Micro-satellites often require the adaptation of existing propulsion systems. Electric propulsion thrusters are perhaps the best candidates to meet these needs and ion engines are among the most scalable. Miniaturizing the ion engine will require novel concepts for the ionizer with perhaps novel propellants. MEMS, nanotechnology and other technological advances are expected to impact on new designs. Our work shows that the ionization of Argon, which is an alternate fuel to Xenon, can be achieved at low voltages by utilizing Micro-Structured Electrode (MSE) Arrays. Copper-clad sheets separated by a dielectric material (fiberglass laminate epoxy resin system combined with a glass fabric substrate) of varying thickness (0.1 mm to 0.4 mm) form the discharge electrodes in the MSE arrays The wafers are drilled with an array of holes and this geometry serves to concentrate the electric field between electrodes enhancing electron emission at the cathode. Minimum breakdown voltages between 240 and 280 Volts at pressures of around 100 mTorr (0.133N/m2) were consistently obtained with arrays of hole diameter ranging from 300 to 500um. These results are consistent with conventional Paschen-curves with two empirical constants that arise from our unconventional geometrical arrangements and from the different material properties.

Impact point dispersion of a direct fire rocket can be drastically reduced with a ring of appropriately sized lateral pulse jets coupled to a trajectory tracking flight control system. The system is shown to work well against uncertainty in the form of initial off-axis angular velocity perturbations as well as atmospheric winds. For an example case examined, dispersion was reduced by a factor of one hundred. Dispersion reduction and mean miss distance are strong functions of the number of individual pulse jets, the pulse jet impulse, and the trajectory tracking window size. Proper selection of these parameters for a particular rocket and launcher combination is required to achieve optimum dispersion reduction to the pulse jet control mechanism. For the lateral pulse jet control mechanism that falls into the category of an impulse control mechanism, the trajectory tracking flight control law provides better reduction in dispersion and mean miss distance than the proportional navigation guidance law especially when small number of individual pulse jets is used. Estimation of body frame components of angular velocity and angular acceleration of a rigid body projectile undergoing general three-dimensional motion using linear acceleration measurements is considered. The results are comparable to those obtained from a conventional Inertial Measurement Unit (IMU) that composes of accelerometers and gyroscopes. From the study of the effect of sensor errors to the measurement and the control performance, the sensitivity of the angular rate estimation to the sensor noise is a strong function of the constellation of these three accelerometers. When more than three point measurements are used, the most effective method to fuse data is with one cluster that contains all sensors. In the conventional IMU, the dispersion and miss distance are less sensitive to the errors from accelerometers than to the gyroscopes. The estimation of angular rates plays essential roles in the performance of the control system in the reduction of dispersion and miss distance. The use of many accelerometers does not guarantee to reduce the sensitivity to errors. The selection of constellation among accelerometers in the data fusion process must be carefully taken into account. / Graduation date: 2002

Thesis (M.S. in M.E.)--School of Mechanical Engineering, Georgia Institute of Technology, 2004. Directed by S.M. Jeter. / Bibliography: leaf 107.

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