<p> An analytical technique for investigating transport aircraft handling qualities is exercised in a study using models of two such vehicles, a Boeing 747 and Lockheed C-5A. Two flight conditions are employed for climb and directional tasks, and a third included for a flare task. The analysis technique is based upon a &ldquo;structural model&rdquo; of the human pilot developed by Hess. The associated analysis procedure has been discussed previously in the literature, but centered almost exclusively on the characteristics of high-performance fighter aircraft. The handling qualities rating level (HQRL) and pilot induced oscillation tendencies rating level (PIORL) are predicted for nominal configurations of the aircraft and for &ldquo;damaged&rdquo; configurations where actuator rate limits are introduced as nonlinearites. It is demonstrated that the analysis can accommodate nonlinear pilot/vehicle behavior and do so in the context of specific flight tasks, yielding estimates of handling qualities, pilot-induced oscillation tendencies and upper limits of task performance. A brief human-in-the-loop tracking study was performed to provide a limited validation of the pilot model employed.</p>

<p> Solar radiation pressure alters satellites' eccentricity by accelerating and decelerating them during each orbit. The accumulated perturbation cancels yearly for geostationary satellites, but meanwhile the perigee radius changes. Disposed satellites must be reorbited higher to compensate, using more fuel. The examined disposal orbit points toward the Sun and uses the satellite's natural eccentricity. This causes the eccentricity vector to only change direction, keeping the perigee radius constant. This thesis verifies this behavior over one year with an analytical derivation and MATLAB simulation, gaining useful insights into its cause. The traditional and proposed disposal orbits are then modeled using NASA's GMAT for more realistic simulations. The proposed orbit's sensitivity to satellite and initialization errors is also examined. Relationships are developed to show these errors' effect on the perigee radius. In conclusion, while this orbit can be used in the short term, margins are necessary to guarantee protection of the geostationary belt.</p>

<p> The problem of controlling the behavior of a spacecraft in an optimal manner is one that has been studied since the beginning of the space era in the late 1950s. Recently, the complexity of such optimization problems has been increased by the introduction of spacecraft that are comparatively small in size and capable of being reconfigured, either in between missions or on-orbit. While such spacecraft have the potential to greatly expand the variety of missions that can be undertaken, they also increase the basic number of design variables that must be optimized. This dissertation presents a novel approach for the design of spacecraft control systems that optimizes both controller gain parameters and physical attributes of the spacecraft <i> in parallel</i>. The central design tool for this new strategy is a genetic algorithm, which applies concepts from evolutionary biology to search a complex design space in an efficient manner. Results are presented for spacecraft of various sizes, and the genetic algorithm design results are compared to a number of more traditional design approaches. </p><p> In the first part of this dissertation the genetic algorithm is applied to the problem of tuning the gain parameters of a nonlinear control law. This controller is used within a small spacecraft performing an attitude tracking maneuver, and must compensate for multiple environmental disturbance moments and the imposition of actuator saturation limits. While the control law under study has proven stability properties, no work has yet been done on optimizing the gain parameters for a specific application. The combined complexity of the controller itself and the spacecraft system make gain tuning via traditional approaches very difficult, and as such a genetic algorithm is utilized. The genetic algorithm can search a broad swath of the overall design space, and does so more efficiently than a human engineer applying their intuition in an "informed" trial-and-error approach to the same problem. </p><p> With the basic efficacy of the genetic algorithm established, in the next phase of the dissertation a novel controller optimization approach known as location-scheduled control is introduced. Under location-scheduled control, the use of the genetic algorithm is extended to not only optimize the gain parameters of a given control law but also the physical location of the control actuators within the spacecraft. This <i>dual</i> optimization of both controller gain parameters and physical properties of the spacecraft yields a catalog of design solutions that can be called upon from mission to mission, which significantly reduces the time required for control system design. The ability to easily relocate the hardware components of a spacecraft control system is enabled by a class of spacecraft known as CubeSats, which will be described in detail. </p><p> In the final portion of this dissertation the location-scheduled control methodology is applied to a real-word testbed system and hardware results are compared to those obtained via simulation. This system makes use of a unique property of superconducting physics known as flux-pinned interfaces that allows CubeSat-scale test articles to be easily reconfigured. The location-scheduled control approach is used to simultaneously determine the optimal configuration of the reconfigurable spacecraft system and the appropriate gains for a single-axis reorientation maneuver. It is shown through hardware testing that the genetic algorithm once again yields a combination of system configuration and controller gain values that outperforms those found by a control systems engineer.</p>

<p> The communications and electronic systems that comprise a distributed control architecture for a robotic manipulator tie the high level control and motion planning to the electromechanical components. Custom solutions to this problem can be expensive in terms of time, cost, and maintenance. The integration of commercial off the shelf (COTS) motion controllers, combined with a robust communication standard, offers the potential to reduce the costs and development times for new robots. This thesis demonstrates an implementation of this architecture using commercial controllers and the CANopen communications bus on two existing dexterous robots. Testing is conducted to quantify the single joint performance of these modules. Additionally, the implementation of the system on a second robot arm was conducted in order to test the flexibility of the system for use with different actuators and feedback.</p>

<p> A robust test bed is needed to facilitate future development of guidance, navigation, and control software for future vehicles capable of vertical takeoff and landings. Specifically, this work aims to develop both a hardware and software simulator that can be used for future flight software development for extra-planetary vehicles. To achieve the program requirements of a high thrust to weight ratio with large payload capability, the vehicle is designed to have a novel combination of electric motors and a micro jet engine is used to act as the propulsion elements.</p><p> The spacecraft simulator underwent several iterations of hardware development using different materials and fabrication methods. The final design used a combination of carbon fiber and fiberglass that was cured under vacuum to serve as the frame of the vehicle which provided a strong, lightweight platform for all flight components and future payloads.</p><p> The vehicle also uses an open source software development platform, Arduino, to serve as the initial flight computer and has onboard accelerometers, gyroscopes, and magnetometers to sense the vehicles attitude. To prevent instability due to noise, a polynomial kalman filter was designed and this fed the sensed angles and rates into a robust attitude controller which autonomously control the vehicle' s yaw, pitch, and roll angles.</p><p> In addition to the hardware development of the vehicle itself, both a software simulation and a real time data acquisition interface was written in MATLAB/SIMULINK so that real flight data could be taken and then correlated to the simulation to prove the accuracy of the analytical model.</p><p> In result, the full scale vehicle was designed and own outside of the lab environment and data showed that the software model accurately predicted the flight dynamics of the vehicle.</p>

<p>Reynolds averaged Navier Stokes (RANS) solvers have become the workhorse for simulating turbulent flows for most practical purposes. While the incompressible turbulence models used with RANS equations have improved considerably in their predictive capability, significant breakthrough has not been achieved for their compressible counterparts. With the advancement in computing power, high resolution direct numerical simulation (DNS) of low Reynolds number turbulent flows has become feasible. DNS of simple turbulent flows provides a detailed database which can be used for developing and testing turbulence models. In this work, we perform DNS of compressible homogeneous turbulence&mdash;decaying isotropic turbulence and homogeneous shear flow&mdash;for a range of initial turbulent Mach numbers, (<i>M_t</i>₀ = 0.05&ndash;0.4) using the more natural initial conditions. Simulations were performed on grids with 128³ and 256³ points. Compressibility effects on the evolution of turbulent kinetic energy were studied. We found negligible compressibility effects for decaying isotropic turbulence, while homogeneous shear flow demonstrated compressibility effects in the growth rate of turbulent kinetic energy. Compressibility corrections to turbulence models in the form of the ratio <i>&epsis;_d/&epsis;_s</i>, have been tested with the results from the simulations. For decaying isotropic turbulence a [special characters omitted] scaling was found to be better than [special characters omitted] while for homogeneous shear flow it was the opposite. The small value of the ratio <i>&epsis;_d/&epsis;_s</i> in decaying isotropic turbulence makes the [special characters omitted] scaling less relevant. Based on the DNS results of homogeneous shear flow, a new correction parameterized by the gradient Mach number, <i> M_g,</i> is proposed. The parameter <i>C_&mu;</i>, which is assumed constant for incompressible two equation eddy viscosity models, is computed explicitly from the DNS data. An <i>M_g,</i> dependence of the parameter, <i>C_&mu;</i>, is proposed. </p>

Spacecraft reorientation can require propellant even when using gyroscopes since these have momentum saturation limits at which control is lost until thrusters are fired to desaturate them. To eliminate this need and thereby reduce cost, this work seeks trajectories that avoid saturation altogether by taking advantage of known disturbance torques. This concept is formulated as an optimal control problem and a direct transcription method is applied to obtain numerical solutions. Unlike recent related work on attitude maneuvers and momentum desaturation using only gyroscopes, this thesis allows the full rotational state (attitude, rate, and momentum) at the start and end of the maneuver to be specified. This thesis establishes the viability of this technique, which can potentially extend the operational lifetime of any gyroscope-equipped spacecraft, by successfully demonstrating it in a flight test in which the International Space Station was rotated 90 deg without propellant.

Acoustic tones can impede safe store separation and amplify structural fatigue in airborne military aircraft with open internal bays. Experimentally simulating such cavity flows is essential to understanding the physical phenomena. This study will demonstrate that a machine learning algorithm can accurately classify flow regimes using a limited number of data points and help identify regions of interest for future experiments. McKay's Latin hypercube method was used to select the best data points from a database comprised of the experimental results of tests conducted in the NASA Langley eight-foot transonic pressure tunnel on a variable geometry rectangular cavity. A Galerkin-derived, adaptive, matrix-free scattered data approximation scheme based on artificial neural networks, called Sequential Function Approximation, was trained using the best data subsets and then used to predict the results of the wind tunnel experiments. We first determined whether Sequential Function Approximation could predict the three classes of observed cavity flow. Then, we used our algorithm to predict both flow class and the occurrence of acoustic resonance. These results favorably compared against solutions from publicly-available support vector machines and pre-built classifier programs.

This thesis is concerned with the optimal flight trajectories in the presence of a three-dimensional windshear. Both the take-off and abort landing problems are studied. A mathematical model of a three-dimensional windshear is developed by the superposition of the flow fields of two symmetric vortex rings with appropriate parameters (circulation strength, radius, height). The flow field produced by this vortex ring pair is close to that of a real microburst. The wind components are functions of the geometric coordinates and can be obtained using either the Biot-Savart law or the properties of the stream function. With this wind model, the strongest windshear and downdraft are located in a vertical plane passing through the central axis of the vortex ring pair. Therefore, in the computation of flight trajectories, the aircraft is assumed to fly in this vertical plane. Two cases are considered: (A) at the initial time, the aircraft is located in the region of strongest headwind; (B) at the initial time, the aircraft is located in the region of weak-to-moderate headwind. Case A implies late detection, while Case B implies early detection of windshear. Optimal trajectories are computed for both take-off and abort landing. For the take-off problem, the performance index being minimized is the peak value of the deviation of the absolute path inclination from a reference value; for the abort landing problem, the performance index being minimized is the peak value of the altitude drop. The resulting optimal control problems are Chebyshev problems, which are converted into Bolza problems via suitable transformations. Then, the Bolza problems are solved by using the sequential gradient-restoration algorithm (SGRA). Numerical computations for both the take-off and abort landing problems lead to the following conclusions: (i) The survival capability of the optimal trajectory is superior to that of the constant pitch trajectory and the maximum angle of attack trajectory; this means that near-optimal guidance schemes should be developed to improve the survival capability of an aircraft in a severe windshear. (ii) For the optimal trajectories, the survival capability in Case B (early detection) is superior to that in Case A (late detection); this indicates that early detection of a windshear can enhance the safety of flight.

Parametric models for the representation of the power spectrum and bispectrum of a bank of data by the use of a two-stage, auto/cross-correlation matching (ACM) technique are developed. First, the applicability of the ACM technique for ordinary spectral modeling is discussed. Then, the parametric bispectral modeling technique is formulated using third-order cumulant information. This autoregressive moving average (ARMA) technique allows for the simultaneous determination of both the AR and MA filter coefficients. This procedure can expedite the analysis of phase coupling, system nonlinearities, and other features which cannot be captured by ordinary spectral analysis. Techniques are demonstrated numerically through the analysis of Space Shuttle flight data.