The equations of motion are derived for the de-spinning of a rigid body payload by the use of weights attached to the ends of unwinding cables of finite mass that are released when colinear with a radius of the payload. / Master of Science

Linear, small deflection plate theory is used to study the stress at the contact axis and the deflection of an infinite plate caused by the impact of an axisymmetric cometary meteoroid. The analysis assumes that momentum exchange is the primary mechanism, that the time of exchange is instantaneous, and that the momentum of the meteoroid is negligible after impact. The stress at the origin is reduced to a single definite integral and the deflection to the Hankel inversion integral, both requiring definition of the particular projectile before further evaluation. A particular cometary meteoroid is mathematically represented in the analysis by its projected momentum per unit area onto the plate. The three specific shapes studies are the usual projectile shapes used in hypervelocity laboratories - cylinder, cone, and sphere - even though the analysis is not intended for the high-strength, high-density laboratory projectiles. Projectile comparisons based on equal mass, diameter, and total momentum indicate that frangible, low-strength cone projectiles cause significantly higher stresses and larger displacements of the plate at short times after impact than similar sphere and cylinder projectiles. / Master of Science

The present study was undertaken to determine the effects of the aerodynamics on a close earth orbit and reentry trajectory. The aerodynamic influence is compared to the effects of the earth’s oblateness, the sun, and the moon. In order to obtain maximum accuracy and computational speed Encke’s perturbative procedures were used during orbital periods and Cowell’s integration procedures during thrust and reentry periods. / M.S.

Two principal issues were.investigated in this experiment: (1) to determine if the performance of an operator controlling a simulated space vehicle was affected by variable transmission delays; and (2) to determine if an approximate predictor cue enhanced the operator's ability to control the vehicle. The study employed two independent variables, delay variability and prediction. There were four levels, or ranges, of delay variability; 2.50 ± 0.00, 2.50 ± 0.25, 2.50 ± 0.50, and 2.50 ± 1.00 s, and two levels of prediction, with and without prediction. The amount of fuel used to complete the task, the time to complete the task, error score (weighted deviations from the desired flight path), and a Cooper-Harper subjective rating were the dependent measures used to gauge the performance of the operator. Each of the eight treatment combinations contained three trials for the 12 operators to perform. The results of this experiment indicate that the greater the delay variability, the greater is the amount of fuel used for each task and the greater is the perceived difficulty. Prediction did not significantly enhance the operator's ability to control the vehicle. This result is probably due to one of two reasons: (1) the task itself was too easy; thus, the predictor did not assist the operators in completing the task, or (2) since the predictor was not completely accurate, the operators may have lacked confidence in its ability to improve their performance. Consequently, this result suggests that a predictor cue may not be useful for this type of situation. Recommendations are suggested for further research efforts associated with predictors used in conjunction with variable delay conditions. / M.S.

The objective of this study was to characterize the effects of the space environment on the engineering properties and chemistry of a chemically modified T300/934 graphite-epoxy composite system. The material was subjected to 1.0 x 10¹⁰ rads of 1.0 MeV electron irradiation under vacuum to simulate 30 years in geosynchronous earth orbit. Monotonic tension tests were performed at room temperature (75° F /24° C) and elevated temperature (250° F/121° C) on 4-ply unidirectional laminates. From these tests, in-plane engineering and strength properties (E₁, E₂, ν₁₂, G₁₂, X_T, Y_T) were determined. Cyclic tests were also performed to characterize energy dissipation changes due to irradiation and elevated temperature. Large diameter graphite fibers were tested to determine the effects of radiation on the stiffness and strength of graphite fibers. No significant changes were observed. Dynamic-mechanical analysis demonstrated that the glass transition temperature was lowered by 50° F (28° C) after irradiation. Thermomechanical analysis showed the occurrence of volatile products generated upon heating of the irradiated material. The chemical modification of the epoxy did not aid in producing a material which was more “radiation resistant" than the standard T300/934 graphite-epoxy system. Irradiation was found to cause crosslinking and chain scission in the polymer. The latter produced low molecular weight products which plasticize the material at elevated temperatures and cause apparent material stiffening at low stresses at room temperature. / M.S.

The power requirements for future spacecraft power systems will be on the order of a few hundred kilowatts to a few megawatts. Because of these power levels, a high-voltage, high-power distribution subsystem may be utilized to transmit power from the source to the different loads. Using current state-of-the-art power conditioning electronics, complex series and parallel configurations will be required at the interface between the source and the distribution subsystem and between the distribution subsystem and the loads. The dynamic response of such a spacecraft power system may be obtained using a general purpose program such as SPICE2. However, for large and complex spacecraft power systems, the input file will be large and complex with correspondingly large computation times. As an alternative, the spacecraft power system can be considered as an interconnection of modular components. Each component is treated as a two-port network, and a state model is written with the port voltages as the inputs. The state model of each component is solved using the state transition matrix and assuming that the port voltages are . clamped for each time step. This calculation proceeds as if all two-port networks are decoupled. After the state variables have been updated, the inputs to all components are calculated using network analysis principles. The solution procedure alternates between solving the dynamic model of all components and the network equations for the component inputs. The modular state variable approach and SPICE2 are compared using two example systems. This comparison shows the advantages of the modular state variable approach. First, for the modular state variable approach the system is considered as an interconnection of modular components. In SPICE2, the system is treated as an interconnection of circuit elements. As a result, the system description for large and complex spacecraft power systems is much _ larger and more complex than a modular state variable description. Secondly, the modular state variable approach requires less CPU time than SPICE2. For one of the example systems presented here, the modular state variable approach uses one-twentieth of the CPU time used by SPICE2. / Ph. D.

An optimal estimation strategy is developed for post-experiment estimation of discretely measured dynamic systems which accounts for system model errors in a much more rigorous manner than Kalman filter-smoother type methods. The Kalman filter-smoother type methods, which currently dominate post-experiment estimation practice, treat model errors via “process noise", which essentially shifts emphasis away from the model and onto the measurements. The usefulness of this approach is subject to the measurement frequency and accuracy. The current method treats model errors by use of an estimation strategy based on concepts from optimal control theory. Unknown model error terms are explicitly included in the formulation of the problem and estimated as a part of the solution. In this manner, the estimate is improved; the model is improved; and an estimate of the model error is obtained. Implementation of the current method is straightforward, and the resulting state trajectories do not contain jump discontinuities as do the Kalman filter-smoother type estimates. Results from a number of simple examples, plus some examples from spacecraft attitude estimation, are included. The current method is shown to obtain significantly more accurate estimates than the Kalman filter-smoother type methods in many of the examples. The difference in accuracy is accentuated when the assumed model is relatively poor and when the measurements are relatively sparse in time and/or of low accuracy. Even for some well-modeled, densely measured applications, the current method is shown to be competitive with the Kalman filter-smoother type methods. / Ph. D. / incomplete_metadata

Comprehensive analyses, including dc, small-signal and large-signal analyses, of the dynamics of various spacecraft power systems are performed. Systems' dynamics are analyzed for various operating modes, such as the shunt, battery-charge and battery-discharge modes, as well as the transition mode. Computer models using the EASY5 program are developed for the Direct Energy Transfer (DET) system, solar array switching system and partial shunt system to facilitate design, analysis and performance verification. Large-signal analyses are performed to identify stability conditions and to predict large-signal dynamic behavior for each mode of operation. The equivalent source and load characteristics of a solar array power system with a constant-power load, shunt regulator, battery charger and discharger, are identified to predict large-signal dynamic behavior. Employing the equivalent source and load, the state trajectories of shunt failure, battery discharger failure and solar array/battery lockup are predicted and verified through time-domain simulations. Small-signal analyses of the DET system are performed for the three modes of operation. The system loop gain is defined. Design guidelines for the feedback control loop of the shunt regulator, battery charger and discharger are developed to shape the system loop gain for the optimum bus dynamic performance and stability of the system. Designed subsystems are simulated both in frequency-domain and time-domain to verify the design concept. Various spacecraft power systems, such as solar array switching systems, a partial shunt system, a peak power tracking system and the COBE (Cosmic Background Explorer) power system are analyzed and simulated. Design guidelines of the power conditioning equipment for each system are provided. / Ph. D.

Numerical schemes for the solution of two-point boundary value problems arising from the application of optimal control theory to mathematical models of dynamic systems, are discussed. Optimal control problems are formulated for rotational maneuvers of multiple rigid body, asymmetric spacecraft configurations with both external torques and/or internal torques. Necessary conditions for optimality are derived through Pontryagin’s principle; solutions to the problems are obtained numerically. Comparison studies using competing numerical methods and various choices of performance indices are reported. / Ph. D.

A computer program for predicting the three-dimensional nonequilibrium viscous shock-layer flows over blunt spherecones, straight. and bent mul ticonics at angle-of-attack has been developed. The method used is the viscous shock-layer approach- for nonequilibrium, multi-component ionizing air. A seven species chemical reaction model with single ionizing species and an eleven species chemical reaction model with five ionizing species are used to represent the chemistry. The seven species model considers 7 reactions whereas the eleven species model considers 26 reactions and the results obtained using these models are compared with perfect gas and equilibrium air results. This code is capable of analyzing shock-slip or no-shock-slip boundary conditions and equilibrium or non-catalytic wall boundary conditions. In this study the diffusion model is limited to binary diffusion. A sphere-cone-cylinder-flare with moderate flare angle, a straight biconic, and a bent biconic with seven deg. bend angle and a sphere-cone at various flight conditions are analyzed using this method. The bent biconic has been analyzed up to an angle-of-attack of 20 deg. with respect to the aft-cone axis and sample results are compared with inviscid and viscous results. The surface pressure distribution computed by this code compares well with that from a parabolized Navier-Stokes method. The diffusion heat transfer is about 15% of the total heat transfer for most cases. The aerodynamic forces and moments at the base of the body and computing time required for all cases are presented. The shock layer profiles at a streamwi se location of 8. 8 nose radii for one case computed using seven and eleven species models compare very well with each other. / Ph. D.