Search

Any teacher of elementary physics can attest to the waning interest of students when all they are exposed to are boxes sliding down planes. In an effort to motivate interest, it is often useful to borrow examples from the real world. This way the students find it easy to identify the relevance of the subject matter. In addition, high-tech applications can be inspirational and serve to motivate the students to look deeper into the phenomena. One example of a technology that makes students sit up and pay attention are railguns. They are easily demonstrated using YouTube videos, especially now that the U.S. Navy has begun to release publicity videos of their latest designs and associated fact sheet and papers. This paper gives some background and simple models of the relevant physics of railguns.

Atmospheric-pressure dielectric barrier discharges for aerodynamic flow control are investigated. The properties of the plasma discharge during positive and negative half-cycles of the driving voltage are studied experimentally and numerically. The simulations are performed in nitrogen. It is shown that during the positive half-cycle the plasma operates in the streamer mode, whereas the negative half-cycle is characterized by a glow-type discharge. The computational results are compared with experimental optical measurements and found to be in good agreement.

We present an analysis of the charging interactivity between surrounding surface materials aboard a spacecraft at geosynchronous altitudes. In particular, bootstrap charging of a small surface may occur if is surrounded by a large negatively charged surface. Here, a negative potential barrier forms above the small surface, resulting in suppression of photo- and secondary electron emission from that surface. Additionally, the small surface experiences an enhancement of the collection of the photo- and secondary electrons emitted from the surrounding surface. This mechanism results in the charging of the small surface to higher levels than that of the patch in isolation, and in many cases the final potential will reach that of the potential of the larger surrounding surface. With this study we examine bootstrap charging behavior with model data and with data collected on orbit. We have modeled the DSCS-III B7 geosynchronous satellite with realistic geometry and spacecraft materials. Additionally, a previous study has shown that bootstrap charging has been observed on the DSCS-III B7 geosynchronous spacecraft. Both Astroquartz and Kapton cloth patches charged up to the frame potential of the satellite during periods of severe frame charging. The results of modeling bootstrap charging of a small Kapton patch floating relative to the DSCS-III frame fixed at a potential of -1,000 V show that the patch will indeed charge up negatively to match the frame potential, with the temporal increase in negative potential following an exponential time characteristic. Index Terms--Bootstrap charging, Defense Satellite Communication System (DSCS-III), differential charging, GEO satellite charging, spacecraft surface charging.

Recent studies have investigated the use of plasma actuators for the active control of the boundary layer on turbine blades. Although the overall effects have been quantified through experiments, the exact nature of the plasma and its momentum-transfer mechanisms have not been well characterized. In this study, particle-in-cell and Monte Carlo methods are used to computationally explore the plasma discharge and its interaction with the flow. The plasma composition, its methods of momentum addition, and the physics of its generation are quantified. Comparisons with experiments are made in order to support the findings. Simulations indicate that the plasma is generated through an electron avalanche in a dielectric harrier discharge. The plasma is created as the electrons stream to the dielectric on the first half of the electrode bias cycle and stream back on the second half. Momentum is imparted to the flow on both half-cycles, but the ionization is not equal during both half-cycles. This results in the plasma actuator producing a net force in one direction.

An analysis of differential charging between dielectric surface materials and the frame of a DSCS-III geosynchronous spacecraft is presented. Charging levels measured by surface potential monitors (SPMs) covered with samples of Kapton and Astroquartz have been recorded for one half of a solar cycle. Both seasonal and solar cycle effects are seen in the daily peak levels of the SPM voltages, with local maxima occurring near the equinoxes and a general trend increasing as solar max is approached. Charge neutralization by an onboard Xe plasma contactor was demonstrated to be effective throughout the mission, with a mean voltage reduction of 86% for Astroquartz and 74% for Kapton. Though a statistical analysis shows a general correlation between the fluence of charging electrons with SPM voltages, the event-specific correlation contains enough variance to cast doubt on the usefulness of an electron sensor as a differential charging alarm. We have found that a Kapton-covered SPM may be better suited than an electron sensor as a differential charging alarm. Index Terms--Geosynchronous orbit, satellite charging, space environmental effects, space weather.

The procedure to construct an inexpensive magnetohydrodynamic (MHD) propulsion boat that can be demonstrated for students in the classroom is detailed. The process of optimizing the geometry can also be used to reinforce and/or teach physical principles relating to electric current transmission.