Flexible Lightweight Radiation Shielding

High atomic number materials, such as tantalum, do not bond well to oxygen- and hydroxyl-rich surfaces, such as glass fibers. These metals often form surface oxides when layered on glass fabric, resulting in flaking of the high atomic number material off the fabric during cutting, folding, and/or handling. To improve coating durability, this invention applies a lower atomic number metal as a tie down layer first before applying the high atomic number metal layer. The tie down layer reduces oxide formation between the substrate and the high atomic number material, promoting adhesion. Titanium has shown strong adhesion with different metals and is effective at reducing oxide formation when diffusion bonded to itself or other materials. It has been shown to be effective at improving durability when thermally sprayed onto a glass fiber fabric as a tie down layer for a subsequent tantalum layer (also applied via RF plasma spray). The titanium layer is only approximately 1 mil thick but results in strong adhesion of the tantalum layer by inter-metallic or diffusion bonding. A thermal spray process may be used, as well. This innovation enables the delivery of high atomic metal coating on glass fiber fabrics and other polymeric substrates that are lower cost, lighter weight, and durable to form a flexible cloth material with Z-graded radiation shielding. Coated samples have been produced and the technology is currently at a technology readiness level (TRL) of 4 (prototype).

There has been much interest in developing polymeric nanocomposites with ultrahigh thermal conductivities, such as with exfoliated graphite or with carbon nanotubes. These materials exhibit thermal conductivity of 3,000 W/mK measured experimentally and up to 6,600 W/mK predicted from theoretical calculations. However, when added to polymers, the expected thermal conductivity enhancement is not realized due to poor interfacial thermal transfer. This technology is a method of forming carbon-based fillers to be incorporated into highly thermal conductive nanocomposite materials. Formation methods include treatment of an expanded graphite with an alcohol/water mixture followed by further exfoliation of the graphite to form extremely thin carbon nanosheets that are on the order of between about 2 and about 10 nanometers in thickness. The carbon nanosheets can be functionalized and incorporated as fillers in polymer nanocomposites with extremely high thermal conductivities.

The Multilayered Fire Protection system uses technology from the space craft flexible heat shield for future planetary missions. By optimizing this material for the fire environment, utilizing heat shield test methods, and experimenting with different materials, the NASA team developed a multilayered fire protection system. This system includes an outer textile layer which reflects over 90 percent of the radiant heat, an insulated layer which protects against convective heat and hot gases, and a non-porous film layer which is a gas barrier layer.

A high density metal, such as tantalum or tungsten is coated onto thin aluminum sheet in precise ratios and thicknesses. The combined sheet is then easily formed into standardized enclosures compatible with CubeSat design and performance specifications.

One inner insulative layer, and one outer robust ablative layer comprise the AMTPS technology. When applying the heat shield to the surface of a spacecraft, the insulative layer is printed first and primarily functions to reduce the amount of heat soak into the vehicle. The formulation of the insulative layer has a slightly lower density (as compared to the robust layer) and is adjusted using a differing constituent ratio of phenolic and/or glass microballoon material. Both formulations combine a phenolic resin with various fillers to control pre- and post-cure properties that can be adjusted by varying the carbon and/or glass fiber content along with rheology modifiers to enhance the fluid flow for deposition systems. The robust layer is applied next and functions as the ablative layer that ablates away or vaporizes when subjected to extremely high temperatures such as those achieved during atmospheric entry. The formulation of the robust layer produces a gas layer as it vaporizes in the extreme heat that acts as a boundary layer. This boundary prevents heat from further penetrating the remaining robust material by pushing away the even hotter shock layer. The shock layer is a region of super-heated compressed gas, positioned in front of the Earth-facing bottom of the spacecraft during atmospheric entry, that results from the supersonic shockwave generated. Commercial space applications for this AMTPS technology include use on any spacecraft that transits a planetary or lunar atmosphere such as Mars or Saturn’s moon Titan. Additionally, the invention may be useful for launch system rockets to provide heat shielding from atmospheric reentry or to protect ground equipment on the launch pad from rocket exhaust plumes. As the number of government and commercial space missions to primary Earth orbits, the Moon, and the Solar System increase, there will be a growing need for cost-effective, on-demand, and timely fabrication of heat shields for space-related activities. AMTPS Formulations – Insulative and Robust Variation is at a technology readiness level (TRL) 5 (component and/or breadboard validation in laboratory environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.