Electrodynamic-tether time-domain reflectometer for analyzing tether faults and degradation

We propose using time-domain-reflectometry (TDR) systems to locate and track faults along electrodynamic tether (EDT) systems. Inclusion of a TDR on long-duration EDT missions would facilitate tracking of the expected performance degradation due to faults caused by hazards such as micrometeors. The TDR technique has long been an effective tool for determining the location of loads and faults along common transmission lines (TLs) such as coaxial cables. Also sometimes known as pulse reflectometry, TDR works by sending an impulse down a TL and recording the reflected energy as a function of time. Measurement of the reflected TDR waveform provides insight into the physical structure of the TL and any loads, i.e., faults, along its length. In addition, the delay between launched and reflected signals determines the location of the load or fault. Hence, the TDR technique requires knowledge of the propagation characteristics of the TL under test. To examine the feasibility of extending the technique to EDTs we use a previously developed model for the tether transmission line. This model has temporal, and hence spatial, limitations, which may be overcome with enhancements to the tether TL model. We present some general parameters governing the development of such a tether TDR system as well as computer simulations of the TDR system’s response. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87361/2/461_1.pd

Enhancement of electrodynamic tether electron current collection using radio frequency power

Tether electron current collection in the Orbital Motion Limited regime is one of the limiting factors in power and thrust generation applications of electrodynamic tethers. Injection of radio frequency power along tethers is considered in order to enhance electron current collection. As a basic assessment tool, Particle-In-Cell modeling of the tether system is performed using a 1-d cylindrical code. Comparison of test electron trajectories shows that the time periodic field distribution created by the RF excitation results in electrons being scattered off their usual OML trajectories, which under some conditions increases their probability of being collected by the tether. Analysis of simulation results reveals that large current enhancements can occur at resonance frequencies of the input reactance (where Xin = 0Xin=0), but at the expense of high RF power. Current enhancement is best measured in terms of the relative current variation per unit of RF power dissipated for every 1-meter section of the tether. Optimum enhancements of about 9% per RF watt per meter were obtained by simulation at low frequencies (75 MHz). Similar enhancements were observed during experimental measurements on tether samples. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87358/2/473_1.pd

Current collection to long, thin probes in a dense high-speed flowing plasma

We describe chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense, high-speed plasma. The geometries tested were cylindrical, flat-ribbon, and sparse-ribbon or mesh. Several important conclusions that can be drawn from the tests are as follows: the currents collected by cylinder are close to what would be predicted via orbital-motion-limited (OML) current collection theory. The tape tether had comparable current levels to a theoretical equal area OML cylinder collector. However, I–V behavior clearly is different at nearest distances ( ∼ 15λD∼15λD tape width) as compared to furthest test distances ( ∼ 6λD∼6λD tape width). The tape tether did better than a theoretical equal mass solid cylinder. A “knee” in the I–V curves can be seen in the tape/mesh data at a potential that is just above the estimated energy of the incoming beam of ions, at least for the closest distances where Debye length is smallest. Below this knee the current increases rapidly as voltage is increased. Above the knee the current increases at a rate one might expect from OML current-collection models depending on the relative width. This likely is an example of high-speed plasma flow effect. Perpendicular tape orientation performed slightly better than parallel. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87360/2/494_1.pd

A Hall probe diagnostic for low density plasma accelerators

A Hall probe diagnostic was developed for use with plasma thrusters. The Hall generators were mounted at the end of a stainless steel tube heat exchanger. Ceramic cement and a Pyrex tube were used as radiation and particle flux shields, respectively. A thermocouple was used to monitor the temperature of the Hall generator. The low voltage output from the probe was amplified within one meter of the transducer to minimize the effect of noise pick up. A National Institute of Standards and Technology traceable Gaussmeter provided an absolute reference for calibration, and relative calibrations were performed both in a strong electric field and in situ during thruster operation to approximate the conditions in the discharge. The overall accuracy of the diagnostic was ±6 G.±6G. The probes were tested with a Hall-effect thruster, and provided sufficiently accurate data to estimate the magnitude of the closed-drift electron current. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69868/2/RSINAK-69-6-2546-1.pd

Aprendizes Robóticos: Aplicação de Realidade Aumentada para Treinamento de Robôs em Fabricação Automatizada / Robotic Learners: Applying Augmented Reality for Robot Training in Automated Manufacturing

No âmbito da Indústria 4.0, é proposto um sistema para potenciar a articulação da Realidade Aumentada com a Manufatura Robotizada na indústria da construção. O objetivo deste sistema é permitir que robôs aprendam a realizar tarefas através da interação direta com operadores humanos. Num primeiro passo, estabeleceu-se uma conexão entre um robô e seu treinador - ou controlador - , no qual o robô imita as ações do operador. Equipamento de Realidade Aumentada é usado para capturar o gestos do treinador e o ambiente circundante. Uma ferramenta digital foi implementada usando Grasshopper e plugins adicionais para controlar o processo

Investigating Miniaturized Electrodynamic Tethers for Picosatellites and Femtosatellites

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143110/1/1.A33629.pd

The Design and Development of a 30-GHz Microwave Electrothermal Thruster

We report initial results on the design and development of a 30-GHz MET suitable for use as a propulsion system on a CubeSat platform. Electromagnetic modeling was used in the design of the 30-GHz thruster to determine the optimal input antenna size and length. A 2.4-mm antenna size was chosen with a length that is flush with the bottom of the cavity. Modeling also shows how accuracy in machining of the cavity radius affects thruster performance. The modeling results indicate that radius inaccuracies on the order of ±0.1 mm result in mode distortion, shifting of the resonant frequency, lowered electric field strength, and poor power transfer to the cavity. The expected power requirement for plasma ignition is 5-10 watts. Initial testing is being performed at a pressure of 30 Torr using helium as the propellant

Laboratory experiments of current collection to long conductors with geometries relevant to bare electrodynamic tethers

We describe chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense, high-speed plasma. The geometries tested and described here were cylindrical and flat-ribbon. Several important conclusions that can be drawn from the tests are as follows: the currents collected by cylinder are close to what would be predicted via orbital-motion-limited (OML) current collection theory. The tape tether had comparable current levels to a theoretical equal area OML cylinder collector. However, I-V behavior clearly is different at nearest distances ( ∼ 16λD∼16λD tape width) as compared to furthest test distances ( ∼ 6λD∼6λD tape width). The tape tether did better than a theoretical equal mass solid cylinder. A “knee” in the I-V curves can be seen in the tape data at a potential that is near the estimated energy of the incoming beam of ions, at least for the closest distances where Debye length is smallest. Below this knee the current increases rapidly as voltage is increased. Above the knee the current increases at a rate near that expected from OML current-collection models depending on the relative width. This likely is an example of high-speed plasma flow effect. Perpendicular tape orientation performed slightly better than parallel. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87700/2/517_1.pd

Spectrum sharing via hybrid cognitive players evaluated by an M/D/1 queuing model

Abstract We consider a cognitive wireless network in which users adopt a spectrum sharing strategy based on cooperation constraints. The majority of cognitive radio schemes bifurcate the role of players as either cooperative or non-cooperative. In this work, however, we modify this strategy to one in which players are hybrid, i.e., both cooperative and non-cooperative. Using a Stackelberg game strategy, we evaluate the improvement in performance of a cognitive radio network with these hybrid cognitive players using an M/D/1 queuing model. We use a novel game strategy (which we call altruism) to “police” a wireless network by monitoring the network and finding the non-cooperative players. Upon introduction of this new player, we present and test a series of predictive algorithms that shows improvements in wireless channel utilization over traditional collision-detection algorithms. Our results demonstrate the viability of using this strategy to inform and create more efficient cognitive radio networks. Next, we study a Stackelberg competition with the primary license holder as the leader and investigate the impact of multiple leaders by modeling the wireless channel as an M/D/1 queue. We find that in the Stackelberg game, the leader can improve its utility by influencing followers’ decisions using its advertised cost function and the number of followers accepted in the network. The gain in utility monotonically increases until the network is saturated. The Stackelberg game formulation shows the existence of a unique Nash equilibrium using an appropriate cost function. The equilibrium maximizes the total utility of the network and allows spectrum sharing between primary and secondary cognitive users

DEMONSTRATION OF DISTRIBUTED SENSOR NETWORKS

The purpose of this project is to determine the critical parameters and topologies needed to set up a distributed sensor network using the ZigBee data transmission standard. The major parameters being observed are the distance within which sensor nodes can transmit data, the rate of data transfer, and consumption of power by the entire network. Humidity and temperature sensors are being used as the source of real-time data for this analysis. Data transfer rates and distances are altered in ascending order, that is, from lowest to highest, until the range of the parameters is determined. # Faculty Mento