Atomic Number (Z)-Grade Radiation Shields from Fiber Metal Laminates

The difference between Layered Energy Depletion Radiation Shielding (LEDRS) and Stacked Energy Depletion Radiation Shielding (SEDRS) is how the piece of matter, or shield, is analyzed as radiation passes through the matter. SEDRS involves using a defined and ordered stack of layers of shielding with different material properties such that the thickness and chemical properties of each material maximizes the absorption of energy from the radiation particles that are most damaging to the target. The SEDRS shielding method aims to provide the maximum level of energy absorption while still keeping shielding mass and volume low. The process of LEDRS involves using layers of shielding material such that the thickness of each material is designed to absorb the maximum amount of energy from the radiation particles that are most damaging to the target after subsequent layers of shielding. The more energy is absorbed by the shielding material, the less energy will be deposited in the target minimizing the required mass to achieve a resulting lower dose for a given geometrical feature. The LEDRS shielding method aims to provide the maximum level of energy absorption. The process for designing LEDRS views potential radiation shields as a cascade of effects from each shielding layer to the next and is helpful for investigating the particular effects of each layer. SEDRS and LEDRS can improve any technology that relies on the controlled manipulation of a radiation field by interaction with a material element.

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.

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.

Current nuclear propulsion technologies do not utilize the additional energy expelled as gamma ray radiation during nuclear fission. This results in the loss of 6.5% of the total fission energy, which could be used to improve propulsion capabilities. The NTAC Augmented Nuclear Electric Propulsion and/or Nuclear Thermal Propulsion design is more efficient than existing technology and captures an additional 6.5% (13.3 MeV) of radiation energy that is currently lost to radiation shielding. In this design the NTAC cell structure surrounds the TRISO (TRi-structural ISOtropic particle fuel) bead-filled rocket chamber, covering all sides and the top of the chamber, therefore capturing additional energy. This structure allows one-way energy flow to then be expelled through the bottom cavity as exhaust gas This technology is lower weight and less elaborate than current radiation shielded-propulsion systems. Equipping nuclear spacecraft systems with the NTAC Augmented Nuclear Electric Propulsion and/or Nuclear Thermal Propulsion design could reduce travel time to Mars by 50%. It has lower radar signatures compared to solar panels and could be used for systems that need to fly undetected, such as Earth observing satellites. Additionally, it has a lower noise output, which could have applications in reducing noise from submarine and aircraft carrier power systems.