||Wright-Patterson AFB, OH 454337542
Hypersonic flights lead to high temperature flows, air dissociation, and cumulative heating of air-frames. Consequently the performance of all on-board sensor systems such as GPS, telemetry, communication, command and control, radar, ladar, and electro-optical sensors are all adversely affected to varying degrees by the hypersonic environment. Further, the dynamic range of parameters that characterize the environment is quite large and is strongly influenced by many factors including altitude, velocity, duration of flight, geometry of the vehicle, airframe, and heat-shield material. For instance, the electron density can vary by several orders during the course of a trajectory. Hence, sensor systems encounter a variety of situations. Some of the issues encountered include signal attenuation, communication blackout, signal distortion due to turbulent flow, radiation from heated optical windows, and emission from hot flows. Communication blackout although old is still a problem and is encountered when the signal frequency is well below the plasma frequency. An adaptive sensor system which uses a diagnostic tool to sense and adaptively match to the environment will be desirable. Even in the case when the signal is above the plasma frequency the boundary layer flow can be dispersive, inhomogeneous, fluctuating, and lossy. This poses challenges to wideband RF system using conformal arrays. With arrays we also face the problem of mutual coupling and impedance mismatch effects on beam forming. Moreover, the signal transmitted from the vehicle may be sufficiently intense to initiate nonlinear processes in the flow. The rapid maneuvers and high velocity place limitations on the integration time of the processing algorithms of the receivers. Although optical sensors are not similarly affected by hypersonic flow as RF sensors, they have their own share of issues. The hot window can radiate at infrared frequencies and the hot flow fields can emit and absorb at optical frequencies thereby seriously affecting the optical and EO/IR sensors on board. Two major problems of concern are beam pointing error and wave front distortions. We are particularly interested in assessing the impact of environment on spectral measurements and imaging. Research opportunities exist in the analyses and mitigation of the above-mentioned issues confronted by sensors aboard hypersonic platforms.
Communication blackout; Turbulent hypersonic flow; Diagnostic tools; Adaptive sensors; Nonlinear processes; Optical windows;