N212-117 TITLE: Infrared (IR) Optical Windows for Hypersonic Aerial Vehicles

RT&L FOCUS AREA(S): General Warfighting Requirements (GWR);Hypersonics;Microelectronics

TECHNOLOGY AREA(S): Materials / Processes

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Design and develop infrared (IR) optical windows that are capable of protecting IR optical sensors and ensuring high-performance sensing during a hypersonic flight.

DESCRIPTION: Hypersonic aerial vehicles require the use of IR windows to protect sensitive opto-electronics from the aggressive aerothermal environment of high-speed flight while providing transparency to the IR optical signal used for intelligence, surveillance, reconnaissance, guidance, and communication applications [Ref 1]. The high temperatures of 3000 �F (1649 �C), or higher, associated with aerothermal impact of a high-speed/hypersonic vehicle during hypersonic flight, pose very challenging operating environments for the window material [Ref 2]. The interface surface or window material must be able to withstand extreme thermal, mechanical, and chemical environments during hypersonic flight that can limit the performance of the IR window and the IR sensor platform [Ref 3]. Furthermore, shock waves and extremely high heat loads produced during flight adversely impart wavefront distortions, and for this reason, affect the fidelity and accuracy of the signal/image detected by the optical sensors. Aerothermal-mechanical loads also create additional thermal requirements for the window to protect and insulate the sensor from the vehicle�s extreme exterior condition [Ref 4].

The Navy requires development and demonstration of a new class of IR windows that can operate at extreme conditions of high-heat fluxes and high-air pressures, and enable high-performance optical sensing during hypersonic flights. The key performance parameters for the windows include:

1. wavelengths of interest: short-wave infrared (SWIR) � 1.4 to 3 �m mid-wave infrared (MWIR) � 3 to 5 �m, and long-wave infrared (LWIR) � 8 to 14 �m;
2. meet aerothermal and pressure loading conditions for hypersonic aerial vehicles;
3. accommodate both flat and non-flat (conformal, ogive, faceted) surface shapes to match vehicle aerodynamic design;
4. maintain electromagnetic and thermo-mechanical properties associated with the intended optical sensor during hypersonic flight;
5. window must endure the high temperatures (3000 �F [1649�C] or higher) and high-dynamic pressures (up to 12,000 lb/ ft�) (5,443.2 kg/0.0929 m�) during hypersonic flight;
6. the optical materials and designs of the windows should have minimum transmission loss in the desired wavelength bandwidths for each of the IR bands during hypersonic flight conditions.

PHASE I: Develop, design, and demonstrate the feasibility of candidate materials for window application through material properties testing. Research and select the IR window candidate materials for each of the IR wavelength band. The testing should include optical transmissivity, structural strength, and thermal properties of the window materials. Use modeling and simulation to estimate the thermal-optical and elastic-optical effects of the window materials and the impacts on transmission amplitude and bandwidth during hypersonic flight. Provide a Phase II plan to develop and test the optical windows in accordance with their performance goals and key technical milestones while addressing technical risks and challenges discovered from the modeling and simulation in Phase I. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Fabricate the optical windows according to the fabrication plan laid out in Phase I. Perform comprehensive tests and evaluations of the fabricated candidate windows regarding their performance and reliability in a relevant hypersonic environment. Iterate the design/fabrication steps to modify the designs and fabrications of the optical windows due to technical challenges discovered in the test and evaluation phase to close the gaps in the performance and survivability endurance gaps.

PHASE III DUAL USE APPLICATIONS: Finalize development based on Phase II results, for transition and integration of the product into a hypersonic vehicle candidate airframe. Conduct flight test units for fielding on Navy experimental flight tests.

Potential commercial applications could include the applications of this research for infrared optical windows for commercial hypersonic re-entry vehicles.

REFERENCES:

1. Chan, C. B. and Singh, N. "Calculation of refractive index around a hypersonic vehicle with infrared sensors." Proceedings IEEE Southeastcon'92, April 1992, pp. 562-565. https://doi.org/10.1109/SECON.1992.202416.
2. Di Clemente, M.; Rufolo, G.; Ianiro, A. and Cardone, G. "Hypersonic test analysis by means of aerothermal coupling methodology and infrared thermography." AIAA journal, 51(7), 2013, pp. 1755-1769. https://doi.org/10.2514/1.J052234.
3. Wan, Z. "Calculating models of cooling IR window and window background radiation." International Society for Optics and Photonics, Targets and Backgrounds: Characterization and Representation IV, Vol. 3375, July 7, 1998, pp. 195-202.. https://doi.org/10.1117/12.327171.
4. Krell, A.; Baur, G. M. and Dahne, C. "Transparent sintered sub-�m Al2O3 with IR transmissivity equal to sapphire." International Society for Optics and Photonics, Window and Dome technologies VIII, Vol. 5078, September 2003, pp. 199-207. https://doi.org/10.1117/12.485770.

KEYWORDS: Hypersonic; Optical Window; Infrared; IR; mid-wave infrared; MWIR; short-wave infrared; SWIR; long-wave infrared; LWIR; Wavefront Distortion; Aerothermal; Thermal-optical