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Daniel Guggenheim School of Aerospace Engineering

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End date: 2024 × Start date: 2010 × Type: Thesis ×

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An Investigation of the Susceptibility and Practical Mitigation of Pitch-Roll Resonance in Fin-Stabilized Liquid Sounding Rockets

2024-04-29 , Nagarajan, Rithvik

Sounding rockets are suborbital vehicles designed to carry scientific payloads and perform experiments in the upper atmosphere. Recently, there has been a focus on reusable liquid sounding rockets to allow faster launch rates and lower costs per mission. Georgia Tech’s Yellow Jacket Space Program aims to contribute to this field by developing a series of liquid rockets with the goal of launching a sub-orbital payload to the Karman line. One of these rockets, Darcy II, experienced a catastrophic anomaly mid-flight. Like other fin-stabilized sounding rockets, Darcy II was designed with a high length-to-diameter ratio for drag optimization. This made the craft susceptible to roll-yaw resonance, where the vehicle spins close to the pitch natural frequency. Previous literature has shown roll-resonant vehicles can exhibit abnormal rolling and yawing motion beyond predictions by linear theory. Referred to as roll lock-in and catastrophic yaw, respectively, these effects can cause an excessive angle of attack and induce high structural loads. This thesis investigates the susceptibility of liquid sounding rockets to roll resonance, using the Darcy-Series rockets as case studies. Drawing from previous literature on roll resonance dynamics, additions are made to a 6DOF numerical simulation – integrating fluid models, configurational asymmetries, and non-linear aerodynamics with Monte Carlo variables. A sensitivity analysis on model components highlights characteristics of liquid rockets that influence roll resonance. This research examines the contribution of roll resonance to the Darcy II anomaly and through this, validates the numerical simulation. Subsequently, a Monte Carlo simulation is established as a practical method to assess the susceptibility of future liquid sounding rocket designs to the roll resonance phenomenon. This method is applied to the Darcy Space design, revealing a high susceptibility to roll resonance. Mitigation strategies are presented by analyzing the effect of fin design and configurational asymmetries on simulation outputs. Additionally, a simple roll control scheme is designed that takes advantage of existing liquid rocket infrastructure. Four attitude control thrusters are fired once in pairs, implementing a bang-bang roll control scheme designed to prevent roll lock-in using minimal amounts of propellant. This research evaluates the effectiveness of this control system in mitigating roll resonance issues.

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Development of an autonomous surveying vehicle for underground lunar environments

2024-04-29 , Jagdish, Nikita

With impending plans for establishing the first long-term lunar base camp, there is a need to find sustainable habitation sites on the Moon. Discovered in 2009, underground lunar lava tubes have shown potential as future habitation sites and have been proposed for devoted exploratory missions. These underground environments could provide protection from the drastic changes in temperature, radiation, and other extreme conditions on the Moon. However, they have only been observed by lunar orbiters and little is known about their internal structure or suitability for habitable structures. Various on-ground robotic systems have been proposed to do this initial survey, but ground vehicles have a high risk of being immobilized in the event of rough terrain. This project aimed to begin the development of an Autonomous Surveying Vehicle (ASV) as a candidate to explore these lava tubes. The ASV will feature a self-contained, refillable propulsion system that provides full mobility, allowing the vehicle to explore the lava tubes with high agility and multiple short-span surveying missions. The propulsion system will utilize an inert cold gas as its propellant to preserve the natural environment and avoid contamination of any potential resources in the lava tubes. The vehicle will also be equipped with on-board sensors, such as inertial sensors and LiDAR, and an autonomous navigation system to simultaneously map and traverse the tubes. The ASV will be compact and inexpensive compared to other proposed systems, putting forth a simpler option for an initial survey of the tubes to determine whether a more extensive exploratory mission is warranted. The vehicle will also be applicable for other surveying missions, such as above-ground environments that are inaccessible or hazardous for rovers and humans. This thesis outlines the mission goals and requirements and begins the development of a prototype cold gas propulsion system for the ASV.

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Turbulent jet mixing in a high temperature crossflow

2024-01-16 , Hatashita, Luis H.

Jet in crossflow (JICF) has been a subject of research for several decades due to its enhanced mixing properties, i.e. greater than free and coaxial jets. It is moreover encountered in nature in the form of volcano plumes, and in industrial applications. Fuel injection and dilution in jet engines or gas turbines are also of interest. Non iso-density ratio jet in a crossflow has only more recently been subject of studies. While jet mixtures are adjusted to alter the density ratio, fewer studies have been reported on varying temperature to achieve the same effect. The current work extends on previous studies to evaluate momentum ratio, crossflow temperature and jet molecular weight on mixing. The knowledge of governing mechanisms of mixing enables optimization of operational conditions, geometry and emissions for gas turbine and combustor applications. High-fidelity numerical simulations are conducted and validated against experimental data, demonstrating the capability of the simulation to predict mixing. Furthermore, the simulation data is evaluated to predict reduced order model decomposition. Results indicate that momentum ratio is the dominant parameter and the governing factor to control macroscopic features of the flow, such as jet penetration and concentration decay. Mixing is also enhanced for the set of fully developed turbulent jets. Crossflow temperature presents different non-negligible effects on mixing both in the near- and far-field, despite not affecting overall flow geometry. Scalar dissipation rate, spatial probability density functions and integral mixing metrics corroborate this result. Turbulence time scales and instantaneous scalar concentration fields demonstrate how temperature affects mixing. Molecular weight (within the range studied) on the other hand is shown to be a minor parameter and does not demonstrate significant changes to the metrics. The influence of temperature on mixing is investigated through Proper Orthogonal and Dynamic Mode decomposition to extract and evaluate coherent structures. It is found that increase in temperature inhibits the formation of coherent structures such as wake vorticies.

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