight environments. As a result, AFRL must upgrade HWIL technologies to account for the higher velocities and accelerations. For EO/IR seekers, the HWIL scene simulator must present realistic scenes that include the dominant effects that degrade IR sensor performance introduced by the atmosphere, aero-dynamic flow, and resulting window heating.  Polaris Sensor Technologies, Inc. proposes to design an HWIL scene simulator that captures both aero-optical and thermal-structural impact to wave propagation through optical windows on high-speed airframes. The technology gap addressed by this proposed effort is the real-time model to provide the window heating-induced effects in a closed-loop trajectory simulation. Implementation for atmospheric and aero-optical effects, which are effectively determined by the instantaneous location / position relative to the target, is straight forward. However, due to the relatively long time scales of the window response, the feasibility of the surrogate approach needs to be evaluated. Polaris proposes to modify an existing 2D Finite Element Model (FEM), previously used for test and evaluation (T&E) of seeker windows, to produce a training set of the required optical parameters. Polaris will develop and anchor a surrogate window-heating model and evaluate the applicability of using this approach in place of the FEM. A key outcome anticipated from the proposed effort is the evaluated real-time, window-heating model. The expected Phase I end state is (1) a design of the surrogate models for atmospheric, aero-optic, and window heating effects, (2) a design of the scene generation code to include these effects, (3) a preliminary hardware configuration and interface control document, and (4) a Phase II plan.