Conventional streamlined autonomous underwater vehicles (AUVs) with a single thruster and stern planes are typically trimmed to be somewhat buoyant or heavy in water. To maintain depth, they must generate a constant hydrodynamic force which requires that they swim at a constant pitch angle. Although tail fins are the typical mechanism for generating this control moment, they become ineffective at low speeds. To enable an existing AUV to travel at lower speeds, one may easily incorporate a modular moving mass actuator. In some cases, it may also be advantageous to include a fixed wing. The equations of motion and equilibrium conditions to regulate depth are derived, and the effectiveness and low-speed efficiency of a fixed wing is evaluated. The effect of the vertical offset of the moving mass is analyzed to establish the relation between the control angle and the moving mass linear position. A description of the design of a one degree of freedom moving mass actuator module and preliminary experiments using the Virginia Tech Miniature AUV is provided. Data is presented for a series of fixed MMA position experiments as well as a dynamic position test. The results illustrate the effectiveness of a moving mass actuator at generating low-speed control moments. With the collected data, parameter identification is performed to get an estimate of the hydrodynamic parameters. / Master of Science

This thesis describes the preliminary design of a system for remote terrain exploration and environmental sampling on worlds with dense atmospheres. The motivation for the system is to provide a platform for long-term scientific studies of these celestial bodies. The proposed system consists of three main components: a buoyancy-driven glider, designed to operate at low altitude; a tethered energy harvester, extracting wind energy at high altitudes; and a base station to recharge the gliders. This system is self-sustaining, extracting energy from the planetary boundary layer. A nine degree of freedom vehicle dynamic model has been developed for the buoyancydriven glider. This model was used to illustrate anecdotal evidence of the stability and controllability of the system. A representative system was simulated to examine the energy harvesting concept. / Master of Science