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Daniel Guggenheim School of Aerospace Engineering

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Now showing 1 - 10 of 172
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On-Board Model-Based Fault Diagnosis for Autonomous Proximity Operations

2018-09 , Schulte, Peter Z. , Spencer, David A.

Because of their complexity and the unforgiving environment in which they operate, aerospace vehicles often require autonomous systems to respond to mission-critical failures. Fault Detection, Isolation, and Recovery (FDIR) systems are used to detect, identify the source of, and recover from faults. Typically, FDIR systems use a rule-based paradigm for fault detection, where telemetry values are monitored against specific logical statements such as static upper and lower limits. The model-based paradigm allows more complex decision logic to be used for FDIR. This study focuses on a state machine approach toward model-based FDIR. The state machine approach is increasingly utilized for FDIR of complex systems because it is intuitive, logic-based, and simple to interpret visually. In current practice, the detection of specific symptoms is directly mapped to the appropriate response for a pre-diagnosed fault, as determined by FDIR engineers at design time. This study advances the state-of-the-art in state machine fault protection by developing an on-board diagnostic system that will assess symptoms, isolate fault sources, and select corrective actions based on models of system behavior. This state machine architecture for FDIR is applicable for a broad range of aerospace vehicles and mission scenarios. To demonstrate the broad applicability of the FDIR approach, two case studies are evaluated for scenarios in very different domains. The first is a terrestrial application involving the use of multi-rotor unmanned aerial vehicles (UAVs). The second is a space-based scenario involving autonomous proximity operations for orbital capture of a Mars Sample Return capsule. The efficacy of the state machine FDIR system is demonstrated via flight testing for the UAV case study and through software-in-the-loop testing in a flight-like simulation environment for the Mars Sample Return case. In each case, the FDIR system is focused on the Guidance, Navigation and Control subsystem. This approach has been successfully shown to detect, diagnose, and respond to faults during testing. State machines allow the autonomous system to handle distinct faults with identical symptoms for initial detection. Each fault has a separate diagnosis and response procedure, and the proper procedure is selected by the state machine. This study demonstrates how a fault protection system may diagnose these faults on-board rather than relying upon a priori ground diagnosis.

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Cupid's Arrow: A Small Satellite Concept to Measure Noble Gases in Venus' Atmosphere

2018-03 , Sotin, Christophe , Avice, Guillaume , Baker, John , Freeman, Anthony , Madzunkov, Stojan , Stevenson, Terry , Arora, Nitin , Darrach, M. R. , Lightsey, E. Glenn , Marty, B.

Getting reliable measurements of noble gases in Venus’ atmosphere with a CubeSat-derived mission concept is very challenging. But if feasible it could change how we make this fundamental geochemical measurement in planetary atmospheres and other gaseous environments (e.g., plumes emanating from icy moons or dwarf planets) across the solar system. Venus poses the most urgent and nearby target for such measurements, to fill in a key piece of the puzzle of Venus’ origin, evolution, and divergence from Earth’s geophysical history. Understanding Venus’ geophysical evolution is also key to interpreting observations of “Earth-like” exoplanets in order to assess whether they are Earth-like or Venus-like, which has obvious implications for their habitability potential. Noble gases are tracers of the evolution of planets. They trace processes such as the original supply of volatiles from the solar nebula, delivery of volatiles by asteroids and comets, escape rate of planetary atmospheres, degassing of the interior, and its timing in the planet’s history. However, a major observational missing link in our understanding of Venus’ evolution is the elementary and isotopic pattern of noble gases and stable isotopes in its atmosphere, which remain poorly known [1]. The concentrations of heavy noble gases (Kr, Xe) and their isotopes are mostly unknown, and our knowledge of light noble gases (He, Ne, Ar) is incomplete and imprecise. The Cupid’s Arrow mission concept would measure those quantities below the homopause where gas compounds are well mixed.

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Judicial Evidential Reasoning for Decision Support Applied to Orbit Insertion Failure

2017-11 , Jaunzemis, Andris D. , Minotra, Dev , Holzinger, Marcus J. , Feigh, Karen M. , Chan, Moses W. , Shenoy, Prakash P.

Realistic decision-making often occurs with insufficient time to gather all possible evidence before a decision must be rendered, requiring an efficient process for prioritizing between potential action sequences. This work aims to develop a decision support system for tasking sensor networks to gather evidence to resolve hypotheses in the face of ambiguous, incomplete, and uncertain evidence. Studies have shown that decision-makers demonstrate several biases in decisions involving probability judgement, so decision-makers must be confident that the evidence-based hypothesis resolution is strong and impartial before declaring an anomaly or reacting to a conjunction analysis. Providing decision-makers with the ability to estimate uncertainty and ambiguity in knowledge has been shown to augment effectiveness. The proposed framework, judicial evidential reasoning (JER), frames decision-maker questions as rigorously testable hypotheses and employs an alternating-agent minimax optimization on belief in the null proposition. This approach values impartiality in addition to time efficiency: an ideal action sequence gathers evidence to quickly resolve hypotheses while guarding against bias. JER applies the Dempster-Shafer theory of belief functions to model knowledge about hypotheses and quantify ambiguity, and adversarial optimization techniques are used to make many-hypothesis resolution computationally tractable. This work includes derivation and application of the JER formulation to a GTO insertion maneuver anomaly scenario.

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Empirical Dynamic Data Driven Detection Tracking Using Detectionless and Traditional FiSSt Methods

2017-09 , Virani, Shahzad , Murphy, Timothy S. , Holzinger, Marcus J. , Jones, Brandon A.

Autonomous search and recovery of resident space object (RSO) tracks is crucial for decision makers in SSA. This paper leverages dynamic data driven approaches to improve methodologies used in real-time detection and tracking of RSOs with a low signal-to-noise ratio (SNR). Detected RSOs are assigned to be tracked using one of two simultaneously operating algorithms. The Gaussian Mixture Proability Hypothesis Density (GM-PHD) filter tracks all RSOs above a certain SNR threshold, while a Detectionless Multi-Bernoulli filter (D-MB) detects and tracks low SNR objects. The D-MB filter uses matched filtering for likelihood computation which is highly non-Gaussian for dim objects. Hence, the D-MB filter is particle based which leads to higher computational complexity. The primary idea proposed in this paper is to balance the computational efficiency of GM-PHD and high sensitivity of the D-MB likelihood computation by dynamically switching tracks between the two filters based on the SNR of the target; allowing for real-time detection and tracking. These algorithms are implemented and tested on real data of objects in the geostationary (GEO) belt using a wide field-of-view camera (18.2 degrees). A star tracking mount is used to inertially stare at the GEO belt and data are collected for 2 hours corresponding to RSOs being observed in 48.2 degrees of the GEO belt.

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Methodology for Optimal Design of a Conformal Ablative Heatshield

2018-06 , Sidor, Adam T. , Braun, Robert D. , Kennedy, Graeme J.

Conformal ablators are low density composite materials comprised of a flexible fibrous substrate and polymer matrix. Recent advancements have improved the efficiency of conformal ablator fabrication through vacuum infusion processing where resin is directly injected into a fiber substrate enclosed in a matched mold. This mold filling process can be numerically simulated to inform mold and process design. An automated methodology pairing a mold filling simulation with an approach for tiling a heatshield geometry leads to designs optimized for manufacturing. Material property estimation generalizes the approach to a range of constituent materials, enabling rapid conceptual evaluation of a conformal ablative heatshield. This work improves on the state of the art which relies on heuristic methods tailored to a particular material and aeroshell geometry. Results for a 4.5 meter, 70 degree sphere-cone aeroshell demonstrate the power of an integrated approach.

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MicroNimbus: A CubeSat Mission for Millimeter-Wave Atmospheric Temperature Profiling

2018-01 , Himani, Tanish , Lightsey, E. Glenn , Frounchi, Milad , Cressler, John D. , Coen, Christopher , Williams, Wyman

MicroNimbus is a small satellite mission being developed by the Georgia Institute of Technology and Georgia Tech Research Institute that will utilize a frequency-agile mmwave radiometer to measure and update the temperature profile of the atmosphere from a 3U CubeSat platform. The on-board radiometer instrument will provide atmospheric temperature profile data at an altitude resolution of 10 km, a geographic resolution of 0.5°, and a temperature resolution of 2K RMS. The mission strongly aligns with the goals set forth in NASA’s Science Plan and will generate data valuable to researchers in the fields of weather forecasting, LIDAR, and laser communications. MicroNimbus has passed its Preliminary Design Review (PDR) phase and is moving towards the Critical Design Review (CDR) for the mission. If successful, MicroNimbus will serve as a first step towards the creation of a constellation of satellites designed to perform near real-time temperature profiling of the atmosphere.

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Real-Time Hardware-in-the-Loop Hand-Off from a Finder Scope to a Larger Telescope

2017-11 , Aguilar-Marsillach, Daniel , Virani, Shahzad , Holzinger, Marcus J.

Electro-optical sensors play an increasingly important role in the SSA domain for tracking satellites and debris objects. Such sensors provide data that complement other methods, like radar based sensing, by providing a higher angular resolution, and thus improving the estimation of an object’s orbit, attitude and physical properties. The acquisition of such data is invaluable for obtaining more accurate collision risk assessments and formulating improved debris mitigation efforts. The Georgia Tech - Space Object Research Telescope aims to improve detection and tracking for agile Raven-class telescopes with narrow fields of view and high angular resolutions. A secondary imaging system was used to correct the Georgia Tech - Space Object Research Telescope’s pointing errors for tracking objects at high angular rates using a closed-loop controller. This paper will focus on the development and results of a real-time hardware-in-the-loop hand-off from a finder scope to a larger telescope.

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Accuracy/Computation Performance of a New Trilateration Scheme for GPS-Style Localization

2018-03 , Cheung, Kar-Ming , Lightsey, E. Glenn , Lee, Charles H.

We recently introduced a new geometric trilateration (GT) method for GPS-style positioning. Preliminary single-point analysis using simplistic error assumptions indicates that the new scheme delivers almost indistinguishable localization accuracy as the traditional Newton-Raphson (NR) approach. Also, the same computation procedure can be used to perform high-accuracy relative positioning between a reference vehicle and an arbitrary number of target vehicles. This scheme has the potential to enable a) new mission concepts in collaborative science, b) in-situ navigation services for human Mars missions, and c) lower cost and faster acquisition of GPS signals for consumer-grade GPS products. The new GT scheme differs from the NR scheme in the following ways: 1. The new scheme is derived from Pythagoras Theorem, whereas the NR method is based on the principle of linear regression. 2. The NR method uses the absolute locations (xi, yi, zi)’s of the GPS satellites as input to each step of the localization computation. The GT method uses the Directional Cosines Ui’s from Earth’s center to the GPS satellite Si. 3. Both the NR method and the GT method iterate to converge to a localized solution. In each iteration step, multiple matrix operations are performed. The NR method constructs a different matrix in each iterative step, thus requires performing a new set of matrix operations in each step. The GT scheme uses the same matrix in each iteration, thus requiring computing the matrix operations only once for all subsequent iterations. In this paper, we perform an in-depth comparison between the GT scheme and the NR method in terms of a) GPS localization accuracy in the GPS operation environment, b) its sensitivity with respect to systematic errors and random errors, and c) computation load required to converge to a localization solution.

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Design and Operation of a Thrust Test Stand for University Small Satellite Thrusters

2018-01 , Stevenson, Terry , Lightsey, E. Glenn

A small, low cost thrust test stand was developed at the Georgia Institute of Technology to support ongoing small spacecraft propulsion research. The test stand is a torsional pendulum with a low natural frequency, designed to respond to thruster pulses in the range of milliseconds to hundreds of milliseconds as if they were instantaneous impulses. The stand displacement is measured by an LVDT, and the magnitude of the oscillation resulting from the thrust is used to determine the impulse delivered. The stand is not actively damped, and is operated with less time between impulses than the oscillations take to decay. A postprocessing method was developed to separate the oscillation caused by an impulse from the previous oscillations, by fitting a damped oscillator equation before and after the impulse, and determining the instantaneous angular velocity change across the impulse. The stand was used to test a thruster developed at Georgia Tech for the NASA BioSentinel mission.

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Feasibility of Supersonic Retropropulsion Based on Assessment of Mars-Relevant Flight Data

2017-09 , Sforzo, Brandon A. , Braun, Robert D.

Flight data provided by SpaceX for flights was analyzed to demonstrate the applicability of telemetry during SRP to Mars relevant conditions. This information was provided under the framework of a public-private partnership with NASA, executed as a Space Act Agreement. Analysis focused on the entry burn portion of the trajectory. Flight conditions were provided to confirm SRP occurred during an applicable range of mach numbers and dynamic pressures to match Mars SRP initiation conditions. Vehicle trajectory and attitude history were provided for the SRP segment as well as onboard sensors for temperature, pressure, heat flux, and strains to compare between missions. Furthermore, NASA airborne assets provided thermal imagery of the first stage during SRP to provide comparison to onboard data. Plume tracking analysis was compared to dynamic data from sensors with little correlation. Analysis of these onboard sensor data and examination of the details for several missions, the performance of the Falcon 9 vehicle during SRP appeared to be well behaved for these flights. This study illustrates that SRP methodology implemented for the Falcon 9 first stage entry does not adversely affect the vehicle and shows promise for future implementation.

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