This innovation blends the merits of multifoil insulation (MFI) with aerogel-based insulation to develop a highly versatile, ultra-low thermally conductive material called hybrid multifoil aerogel thermal insulation (HyMATI). The density of the opacified aerogel is 240 mg/cm3 and has thermal conductivity in the 20 mW/mK range in high vacuum and 25 mW/mK in 1 atmosphere of gas (such as argon) up to 800 ºC. It is stable up to 1,000 ºC. This is equal to commercially available high-temperature thermal insulation. The thermal conductivity of the aerogel is 36 percent lower compared to several commercially available insulations when tested in 1 atmosphere of argon gas up to 800 ºC.

HyMATI Blends Multiple Layers of Foil Separated by Fiber Reinforced, Opacified Aerogel. Fabrication consists of: (a) stacking alternating layers of reflective metal foil and high purity quartz fiber, (b)applying slight pressure to the stack to control the spacing between metal foil layers, and (c) permeating the liquid aerogel precursor into the stack, followed by solidification and supercritical drying.
Layers of metal foil block infrared radiation (IR), which are separated by thin (100–1,000-micron) layers of opacified aerogel (see figure) The aerogel further reduces IR transport and, more importantly, significantly reduces gas and solid conduction when compared to the astroquartz used in heritage MFI (that used 7.6-micron thick molybdenum foil separated by ≈90-micron thick astroquartz with 60 layers of each forming a stack 1.7 cm thick). By replacing the astroquartz with JPL-developed aerogel, the overall mass of MFI is reduced by 36 percent. Further reductions in mass may also be had by selecting lower density metal foils, such as titanium, zirconium, or reflective Grafoil®. In addition to mass reduction benefits, HyMATI is a tunable insulation that can be tailored for use in various temperature ranges up to 1,000 ºC, and can be considered for use in space vacuum, with a cover gas such as argon or xenon or on other planets with atmosphere.

By replacing heritage MFI with aerogel, the HyMATI will reduce the mass of future RPS (radioisotope power systems) technology. Also, the aerogel has the lowest gas conductivity of any material in its class, enabling RPS operation in vacuum, cover gas, or atmosphere. This means enabling a single RPS design for all NASA missions requiring RPS as opposed to current situations where NASA has a Multi-Mission RTG (for Mars Science Laboratory, for example) and GPHS-RTG (General-Purpose Heat Source-Radioisorope Thermoelectric Generator) for deep-space exploration.

This work was done by Jeffrey Sakamoto, Jong-Ah Paik, Steven Jones, and Bill Nesmith of Caltech for NASA's Jet Propulsion Laboratory.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, NASA Management Office–JPL. Refer to NPO-45219.

Topics:
Conductivity Downsizing Fibers Forming Gases Hazardous materials Hazards and emergency operations Insulation Manufacturing processes Materials Materials properties Metals Radiation Titanium Vacuum
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Hybrid Multifoil Aerogel Thermal Insulation

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NASA Tech Briefs Magazine

This article first appeared in the October, 2008 issue of NASA Tech Briefs Magazine (Vol. 32 No. 10).

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Overview

The document discusses the development of Hybrid Multifoil Aerogel Thermal Insulation (HyMATI) by NASA's Jet Propulsion Laboratory (JPL), aimed at improving the efficiency and performance of Radioisotope Power Systems (RPS). Traditional RPS technology utilizes multifoil insulation (MFI) made from layers of metal foil separated by astroquartz fabric, which has a high density of approximately 860 mg/cm³ and provides limited thermal insulation. This insulation constitutes a significant portion of the overall mass of the RPS, which currently delivers about 5W electrical/kg. NASA is targeting advancements to exceed 8W electrical/kg in future RPS designs.

The JPL-developed aerogel has a density of 240 mg/cm³ and exhibits thermal conductivity in the 20 mW/mK range in high vacuum, remaining stable up to 1,000 °C. This aerogel is 33% lighter than traditional insulation materials and demonstrates significantly lower thermal conductivity compared to commercially available insulations when tested in argon gas at elevated temperatures. The proposed HyMATI concept aims to replace the astroquartz with this aerogel, potentially reducing the overall mass of the insulation by 36% and enhancing thermal performance.

HyMATI combines the benefits of MFI and aerogel-based insulation, utilizing layers of metal foil to block infrared radiation, separated by thin layers of opacified aerogel. This design not only reduces infrared transport but also minimizes gas and solid conduction, making it suitable for use in various environments, including space vacuum and planetary atmospheres. The tunable nature of HyMATI allows it to be tailored for different temperature ranges, making it versatile for future missions.

The document emphasizes the potential impact of HyMATI on NASA's mission budgets, as a single RPS design could streamline operations and reduce costs significantly compared to the current multi-mission approach. The research highlights the importance of developing advanced insulation materials to meet the challenges of future space exploration, ensuring that RPS technology can operate efficiently in diverse conditions.

In summary, the document outlines a significant advancement in thermal insulation technology that could revolutionize the design and efficiency of power systems used in space exploration, ultimately benefiting NASA's future missions.