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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Magnetic Field Response Measurement Acquisition System

Magnetic field response sensors designed as passive inductor- capacit or circuits produce magnetic field responses whose harmonic frequenci es correspond to states of physical properties for which the sensors measure. Power to the sensing element is acquired using Faraday induc tion. A radio frequency antenna produces the time varying magnetic fi eld used for powering the sensor, as well as receiving the magnetic field response of the sensor. An interrogation architecture for disce rning changes in sensor's response frequency, resistance and amplitud e is integral to the method thus enabling a variety of measurements. Multiple sensors can be interrogated using this method, thus eliminat ing the need to have a data acquisition channel dedicated to each se nsor. The method does not require the sensors to be in proximity to a ny form of acquisition hardware. A vast array of sensors can be used as interchangeable parts in an overall sensing system.

Woodward, Stanley E.↗
NASA NTRS1972

Ogo 5 observations of LHR noise, emissions, and whistlers near the plasmapause at several earth radii during a large magnetic storm.

On May 15, 1969, Ogo 5 crossed the plasmapause during a major storm that produced severe geomagnetic disturbances (Kp up to 8-), large and rapid variations in ring-current intensity (as measured by Dst), intense low-latitude aurora, and persistent SAR arcs. Near the highly structured plasmasphere boundary, the electric- and magnetic-field sensors on Ogo 5 detected lower-hybrid-resonance noise bursts, whistlers, ELF hiss, and other discrete signals or emissions. Some LHR noise bursts were associated with whistlers, and these high-altitude phenomena resembled the corresponding ionospheric ones. This report contains a description of the VLF observations. We also show that intense ULF magnetic signals were present near the plasmapause, and we attempt to relate these observations to the predictions of various theories of proton ring-current decay and SAR-arc formation.

Scarf, F. L.↗
NASA NTRS2016

Development of a Magneto-Resistive Angular Position Sensor for Space Mechanisms

Magnetic microsystems in the form of magneto-resistive (MR) sensors are firmly established in automobiles and industrial applications. They are used to measure travel, angle, electrical current, or magnetic fields. MR technology opens up new sensor possibilities in space applications and can be an enabling technology for optimal performance, high robustness and long lifetime at reasonable costs. In some science missions, the technology is already applied, however, the designs are proprietary and case specific, for instance in case of the angular sensors used for JPL/NASA's Mars rover Curiosity [1]. Since 2013 HTS GmbH and Sensitec GmbH have teamed up to develop and qualify a standardized yet flexible to use MR angular sensor for space mechanisms. Starting with a first assessment study and market survey performed under ESA contract, a very strong industry interest in novel, contactless position measurement means was found. Currently a detailed and comprehensive development program is being performed by HTS and Sensitec. The objective of this program is to advance the sensor design up to Engineering Qualification Model level and to perform qualification testing for a representative space application. The paper briefly reviews the basics of magneto-resistive effects and possible sensor applications and describes the key benefits of MR angular sensors with reference to currently operational industrial and space applications. The key applications and specification are presented and the preliminary baseline mechanical and electrical design will be discussed. An outlook on the upcoming development and test stages as well as the qualification program will be provided.

Hahn, Robert↗
NASA NTRS1966

Unconventional inertial sensors.

Inertial sensors, discussing magnetic resonance and superconductor gyroscopes, ring lasers, fluid dynamical devices, electrostatic gyroscopes, etc

CRYOGENIC GYROSCOPE↗
NASA NTRS1988

Super magnets for large tunnels

The development and use of a large Magnetic Suspension and Balance System (MSBS) in wind tunnels is examined, discussing NASA-sponsored research to develop a large MSBS, and the 2 MSBS already in use. The MSBS holds the model in an arbitrary position in the wind tunnel test section and measures the forces and moments acting on the model. Technologies for building a large MSBS have been developed, and research is being done to reduce building costs. Magnetic suspension is advantageous because it completely eliminates interference from mechanical support systems such as stings or struts and it allows for easy rotation and translation of the model. Advances allowing operation at higher temperatures, probably using liquid nitrogen instead of liquid helium may reduce the cost of MSBS operation. A large MSBS would require power controllers with capacity up to 10 MW, efficiency approaching 98 percent and the ability to reverse the sign of both voltage and current. Technologies include the electro-magnetic position sensor, model positioning sensing, digital controller, and a precalibrated resistance strain-gage balance.

Boyden, Richmond P.↗
NASA NTRS1991

Critical speeds and forced response solutions for active magnetic bearing turbomachinery, part 2

The need for better performance of turbomachinery with active magnetic bearings has necessitated a study of such systems for accurate prediction of their vibrational characteristics. A modification of existing transfer matrix methods for rotor analysis is presented to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of the rotor system is studied. The modified algorithm is validated using a simpler Jeffcott model described previously. The effect of changing from a rotating unbalance excitation to a constant excitation in a single plane is also studied. A typical eight stage centrifugal compressor rotor is analyzed using the modified transfer matrix code. The results for a two mass Jeffcott model were presented previously. The results obtained by running this model with the transfer matrix method were compared with the results of the Jeffcott analysis for the purposes of verification. Also included are plots of amplitude versus frequency for the eight stage centrifugal compressor rotor. These plots demonstrate the significant influence that sensor location has on the amplitude and critical frequencies of the rotor system.

Rawal, D.↗
NASA NTRS1991

Description and interpretation of aircraft lightning attachment electric and magnetic field measurements and video observation

In 1988, ONERA carried out a complete airborne lightning characterization program. Among other features, the program has provided a significant amount of data from analog records of electric and magnetic field sensors to give a description of all stages of the lightning process. The initiation phase has a description of all stages of the lightning process. The initiation phase has been described in the past, so the present objective is to give a description of the other stages of the discharge, based on the observation of analog electromagnetic waveforms and of fast video (200 f/s) image processed pictures. During lightning attachment, the aircraft remains electrically connected to the lightning channel where a large variety of physical processes occur. These physical processes include recoil streamers, return strokes, and even other initiation processes of secondary discharges. Typical records of analog electromagnetic field along with relative luminosity variation of the channel, which shows that there is no extinction of the continuous current throughout the discharge process. A computation of current and potential waveforms using the transmission line formalism is presented and gives satisfactory results for the representation of two of the typical waveforms observed in the recoil streamer processes.

Moreau, J. P.↗
NASA NTRS1992

Measuring Effects Of Lightning On Power And Telephone Lines

Spherical antenna senses both horizontal and vertical fields simultaneously. Measures "fast" components of electric field used in conjunction with other equipment, including antenna measuring "slow" vertical component of electric field; microphone that senses thunder; cameras making visual records, which locate lightning; magnetic-field sensor; optical sensors; and instruments measuring speed and direction of wind.

Jafferis, William↗
NASA NTRS1992

Present status of the MIT/NASA Langley 6-inch MSBS

The latest improvements are described which were made to the MIT/NASA Langley 6 Inch Magnetic Suspension and Balance System and its operational capabilities. Since its relocation from MIT in 1984, the system has suffered from reliability problems with original equipment. System performance is ultimately limited by noise and antiquated power supplies. Although a limited amount of funding and man hours has been expended, some significant improvements were made to the system. The design and implementation of a new electro-magnetic position sensor has significantly reduced system noise and drift. The system was shown fully operational for the first time since its arrival at NASA Langley. An ogive cylinder test model was suspended while running the wind tunnel at its maximum of approx. Mach 0.5. Other aerodynamic models were suspended with wind on. Also, the simulation of low speed cavity store separation using an ogive cylinder test model is described. Methods used for flow visualization for this test are also discussed. The system is ideally suited for this type of low speed testing.

Schott, Timothy↗
NASA NTRS1991

Arcsecond grating drive mechanism for operation at 4 K

A grating drive mechanism that achieves arcsecond positional control at both room temperature and 4 K is described. The mechanism accommodates eight equally spaced facets on a 360-deg drum, with each facet having arcsecond control over an angular range of +/-3 deg. The cryogenic portion consists of dry lubricated angular contact bearings, a dc brushless torque motor, and a compact magnetic position sensor capable of less than 1 arcsec rms resolution. Test results demonstrate angular repeatability of less than 2 arcsec rms at 4 K and static power dissipation to the helium bath of less than 100 microW.

Downey, C. H.↗
NASA NTRS1993

Edge-Geometry SNS Devices Made Of Y/Ba/Cu/O

Superconductor/normal-conductor/superconductor (SNS) devices in which electronically active layers consist solely of materials in Y/Ba/Cu/O system fabricated in edge geometry. Made of different materials described in "SNS Device Made With Edge-Defined Geometry" (NPO-18303). Advantages include desirable electrical characteristics and less difficulty in fabrication. Attractive for development into high-frequency oscillators, magnetic-field sensors, and submillimeter-wave mixers.

Hunt, Brian D.↗
NASA NTRS1994

An active antenna for ELF magnetic fields

The work of Nikola Tesla, especially that directed toward world-wide electrical energy distribution via excitation of the earth-ionosphere cavity resonances, has stimulated interest in the study of these resonances. Not only are they important for their potential use in the transmission of intelligence and electrical power, they are important because they are an integral part of our natural environment. This paper describes the design of a sensitive, untuned, low noise active antenna which is uniquely suited to modern earth-ionosphere cavity resonance measurements employing fast-Fourier transform techniques for near-real-time data analysis. It capitalizes on a little known field-antenna interaction mechanism. Recently, the authors made preliminary measurements of the magnetic fields in the earth-ionosphere cavity. During the course of this study, the problem of designing an optimized ELF magnetic field sensor presented itself. The sensor would have to be small, light weight (for portable use), and capable of detecting the 5-50 Hz picoTesla-level signals generated by the natural excitations of the earth-ionosphere cavity resonances. A review of the literature revealed that past researchers had employed very large search coils, both tuned and untuned. Hill and Bostick, for example, used coils of 30,000 turns wound on high permeability cores of 1.83 m length, weighing 40 kg. Tuned coils are unsuitable for modern fast-Fourier transform data analysis techniques which require a broad spectrum input. 'Untuned' coils connected to high input impedance voltage amplifiers exhibit resonant responses at the resonant frequency determined by the coil inductance and the coil distributed winding capacitance. Also, considered as antennas, they have effective areas equal only to their geometrical areas.

Sutton, John F.↗
NASA NTRS1995

Observational magnetometer calibration with the Hubble Space Telescope's new magnetometers

The two magnetometers recently replaced on the Hubble Space Telescope during the STS-61 Servicing Mission are now being used successfully for Coarse Attitude Determination during spacecraft vehicle safemode recovery operation. The magnetometer alignments relative to the spacecraft's vehicle's reference frame and the magnetic coupling of the sensors to the four magnetic torquer bars were determined. Coarse Attitude determination errors are now reduced to an average of 0.6 deg. Magnetometer Sensing System calibration and Coarse Attitude determination testing with the new calibration parameters is a geometrical problem. Telemetered earth magnetic field data was collected at twenty-six different vehicle attitudes. The spacecraft attitudes selected were distributed as widely apart as possible throughout the Geocentric Inertial Coordinate reference frame. It is also desirable to sample the Earth's magnetic field over as many different locations of the spacecraft's passage over the Earth as possible, within the limitation of the +/- 28.5 deg orbital inclination. A full range of magnetic moment outputs from the torquer bars needs to be sampled, +/- 3600 ampmeters squared, as well as data when the torquer bars have zero current. Graphic utilities were also developed to visually aid in optimizing the data collection process. Finally, a brief discussion of a method for collecting data for future calibrations is suggested.

Broude, Sidney M.↗
NASA NTRS1995

The Polar Plasma Wave Instrument

The Plasma Wave Instrument on the Polar spacecraft is designed to provide measurements of plasma waves in the Earth's polar regions over the frequency range from 0.1 Hz to 800 kHz. Three orthogonal electric dipole antennas are used to detect electric fields, two in the spin plane and one aligned along the spacecraft spin axis. A magnetic loop antenna and a triaxial magnetic search coil antenna are used to detect magnetic fields. Signals from these antennas are processed by five receiver systems: a wideband receiver, a high-frequency waveform receiver, a low-frequency waveform receiver, two multichannel analyzers; and a pair of sweep frequency receivers. Compared to previous plasma wave instruments, the Polar plasma wave instrument has several new capabilities. These include (1) an expanded frequency range to improve coverage of both low- and high-frequency wave phenomena, (2) the ability to simultaneously capture signals from six orthogonal electric and magnetic field sensors, and (3) a digital wideband receiver with up to 8-bit resolution and sample rates as high as 249k samples s(exp -1).

Gurnett, D. A.↗
NASA NTRS1999

TRMM On Orbit Attitude Control System Performance

This paper presents an overview of the Tropical Rainfall Measuring Mission (TRMM) Attitude Control System (ACS) along with detailed in-flight performance results for each operational mode. The TRMM spacecraft is an Earth-pointed, zero momentum bias satellite launched on November 27, 1997 from Tanegashima Space Center, Japan. TRMM is a joint mission between NASA and the National Space Development Agency (NASDA) of Japan designed to monitor and study tropical rainfall and the associated release of energy. Launched to provide a validation for poorly known rainfall data sets generated by global climate models, TRMM has demonstrated its utility by reducing uncertainties in global rainfall measurements by a factor of two. The ACS is comprised of Attitude Control Electronics (ACE), an Earth Sensor Assembly (ESA), Digital Sun Sensors (DSS), Inertial Reference Units (IRU), Three Axis Magnetometers (TAM), Coarse Sun Sensors (CSS), Magnetic Torquer Bars (MTB), Reaction Wheel Assemblies (RWA), Engine Valve Drivers (EVD) and thrusters. While in Mission Mode, the ESA provides roll and pitch axis attitude error measurements and the DSS provide yaw updates twice per orbit. In addition, the TAM in combination with the IRU and DSS can be used to provide pointing in a contingency attitude determination mode which does not rely on the ESA. Although the ACS performance to date has been highly successful, lessons were learned during checkout and initial on-orbit operation. This paper describes the design, on-orbit checkout, performance and lessons learned for the TRMM ACS.

Robertson, Brent↗
NASA NTRS1968

Use of a Magnetic Azimuth-Indicator System Developed for Balloon Payloads of the Planetary Entry Parachute Program

An azimuth-sensing system was used for continuous ground monitoring of the azimuth orientation of the balloon-borne Planetary Entry Parachute Program (PEPP) spacecraft. The system utilized two magnetic field sensors located in the spacecraft so as to produce a unique set of voltage outputs for any azimuth. Electronics onboard the spacecraft encoded the magnetometer outputs and fed the encoded signal to a C-band modulator which imposed the intelligence onto the radar tracking beacon pulses. A conveniently located ground radar received the modulated pulses and the magnetometer outputs were reproduced after demodulation. For fast, direct readout, an X-Y plotter was calibrated to cross plot the reproduced signal of the two magnetometers on a combination rectangular-polar graph indicating the correct true azimuth in real time. The method was used successfully on three of the PEPP balloon-borne spacecraft to determine when the spacecraft was pointed in the most advantageous direction for release from the balloon, at 130,000 ft altitude. The use of such a system of azimuth monitoring is suitable to balloon payloads which are virtually stable with respect to the horizontal but may be rotating about the vertical axis. Angular accuracies within plus or minus 10 deg. could generally be expected.

Darnell, Wayne L.↗