The control of a remotely operated vehicle (ROV) for moving stably at very low speed presents several difficulties due to the nonlinear dynamics of the vehicle. Therefore, precise motion control relies on a good understanding of the vehicle response in correspondence with the input thrust of thrusters. This study developed a measurement system capable of measuring the thrust performance of a thruster. The thrust measurement system utilizes the lever principle to magnify output force and consequently increase the thrust measurement resolution. A voltage meter and a current meter are coupled to a power supply to continuously measure the voltage and current input to the thruster. The thrust measurement error resulting for friction and poor stiffness of the lever is significant. The thrust measuremnt is also disturbed by the electromagnetic interference from the thruster. Therefore, the stiffness of the lever is improved and a static preload is applied on the lever to reduce the error in thrust measurement. In addition, proper system grounding and optical isolation are designed in the measurement system for reducing electromagnetic interference in thrust measurement. To control the thruster by the ROV general purpose controller developed by the Institute of Undersea Technology, National Sun Yat-sen University, this study developed a DC motor controller. The motor controller includes a L298n motor driver and uses an ultra low power MSP430 microprocessor to control the speed and direction of a thruster. The performance of three commercial thrusters were tested by the thrust measurment system with different motor drivers. The measurement results of the thruster performance are in agreement with the data obtained from the thruster data sheets, which verifies the measurement accuracy and reliability of the thrust measurement system.

Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 04/19/10). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

The need for low propellant weight, high efficiency propulsion systems is a glaring need for various space missions. This thesis presents the thrust modeling of the Dense Plasma Focus plasma motion phases. It also contrasts some of the engineering tradeoffs between the existing coaxial plasma thrusters and the Dense Plasma Focus. Modeling the thrust generated by the DPF started with seeing how far the working models for the MPD would take the DPF. The effect of pulsed compared to quasi-steady state operation is computed. There is no known experimental data regarding thrust measurements for any DPF, so the thrust is analytically calculated using experimental data for the TAMU DPF. The calculated thrust is slightly higher than the thrust predicted by the models. The developed model shows that the force generated by the DPF will produce a thrust roughly three times the thrust for the MPD for similar input currents and electrode geometry. For the TAMUDPF to compete with the MPD as a thruster, it will need to be able to fire roughly 75 more times a second than the MPD.

The need for low propellant weight, high efficiency propulsion systems is a glaring need for various space missions. This thesis presents the thrust modeling of the Dense Plasma Focus plasma motion phases. It also contrasts some of the engineering tradeoffs between the existing coaxial plasma thrusters and the Dense Plasma Focus. Modeling the thrust generated by the DPF started with seeing how far the working models for the MPD would take the DPF. The effect of pulsed compared to quasi-steady state operation is computed. There is no known experimental data regarding thrust measurements for any DPF, so the thrust is analytically calculated using experimental data for the TAMU DPF. The calculated thrust is slightly higher than the thrust predicted by the models. The developed model shows that the force generated by the DPF will produce a thrust roughly three times the thrust for the MPD for similar input currents and electrode geometry. For the TAMUDPF to compete with the MPD as a thruster, it will need to be able to fire roughly 75 more times a second than the MPD.

Plasmas involving strong electron drift in crossed electric and magnetic fields are of great interest for a number of applications such as space propulsion and material processing plasma sources. Specific applications include Hall thrusters, which are high efficiency, low thrust propulsion systems used on many missions for satellite orbit corrections and for future planned interplanetary missions, as well as magnetrons of various configurations used in plasma deposition devices. Similar conditions also exist in the E-layer of the ionosphere and on the Sun. Despite many successful applications of Hall thrusters and other Hall plasma sources, some aspects of their operation are still poorly understood. A particularly important problem is the anomalous electron transport, which greatly exceeds classical collisional values. Hall plasma devices exhibit numerous turbulent fluctuations in a wide frequency range and it is believed that fluctuations resulting from plasma instabilities are likely one of the main causes of the observed anomalous transport. Plasma turbulence also affects many other important processes such as electron injection, location of the ionization region and wall erosion among others that influence the operation and efficiency of Hall thrusters. In Hall thrusters, the E0xB0 flow is made unstable due to gradients in the plasma density, temperature and magnetic field. The gradient drift instabilities are long wavelength instabilities that propagate in the azimuthal direction. A fluid theory of these unstable modes is proposed. It is shown that a full account of the compressibility of the electron flow in inhomogeneous magnetic field leads to quantitative modifications of the previously obtained instability criteria and characteristics of the unstable modes. The ExB drift also drives ion sound type instabilities in Hall thrusters. The reactive/dissipative response of the closure current to the thruster walls drives these negative energy modes. A model for this type of instabilities is proposed and analyzed for typical Hall thruster conditions. It is shown how wall parameters modify the characteristic growth rate and frequency of the unstable modes and the related anomalous transport. Nonlinear phenomena are important to understand different aspects of the Hall thruster plasma dynamics. A nonlinear fluid model for the typical Hall thruster plasma is proposed. The model takes into account electron inertia, electron collisions with neutrals, density gradients as well as various nonlinear terms that arise from the electron drift and nonlinear polarization that were included via the gyroviscous cancellation. The proposed model includes the long wavelength and the low hybrid modes destabilized by density gradients and collisions. This system of fluid equations was implemented using the computational framework BOUT++ from which a set of nonlinear simulations of plasma turbulence was performed. It is shown from these first principles nonlinear simulations that small scale low hybrid oscillations result in an anomalous electron current significantly exceeding the classical collisional current.

No description available.

This study presents the overall design of a 3U CubeSat equipped with commercial-off-the shelf hardware, Teflon-fueled micro-Pulsed Plasma Thrusters (µPPT) and an attitude determination and control system. The µPPT is sized by the impulse bit and pulse frequency required for continuous compensation of expected maximum disturbance torques at altitudes between 400 and 1000 km, and to perform stabilization of up to 20 deg/s and slew maneuvers of up to 180 degrees. The study involves realistic power constraints anticipated on the 3U CubeSat. Attitude estimation is implemented using the q-method for static attitude determination of the quaternion using pairs of the spacecraft-sun and magnetic field vectors. The quaternion estimate and the gyroscope measurements are used with an extended Kalman filter to obtain the attitude estimates. Proportional and derivative control algorithms use the static attitude estimation in order to calculate the angular momentum required to compensate for the disturbance torques and to achieve specified stabilization and slewing maneuvers or combinations. Two control methods are developed: paired firing method, and separate control algorithm and thruster allocation methods which determines the optimal utilization of the available thrusters and introduces redundancy. Simulations results are presented for a 3U CubeSat under stabilization, pointing, and pointing and spinning scenarios.

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 52-53).

Thesis (M.S. in in Aeronautical Engineering)--Air Force Institute of Technology, March 2008. / "Presented to the Faculty, Department of Aeronautics and Astronautics Graduate School of Engineering and Management, Air Force Institute of Technology Air University, Air Education and Training Command in partial fulfillment of the requirements for the Degree of Master of Science in Aeronautical Engineering, March 2008."--P. [ii]. Thesis advisor: Dr. William Hargus. "March 2008." "AFIT/GA/ENY/08-M01." Includes bibliographical references. Also available online in PDF from the DTIC Online Web site.

Chemical thrusters are widely used in spacecraft for attitude control and orbital manoeuvres. They produce a plume of neutral gas which produces ions via photoionisation and charge exchange. Measurements of local plasma properties will be aff ected by perturbations caused by the coupling between the newborn ions and the plasma. A model of neutral expansion has been used in conjunction with a fully three-dimensional hybrid code to study the evolution and ionisation over time of the neutral cloud produced by the ring of a mono-propellant hydrazine thruster as well as the interactions of the resulting ion cloud with the ambient solar wind. A parameter survey was performed for varying angles of injection and injection rates, particle kinetics were also investigated. Results are presented which show that the plasma in the region near to the spacecraft will be perturbed for an extended period of time with the formation of an interaction region around the spacecraft, a moderate amplitude density bow wave bounding the interaction region and evidence of an instability at the forefront of the interaction region which causes clumps of ions to be ejected from the main ion cloud quasi periodically and the ways in which these features are modifi ed by the degree of solar wind mass loading and the relative orientation of the magnetic fi eld to the angle of injection. This may a ffect Solar Probe Plus for a signifi cant duration as data taking and delicate sensory equipment may be required to cease operation until local fluctuations return to a more moderate level. The scale of the fluctuations seen are dependent upon the duration of the thruster ring and the speci fic geometry and therefore e ffects may vary in-situ.