Computer-implemented energy depletion radiation shielding

This technology is a flexible, lighter weight radiation shield made from hybrid carbon/metal fabric and based on the Z-grading method of layering metal materials of differing atomic numbers to provide radiation protection for protons, electrons, and x-rays. To create this material, a high density metal is plasma spray-coated to carbon fiber. Another metal with less density is then plasma spray-coated, followed by another, and so on, until the material with the appropriate shielding properties is formed. Resins can be added to the material to provide structural adhesion, reducing the need for mechanical bonding. This material is amenable to molding and could be used to build custom radiation shielding to protect cabling and electronics in situations where traditional metal shielding is difficult to place.

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.

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).

The thin, lightweight radiation shielding is comprised of a low Z/high Z/low Z layered structure wherein the low Z layer is composed of titanium and the high Z layer is composed of either tantalum or antimony. Modelling of radiation shielding performance from a Cobalt 57 source shows a 10 times reduction in gamma radiation when using tantalum and a 25 times reduction when using antimony as compared with a single layer of lead. In addition, the Z-shielding is 25% lighter than a single lead layer with the same thickness (0.35-0.36 mm). The direct textile spraying innovation outlined by this invention enables the ability to shape this shielding into garments via the sewing of metal coated fibers. The refractory metal shielding can be added onto a variety of commodity-based fabrics including glass fabrics.

Reentry heating comes from two primary sources: Convective heating from both the flow of hot gas past the surface of the vehicle and catalytic chemical recombination reactions at the surface; and Radiation heating from the energetic shock layer in front of the vehicle. The magnitude of stagnation heating is dependent on a variety of parameters, including reentry speed, vehicle effective radius, and atmospheric density. As reentry speed increases, both convective and radiation heating increase. At high speeds, radiation heating can quickly dominate and as the effective vehicle radius increases, convective heating decreases, but radiation heating increases. Radiation during reentry is a function of reentry speed which occurs very early in reentry for very specific wave-lengths and is dependent upon atmospheric composition. The Biologically-Inspired Radiation-Reflecting Ablator (BIRRA) approach converts amorphous silica of diatoms to a more refractory material, Silicon carbide (SiC), and incorporates it into a Thermal Protection System (TPS), especially near the surface to provide enhanced reflection during the initial stage of reentry into planetary atmospheres at high speeds. Different diatom species reflect different wavelengths. This conversion is performed in a fluidized bed reactor or other type of reactor to convert naturally ordered structures to higher temperature materials with a photonic structure that can better reflect radiation. TPS that shields vehicles from both radiative and convective heat would allow reduction of the mass fraction of the TPS, which will increase the mass fraction available for payload or reduce the overall mass and thus launch and propulsion requirements.