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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

The Diagnostics of the External Plasma for the Plasma Rocket

The plasma rocket is located at NASA Johnson Space Center. To produce a thrust in space. an inert gas is ionized into a plasma and heated in the linear section of a tokamak fusion device to 1 x 10(exp 4) - 1.16 x 10(exp 6)K(p= 10(exp 10) - 10(exp 14)/cu cm ). The magnetic field used to contain the plasma has a magnitude of 2 - 10k Gauss. The plasma plume has a variable thrust and specific impulse. A high temperature retarding potential analyzer (RPA) is being developed to characterize the plasma in the plume and at the edge of the magnetically contained plasma. The RPA measures the energy and density of ions or electrons entering into its solid angle of collection. An oscilloscope displays the ion flux versus the collected current. All measurements are made relative to the facility ground. A RPA is being developed in a process which involves the investigation of several prototypes. The first prototype has been tested on a thermal plasma. The knowledge gained from its development and testing were applied to the development of a RPA for collimated plasma. The prototypes consist of four equally spaced grids and an ion collector. The outermost grid is a ground. The second grid acts as a bias to repel electrons. The third is a variable v voltage ion suppressor. Grid four (inner grid) acts to repel secondary electrons, being biased equal to the first. Knowledge gained during these two stages are being applied to the development of a high temperature RPA Testing of this device involves the determination of its output parameters. sensitivity, and responses to a wide range of energies and densities. Each grid will be tested individually by changing only its voltage and observing the output from the RPA. To verify that the RPA is providing proper output. it is compared to the output from a Langmuir or Faraday probe.

Karr, Gerald R.↗
NASA NTRS2017

Inner Front Pole Cover Erosion in the 12.5 kW HERMeS Hall Thruster Over a Range of Operating Conditions

Erosion characteristics on the cover of the inner front pole in a 12.5 kW Hall thruster were measured over a wide range of operating conditions in tests of 6 to 14 hours duration using an accelerated test method and a very sensitive radioactive tracer-based erosion diagnostic. The operating points included the nominal 300 - 600 V conditions on a constant 20.8 A throttle curve, but included additional conditions at other currents spanning the throttling envelope and measurements at varying magnetic eld strength, facility pressure, and discharge voltage oscillation amplitude. The results show that the 300 V condition produces the highest wear rates on the 20.8 A throttle curve, but that rates actually increase with decreasing current. The wear rate was insensitive to discharge voltage ripple, but increased monotonically with magnetic eld strength, particularly near the inner radius of the pole cover. The inner region was also sensitive to facility pressure, showing lower rates at a higher pressure level. Separate experiments in which the energy distributions of ions generated by the hollow cathode were measured suggest that the cathode plume may be a source of energetic ions responsible for some of the erosion trends, in addition to ions originating in the thruster plume. The Hall thruster simulation code Hall2De is able to reproduce the erosion characteristics observed at 600 V, 20.8 A, but cannot currently match the rates measured at lower voltages and currents.

Lopez Ortega, Alejandro↗
NASA NTRS1991

Reconnection voltage as a function of IMF clock angle

Magnetic reconnection between the IMF and the geomagnetic field is thought to play a major role in the transfer of solar wind momentum and energy to the magnetosphere. Both analytic modeling and analysis of geophysical data have shown that this coupling process should be a sensitive function of the clock angle of the IMF. Results are presented from a three-dimensional, MHD, global numerical simulation code for the reconnection voltage between the closed geomagnetic field and the IMF as a function of the IMF clock angle. These results are consistent with a sin(theta/2) functional behavior.

Fedder, J. A.↗
NASA NTRS1988

Tethered system/space platform integration - TSS lessons learned

Tethered spacecraft systems must be integrated with their user platforms in a way that allows both to carry out their design functions efficiently and safely. This paper describes the lessons learned about tethered system integration with a space platform from the NASA/PSN Tethered Satellite System. Items discussed include platform attitude control, induced voltage and current control, satellite tracking and tether length measurement, satellite communications and system operations sensitivities. A number of engineering issues yet to be resolved are noted. Tethered systems are complex and require careful design to ensure successful operation.

Rudolph, L. K.↗
NASA NTRS1991

Imaging analysis of LDEF craters

Two small craters in Al from the Long Duration Exposure Facility (LDEF) experiment tray A11E00F (no. 74, 119 micron diameter and no. 31, 158 micron diameter) were analyzed using Auger electron spectroscopy (AES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), low voltage scanning electron microscopy (LVSEM), and SEM energy dispersive spectroscopy (EDS). High resolution images and sensitive elemental and molecular analysis were obtained with this combined approach. The result of these analyses are presented.

Radicatidibrozolo, F.↗
NASA NTRS2008

Embedded ESD Protection Proof of Concept

The purpose of this project is to characterize and correlate Electrostatic Discharge (ESD) sensitivity levels of an Integrated Circuit (IC) package using Transmission Line Pulse (TLP) and Human Body Model (HBM) methods. This characterization will be used as a baseline ESD sensitivity level to demonstrate improvement to the ESD sensitivity of the IC package through the use of EPI-FLO(Trade Mark) Polymer Voltage Suppression (PVS) protection devices developed and manufactured by Electronic Polymers, Inc. (EPI).

Human Body Model (HBM) methods↗
NASA NTRS2012

Gas Composition Sensing Using Carbon Nanotube Arrays

This innovation is a lightweight, small sensor for inert gases that consumes a relatively small amount of power and provides measurements that are as accurate as conventional approaches. The sensing approach is based on generating an electrical discharge and measuring the specific gas breakdown voltage associated with each gas present in a sample. An array of carbon nanotubes (CNTs) in a substrate is connected to a variable-pulse voltage source. The CNT tips are spaced appropriately from the second electrode maintained at a constant voltage. A sequence of voltage pulses is applied and a pulse discharge breakdown threshold voltage is estimated for one or more gas components, from an analysis of the current-voltage characteristics. Each estimated pulse discharge breakdown threshold voltage is compared with known threshold voltages for candidate gas components to estimate whether at least one candidate gas component is present in the gas. The procedure can be repeated at higher pulse voltages to estimate a pulse discharge breakdown threshold voltage for a second component present in the gas. The CNTs in the gas sensor have a sharp (low radius of curvature) tip; they are preferably multi-wall carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs), to generate high-strength electrical fields adjacent to the tips for breakdown of the gas components with lower voltage application and generation of high current. The sensor system can provide a high-sensitivity, low-power-consumption tool that is very specific for identification of one or more gas components. The sensor can be multiplexed to measure current from multiple CNT arrays for simultaneous detection of several gas components.

Li, Jing↗
NASA NTRS2003

Characterization of Downstream Ion Energy Distributions From a High Current Hollow Cathode in a Ring Cusp Discharge Chamber

The presence of energetic ions produced by a hollow cathodes operating at high emission currents (greater than 10 Angstroms) has been documented in the literature. As part of an ongoing effort to uncover the underlying physics of the formation of these ions, ion efflux from a high current hollow cathode operating in an ion thruster discharge chamber was investigated. Using a spherical sector electrostatic energy analyzer located downstream of the discharge cathode, the ion energy distribution over a 0 to 60 eV energy range was measured. The sensitivity of the ion energy distribution function to zenith angle was also assessed at 3 different positions: 0, 15, and 25 degrees. The measurements suggest that the majority of the ion current at the measuring point falls into the analyzer with an energy approximately equal to the discharge voltage. The ion distribution, however, was found to be quite broad. The high energy tail of the distribution function tended to grow with increasing discharge current. Sensitivity of the profiles to flow rate at fixed discharge current was also investigated. A simple model is presented that provides a potential mechanism for the production of ions with energies above the discharge voltage.

Foster, John E.↗
NASA NTRS2022

Simulation-based Study of Single-Event Burnout in 4H-SiC High-Voltage Vertical Superjunction DMOSFET: Physical Failure Mechanism and Robustness vs. Performance Tradeoffs

We explore and elucidate physical failure mechanisms in a 4H-SiC, high voltage, superjunction (SJ) vertical DMOSFET from a single heavy ion strike using three-dimensional electro-thermal transient simulations. The single-event burnout (SEB) failure is thermal runaway from second breakdown, initiated by impact ionization and terminated with mesoplasma formation, at the center of the P-pillar/N+ substrate interface. We also demonstrate that the SEB performance of this SiC SJ DMOSFET is insensitive to the pillar width but sensitive to the strike location with ion strike at the P-pillar causing SEB at a lower blocking voltage than at the N-pillar. Compared to commercially available 1.2 kV blocking-rated non-SJ DMOSFETs, which have been demonstrated to survive SEB up to 525 V, the SJ DMOSFET increases SEB survival threshold voltage (VSEB) by a factor of 2.2, making it close to 1200 V, while the on-resistance is increased by only 11%. Using our recently developed figure of merit (FoM), which considers the trade-off between VSEB and on-state performance, we find that the SiC SJ DMOSFET achieves a FoM that is 14 times better, making it superior to conventional 1.2 kV SiC DMOSFETs for long-term radiation-tolerant operation in space applications.

Silicon Carbide↗
NASA NTRS1973

Characteristics of capacitor-type micrometeoroid flux detectors when impacted with simulated micrometeoroids

A series of impact tests are described and data presented which characterize the operation of the capacitor-type micrometeoroid flux detectors used on the Meteoroid Technology Satellite (MTS). Capacitor-type detectors with silicon dioxide dielectric thickness of 0.4 and 1.0 microns were tested in the micrometeoroid impact simulator at the Langley Research Center, a 4-MV Van de Graaff electrostatic accelerator. The carbonyl iron projectiles were from 0.5 to 5.0 microns in diameter with velocities from 4 to 10.0 km/sec. The detector bias voltage was varied from -20 to -60 V; some tests were at detector temperatures of 90 C to -100 C; and the angle of impact varied from 0 deg to 75 deg from the normal to the detector. These tests showed that: (1) the detector operation is reliable when the bias voltage is greater than 30 V; (2) after an impact the detector returns to its original condition with an insignificant loss of active area; and (3) the sensitivity of the detector is inversely proportional to the detector thickness. The test results suggest a theoretical model in which the signal is an arc triggered by the impacting projectile, and the detector bias voltage must be high enough to insure that an arc will form.

Kassel, P. C., Jr.↗
NASA NTRS1974

Surface-state spectra from thick-oxide MOS tunnel junctions

The conductance and capacitance of thick-oxide MOS tunnel junctions (SiO2 thickness 40 to 65 A) have been measured from 35 Hz to 210 kHz. It is demonstrated that the use of a thick-oxide MOS tunnel junction makes it possible to obtain the surface-state data throughout the whole silicon band gap with better resolution and better sensitivity than the conventional MOS capacitance techniques. A slight departure from equilibrium may occur in the voltage range where large tunnel current flows. Corrections to the energy scale must be made in this voltage range. A method for the evaluation of the junction quality is discussed. The simplified equivalent circuits necessary for the calculation of surface-state data are constructed under various bias conditions by an approach different from that used in a previously published work. The present work supports the model that at least some of the observed surface states are a consequence of the diffusion of contact metals into the oxide.

Ma, T. P.↗
NASA NTRS1992

Capacitive Proximity Sensor Has Longer Range

Capacitive proximity sensor on robot arm detects nearby object via capacitive effect of object on frequency of oscillator. Sensing element part of oscillator circuit operating at about 20 kHz. Total capacitance between sensing element and ground constitutes tuning capacitance of oscillator. Sensor circuit includes shield driven by replica of alternating voltage applied to sensing element. Driven shield concentrates sensing electrostatic field in exterior region to enhance sensitivity to object. Sensitivity and dynamic range has corresponding 12-to-1 improvement.

Vranish, John M.↗
NASA NTRS1993

Capaciflector camera

A capacitive type proximity sensor having improved range and sensitivity between a surface and an intruding object in the vicinity of the surface having a voltage source, a number of outer electrical conductors on the surface with each forming one electrode of a number of sensor capacitors, the other electrode for each sensor capacitor being the object is described. The outer conductors are made from thin sheets of conductive material covered with insulation. An intermediate electrical conductor is located between the outer conductors and the surface and is of a size larger than the outer conductors to act as a shield for reducing the parasitic capacitance between the outer conductors and the surface. The intermediate conductor is also made from a thin sheet of conductive material covered with insulation. The outer conductors and the intermediate conductor are attached to the surface with no gap between the insulation on the conductors and no gap between the surface and the insulation on intermediate conductor, the outer conductors and the intermediate conductor conjoining with each other and with the surface, with the surface acting as a ground plane. A current-measuring voltage follower circuit is connected to the voltage source for coupling in phase and amplitude the instantaneous voltage at the voltage source to the outer electrical conductors and the intermediate electrical conductor. This circuit is responsive to the change in capacitance of the sensor capacitors and generates a number of output signals.

Vranish, John M.↗
NASA NTRS1998

Long-Wavelength 640 x 486 GaAs/AlGaAs Quantum Well Infrared Photodetector Snap-Shot Camera

A 9-micrometer cutoff 640 x 486 snap-shot quantum well infrared photodetector (QWIP) camera has been demonstrated. The performance of this QWIP camera is reported including indoor and outdoor imaging. The noise equivalent differential temperature (NE.deltaT) of 36 mK has been achieved at 300 K background with f/2 optics. This is in good agreement with expected focal plane array sensitivity due to the practical limitations on charge handling capacity of the multiplexer, read noise, bias voltage, and operating temperature.

Gunapala, Sarath D.↗
NASA NTRS1994

Uncooled tunneling infrared sensor

An uncooled infrared tunneling sensor in which the only moving part is a diaphragm which is deflected into contact with a micromachined silicon tip electrode prepared by a novel lithographic process. Similarly prepared deflection electrodes employ electrostatic force to control the deflection of a silicon nitride, flat diaphragm membrane. The diaphragm exhibits a high resonant frequency which reduces the sensor's sensitivity to vibration. A high bandwidth feedback circuit controls the tunneling current by adjusting the deflection voltage to maintain a constant deflection of the membrane which would otherwise change deflection depending upon incident infrared radiation. The resulting infrared sensor will meet or exceed the performance of all other broadband, uncooled, infrared sensors and can be miniaturized to pixel dimensions smaller than 100 .mu.m. The technology is readily implemented as a small-format linear array suitable for commercial and spacecraft applications.

Kenny, Thomas W.↗
NASA NTRS1995

Uncooled tunneling infrared sensor

An uncooled infrared tunneling sensor in which the only moving part is a diaphragm which is deflected into contact with a micromachined silicon tip electrode prepared by a novel lithographic process. Similarly prepared deflection electrodes employ electrostatic force to control the deflection of a silicon nitride, flat diaphragm membrane. The diaphragm exhibits a high resonant frequency which reduces the sensor's sensitivity to vibration. A high bandwidth feedback circuit controls the tunneling current by adjusting the deflection voltage to maintain a constant deflection of the membrane. The resulting infrared sensor can be miniaturized to pixel dimensions smaller than 100 .mu.m. An alternative embodiment is implemented using a corrugated membrane to permit large deflection without complicated clamping and high deflection voltages. The alternative embodiment also employs a pinhole aperture in a membrane to accommodate environmental temperature variation and a sealed chamber to eliminate environmental contamination of the tunneling electrodes and undesireable accoustic coupling to the sensor.

Kenny, Thomas W.↗
NASA NTRS1994

Capaciflector camera

A capacitive type proximity sensor having improved range and sensitivity between a surface and an intruding object in the vicinity of the surface having a voltage source, a number of outer electrical conductors on the surface with each forming one electrode of a number of sensor capacitors, the other electrode for each sensor capacitor being the object. The outer conductors are made from thin sheets of conductive material covered with insulation. An intermediate electrical conductor is located between the outer conductors and the surface and is of a size larger than the outer conductors to act as a shield for reducing the parasitic capacitance between the outer conductors and the surface. The intermediate conductor is also made from a thin sheet of conductive material covered with insulation. The outer conductors and the intermediate conductor are attached to the surface with no gap between the insulation on the conductors and no gap between the surface and the insulation on intermediate conductor, the outer conductors and the intermediate conductor conjoining with each other and with the surface, with the surface acting as a ground plane. A current-measuring voltage follower circuit is connected to the voltage source for coupling in phase and amplitude the instantaneous voltage at the voltage source to the outer electrical conductors and the intermediate electrical conductor. This circuit is responsive to the change in capacitance of the sensor capacitors and generates a number of output signals.

Vranish, John M.↗
NASA NTRS2008

Inertial Orientation Trackers with Drift Compensation

A class of inertial-sensor systems with drift compensation has been invented for use in measuring the orientations of human heads (and perhaps other, similarly sized objects). These systems can be designed to overcome some of the limitations of prior orientation-measuring systems that are based, variously, on magnetic, optical, mechanical-linkage, and acoustical principles. The orientation signals generated by the systems of this invention could be used for diverse purposes, including controlling head-orientation-dependent virtual reality visual displays or enabling persons whose limbs are paralyzed to control machinery by means of head motions. The inventive concept admits to variations too numerous to describe here, making it necessary to limit this description to a typical system, the selected aspects of which are illustrated in the figure. A set of sensors is mounted on a bracket on a band or a cap that gently but firmly grips the wearer s head to be tracked. Among the sensors are three drift-sensitive rotationrate sensors (e.g., integrated-circuit angular- rate-measuring gyroscopes), which put out DC voltages nominally proportional to the rates of rotation about their sensory axes. These sensors are mounted in mutually orthogonal orientations for measuring rates of rotation about the roll, pitch, and yaw axes of the wearer s head. The outputs of these rate sensors are conditioned and digitized, and the resulting data are fed to an integrator module implemented in software in a digital computer. In the integrator module, the angular-rate signals are jointly integrated by any of several established methods to obtain a set of angles that represent approximately the orientation of the head in an external, inertial coordinate system. Because some drift is always present as a component of an angular position computed by integrating the outputs of angular-rate sensors, the orientation signal is processed further in a drift-compensator software module.

Foxlin, Eric M.↗