Browsing by Author "Spicer, Randy Lee"
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- Additive Manufacturing in Spacecraft Design and In-Space Robotic Fabrication of Large StructuresSpicer, Randy Lee (Virginia Tech, 2023-08-31)Additive Manufacturing (AM, 3D printing) has made significant advancements over the past decade and has become a viable alternative to traditional machining techniques. AM offers several advantages over traditional manufacturing techniques including improved geometric freedom, reduction in part lead time, cost savings, enhanced customization, mass reduction, part elimination, and remote production. There are many different AM processes with the most commonly used process being Fused Filament Fabrication (FFF). Small satellites have also made significant advancements over the past two decades with the number of missions launched annually increased by orders of magnitude over that time span. Small satellites offer several advantages compared to traditional spacecraft architectures including increased access to space, lower development costs, and disaggregated architectures. On-orbit manufacturing and assembly have become major research and development topics for government and commercial entities seeking the capability to build very large structures in space. AM is well suited on-orbit manufacturing since the process is highly automated, produces little material waste, and allows for a large degree of geometric freedom. This dissertation seeks to address three major research objectives regarding applications of additive manufacturing in space systems: demonstrate the feasibility of 3D printing an ESPA class satellite using FFF, develop a FFF 3D printer that is capable of operating in high vacuum and characterize its performance, and analyze the coupled dynamics between a satellite and a robot arm used for 3D printing in-space. This dissertation presents the design, finite element analysis, dynamic testing, and model correlation of AdditiveSat, an additively manufactured small satellite fabricated using FFF. This dissertation also presents the design, analysis, and test results for a passively cooled FFF 3D printer capable of manufacturing parts out of engineering grade thermoplastics in the vacuum of space. Finally, this dissertation presents a numerical model of a free-flying small satellite with an attached robotic arm assembly to simulate 3D printing structures on-orbit with analysis of the satellite controls required to control the dynamics of the highly coupled system.
- Validation of the DRACO Particle-in-Cell Code using Busek 200W Hall Thruster Experimental DataSpicer, Randy Lee (Virginia Tech, 2007-06-29)This thesis discusses the recent developments to the electric propulsion plume code DRACO as well as a validation and sensitivity analysis of the code using data from an AFRL experiment using a Busek 200 W Hall Thruster. DRACO is a PIC code that models particles kinematically while using finite differences schemes to solve the electric potential and field. The DRACO code has been recently modified to improve simulation results, functionality and performance. A particle source has been added that uses the Hall Thruster device code HPHall as input for a source to model Hall Thrusters. The code is now also capable of using a non-uniform mesh that uses any combination of uniform, linear and exponential stretching schemes in any of the three directions. A stretched mesh can be used to refine simulation results in certain areas, such as the exit of a thruster, or improve performance by reducing the number of cells in a mesh. Finally, DRACO now has the capability of using a DSMC collision scheme as well as performing recombination collisions. A sensitivity analysis of the newly upgraded DRACO code was performed to test the new functionalities of the code as well as validate the code using experimental data gathered at AFRL using a Busek 200 W Hall Thruster. A simulation was created that attempts to numerically recreate the AFRL experiment and the validation is performed by comparing the plasma potential, polytropic temperature, ion number density of the thruster plume as well as Faraday and ExB probe results. The study compares the newly developed HPHall source with older source models and also compares the variations of the HPHall source. The field solver and collision model used are also compared to determine how to achieve the best results using the DRACO code. Finally, both uniform and non-uniform meshes are tested to determine if a non-uniform mesh can be properly implemented to improve simulation results and performance. The results from the validation and sensitivity study show that the DRACO code can be used to recreate a vacuum chamber simulation using a Hall Thruster. The best results occur when the newly developed HPHall source is used with a MCC collision scheme using a projected background neutral density and CEX collision tracking. A stretched mesh was tested and proved results that are as accurate as a uniform mesh, if not more accurate in locations of high mesh refinement.