Development of Zinc Sulfide Seeker Window Material

Ground based interceptors can benefit significantly from the use of a dual color focal planes and wideband seekers for improved target acquisition and target discrimination. Zinc sulfide has been under evaluation as a replacement window for the THAAD seeker system to replace the current sapphire window. Zinc sulfide presents a wideband capability and will result in a significant system cost reduction of 70%-80% for the seeker window. The transmission capabilities of the current window material have a limited waveband. A material which has the ability to transmit at a higher waveband will be beneficial for target acquisition and target discrimination. Analysis has been conducted on alternate seeker window materials using rigorous computational fluid dynamics to predict the worst case aerodynamic heating combined with finite element thermal and structural analysis used to construct a statistical analysis model. In addition to the analysis conducted, thermophysical property testing and optical property testing has been accomplished under the Phase I Sbir effort to verify analytical predictions. This model, supported by test data, shows that ZnS can withstand worst case heating and will provide improved optical properties as compared to sapphire. To prepare zinc sulfide for system consideration, flight test, and Block Upgrade, thermostructural evaluation under worst case flight conditions and high fidelity over-testing of the worst case thermal conditions will be conducted to validate the selection of zinc sulfide. Commercially available multispectral zinc sulfide, which contains an anti-reflective coating, will be tested in the AEDC/WO Hypersonic Wind Tunnel to validate its thermostructural capabilities. A total of 10 test runs will be conducted consisting of three (3) calibration runs followed by the testing of seven (7) ZnS windows in order to obtain statistical data. Fully instrumented, full-scale forecones and windows will be used for these tests. The resulting data will be used to conduct a 3D structural analysis and verify ZnS probability of survival.