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Articles 31 - 60 of 115
Full-Text Articles in Aerospace Engineering
Performance Study Of Post-Processed Additively Manufactured Low Thrust Nozzles, Tyler W. Gerhold
Performance Study Of Post-Processed Additively Manufactured Low Thrust Nozzles, Tyler W. Gerhold
Theses and Dissertations
This research explores metal post-processing techniques to effectively reduce the large anomalous protrusions found in small additively manufactured low thrust rocket nozzles. Research has found that nozzles of this kind can experience losses in thrust of over 40%. Analytic theory of adiabatic nozzle flow with viscous losses for additively manufactured nozzles does not align with what has been found when tested experimentally. Compressible flow losses, such as shock wave formation inside the nozzle diverging cone, are likely the leading causes of such loss. Reduction in nozzle irregularities can likely yield results seen in analytic theory with similar performance to traditional …
Survivability Analysis In The Shadow Of Apollo: Part Ii - Spacecraft Charging Vulnerability Near The Stable Earth-Moon Lagrange Points, Robert A. Bettinger, Nathan R. Boone, Nicholas S. Hamilton, Bryan D. Little
Survivability Analysis In The Shadow Of Apollo: Part Ii - Spacecraft Charging Vulnerability Near The Stable Earth-Moon Lagrange Points, Robert A. Bettinger, Nathan R. Boone, Nicholas S. Hamilton, Bryan D. Little
Faculty Publications
Though the reality of routine travel and sustained operations in space likely remains several decades away, the building blocks of space exploration and space system development necessary to realize this reality are currently being laid by peer, near-peer, and emerging space-faring nations. The pursuance of sustained cislunar space operations will necessitate a renewed examination of spacecraft survivability and the capability of spacecraft to avoid and/or withstand the natural and manmade environmental risks posed by this “new” ultimate high ground.
Design Of An Electro-Thermal Nanosatellite Propulsion System, James H. Founds
Design Of An Electro-Thermal Nanosatellite Propulsion System, James H. Founds
Theses and Dissertations
This research focused on designing an arcjet system with water as the propellant. Previous research developed a compact, reliable, and safe propellant storage and feed system. The goal is to combine the arcjet with the previous tank to achieve thrust and specific impulse characteristics greater than cold gas or resistojet system. This platform features a 1 U, non-hazardous, and sub-kilowatt powered propulsion system for nanosatellites. A simplified analysis of the design predicts thrust and specific impulse greater than can be achieved by cold gas or resistojet thrusters. Testing resulted in oxidation of the electrodes raising concerns about the longevity of …
Differential Game-Based Defensive Architecture Study Employing Ground-Based Interceptors, Stephen T. Zittrouer
Differential Game-Based Defensive Architecture Study Employing Ground-Based Interceptors, Stephen T. Zittrouer
Theses and Dissertations
A study of defensive architectures for combating hypersonic glide vehicles (HGVs) via interception with a ground-based interceptor (GBI) is presented. Pursuit-evasion differential games are formulated for numerical simulation of the interception engagements. A one-sided optimal control problem wherein the evader HGV is optimized and the pursuer GBI employs a suboptimal proportional navigation control strategy is solved. The solution space is characterized by varying the pursuer initial velocity advantage relative to the evader. A two-sided optimal control problem in which both players behave optimally is solved via the semi-direct collocation with nonlinear programming (semiDCNLP) method. The resulting state and control trajectories …
Underactuated Attitude Control Of A Cubesat Using Cold Gas Thrusters And Nonlinear Control Methods, Adam S. Cottrell
Underactuated Attitude Control Of A Cubesat Using Cold Gas Thrusters And Nonlinear Control Methods, Adam S. Cottrell
Theses and Dissertations
Impulsive thrusters on small satellites, such as CubeSats, are typically used for attitude control. However, to become more agile, small CubeSats must also look to propulsion systems utilizing impulsive thrusters, such as cold-gas, for translational maneuvers. The combined thrust vector is often misaligned with the system's center of mass resulting in a disturbance torque. This must be counteracted by either an attitude determination and control system (ADCS), additional thrusters, or a control method to keep the satellite's attitude at or near equilibrium. Nonlinearities generated by the impulsive maneuvers are overcome via control techniques explored in this research to include on-off …
Aeroelasticity Of Six Degree-Of-Freedom Satellite Bus Configurations During Terminal Reentry, Jinhee F. Byun
Aeroelasticity Of Six Degree-Of-Freedom Satellite Bus Configurations During Terminal Reentry, Jinhee F. Byun
Theses and Dissertations
With disposable equipment on board, the emphasis on structural strength and robust thermal protection system (TPS) pales for a conventional satellite in comparison to reentry capsules, which are specifically designed to withstand the intense aerothermodynamic effects experienced during reentry. In this research, six degree-of-freedom (6DOF) analyses of three distinct non-aerodynamic satellite bus configurations were performed with emphasis on the investigation of their terminal reentry characteristics, and thermal and deceleration loading on the satellite body. Aeroelastic effects on their respective solar panel structures were also analyzed focusing on characterizing bending stress at their attachment/deployment mechanism. It was found that the Terra …
Survivability Analysis In The Shadow Of Apollo: Part I - Cislunar Debris Propagation And Spacecraft Vulnerability, Nathan R. Boone, Robert A. Bettinger
Survivability Analysis In The Shadow Of Apollo: Part I - Cislunar Debris Propagation And Spacecraft Vulnerability, Nathan R. Boone, Robert A. Bettinger
Faculty Publications
Although the reality of routine travel and sustained operations and habitation in space likely remains several decades away, the building blocks of space exploration and space system development necessary to realize this reality are currently being laid by peer, near-peer, and emerging space-faring nations. Traditionally, global space operations were notionally limited to near-Earth space, with mission altitudes extending to geosynchronous or even highly elliptical orbits. During the 2010s, however, space operations began moving beyond this paradigm to encompass cislunar space with reinvigorated U.S. initiatives to return to the Moon via the Artemis program, planned commercial space projects, and an accelerated …
Autonomous Mission Planning For Spacecraft Rendezvous And Proximity Operations, Julia C. Bell
Autonomous Mission Planning For Spacecraft Rendezvous And Proximity Operations, Julia C. Bell
Theses and Dissertations
The evolving space environment has created a demand for autonomous spacecraft that can maneuver in complex and sometimes contentious environments. Constraint enforcement, such as an avoidance zone to prevent collision with a target, is a key component of autonomous control to ensure safety and performance requirements are met. Finite-horizon Model Predictive Control (MPC) is a popular control method due to its improved computation time while optimizing performance. Two areas of MPC in need of expansion are time-varying constraints and phase transitions in multi-phase applications. In this work, MPC is employed to track the reference trajectory of a multi-phase satellite inspection …
Six Degree-Of-Freedom Mission Planning For Reentry Trajectories, Peter Davis
Six Degree-Of-Freedom Mission Planning For Reentry Trajectories, Peter Davis
Theses and Dissertations
Traditional reentry dynamics and planning has typically explored 3 Degrees-of- Freedom (3 DOF) or pseudo 6-DoF problem formulations. This research expands upon previous work and presents a path-constrained optimal control formulation of a fully 6 Degrees-of-Freedom (3 DOF) dynamic system for an unpowered Reentry Vehicle (RV). In a full 6-DoF dynamic system, the translation, rotation and rotational rates are continually tracked. A system of equations of motion are developed to express the dynamics of the RV in terms of defined states and the RV's physical control detections. A neural-network is used to approximate the aerodynamic database of an exemplary RV. …
Cubesat Attitude Determination And Control System (Adacs) Characterization And Testing For Rendezvous And Proximity Operations (Rpo), Steven T. Bednarski
Cubesat Attitude Determination And Control System (Adacs) Characterization And Testing For Rendezvous And Proximity Operations (Rpo), Steven T. Bednarski
Theses and Dissertations
This research endeavors to evaluate and characterize the performance of CubeSat specific commercial-off-the-shelf (COTS) Attitude Determination and Control Systems (ADACS) for Mission suitability. To ensure COTS components are capable of meeting CubeSat mission requirements, deliberate performance testing of critical CubeSat subsystems in flight-like conditions is essential. This effort focuses on testing the MAI-401 ADACS subsystem as configured to support the Grissom-1 CubeSat mission, as mounted to an air bearing, residing within a 3-axis Helmholtz Cage, and subjected to a simulated magnetic environment of various orbital parameters.
Density Measurements Of Neutral Xenon Using Multiphoton Ionization And Microwave Spectroscopy In A Hall Effect Thruster, Taylor J. Foy
Density Measurements Of Neutral Xenon Using Multiphoton Ionization And Microwave Spectroscopy In A Hall Effect Thruster, Taylor J. Foy
Theses and Dissertations
A new dye laser and microwave scattering system for measuring low speed xenon particles was installed to characterize a commercially sourced 600 W Hall effect thruster. The new system uses multiphoton ionization and microwave spectroscopy to determine number density and velocity measurements of neutral xenon atoms in the plume of a Hall thruster. A study was conducted to ensure the new system will be able to accurately measure these neutrals in future work. The ultimate goal of this new system is to isolate and characterize the extra thrust produced in Hall Effect Thrusters due to finite volume vacuum chambers.
Cislunar Debris Propagation Following A Catastrophic Spacecraft Mishap, Nathan R. Boone
Cislunar Debris Propagation Following A Catastrophic Spacecraft Mishap, Nathan R. Boone
Theses and Dissertations
This research involves theoretical analysis of the short- and long-term motion of space debris in cislunar trajectories following a spacecraft catastrophic mishap. Specifically, the research formulates a debris propagation model using four-body dynamics and determines debris trajectories following breakup events for a variety of different initial orbital positions. A spacecraft survivability model is then used to quantify the risks from the debris to other cislunar spacecraft. First, a study of the risks due to natural debris comprising the Kordylewski clouds at the Earth-Moon ��4 and ��5 Lagrange points is conducted as an introduction to cislunar debris propagation. Next, …
A Framework For Autonomous Cooperative Optimal Assignment And Control Of Satellite Formations, Devin E. Saunders
A Framework For Autonomous Cooperative Optimal Assignment And Control Of Satellite Formations, Devin E. Saunders
Theses and Dissertations
A decentralized, cooperative multi-agent optimal control framework is presented to offer a solution to the assignment and control problems associated with performing multi-agent tasks in a proximity operations environment. However, the framework developed may be applied to a variety domains such as air, space, and sea. The solution presented takes advantage of a second price auction assignment algorithm to optimally task each satellite, while model predictive control is implemented to control the agents optimally while adhering to safety and mission constraints. The solution is compared to a pseudospectral collocation method, and a study on tuning parameters is included.
Safe Spacecraft Rendezvous And Proximity Operations Via Reachability Analysis, Paul A. Grossi
Safe Spacecraft Rendezvous And Proximity Operations Via Reachability Analysis, Paul A. Grossi
Theses and Dissertations
The rapid expansion of the utilization of space by nations and industry has presented new challenges and opportunities to operate efficiently and responsibly. Reachability analysis is the process of computing the set of states that can be reached given all admissible controls and can be a valuable component in an autonomous mission planning system if conducted efficiently. In the current research, reachability analysis is used with several relative motion models to show that all ranges of orbits can be computed in milliseconds, and that it is a feasible approach for on-board autonomous mission planning. Reachability analysis is then combined with …
A Reference Architecture For Rapid Cubesat Development, Sean R. Kelly
A Reference Architecture For Rapid Cubesat Development, Sean R. Kelly
Theses and Dissertations
The CubeSat class of nanosatellites has lowered the barrier of entry to space and has rapidly gained popularity in recent years. To successfully design a CubeSat system in a rapid cycle conducive to academic timelines, a Reference Architecture geared towards University CubeSat development would be helpful. A Reference Architecture would speed up the development process by providing a template, capturing previous work and lessons learned from subject matter experts, providing a framework to focus on the CubeSats design rather than the fine details of modeling software. A Reference Architecture can also add functionality that student teams could use and improve …
Comparison Of Decision Analysis Methods For A Cubesat Propulsion System, Jared L. Pilcher
Comparison Of Decision Analysis Methods For A Cubesat Propulsion System, Jared L. Pilcher
Theses and Dissertations
Low Earth Orbit (LEO) is becoming an increasingly congested orbital regime. As a result, propulsion systems on CubeSats are becoming a more desirable feature to provide them with collision avoidance capabilities. To date, there have been very few CubeSat launches with a propulsion system on them. Due to the relatively high cost of a propulsion system compared to the budget of small educational organizations, a decision analysis model is needed so that these organizations can make the best decision between whether to purchase a Commercial-Off-The-Shelf (COTS) product or to develop one within the organization. This research applies three decision analysis …
Cubesat Development Framework, William D. Sousa
Cubesat Development Framework, William D. Sousa
Theses and Dissertations
AFITs Center for Space Research and Assurance (CSRA) has developed several small satellites without a detailed developmental framework in place but future work will focus on CubeSat development with the intent of managing multiple builds concurrently. With the goal of each satellite being completed in three years, a comprehensive process needs to be established. Research revealed that the Department of Defense (DoD), U.S. Air Force (USAF), and National Aeronautics and Space Administration (NASA) guidance on the acquisition and systems engineering processes require more reviews and deliverables than appropriate for CSRAs projects. The development processes from other universities divulge some aspects …
Satellite Tracking With Neuromorphic Cameras For Space Domain Awareness, Joseph G. Bacon Jr.
Satellite Tracking With Neuromorphic Cameras For Space Domain Awareness, Joseph G. Bacon Jr.
Theses and Dissertations
A significant number of objects orbit the space around Earth. Each of these objects, be it debris, a functioning satellite, or even a staffed space station, circle the planet at extreme speeds relative to most objects on the Earth's surface. Any collision would result in disaster thanks to the extreme amount of kinetic energy involved. Space Domain Awareness (SDA) includes the detection, identification, cataloging, and tracking of orbiting objects to prevent such catastrophes. SDA is maintained in multiple ways to include radar, lidar, telescopes, and other sensors. This research investigates the maturing technology of neuromorphic cameras to determine their applicability …
Applied Reachability Analysis For Time-Optimal Spacecraft Attitude Reorientations, Layne C. Barrett
Applied Reachability Analysis For Time-Optimal Spacecraft Attitude Reorientations, Layne C. Barrett
Theses and Dissertations
Satellite attitude reorientation has been of significant interest in astronautical engineering, and being able to reorient in a time-optimal manner has been of exceeding interest since the 1970s. Ensuring a spacecraft mission set can be conducted within a certain amount of time begs the question of whether or not a certain maneuver can be completed with a bounded control. This thesis answers that question by using the concept of reachability to provide reachable sets for different spacecraft reorientation scenarios. The reachable sets generated provide a range of initial states that guarantee a satellite reach a desired end orientation given a …
Deep Reinforcement Learning Applied To Spacecraft Attitude Control And Moment Of Inertia Estimation Via Recurrent Neural Networks, Nathaniel A. Enders
Deep Reinforcement Learning Applied To Spacecraft Attitude Control And Moment Of Inertia Estimation Via Recurrent Neural Networks, Nathaniel A. Enders
Theses and Dissertations
This study investigated two distinct problems related to unknown spacecraft inertia. The first problem explored the use of a recurrent neural network to estimate spacecraft moments of inertia using angular velocity measurements. Initial results showed that, for the configuration examined, the neural network can estimate the moments of inertia when there is a known external torque. The second problem trained a reinforcement learning agent, via proximal policy optimization, to control the attitude of a spacecraft. The results demonstrated that reinforcement learning may be a viable option for guidance and control solutions where the spacecraft model may be unknown. The trained …
Hybridized Spacecraft Attitude Control Via Reinforcement Learning Using Control Moment Gyroscope Arrays, Cecily C. Agu
Hybridized Spacecraft Attitude Control Via Reinforcement Learning Using Control Moment Gyroscope Arrays, Cecily C. Agu
Theses and Dissertations
Machine learning techniques in the form of reinforcement learning (RL) can solve complex nonlinear problems found within spacecraft attitude determination and control systems (ADCS). Three CMG arrays were implemented in two simulated spacecraft environments using a reinforcement learning controller. The performance of the controllers were evaluated using target profiles from traditional control law implementations, singularity measure, and variable initial state values. The current research demonstrates that while RL techniques can be implemented, further exploration is needed to investigate the operational efficacy of an approach for producing comparable performance attributes with respect to traditional control laws.
Neuromorphic Vision Sensors For Space-Based Applications, Jessica L. Horn
Neuromorphic Vision Sensors For Space-Based Applications, Jessica L. Horn
Theses and Dissertations
This research examines the viability of event-based vision (neuromorphic) sensors for future use on satellites. Outputting single pixel events only when a change in intensity is detected, event-based vision sensors offer a potential low power, low latency, high temporal resolution, and high dynamic range solution as compared to traditional CCD or CMOS camera technology. The commercial off-the-shelf DVS240C sensor, is analyzed to determine if operability is affected by launch conditions and the low Earth space environment through vacuum, thermal vacuum, and vibration tests. No appreciable changes in sensor operation was observed throughout testing. Additionally, the sensor was able to detect …
Understanding Flow Characteristics In Metal Additive Manufacturing, Carl R. Hartsfield, Travis E. Shelton, Gregory R. Cobb, Ryan A. Kemnitz, Joseph Weber
Understanding Flow Characteristics In Metal Additive Manufacturing, Carl R. Hartsfield, Travis E. Shelton, Gregory R. Cobb, Ryan A. Kemnitz, Joseph Weber
Faculty Publications
In fluid flow, the frictional effects from interior surfaces of flow components create pressure loss across the surface. Understanding this inherent pressure loss due to friction and other phenomena is important when designing a flow system. For conventional manufacturing, friction loss has been empirically studied and is well known in the engineering community. However, newer manufacturing techniques, such as laser powder bed fusion (LPBF), an additive manufacturing technique, need to be understood. The inherent flow conditions resulting from the additive processes were studied. Test samples were printed with the flow path oriented in the vertical direction with different channel diameters …
An Argument Against Satellite Resiliency: Simplicity In The Face Of Modern Satellite Design, Dax Linville, Robert A. Bettinger
An Argument Against Satellite Resiliency: Simplicity In The Face Of Modern Satellite Design, Dax Linville, Robert A. Bettinger
Faculty Publications
The US Air Force and the wider US government rely heavily on space-based capabilities in various orbital regimes to project national security and sovereignty. However, these capabilities are enabled by the design, launch, and operation of satellites produced with a design methodology that favors large, monolithic, and technologically exquisite space systems. Despite the ability for these satellites to provide enduring and resilient capabilities, they suffer from a woefully long acquisition process that debilitates any prospect of rapid satellite reconstitution in the event of a space war.
Investigation Of Ultem 9085 For Use In Printed Orbital Structures, William R. Gallagher
Investigation Of Ultem 9085 For Use In Printed Orbital Structures, William R. Gallagher
Theses and Dissertations
Additive manufacturing is revolutionizing industries ranging from medicine to space. However, the structural characteristics of plastic parts created by these methods are not as well understood as their more established counterparts. This research explored two relevant areas: how the structural characteristics of ULTEM 9085 plastic behaved after exposure to orbital conditions and the design of the cross-sectional area of a beam to be 3-D printed in microgravity based on the expected loads from the printer. To study orbital effects, ULTEM 9085 was printed into 1/4th scale ASTM D638- 14 dogbones using a Stratasys 450mc printer. These dogbones were placed in …
Space-Based Localization Of Radio Frequency Transmitters Utilizing Macaulay Resultant And Heuristic Optimization Methods, Jessica M. Wightman
Space-Based Localization Of Radio Frequency Transmitters Utilizing Macaulay Resultant And Heuristic Optimization Methods, Jessica M. Wightman
Theses and Dissertations
This research focuses on radio frequency geolocation of space objects utilizing space-based platforms. Geolocation has long been the solution for locating objects. In particular, this study examines the scenario of two cooperative receivers geolocating a transmitter in close proximity. An algorithm is developed to calculate the initial estimated transmitter location and projected orbital trajectory. The algorithm uses the Macaulay method of solving a system of polynomials as well as heuristic optimization techniques to locate a transmitter with respect to receivers at different time intervals. For the scenarios investigated, both Macaulay and heuristic optimization methods achieve initial relative orbit determination.
Spacecraft Position Estimation And Attitude Determination Using Terrestrial Illumination Matching, Liberty M. Shockley
Spacecraft Position Estimation And Attitude Determination Using Terrestrial Illumination Matching, Liberty M. Shockley
Theses and Dissertations
An algorithm to conduct spacecraft position estimation and attitude determination via terrestrial illumination matching (TIM) is presented consisting of a novel method that uses terrestrial lights as a surrogate for star fields. Although star sensors represent a highly accurate means of attitude determination with considerable spaceflight heritage, with Global Positioning System (GPS) providing position, TIM provides a potentially viable alternative in the event of star sensor or GPS malfunction or performance degradation. The research defines a catalog of terrestrial light constellations, which are then implemented within the TIM algorithm for position acquisition of a generic spacecraft bus. With the algorithm …
Linear Regression Models Applied To Imperfect Information Spacecraft Pursuit-Evasion Differential Games, Dax Linville
Linear Regression Models Applied To Imperfect Information Spacecraft Pursuit-Evasion Differential Games, Dax Linville
Theses and Dissertations
Within satellite rendezvous and proximity operations lies pursuit-evasion differential games between two spacecraft. The extent of possible outcomes can be mathematically bounded by differential games where each player employs optimal strategies. A linear regression model is developed from a large data set of optimal control solutions. The model is shown to map pursuer relative starting positions to final capture positions and estimate capture time. The model is 3.8 times faster than the indirect heuristic method for arbitrary pursuer starting positions on an initial relative orbit about the evader. The linear regression model is shown to be well suited for on-board …
The Potentiality Of Space Enterprise Force Reconstitution: Nationalizing Civilian Satellites During Kinetic Conflicts, Robert A. Bettinger, Sara Schmitt
The Potentiality Of Space Enterprise Force Reconstitution: Nationalizing Civilian Satellites During Kinetic Conflicts, Robert A. Bettinger, Sara Schmitt
Faculty Publications
This article will discuss the possibility of employing a policy of civilian satellite nationalization during a space war as a means of US Space Enterprise force re- constitution to ensure continued access to space capabilities necessary for the execution of the national strategy, as well as deterring potential adversaries from initiating counterspace hostilities. In terms of structure, the authors will examine the thesis by answering these questions. First, what historical precedent exists for the rapid military acquisition of civilian assets via nationalization? Second (given the unique nature of space as an operational environment), can that historical precedent be applied to …
Limited-Duty-Cycle Satellite Formation Control Via Differential Drag, Talon A. Townley
Limited-Duty-Cycle Satellite Formation Control Via Differential Drag, Talon A. Townley
Theses and Dissertations
As CubeSat formation flying missions relying on differential drag control become increasingly common, additional missions based on this control must be studied. A mission planning tool is investigated to control the relative spacing of a CubeSat formation where differential drag is the sole control mechanism. System performance is investigated under varying perturbations and a range of system parameters, including limiting the control duty cycle. Optimal solutions based on using a pseudo spectral numerical solver, GPOPS-II, to minimize maneuver time. This study includes the development of a mission planning tool to work with the modeled CubeSat mission to calculate optimal maneuvers …