OUSD (R&E) MODERNIZATION PRIORITY: Quantum Sciences TECHNOLOGY AREA(S): Space Platform; Materials 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 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. Please direct questions to the Air Force SBIR/STTR HelpDesk: usaf.team@afsbirsttr.us. OBJECTIVE: The goal of this STTR is to create a variable emissivity thermal control device or coating that can adopt at least two states that differ in emissivity by at least 0.5 and can either adopt either a very low emissivity state, specifically a state with less than 0.1 emissivity, or a very high emissivity state, specifically a state with an emissivity greater than 0.9, that is robust enough to tolerate extended use on an orbital platform. The emissivity change of this device should be triggered either by input from an external user or by a change in temperature. User input triggered variable emissivity devices should have low Size, Weight, and Power (SWAP) requirements and be easy to use and integrate existing systems. Temperature triggered variable emissivity coatings or devices should adopt a high emissivity state the system it is thermally regulating is hot and a low emissivity state when this system is cold. DESCRIPTION: Keeping an orbital asset at an optimal operating temperature can be extremely challenging as orbiting spacecraft experience large temperature swings as the extent it is illuminated by the Sun changes as it enters and leaves eclipse, the difficulty in getting hardware into space, the limited amount of volume available on spacecraft, the limited amount of power available on spacecraft, and the restriction that any heat that is released from a spacecraft must leave radiatively as spacecraft operate in a vacuum. To alleviate thermal control challenges, this STTR seek to combine the academic expertise of universities and the product development expertise of small businesses to develop space tolerant variable emissivity devices or coatings that can radiatively release heat from a spacecraft when it becomes too hot and curtail the heat released from a spacecraft when it is too cold. As a technology to support spacecraft operations, the variable emissivity technology sought by this STTR should provide good thermal control, have low Size, Weight, And Power (SWAP) requirements, be robust enough to tolerate the hostile conditions found in orbit, is easy to use, and is simple to incorporate into existing spacecraft designs. The degree of thermal control the technology can provided will be assessed by the maximum emissivity the technology can establish, the minimum emissivity the technology can establish, the total change in emissivity the technology can provide, and the extent the technology can establish the optimal emissivity when the spacecraft is at different temperatures. Overall SWAP will be considered as the amount of mass, volume, and power needed to install and operate the system. Robustness will be assessed as the extent the device or coating can tolerate temperature cycling and endure extended exposure to high energy photons and charged particles found in space. Ease of use will be measured by how difficult it is to get the variable emissivity technology to adopt the desired emissivity and how few reasonably probable ways the variable emissivity technology can fail can be identified. Finally, amenability to integration into existing spacecraft designs will be assessed by extent the form of the variable emissivity technology developed by this STTR can be tailored to accommodate different spacecraft architectures. The proposals sought for this STTR will present an innovative new approach to create a variable emissivity device thermal control device or detail a convincing plan to improve the performance of approaches explored in the past. If an innovative new approach is proposed, it would be useful if the proposer articulated why this new approach is promising. If the proposed approach utilizes some form of reversible electroplating, it would be useful if the proposers provided discussion on how they plan to overcome limitations with the low IR transparency of electrical conductors. If the proposed approach utilizes oxidation changes or charge migration, it would be useful if the proposers discuss why their approach is still anticipated to function when exposed to the charged particle and radiation environment found in space. If the proposed approach utilizes a phase change, it would be useful if the proposers articulate why they believe their proposed approach will tolerate repeated cycling between a high and low emissivity configuration. With any approach presented, it is important for the proposers to detail why they believe their proposed approach will be able to provide the desired thermal control and why they believe their proposed approach will be suitable for extended use on an orbital asset. PHASE I: Complete a laboratory demonstration of a variable emissivity device that can adopt a high emissivity state when hot and a low emissivity state when cold. PHASE II: Prepare a robust variable emissivity thermal device or coating that can provide at least 0.5 emissivity change, can adopt an emissivity state above 0.8 or below 0.2, and is packaged in such a way that it can be deployed to space where its performance while on orbit can be assessed. PHASE III DUAL USE APPLICATIONS: Work with a spacecraft manufacturer to design a spacecraft that utilizes the variable emissivity thermal control device or coating developed by this STTR. Reach out to the Department of Energy and infrastructure manufacturers to explore utilizing the devices or coatings developed by this STTR for terrestrial thermal control applications. REFERENCES: Wu, X et al., Passive Smart Thermal Control Coatings Incorporating CaF2/VO2 Core Shell Microsphere Structures , Nano Lett. 2021, 21, pp. 3908-3914; Athanasopoulos, N. et al., Variable emissivity through multilayer patterned surfaces for passive thermal control: preliminary thermal design of a nano-satellite , 48th International Conference on Environmental Systems, 8-12 July 2018, Albuquerque, New Mexico; Vlassov, V. V. et al., Analysis of Concept Feasibility and Results of Numerical Simulation of a Two-Stage Space RadiatorWith Variable Emissivity Coating , Heat Transfer Engineering 2017, 38, 10, pp. 963-974; Vlassov, V.V. et al., New Concept of Space Radiator with Variable Emittance , J. of the Braz. Soc. Of Mech. Sci. & Eng. 2010, 32, 4, pp. 400-408; Darrin, A.G. et al., "Variable emissivity through MEMS technology," ITHERM 2000. The Seventh Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (Cat. No.00CH37069), 2000, pp. 264-270 KEYWORDS: Variable emissivity; thermal control; reversible electroplating; phase change; electrochromic; smart windows; functional paint; space; spacecraft
