SBIR-STTR Award

Multispectral zinc sulfide (ZnS) has been identified as a candidate seeker window material for defensive interceptor applications. Zinc sulfide is currently being tested for thermophysical and optical properties to confirm its performance and validate analytical predictions. The ZnS currently being tested does not contain an antireflective (AR) coating. Due to the increase in spectral bandwidth for ZnS, a broadband AR coating will be required to optimize its transmission characteristics. The objective of this effort is to develop and demonstrate multilayer antireflective coating(s) applied to ZnS. Optical transmission testing will be conducted at incidence angles from near normal up to 60 degrees at ambient and service temperature levels using the a bandwidth of 3um to 11um. Material test coupons will be prepared using current THAAD specifications for machining and polishing of the ZnS substrate surfaces. The AR coatings will be selected based on durability, ability to withstand the thermal environment, compatibility with to the ZnS bandwidth, abrasion resistance and cost. The resulting data will be compared to uncoated materials and analysis conducted to identify application performance capabilities

Ground based interceptors will benefit from the use of a dual color focal plane and wideband seekers for improved target acquisition and target discrimination. Zinc Sulfide (ZnS), uncoated and anti-reflective coated, has been under evaluation as a “bolt-in” replacement window for the THAAD seeker system to replace the current sapphire window. The resulting data from the Phase I development efforts has shown that Zinc sulfide presents a wideband capability, has the structural properties, demonstrates superior optical properties, and will result in a significant system cost reduction of 70%-80% for the seeker window. The optical transmission capabilities of the current sapphire window exhibit a limited waveband. A seeker window which has the ability to transmit at a wider waveband will be beneficial for target acquisition and target discrimination. The selection of ZnS as an alternate seeker window material commenced with a rigorous computational fluid dynamics effort to predict the worst case aerodynamic heating combined with finite element thermal and structural analysis used to construct a statistical analysis model. The thermophysical property testing and optical property testing conducted under two (2) independent MDA Phase I Sbir efforts has validated this analysis. It was shown that ZnS provides the thermostructural properties and optical properties for uncoated material and anti-reflective coated material. To prepare ZnS 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 fabricated and 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.

Keywords:
Zinc Sulfide, Seeker Windows, Thermostructural Tes