Compensated control loops for a 30-cm ion thruster

The vaporizer dynamic control characteristics of a 30-cm diameter mercury ion thruster were determined by operating the thruster in an open loop steady state mode and then introducing a small sinusoidal signal on the main, cathode, or neutralizer vaporizer current and observing the response of the beam current, discharge voltage, and neutralizer keeper voltage, respectively. This was done over a range of frequencies and operating conditions. From these data, Bode plots for gain and phase were made and mathematical models were obtained. The Bode plots and mathematical models were analyzed for stability and appropriate compensation networks determined. The compensated control loops were incorporated into a power processor and operated with a thruster. The time responses of the compensated loops to changes in set points and recovery from arc conditions are presented

Travail to No Avail? Working Poverty in Australia

During the last decade or so Australia has experienced high rates of economic growth and low levels of unemployment, conditions that are expected to impact favourably on working people at the lower end of the income distribution. But similar conditions in other countries have been accompanied by unexpectedly high rates of poverty among working people and their dependents. This paper investigates the extent and nature of working poverty in Australia. Its aim is to determine whether or not working poverty is the “new face of poverty in post-industrial Australia”.Working Poverty, working poor

The 7.5 kW solar array simulator

A high power solar array simulator capable of providing the input power to simultaneously operate two 30 cm diameter ion thruster power processors was designed, fabricated, and tested. The maximum power point is set to between 150 and 7500 watts representing an open circuit voltage from 50 to 300 volts and a short circuit current from 4 to 36 amps. Illuminated solar cells are used as the control element to provide a true solar cell characteristic and permit the option of simulating changes in this characteristic due to variations in solar intensity and/or temperature of the solar array. This is accomplished by changing the illumination and/or temperature of the control cells. The response of the output to a step change in load closely approximates that of an actual solar array

Ion-beam technology and applications

Ion propulsion research and development yields a mature technology that is transferable to a wide range of nonpropulsive applications, including terrestrial and space manufacturing. A xenon ion source was used for an investigation into potential ion-beam applications. The results of cathode tests and discharge-chamber experiments are presented. A series of experiments encompassing a wide range of potential applications is discussed. Two types of processes, sputter deposition, and erosion were studied. Some of the potential applications are thin-film Teflon capacitor fabrication, lubrication applications, ion-beam cleaning and polishing, and surface texturing

Electrometer system measures nanoamps at high voltage

Floating electrometer eliminates major source of error since any leakage from electrometer case, which is at high voltage, appears only as load on high voltage supply and not as part of current being measured. Commands to and data from floating electrometer are transferred across high voltage interface by means of optical channels

A 10kW series resonant converter design, transistor characterization, and base-drive optimization

Transistors are characterized for use as switches in resonant circuit applications. A base drive circuit to provide the optimal base drive to these transistors under resonant circuit conditions is developed and then used in the design, fabrication and testing of a breadboard, spaceborne type 10 kW series resonant converter

Efficient Follow-Up of Exoplanet Transits Using Small Telescopes

11 pages, 5 figures, to be published in PASP, comments welcomeHere, we introduce an online tool for the prediction of exoplanet transit light curves. Small telescopes can readily capture exoplanet transits under good weather conditions when the combination of a bright star and a large transiting exoplanet results in a significant depth of transit. However, in reality there are many considerations that need to be made to obtain useful measurements. This paper and the accompanying website lay out a procedure based on timeseries differential photometry that has been successfully employed using 0.4 m aperture telescopes to predict the expected precision for a whole light curve. This enables robust planning to decide whether the observation of a particular exoplanet transit should be attempted, and in particular to be able to readily see when it should not to be attempted. This may result in a significant increase in the number of transit observations captured by non-specialists. The technique and website are also appropriate for planning a variety of variable star observations where a prediction of the light curve can be made.Peer reviewe

Unstable and elusive superconductors

We briefly review earlier and report original experimental results in the context of metastable or possible superconducting materials. We show that applied electric field induces conducting state in Copper Chloride (CuCl) whose characteristics resemble behavior of sliding charge-density-wave(s) (CDW). We discuss whether the sliding CDW or collective transport of similar ordered charge phase(s) may account for the problem of "high-temperature superconductivity" observed in this and other materials, including Cadmium Sulfide (CdS), metal-ammonia solutions, polymers, amorphous carbon and tungsten oxides. We also discuss a local superconductivity that occurs at the surface of graphite and amorphous carbon under deposition of foreign atoms/molecules.Comment: Invited review article published in a special edition on Superconducting Materials in honor of the 95th birthday year of Ted Geballe, edited by M. B. Maple, J. Hirsch, and F. Marsigli