Browsing by Author "Black, Jonathan T."

Now showing 1 - 20 of 53
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    A* Node Search and Nonlinear Optimization for Satellite Relative Motion Path Planning
    Connerney, Ian Edward (Virginia Tech, 2021-11-03)
    The capability to perform rendezvous and proximity operations about space objects is central to the next generation of space situational awareness. The ability to diagnose and respond to spacecraft anomalies is often hampered by the lack of capability to perform inspection or testing on the target vehicle in flight. While some limited ability to perform inspection can be provided by an extensible boom, such as the robotic arms deployed on the space shuttle and space station, a free-flying companion vehicle provides maximum flexibility of movement about the target. Safe and efficient utilization of a companion vehicle requires trajectories capable of minimizing spacecraft resources, e.g., time or fuel, while adhering to complex path and state constraints. This paper develops an efficient solution method capable of handling complex constraints based on a grid search A* algorithm and compares solution results against a state-of-the-art nonlinear optimization method. Trajectories are investigated that include nonlinear constraints, such as complex keep-out-regions and thruster plume impingement, that may be required for inspection of a specific target area in a complex environment. This work is widely applicable and can be expanded to apply to a variety of satellite relative motion trajectory planning problems.
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    Adaptive Controller Development and Evaluation for a 6DOF Controllable Multirotor
    Furgiuele, Theresa Chung Wai (Virginia Tech, 2022-10-03)
    The omnicopter is a small unmanned aerial vehicle capable of executing decoupled translational and rotational motion (six degree of freedom, 6DOF, motion). The development of controllers for various 6DOF controllable multirotors has been much more limited than development for quadrotors, which makes selecting a controller for a 6DOF multirotor difficult. The omnicopter is subject to various uncertainties and disturbances from hardware changes, structural dynamics, and airflow, making adaptive controllers particularly interesting to investigate. The goal of this research is to design and evaluate the performance of various position and attitude controller combinations for the omnicopter, specifically focusing on adaptive controllers. Simulations are first used to compare combinations of three position controllers, PID, model reference adaptive control, augmented model reference adaptive control (aMRAC), and four attitude controllers, PI/feedback linearization (PIFL), augmented model reference adaptive control, backstepping, and adaptive backstepping (aBack). For the simulations, the omnicopter is commanded to point at and track a stationary aim point as it travels along a $C^0$ continuous trajectory and a trajectory that is $C^1$ continuous. The controllers are stressed by random disturbances and the addition of an unaccounted for suspended mass. The augmented model reference adaptive controller for position control paired with the adaptive backstepping controller for attitude control is shown to be the best controller combination for tracking various trajectories while subject to disturbances. Based on the simulation results, the PID/PIFL and aMRAC/aBack controllers are selected to be compared during three different flight tests. The first flight test is on a $C^1$ continuous trajectory while the omnicopter is commanded to point at and track a stationary aim point. The second flight test is a hover with an unmodeled added weight, and the third is a circular trajectory with a broken blade. As with the simulation results, the adaptive controller is shown to yield better performance than the nonadaptive controller for all scenarios, particularly for position tracking. With an added weight or a broken propeller, the adaptive attitude controller struggles to return to level flight, but is capable of maintaining steady flight when the nonadaptive controller tends to fail. Finally, while model reference adaptive controllers are shown to be effective, their nonlinearity can make them difficult to tune and certify via standard certification methods, such as gain and phase margin. A method for using time delay margin estimates, a potential certification metric, to tune the adaptive parameter tuning gain matrix is shown to be useful when applied to an augmented MRAC controller for a quadrotor.
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    Additive Manufacturing in Spacecraft Design and In-Space Robotic Fabrication of Large Structures
    Spicer, 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.
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    Advancements in the Design and Development of CubeSat Attitude Determination and Control Testing at the Virginia Tech Space Systems Simulation Laboratory
    Wolosik, Anthony Thomas (Virginia Tech, 2018-09-07)
    Among the various challenges involved in the development of CubeSats lies the attitude determination and control of the satellite. The importance of a properly functioning attitude determination and control system (ADCS) on any satellite is vital to the satisfaction of its mission objectives. Due to this importance, three-axis attitude control simulators are commonly used to test and validate spacecraft attitude control systems before flight. However, these systems are generally too large to successfully test the attitude control systems on-board CubeSat-class satellites. Due to their low cost and rapid development time, CubeSats have become an increasingly popular platform used in the study of space science and engineering research. As an increasing number of universities and industries take part in this new approach to small-satellite development, the demand to properly test, verify, and validate their attitude control systems will continue to increase. An approach to CubeSat attitude determination and control simulation is in development at the Virginia Tech Space Systems Simulation Laboratory. The final test setup will consist of an air bearing platform placed inside a square Helmholtz cage. The Helmholtz cage will provide an adjustable magnetic field to simulate that of a low earth orbit (LEO), and the spherical air bearing will simulate the frictionless environment of space. In conjunction, the two simulators will provide an inexpensive and adjustable system for testing any current, and future, CubeSat ADCS prior to flight. Using commercial off the shelf (COTS) components, the Virginia Tech CubeSat Attitude Control Simulator (CSACS), which is a low cost, lightweight air bearing testing platform, will be coupled with a 1.5-m-long square Helmholtz cage design in order to provide a simulated LEO environment for CubeSat ADCS validation.
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    Analysis of a CubeSat Orbit Using STK
    Funada, Kenta Patrick (Virginia Tech, 2023-09-05)
    This thesis presents an analysis of CubeSat orbits for both Low Earth Orbit (LEO) and Sun-Synchronous Orbit (SSO) missions using Systems Tool Kit (STK). The study focuses on analyzing communication, power generation, and radiation exposure while considering various factors. The analysis is based on the 3U CubeSat called UT-ProSat-1, developed by students at Virginia Polytechnic Institute and State University (VT) for an upcoming mission. The orbit size and mass adjustments were made for the LEO mission to enhance communication performance. The influence of solar activity on CubeSat lifetime and access time was examined, highlighting the significance of mass and solar activity. The impact of increasing orbit size on communication time was analyzed, emphasizing the trade-offs between mass, orbit size, and communication performance. The SSO mission prioritized power generation optimization resulted in generating sufficient power for the nominal phase of the mission. It also considered the effects of the South Atlantic Anomaly (SAA) on radiation exposure. Effective risk management of increasing the shielding for the avionics were emphasized which consequently will stabilize the orbit and prolong its lifetime. Additionally, temperature dynamics were investigated, indicating the need for further analysis considering heat dissipation and utilizing a more accurate CubeSat model. The insights gained from this study contribute to the improved the performance of CubeSats and validate the mission results, providing valuable information for successful missions in the future.
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    Analysis of Firmware Security in Embedded ARM Environments
    Brown, Dane Andrew (Virginia Tech, 2019-09-30)
    Modern enterprise-grade systems with virtually unlimited resources have many options when it comes to implementing state of the art intrusion prevention and detection solutions. These solutions are costly in terms of energy, execution time, circuit board area, and capital. Sustainable Internet of Things devices and power-constrained embedded systems are thus forced to make suboptimal security trade-offs. One such trade-off is the design of architectures which prevent execution of injected shell code, yet have allowed Return Oriented Programming (ROP) to emerge as a more reliable way to execute malicious code following attacks. ROP is a method used to take over the execution of a program by causing the return address of a function to be modified through an exploit vector, then returning to small segments of otherwise innocuous code located in executable memory one after the other to carry out the attacker's aims. We show that the Tiva TM4C123GH6PM microcontroller, which utilizes anARM Cortex-M4F processor, can be fully controlled with this technique. Firmware code is pre-loaded into a ROM on Tiva microcontrollers which can be subverted to erase and rewrite the flash memory where the program resides. That same firmware is searched for a Turing-complete gadget set which allows for arbitrary execution. We then design and evaluate a method for verifying the integrity of firmware on embedded systems, in this case Solid State Drives (SSDs). Some manufacturers make firmware updates available, but their proprietary protections leave end users unable to verify the authenticity of the firmware post installation. This means that attackers who are able to get a malicious firmware version installed on a victim SSD are able to operate with full impunity, as the owner will have no tools for detection. We have devised a method for performing side channel analysis of the current drawn by an SSD, which can compare its behavior while running genuine firmware against its behavior when running modified firmware. We train a binary classifier with samples of both versions and are able to consistently discriminate between genuine firmware and modified firmware, even despite changes in external factors such as temperature and supplied power.
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    Analytic Costate Initialization from Rough State-Trajectory Estimates
    Skamangas, Emmanuel E.; Lawton, John A.; Black, Jonathan T. (American Institute of Aeronautics and Astronautics, 2021-09-07)
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    Analyzing Attitude Correction of a Spacecraft Due to the Motion of a Robotic Arm Payload
    Molitor, Rowan Larson (Virginia Tech, 2024-06-06)
    There are millions of pieces of space debris in orbit around Earth that pose threats to operating spacecraft. Some of these debris can be attributed to satellite failure, or end-of-life protocols. With a continual increase in commercial satellite launches per year, decommissioned spacecraft act as more debris polluting the space environment. Not only can robotic arms assist with active orbital debris removal to be more sustainable, they also support robotic on-orbit servicing (OOS). Additionally, using a robotic manipulator enables different servicing operations to take place, allowing for life extension capabilities for expired spacecraft. These life extension services allow for a broader application for robotic arms, which includes rendezvous proximity operations and docking. Robotic arms can also be used for assembly and manufacturing cases, establishing a more sustained presence and creating permanent structures in space. When considering any robotic rendezvous maneuvers or servicing, assembly, and manufacturing tasks aboard a spacecraft, it is important for the parent satellite to maintain attitude throughout robot motion, as in a zero gravity setting, any forces created by the robot act as equal and opposite forces applied to the parent spacecraft. The research performed in this thesis aims to create a model to describe changes in attitude throughout planned robot motion, as well as introduce methods for compensating for potential disturbances. Additionally, methods for describing the kinematics of a robot manipulator are presented and the forces and torques experienced by each joint are calculated using Newton-Euler inverse dynamics. Based on a calculated trajectory of the end effector, these torques are propagated to the parent spacecraft to determine the change in angular velocity. The results of this analysis are used to determine the required angular velocity to apply to the parent spacecraft in order to maintain attitude.
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    Ancillary Scientific Instrument Attachment (ASIA):  A Distributed Hitchhiker Payload Carrier
    Scheid, Robert Jon (Virginia Tech, 2018-05-18)
    As more spacecraft reach more locations in the solar system, and with increasing residual capability of those spacecraft, an opportunity exists to improve scientific return at low cost to the satellite operator and minimal effect on its primary mission, regardless of the nature of that mission. The practicality of permanently attaching a small, mass-produced, non-deployable hitchhiker payload to modern spacecraft buses is investigated, and a case study of one such payload is presented. The Ancillary Scientific Instrument Attachment (ASIA) is a modified CubeSat bus that can be mass produced, independently tested, and delivered to spacecraft manufacturers with the design, analysis, integration, test, and software development already complete. All it requires are single-string power and data connections, and a location to mount the bus structure. The unit includes power regulation; data collection and storage; command processing; thermal control; and structural support. As many as five small scientific instruments can be included, all of which increase scientific value of the host spacecraft's primary mission without significantly interfering with that mission. Generally, ASIA would operate independently, with a minimum of interaction from the host spacecraft operations team; only routine data dumps for scientific return need be executed. Scientific data processing, distribution, and bus subsystem troubleshooting are offloaded to an independent facility. One possible scientific instrument loadout is described, designed to collect data about the space environment at any location in the solar system. Recommended forward steps for designing, testing, demonstrating, and implementing such a space-based system and its ground elements are presented.
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    An Assessment of 3D Tracking Systems and Lidar Data for RPO Simulation
    Meland, Tallak Edward (Virginia Tech, 2023-08-30)
    This thesis aimed to develop a rendezvous and proximity operation simulation to be tested with physical sensors and hardware, in order to assess the fidelity and performance of low-cost off-the-shelf systems for a hardware-in-the-loop testbed. With the push towards complex autonomous rendezvous missions, a low barrier to entry spacecraft simulator platform allows researchers to test and validate robotics systems, sensors, and algorithms for space applications, without investing in multimillion dollar equipment. This thesis conducted drone flights that followed a representative rendezvous trajectory while collecting lidar data of a target spacecraft model with a lidar sensor affixed to the drone. A relative orbital motion simulation tool was developed to create trajectories of varying orbits and initial conditions, and a representative trajectory was selected for use in drone flights. Two 3D tracking systems, OptiTrack and Vive, were assessed during these flights. OptiTrack is a high-cost state-of-the-art motion capture system that performs pose estimation by tracking reflective markers on a target in the tracking area. Vive is a lower-cost tracking system whose base stations emit lasers for its tracker to detect. Data collection by two lidar types was also assessed during these flights: real lidar data from a physical sensor, and virtual lidar data from a virtual sensor in a virtual environment. Drone flights were therefore performed in these four configurations of tracking system and lidar type, to directly compare the performance of higher-cost configurations with lower-cost configurations. The errors between the tracked drone position time history and the target position time history were analyzed, and the low-cost Vive and real lidar configuration was demonstrated to provide comparable error to the OptiTrack and real lidar configuration because of the dominance of the drone controller error over the tracking system error. In addition, lidar data of a target satellite model was collected by real and virtual lidar sensors during these flights, and point clouds were successfully generated. The resulting point clouds were compared by visualizing the data and noting the characteristics of real lidar data and its error, and how it compared to idealized virtual lidar data of a virtual target satellite model. The resulting real-world data characteristics were found to be modellable which can then be used for more robust simulation development within virtual reality. These results demonstrated that low-cost and open-source hardware and software provide satisfactory results for simulating this kind of spacecraft mission and capturing useful and usable data.
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    Assessment of a Low Cost IR Laser Local Tracking Solution for Robotic Operations
    Du, Minzhen (Virginia Tech, 2021-05-14)
    This thesis aimed to assess the feasibility of using an off-the-shelf virtual reality tracking system as a low cost precision pose estimation solution for robotic operations in both indoor and outdoor environments. Such a tracking solution has the potential of assisting critical operations related to planetary exploration missions, parcel handling/delivery, and wildfire detection/early warning systems. The boom of virtual reality experiences has accelerated the development of various low-cost, precision indoor tracking technologies. For the purpose of this thesis we choose to adapt the SteamVR Lighthouse system developed by Valve, which uses photo-diodes on the trackers to detect the rotating IR laser sheets emitted from the anchored base stations, also known as lighthouses. Some previous researches had been completed using the first generation of lighthouses, which has a few limitations on communication from lighthouses to the tracker. A NASA research has cited poor tracking performance under sunlight. We choose to use the second generation lighthouses which has improved the method of communication from lighthouses to the tracker, and we performed various experiments to assess their performance outdoors, including under sunlight. The studies of this thesis have two stages, the first stage focused on a controlled, indoor environment, having an Unmanned Aerial Vehicle (UAS) perform repeatable flight patterns and simultaneously tracked by the Lighthouse and a reference indoor tracking system, which showed that the tracking precision of the lighthouse is comparable to the industrial standard indoor tracking solution. The second stage of the study focused on outdoor experiments with the tracking system, comparing UAS flights between day and night conditions as well as positioning accuracy assessments with a CNC machine under indoor and outdoor conditions. The results showed matching performance between day and night while still comparable to industrial standard indoor tracking solution down to centimeter precision, and matching simulated CNC trajectory down to millimeter precision. There is also some room for improvement in regards to the experimental method and equipment used, as well as improvements on the tracking system itself needed prior to adaptation in real-world applications.
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    Autonomous and Responsive Surveillance Network Management for Adaptive Space Situational Awareness
    Nastasi, Kevin Michael (Virginia Tech, 2018-08-28)
    As resident space object populations grow, and satellite propulsion capabilities improve, it will become increasingly challenging for space-reliant nations to maintain space situational awareness using current human-in-the-loop methods. This dissertation develops several real-time adaptive approaches to autonomous sensor network management for tracking multiple maneuvering and non-maneuvering satellites with a diversely populated Space Object Surveillance and Identification network. The proposed methods integrate suboptimal Partially Observed Markov Decision Processes (POMDPs) with covariance inflation or multiple model adaptive estimation techniques to task sensors and maintain viable orbit estimates for all targets. The POMDPs developed in this dissertation use information-based and system-based metrics to determine the rewards and costs associated with tasking a specific sensor to track a particular satellite. Like in real-world situations, the population of target satellites vastly outnumbers the available set of sensors. Robust and adaptable tasking algorithms are needed in this scenario to determine how and when sensors should be tasked. The strategies developed in this dissertation successfully track 207 non-maneuvering and maneuvering spacecraft using only 24 ground and space-based sensors. The results show that multiple model adaptive estimation coupled with a multi-metric, suboptimal POMDP can effectively and efficiently task a diverse network of sensors to track multiple maneuvering spacecraft, while simultaneously monitoring a large number of non-maneuvering objects. Overall, this dissertation demonstrates the potential for autonomous and adaptable sensor network command and control for real-world space situational awareness.
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    Collocation Method and Model Predictive Control for Accurate Landing of a Mars EDL vehicle
    Srinivas, Neeraj (Virginia Tech, 2021-02-02)
    This thesis aims at investigating numerical methods through which the accuracy in landing of a Mars entry-descent-landing (EDL) vehicle can be improved. The methods investigated include the collocation method and model predictive control (MPC). The primary control variable utilized in this study is the bank angle of the spacecraft, which is the angle between the lift vector and the vertical direction. Modulating this vector affects the equations of system of equations and the seven state variables, namely altitude, velocity, latitude, longitude, flight path angle, heading angle and total time taken. An optimizer is implemented which utilizes the collocation method, through which the optimal bank angle is found at every discretized state along the trajectory which are equally separated through a definite timestep, which is a function of the end time state. A 3-sigma wind disturbance model is introduced to the system, as a function of the altitude, which introduces uncertainties to the system, resulting in a final state deviating from the targeted location. The trajectory is split into two parts, for better control of the vehicle during the end stages of flight. The MPC aims at reducing the end state deviation, through the implementation of a predictor-corrector algorithm that propagates the trajectory for a certain number of timesteps, followed by running the optimizer from the current disturbed state to the desired target location. At the end of this analysis, a new set of optimal bank angle are found, which account for the wind disturbances and navigates the EDL vehicle to the desired location.
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    Computer Vision Tracking of sUAS From a Pan/Tilt Platform
    Ogorzalek, Jeremy Patrick (Virginia Tech, 2019-06-24)
    The ability to quickly, accurately, and autonomously identify and track objects in digital images in real-time has been an area of investigation for quite some time. Research in this area falls under the broader category of computer vision. Only in recent decades, with advances in computing power and commercial optical hardware, has this capability become a possibility. There are many different methods of identifying and tracking objects of interest, and best practices are still being developed, varying based on application. This thesis examines background subtraction methods as they apply to the tracking of small unmanned aerial systems (sUAS). A system combining commercial off-the-shelf (COTS) cameras and a pan-tilt unit (PTU), along with custom developed code, is developed for the purpose of continuously pointing at and tracking the motion of a sUAS in flight. Mixtures of Gaussians Background Modeling (MOGBM) is used to track the motion of the sUAS in frame and determine when to command the PTU. When the camera is moving, background subtraction methods are unusable, so additional methods are explored for filling this performance gap. The stereo vision capabilities of the system, enabled by the use of two cameras simultaneously, allow for estimation of the three-dimensional position and trajectory of the sUAS. This system can be used as a supplement or replacement to traditional tracking methods such as GPS and RADAR as part of a larger unmanned aerial systems traffic control (UTC) infrastructure.
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    Data Reduction for Diverse Optical Observers through Fundamental Dynamic and Geometric Analysis
    Sease, Bradley Jason (Virginia Tech, 2016-05-05)
    Typical algorithms for processing unresolved space imagery from optical systems make broad assumptions about the expected behavior of the sensors during collection. While these techniques are often successful at data reduction for a particular mission, they rarely extend to sensors in different operating modes. Such specialized techniques therefore reduce the number of sensors able to contribute imagery. By approaching this problem with analysis of the fundamental dynamic equations and geometry at play, we can gain a deeper understanding into the behavior of both stars and space objects viewed through optical sensors. This type of analysis has the potential to enable data collection from a wider variety of sensors, increasing both the quantity and quality of data available for space object catalog maintenance. This dissertation will explore the implications of this approach to unresolved data processing. Sensor-level motion descriptions will be derived and applied to the problem of space object discrimination and tracking. Results of this processing pipeline as applied to both simulated and real optical data will be presented.
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    A Defense-In-Depth Security Architecture for Software Defined Radio Systems
    Hitefield, Seth D. (Virginia Tech, 2020-01-27)
    Modern wireless communications systems are constantly evolving and growing more complex. Recently, there has been a shift towards software defined radios due to the flexibility soft- ware implementations provide. This enables an easier development process, longer product lifetimes, and better adaptability for congested environments than conventional hardware systems. However, this shift introduces new attack surfaces where vulnerable implementa- tions can be exploited to disrupt communications or gain unauthorized access to a system. Previous research concerning wireless security mainly focuses on vulnerabilities within pro- tocols rather than in the radios themselves. This dissertation specifically addresses this new threat against software radios and introduces a new security model intended to mitigate this threat. We also demonstrate example exploits of waveforms which can result in either a denial-of-service or a compromise of the system from a wireless attack vector. These example exploits target vulnerabilities such as overflows, unsanitized control inputs, and unexpected state changes. We present a defense-in-depth security architecture for software radios that protects the system by isolating components within a waveform into different security zones. Exploits against vulnerabilities within blocks are contained by isolation zones which protects the rest of the system from compromise. This architecture is inspired by the concept of a microkernel and provides a minimal trusted computing base for developing secure radio systems. Unlike other previous security models, our model protects from exploits within the radio protocol stack itself and not just the higher layer application. Different isolation mechanisms such as containers or virtual machines can be used depending on the security risk imposed by a component and any security requirements. However, adding these isolation environments incurs a performance overhead for applications. We perform an analysis of multiple example waveforms to characterize the impact of isolation environments on the overall performance of an application and demonstrate the overhead generated from the added isolation can be minimal. Because of this, our defense-in-depth architecture should be applied to real-world, production systems. We finally present an example integration of the model within the GNU Radio framework that can be used to develop any waveform using the defense-in-depth se- curity architecture.
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    Design and thermal analysis for a novel EMCCD camera payload in a 1U CubeSat form factor
    Angle, Nicholas Blake (Virginia Tech, 2024-06-24)
    Nüvü Camēras, a Canadian company that designs a range of CCD and EMCCD cameras and controllers, recently began development on a miniaturized EMCCD controller for a CubeSat form factor. The detector for this payload requires near-cryogenic temperatures, approximately 188K, for performance operation. A temperature requirement of that magnitude for a CubeSat form factor is challenging given the low thermal mass, volume, surface area, and power availability for heat storage, dissipation and control systems that would typically be available for larger form factor spacecraft. The goal of this project is to design and per- form thermal analysis for the Nüvü Camēras CubeSat EMCCD Controller that allows for cold-biased active temperature control of both the controller electronics and detector. The EMCCD controller had an operational temperature range of −35◦C to +60◦C while the detector had a performance range of −110◦C to −85◦C with a desire to maintain a resolu- tion of ±0.25◦C. To meet these requirements, a system was designed within 3D modeling software Autodesk Inventor and imported into Thermal Desktop for thermal analysis and iteration. Models were updated based on thermal analysis results, adjusted by hand, and then tested again until a passive cooling and active heating system that met the require- ments was achieved. The final control system was shown to be capable of cooling from 20◦C (293.15K) to −85◦C (188.15K) and beyond given a Sun Synchronous orbit at 600km with attitude control and operational requirements. It was also shown to be capable of heating up, using resistive heaters on key components, beyond the thermal inertia of the system and environment, indicating viable control on orbit. In the future a PID control method can be implemented, and its use is being investigated by Nüvü Camēras for achieving the desired resolution of ±0.25◦C in the future.
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    Design of a Co-Orbital Threat Identification System
    Whited, Derick John (Virginia Tech, 2022-03-15)
    With the increase in space traffic, proliferation of inexpensive launch opportunities, and interest from many countries in utilizing the space domain, threats to existing space assets are likely to increase dramatically in the coming years. The development of a system that can identify potential threats and alert space operators is vital to maintaining asset resiliency and security. The focus of this thesis is the design and evaluation of such a system. The design is comprised of the development of a classification hierarchy and the selection of machine learning models that will enable the identification of anomalous object behavior. The hierarchy is based on previous examples applied to object classification while reconsidering the assumption that a satellite may perform only one mission. The selected machine learning models perform both supervised classification of actively maneuvering objects and unsupervised identification of anomalous behavior within large satellite constellations. The evaluation process considers the independent adjustment of model hyperparameters to achieve optimal model settings. The optimal models perform both classification functions and return moderate accuracy. The system is applied to several case studies examining edge cases and what factors constitute a threatening object and what factors do not. Suggestions for improvement of the system in the future are presented.
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    Designing Transfers Between Earth-Moon Halo Orbits Using Manifolds and Optimization
    Brown, Gavin Miles (Virginia Tech, 2020-09-03)
    Being able to identify fuel efficient transfers between orbits is critical to planning and executing missions involving spacecraft. With a renewed focus on missions in cislunar space, identifying efficient transfers in the dynamical environment characterized by the Circular Restricted Three-Body Problem (CR3BP) will be especially important, both now and in the immediate future. The focus of this thesis is to develop a methodology that can be used to identify a valid low-cost transfer between a variety of orbits in the CR3BP. The approach consists of two distinct parts. First, tools related to dynamical systems theory and manifolds are used to create an initial set of possible transfers. An optimization scheme is then applied to the initial transfers to obtain an optimized set of transfers. Code was developed in MATLAB to implement and test this approach. The methodology and its implementation were evaluated by using the code to identify a low-cost transfer in three different transfer cases. For each transfer case, the best transfers from each set were compared, and important characteristics of the transfers in the first and final sets were examined. The results from those transfer cases were analyzed to determine the overall efficacy of the approach and effectiveness of the implementation code. In all three cases, in terms of cost and continuity characteristics, the best optimized transfers were noticeably different compared to the best manifold transfers. In terms of the transfer path identified, the best optimized and best manifold transfers were noticeably different for two of the three cases. Suggestions for improvements and other possible applications for the developed methodology were then identified and presented.
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    Development and Initial Testing of a Micro-Newton Torsion Pendulum with Gas-Dynamic Calibration
    Smith, Brandon Joseph (Virginia Tech, 2019-03-05)
    A novel torsion pendulum thrust test stand for micro-Newton-scale spacecraft thrusters is described. The stand is designed to be robust against electromagnetic interference effects internal or external to the thruster being tested. The design and testing of a gas-dynamic calibration thruster is included. This thruster is fully self-contained on the pendulum arm, with no external wires or feedlines connected to the device and impacting the dynamic response of the underlying pendulum. Initial calibration results are shown. Zero drift and hysteresis are present in the results, evidenced by a constant steady-state displacement drift and a return to a different displacement after shutdown of the calibration thruster. Results are compared to theoretical solutions of the equation of motion. An external forcing function of facility effects is described for discrepancies between results and the theoretical solution. Further work to eliminate these effects and add damping are proposed.