A systems engineering approach was used to produce a preliminary design configuration for an ion-propelled orbital transfer vehicle system. The four components of the system are: ground software, ground hardware, the orbital transfer vehicle and the space shuttle. The orbital transfer vehicle uses electrostatic propulsion to transfer payload satellites from a low earth orbit, to any other desired orbit. The system maintenance concept, and a conceptual design are derived from the statement of need and the system operational requirements. The resulting design, maintainability, reliability and support requirements are discussed. A discussion of the feasibility of an ion propelled orbital transfer vehicle is included. / Master of Science

A design method for a multi-loop mixed discrete/continuous trajectory following pitch control algorithm for a generic aerospace vehicle is presented. This design methodology is facilitated by a time scale separation observed in the dynamical system. Two variations of this algorithm are considered, with features and drawbacks of both evaluated. The algorithm is then tested by simulations with two vehicles flying arbitrary trajectories. Results are presented for a thrust-vector controlled high-performance missile without atmospheric effects, and for a single-stage-to-orbit hypersonic vehicle with both elevator and thrust-vector control. It is shown that the control algorithm results in a pitch loop feedback controller that is robust and very stable, and is at least near optimal for the class of trajectories considered. No claims of optimality are made for the outer loop, but it is shown in the simulations that the outer loop tracker can do a reasonable job of following the prescribed nominal trajectory. / Ph. D.

Hemolymph trehalose concentrations of male and female Heliothis zea were quantitated by high performance thin-layer chromatography (HPTLC) at various ages and times of the day and related to flight activity. Effects of octopamine injection or stress on trehalose levels were also quantified. Flight activity was measured with a 32-channel computerized actograph that simulated sunrise at 0300 EST (Eastern Standard Time) and sunset at 1700. Males exhibited greater flight activity than females at all ages examined. Flight began near sunset, continuing through the night and ending around sunrise. Females flew continuously throughout the night, whereas males exhibited two peaks in activity: the first between 1700 and 1900, followed by a second peak between 2000 and 2400. Flight activity peaked on days 3-4 in males and days 4- 5 in females. Trehalose was the predominant hemolymph sugar, comprising 82-100% of total hemolymph sugars. Glucose was the second most frequently observed sugar. Trehalose concentrations were variable, ranging from < 1 ug/ul to 37 ug/ul. Lab-reared moths had higher and more variable trehalose concentrations than field collected (wild) moths. Trehalose levels were relatively constant several days after emergence in both sexes but decreased significantly by day 6 in males. When examined over a 24 hour period, trehalose concentrations gradually increased throughout the day in day 4 males and females, peaking one hour before sunset at approximately 18 ug/ul. This peak is hypothesized to be related to flight preparation. Females showed a second peak in trehalose levels at 1800, but males’ trehalose levels continued to decline until 1900. Males and females exhibited more similar patterns in trehalose concentrations when sampled every 15 minutes over the sunset period (1500-1900) than when sampled at hour intervals. Injections of octopamine, reputed to induce hyperglycemia in other insects, failed to elicit significant increases in trehalose levels in either fed or starved moths. Starved moths had lower trehalose concentrations than fed moths. Method of analysis (HPLC, HPTLC and anthrone) produced no differences in measured levels of trehalose or glucose. Various forms of stress (handling, shaking), also reported to induce hyperglycemia in other insects, similarly did not significantly increase trehalose titers in moths. / Ph. D.

A review of aeroplane spin literature is presented, including early spin research history and lessons learned from spinning trials. Despite many years of experience in spinning evaluation, it is difficult to predict spin characteristics and problems have been encountered and several prototype aeroplanes have been lost. No currently published method will reliably predict an aeroplane’s spin recovery characteristics. Quantitative data is required to study the spin motion of the aeroplane in adequate detail. An alternative method, Vision Based State Estimation, has been used to capture the spin motion. This alternative method has produced unique illustrations of the spinning research aeroplane and data has been obtained that could possibly be very challenging to obtain using traditional methods. To investigate the aerodynamic flow of a spinning aeroplane, flights have been flown using wool tufts on wing, aft fuselage and empennage for flow visualization. To complement the tuft observations, the differential pressure between the upper and lower horizontal tail and wing surfaces have been measured at selected points. Tufts indicate that a large-scale Upper Surface Vortex forms on the outside wing. This USV has also been visualized using a smoke source. The flow structures on top of both wings, and on top of the horizontal tail surfaces, have also been studied on another aeroplane model. The development of these rotational flow effects has been related to the spin motion. It is hypothesized that the flow structure of the turbulent boundary layer on the outside upper wing surface is due to additional accelerations induced by the rotational motion of the aeroplane. The dynamic effects have been discussed and their importance for the development of the spin considered. In addition, it is suggested that another dynamic effect might exist due to the additional acceleration of the turbulent boundary layer due to the rotational motion of the aeroplane. It is recommended that future spin recovery prediction methods account for dynamic effects, in addition to aerodynamic control effectiveness and aeroplane inertia, since the spin entry phase is important for the subsequent development of the spin. Finally, suggestions for future research are given.

Demonstration of spanwise-periodic discrete roughness element laminar flow control (DRE LFC) technology at operationally relevant flight regimes requires extremely stable flow conditions in flight. A balance must be struck between the capabilities of the host aircraft and the scientific apparatus. A safe, effective, and efficient flight experiment is described to meet the test objectives, a flight test technique is designed to gather research-quality data, flight characteristics are analyzed for data compatibility, and an experiment is designed for data collection and analysis. The objective is to demonstrate DRE effects in a flight environment relevant to transport-category aircraft: [0.67 – 0.75] Mach number and [17.0M – 27.5M] Reynolds number. Within this envelope, flight conditions are determined which meet evaluation criteria for minimum lift coefficient and crossflow transition location. The angle of attack data band is determined, and the natural laminar flow characteristics are evaluated. Finally, DRE LFC technology is demonstrated in the angle of attack data band at the specified flight conditions. Within the angle of attack data band, a test angle of attack must be maintained with a tolerance of ± 0.1° for 15 seconds. A flight test technique is developed that precisely controls angle of attack. Lateral-directional stability characteristics of the host aircraft are exploited to manipulate the position of flight controls near the wing glove. Directional control inputs are applied in conjunction with lateral control inputs to achieve the desired flow conditions. The data are statistically analyzed in a split-plot factorial that produces a system response model in six variables: angle of attack, Mach number, Reynolds number, DRE height, DRE spacing, and the surface roughness of the leading edge. Predictions on aircraft performance are modeled to enable planning tools for efficient flight research while still producing statistically rigorous flight data. The Gulfstream IIB aircraft is determined to be suitable for a laminar flow control wing glove experiment using a low-bank-angle-turn flight test technique to enable precise, repeatable data collection at stabilized flight conditions. Analytical angle of attack models and an experimental design were generated to ensure efficient and effective flight research.

A homotopy approach for solving constrained parameter optimization problems is examined. The first order necessary conditions, with the complementarity conditions represented using a technique due to Mangasarian, are solved. The equations are augmented to avoid singularities which occur when the active constraint set changes. The Chow-Yorke algorithm is used to track the homotopy path leading to the solution to the desired problem at the terminal point. Since the Chow-Yorke algorithm requires a fairly accurate computation of the Jacobian matrix, analytical representation of the system of equations is desired. Consequently, equations obtained using the true anomaly regularization of the governing equations were employed for the above purpose. A homotopy map suited for the space-flight rendezvous problem including a minimum radius constraint is developed, which can naturally deform any initial problem into some other valid desired problem. Several coplanar and non-coplanar solutions for circular and elliptic cases have been presented for the restricted time problem with a minimum radius constraint. / Ph. D.

The problem of developing a generalized impulse as a function of a set of parameters is investigated. The proposed generalized impulse alters an existing orbit by producing, over some period of time, a change in velocity, ΔV, as well as a change in position, Δr. The generalized impulse is described by parameters associated with an instantaneous change in velocity as well as parameters associated with an atmospheric skip trajectory. Closed form solutions are obtained through several changes of independent variable, the use of modified Chapman variables and the consequent analytical integration of the uncoupled equations. The closed form solutions contain between two and six parameters depending on the complexity of the desired skip trajectory. Fuel optimal transfer orbits are obtained using the generalized impulse along with Keplerian arcs and instantaneous changes in velocity. Families of coplanar and noncoplanar transfers for circular orbit to circular orbit are numerically generated. The generated transfer trajectories involve the rendezvous of two vehicles. The orbits are not globally optimal but rather optimal for the specified number and type of velocity impulses specified. The optimal solution to the nonlinear problem is determined via sequential quadratic programming which satisfies the Kuhn-Tucker optimality conditions for constrained minimization. It is found that for transfer between coplanar and noncoplanar orbits, solutions using the generalized impulse compare favorably with solutions obtained by optimal control theory. Numerical solution to complex problems involving transfer from general orbit to general orbit were not obtained. / Master of Science

In this work, we describe all the possible radiative processes occurring in a low temperature hydrogen plasma. Some of the fundamental concepts involving ionized gases and collision phenomena are presented, and a rigorous approach is used to show that classical mechanics is quite appropriate to our study. As an application to a laser engine, we investigate the effects of the maximum temperature, the temperature gradient, the stretching of the plasma shape, the engine pressure, and the equivalent sphere radius, on the total emitted power, including absorbing mechanisms through the equation of radiative transfer. Graphs related to spectral radiative exitances are included, and a complete set of graphs of the total power, permitting interpolations with respect to the above relevant parameters, are also provided. / Master of Science

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