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Cislunar Orbital Debris Removal Feasibility Analysis Using NRHO to DRO Transfers at Varying Solar Angles
No full textThe resurgence of lunar exploration necessitates the expansion of space situational awareness into cislunar space. The current tracking technologies for cislunar objects are insufficient to determine vacant orbital regimes for human spaceflight. Orbital debris generated in the cislunar environment often evolves along complex and chaotic trajectories due to the influence of multi-body dynamics. Current research into methods of removing orbital debris from space is limited to debris in Earth orbits. For cislunar orbits, debris disposal options are slowly gaining research, mostly centered on hypothetical solutions for active missions. Lunar impact and escape to heliocentric space are low-cost options, but serve to push the debris problem elsewhere without a sustainable long-term solution. Disposal orbits can hold objects indefinitely and have several beneficial properties that help to advance cislunar space situation awareness and ensure useful areas are kept clear. This research focuses on moving debris generated from the 9:2 Southern L2 near rectilinear halo orbit (NRHO) out to the 70,000 km distant retrograde orbit (DRO). Using the bicircular restricted four-body problem (BCR4BP) system dynamics, the transfers are completed with brute force optimization methods on instantaneous burns, low-thrust electric propulsion, and solar sail as a preliminary treatment of potential disposal options for various mission architectures. It was found that the delta-v for simple transfers can vary greatly based on the starting angle of the Sun with respect to the fixed Earth-Moon system. The lowest found used solar sail augmentation to obtain 293.8 m/s, showing that this method of debris disposal is viable for cislunar space
Chemical Recycling of PET Plastic Waste
Get PDFThe growing accumulation of plastic waste, specifically polyethylene terephthalate (PET), has driven the need for more efficient and scalable chemical recycling methods. This study investigated the methanolysis of PET using zinc oxide (ZnO) nanoparticles as a catalyst and tetrabutylammonium chloride (NBu₄Cl) as an ionic liquid, aiming to reduce methanol consumption while achieving high PET conversion efficiency. ZnO nanoparticles were synthesized via wet chemistry and characterized using Dynamic Light Scattering (DLS), which showed an average particle size of 13.5 nm with a polydispersity index of 0.1556, indicating a moderately-high monodisperse distribution of particles sufficient for reactions. The main conversion product, dimethyl terephthalate (DMT), was confirmed and analyzed for purity using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), and Hydrogen Nuclear Magnetic Resonance (1 H NMR). PET conversion experiments showed that while a high methanol-to-PET ratio of 30:1 yielded up to 98% conversion without any catalyst, comparable efficiency was achieved using only a 10:1 ratio when 5 wt% ZnO nanoparticles were introduced, with or without the ionic liquid NBu₄Cl. At intermediate ZnO concentrations (3 wt%), the addition of NBu₄Cl improved PET conversion from 66% to 80%, indicating a potential synergistic effect under specific conditions. A cost analysis revealed that the nanoparticlecatalyzed method reduced estimated industrial-scale processing costs by 26%. These findings demonstrated the potential of ZnO nanoparticles as an effective, low-cost, and scalable catalyst for sustainable PET chemical recycling, while highlighting the need for further research into the functional contribution of the ionic liquid NBu₄Cl
Investigation Into Silicone-Silicate Conversion Due to Atomic Oxygen in the Low Earth Orbit Environment
Get PDFSilicones have been widely used over the years in spacecraft for a variety of functions, but atomic oxygen (AO) exposure in Low Earth Orbit causes a silicate (SiO2) surface layer to rapidly develop on the silicone which results in a permanent change in its thermal and optical properties. Although this silicone to silicate conversion is known to occur, statistical predictions of layer formation as a function of time on orbit are not found in literature. This thesis utilized optical and scanning electron microscopy, Fourier-Transform Infrared Spectroscopy, diffuse reflectance spectroscopy, and nonlinear regression statistical techniques after RF plasma asher exposure tests to study this phenomenon. Samples were exposed to AO fluences ranging from 2.83 ± 0.214 ×1019 to 1.88 ± 0.0520 ×1021 atoms/cm2. The estimated time at the International Space Station altitude and orbit for CV-2960 and RTV-S691 silicones to form a fully-developed silicate layer is predicted to be between four to nine days, depending on the solar activity. Percent of sample surface area occupied by cracks ranged from 0% to 52.8% and was found to follow a logarithmic model for both CV-2960 and RTV-S691 silicones (R2 = 0.974 and 0.981, respectively) and was significantly linked to AO fluence (p \u3c .0001). CV-2960 silicone was observed to develop a surface silicate layer more readily than the phenyl-containing RTV-S691. Ground-exposed DC 93-500 samples were compared to DC 93-500 MISSE-6 flight articles and were observed to correlate very well in diffuse reflectance features at similar fluence values. Phenyl-containing silicones may be more resistant to AO-induced silicate layer formation which leads to a longer time on orbit before this layer becomes saturated with crack structures
