Thesis Defense- Gabriel Maestas
INVESTIGATION OF A FLUID-FILLED CELLULAR COMPOSITE FOR RADIATION SHIELDING IN MEDIUM EARTH ORBIT AND INTERPLANETARY SPACE
One of the primary challenges associated with manned deep space missions is the danger imposed on crew and sensitive electronics by ionizing radiation. There are multiple methods NASA has determined that reduce radiation exposure risk including decreasing transit time, adding active radiation shielding, and increasing passive shielding, among others. Of these methods, it has been determined that the addition of passive radiation shielding with multiuse materials is one of the most viable when considering size and weight constraints necessary for interplanetary travel. It is understood that hydrogen-dense materials perform exceptionally well for radiation shielding purposes, though the materials with the highest density of hydrogen tend to be difficult to implement, as they are: polyethylene, liquid water, and liquid hydrogen. Often discounted for use or retrofitted as an afterthought, the shielding capability of these materials is substantial and would provide noticeable benefits if applicable in multiuse materials.
These hydrogen-dense materials have potential implementation in the Fluid-Filled Cellular Composite (FFCC) for improved radiation shielding capabilities over that of traditional shielding materials like lead, tantalum, and aluminum. The FFCC is a layered composite material inspired by the human skull, where skin layers surround a porous core whose interstitial space is filled with a fluid chosen on a mission-wise basis. From this biomimetic structure, as determined from prior testing, the FFCC has been found to have multiple functions including mechanical structure [1,2], acoustic dampening , high strain rate impact resistance , thermal management , and potential in radiation shielding . As the skull maintains a strong housing and a safe, consistent environment for the mammalian brain, the FFCC can be designed to provide similar protection for crew on a spacecraft.
One of the difficulties associated with prior investigations of the FFCC as well as other investigations of nonhomogeneous materials is in modeling the heterogenous layers for analysis in the Space Environment Information System (SPENVIS). In a past investigation, the fluid-filled porous core was modeled as multiple stacked layers of its homogenous components, however this method is suboptimal since layer order affects results in SPENVIS. This is remedied in the current investigation by use of a homogenization process, as discussed in Section Chapter 3, allowing for a more accurate analysis of the FFCC.
Here, the FFCC has been considered for Total Ionizing Dose (TID) after shielding in a silicon detector by computation with the Multi-Layered Shielding Simulation (MULASSIS) tool from GEANT4 in SPENVIS. This has been done in an effort to model the FFCC radiation shielding capabilities in two space environments, Medium Earth Orbit and Interplanetary Space. It has been found that a variety of the tested FFCC compositions have outperformed traditional shielding materials by a Quality Function Deployment (QFD) methodology of shielding, density, and cost. Dependent on specific composition, the FFCC either meets or exceeds the shielding capability of polyethylene, the NASA standard for shielding materials, while maintaining its broad range of multifunctionality . It is this combination of improved shielding with multifunctionality that advances the FFCC as a potential Mars-class material for use as a spacecraft structural layer or within an off-world habitat.