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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Multifrequency studies of bright radio supernova remnants. 2: W49B

We report radio observations of the supernova remnant W49B using the Very Large Array (VLA) of the NRAO at 90, 20, and 6 cm. This work continues the study of the properties of young, bright supernova remnants (SNRs) begun with 3C 391 (Moffett & Reynolds 1994). Here we present high-resolution images of total intensity, polarization, and spectral index of W49B. In large-scale morphology it is basically a box-shaped remnant expanding into an apparently inhomogeneous medium, but we also find small-scale structures, arcs and filaments, which lie interior to the outer shell in projection. The actual spatial position of the filaments is unknown, though we suspect that they are in the remnant interior rather than on the front or back face of the blast wave. In addition, their distribution in two dimensions suggests the projection of a helical structure. The shell edge, sharply rising in brightness for at least 3/4 of its circumference, still remains unresolved at our highest resolution (4 sec). This for our assumed distance of 8 kpc, the width of the region in which the emission appears is less than 0.16 pc, indicating short mean free paths for shock-accelerated electrons and high levels of MHD turbulence presumably causing the scattering. We find no polarized flux at 90 or 20 cm, with 3 sigma upper limits in polarized intensity of 36 mJy at 90 cm (45 sec resolution) and 7.2 mJy at 20 cm (5 sec resolution), or 22 micro-Jy/sq arcsec and 370 micro-jy/sq arcsec, respectively, for any emission extended on those scales. Polarized flux is present at 6 cm, but at a very low mean polarized fraction (total polarized flux divided by total flux) of 0.44% +/- 0.06%, which, as for 3C 391, is much lower than typical for bright SNRs at this frequency. The morphology in polarized intensity is poorly correlated with that in total intensity. We see excursions in the polarized fraction up to at least 10% in a few locations, but even where polarization is seen, typical levels are a few percent. Tangled or disordered magnetic fields in the emitting region of the radio shell may be responsible for depolarizing the radio synchrotron radiation, but some form of internal Faraday depolarization may also occur. We estimate the foreground Faraday rotation measure to be about -450 rad/sq m, similar to that found for 3C 391, which is also the Galactic plane and just about as distant. Spectral index images created from the total intensity images show that the spectral index across W49B is constant to within about Delta alpha approximately 0.1 in bright regions. This result weakly supports a common origin of the radio-emitting electrons, as in the blast wave, rather than in inhomogeneous turbulent regions of differing properties due to the stochastic (second-order Fermi) acceleration process. Variations at the level of Delta alpha approximately 0.1 are seen, but their significance is doubtful. New observations at 90 cm, using experimental three-dimensional imaging technology, may improve on this limit.

Moffett, David A.↗
NASA NTRS1974

Two high resolution velocity vector analyzers for cosmic dust particles

Methods are described to measure velocities and angles of incidence of charged cosmic dust particles with precisions of about 1 percent and 1 degree, respectively. Both methods employ four one-dimensional position-sensitive detectors in series. The first method utilizes a charge-dividing technique while the second utilizes a time-of-flight technique for determining the position of a particle inside the instrument. The velocity vectors are measured although mechanical interaction between the particle and the instrument is completely avoided. Applications to cosmic dust composition and collection experiments are discussed. The range of radii of measurable particles is from about 0.01 to 100 microns at velocities from 1 to 80 km/s.

Aver, S.↗
NASA NTRS1981

GRID3O: Computer program for fast generation of multilevel, three-dimensional boundary-conforming O-type computational grids

A fast algorithm was developed for accurately generating boundary-conforming, three-dimensional, consecutively refined computational grids applicable to arbitrary wing-body and axial turbomachinery geometries. The method is based on using an analytic function to generate two-dimensional grids on a number of coaxial axisymmetric surfaces positioned between the centerbody and the outer radial boundary. These grids are of the O-type and are characterized by quasi-orthogonality, geometric periodicity, and an adequate resolution throughout the flow field. Because the built-in nonorthogonal coordinate stretching and shearing cause the grid lines leaving the blade or wing trailing edge to end at downstream infinity, the numerical treatment of the three-dimensional trailing vortex sheets is simplified.

Dulikravich, D. S.↗
NASA NTRS1982

Inductive electric field at the magnetopause

The electric field data for two crossings of the magnetopause by ISEE-1 on November 20, 1977, have been analyzed with high time resolution. In both cases the electric field has a negative dawn-dusk component in the boundary layer, so it must reverse somewhere within the current layer to the positive value outside. If there is a component parallel to the moving magnetopause current it is small, and by no means obvious. In the case of the exit crossing from the boundary layer to the magnetosheath the data show that the electric field vector is turning for about two seconds at roughly the satellite spin rate; this changing direction suggests that the electric field has a curl. Such a curl could be caused by a travelling localized perturbation of the magnetopause surface current associated with impulsive plasma transport through the magnetopause.

Heikkila, W. J.↗
NASA NTRS1984

The Orion Molecular Cloud at Far-infrared Wavelengths

A new, 34 in resolution far-infrared continuum map of Orion Molecular Cloud 1 and its environs, including M43 is presented. The source is dominated by a single, bright peak at the position of the embedded infrared cluster, with the 60 micro m flux density falling off steeply in all directions away from it. A total luminosity for IRc2 of 20,000 L(solar) is estimated, although this may be a lower limit, depending upon the transfer of radiation in the vicinity of the object. Several condensations appear in this map, which, along with radio molecular observations, support the view that significant fragmentation has taken place within the cloud.

Thronson, H. A., Jr.↗
NASA NTRS1984

SARSAT 121.5/243 MHz technical evaluation

The NOAA 8 SARSAT system performance was tested at 121.5/243 MHz to measure detection probability, detection threshold, location accuracy, ambiguity resolution, and multiple access capacity. Detection probability exceeds 0.95 for a single satellite pass. Detection threshold margin varies from 2 dB (243 MHz, incoherent) to 20 dB (121.5, coherent). Position location error is 20 km 68% of the time. Ambiguity is resolved 75% of the time. The system can locate 10 separate test signals.

Hayes, E. J.↗
NASA NTRS1986

Algorithm for Calibrating Robot Arms

Robots made to less demanding specifications and yet be more accurate. Method, described in published paper, used on any serial-link robot with any combination of revolute and primatic joints. Increases accuracy of positioning manipulator at any point in workspace relative to fixed coordinate system. Accurate absolute positioning capability particularly useful for those tasks where robot is issued target location by external sensory devices, such as vision system. With new method, ultraprecise manufacturing and high-resolution measurements of robot components unnecessary. Method therefore reduces cost of robots in addition to increasing robot accuracy.

Hayati, S. A.↗
NASA NTRS1990

The systematic radial downflow in the transition region of the quiet sun from limb-to-limb observations of the C IV resonance lines

This paper presents absolute velocities of C IV 1548, 1550 nm measured as a function of position along the solar equator, which was free of both active regions and coronal holes, and uniformly representative of the quiet sun. These observations were made with moderate spatial resolution (18 arcsec) using an EUV spectrometer dedicated to measuring absolute wavelengths (velocities) by direct comparison with a platinum spectrum generated on board the sounding rocket. On the assumption that systematic horizontal motions cancel statistically so that the line-of-sight velocities approach zero at the limb, a net radial downflow of 7.5 + or - 1.0 km/sec was found. The assumption was tested using the wavelength reference and found to be valid within the absolute accuracy of the rest wavelengths of the C IV lines.

Rottman, Gary J.↗
NASA NTRS1990

Digital angular position sensor using wavelength division multiplexing

Future aircraft will use fly-by-light control systems with fiber-linked optical sensors for such measurands as temperature, pressure, and linear and angular position. A digital optical sensor is described which was developed to transmit the angular position of such slowly rotating parts as a throttle of fuel flow control valve on an aircraft. The sensor employs a reflective code plate with ten channels providing a resolution of 0.35 degrees. Two light-emitting diodes with overlapping spectra are used as light sources. A single microoptic multiplexer-demultiplexer composed of a GRIN rod lens and a miniature grating is used to disperse the spectrum and recombine the spectral components from each channel after reflection by the code plate. The results of preliminary environmental tests of this unit are discussed. The sensor has been operated for brief periods of time between -60 C and +125 without adverse effects. Preliminary vibration tests indicate that the unit will work properly at the maximum vibration levels expected in a jet-engine environment.

Fritsch, Klaus↗
NASA NTRS2005

Conceptual Design and Dynamics Testing and Modeling of a Mars Tumbleweed Rover

The NASA Langley Research Center has been developing a novel concept for a Mars planetary rover called the Mars Tumbleweed. This concept utilizes the wind to propel the rover along the Mars surface, bringing it the potential to cover vast distances not possible with current Mars rover technology. This vehicle, in its deployed configuration, must be large and lightweight to provide the ratio of drag force to rolling resistance necessary to initiate motion from rest on the Mars surface. One Tumbleweed design concept that satisfies these considerations is called the Eggbeater-Dandelion. This paper describes the basic design considerations and a proposed dynamics model of the concept for use in simulation studies. It includes a summary of rolling/bouncing dynamics tests that used videogrammetry to better understand, characterize, and validate the dynamics model assumptions, especially the effective rolling resistance in bouncing/rolling dynamic conditions. The dynamics test used cameras to capture the motion of 32 targets affixed to a test article s outer structure. Proper placement of the cameras and alignment of their respective fields of view provided adequate image resolution of multiple targets along the trajectory as the test article proceeded down the ramp. Image processing of the frames from multiple cameras was used to determine the target positions. Position data from a set of these test runs was compared with results of a three dimensional, flexible dynamics model. Model input parameters were adjusted to match the test data for runs conducted. This process presented herein provided the means to characterize the dynamics and validate the simulation of the Eggbeater-Dandelion concept. The simulation model was used to demonstrate full scale Tumbleweed motion from a stationary condition on a flat-sloped terrain using representative Mars environment parameters.

Calhoun Philip C.↗
NASA NTRS2011

Fiber Optic Strain Sensor for Planetary Gear Diagnostics

This paper presents a new sensing approach for helicopter damage detection in the planetary stage of a helicopter transmission based on a fiber optic strain sensor array. Complete helicopter transmission damage detection has proven itself a difficult task due to the complex geometry of the planetary reduction stage. The crowded and complex nature of the gearbox interior does not allow for attachment of sensors within the rotating frame. Hence, traditional vibration-based diagnostics are instead based on measurements from externally mounted sensors, typically accelerometers, fixed to the gearbox exterior. However, this type of sensor is susceptible to a number of external disturbances that can corrupt the data, leading to false positives or missed detection of potentially catastrophic faults. Fiber optic strain sensors represent an appealing alternative to the accelerometer. Their small size and multiplexibility allows for potentially greater sensing resolution and accuracy, as well as redundancy, when employed as an array of sensors. The work presented in this paper is focused on the detection of gear damage in the planetary stage of a helicopter transmission using a fiber optic strain sensor band. The sensor band includes an array of 13 strain sensors, and is mounted on the ring gear of a Bell Helicopter OH-58C transmission. Data collected from the sensor array is compared to accelerometer data, and the damage detection results are presented

Kiddy, Jason S.↗
NASA NTRS2019

Deep Mapping of Small Solar System Bodies with Galactic Cosmic Ray Secondary Particle Showers

We will investigate the use of galactic cosmic ray (GCR) secondary particles to probe the deep interiors of small solar system bodies (SSBs), including comets, asteroids, and geologic structures on the surfaces of airless bodies. Applications include solar system science, planetary defense, and resource utilization. Our Phase I study demonstrated that muons, the long-range charged component of GCR showers, can penetrate SSBs up to a km in diameter, providing information on their interior structure. Muons produced in Earth’s atmosphere have been applied to image the interior of large objects for science and engineering. In Phase I, we found that the production of muons in the solid surfaces of airless bodies is much smaller than in Earth’s atmosphere. Nevertheless, the flux of transmitted muons is sufficient to detect inclusions within an asteroid or comet in a reasonable amount of time, ranging from hours to weeks, depending on the size of the SSB and the density contrast, position and size of the inclusion. For asteroids and comets, large density variations (e.g., porous soil or ice versus solid rock) are relatively easy to detect. The intrinsic spatial resolution of muon radiography (“muography”) is on the scale of a few meters. The spatial resolution that can be achieved in practice depends on signal intensity and integration time (counting statistics), the angular resolution of the muon tracker (hodoscope) and details of data reduction and analysis methodology. Our Phase II project will assess remaining unknowns for the application of muography to determining the interior structure of SSBs, assess risks for implementation, and provide a roadmap for development of SSB muography beyond the NIAC program. To achieve our objectives, we will focus on four interrelated tasks: Task1) Signal and background characterization: Characterize the production and transmission of muons and secondary particle backgrounds made by cosmic ray showers in SSBs; and near-surface features from radiographic and tomographic data; Task2) Imaging studies: Develop methods to determine the density structure of SSB interiors and near-surface features from radiographic and tomographic data; Task3) Instrument design: Using simulations and bench-top laboratory experiments, investigate specific concepts for the design of compact hodoscopes and components; Task4) Synthesis: Combine the results of the first three tasks to determine the range of applicability of the method, identify the steps needed for maturation of the concept, and explore concepts for a pilot muography mission.

Prettyman, Thomas H.↗
NASA NTRSDate not supplied

Results of First Long Duration Space Flight of Hybrid Perovskite Thin Film

In support of NASA's Artemis program with the goal of a sustained human-lunar presence, there is a need for very large (>100kW) and high-voltage-capable solar arrays, estimated to cost over $150M. Perovskite-based thin-film photovoltaics offer substantial advantages over state-of-the-art solar arrays from the perspective of manufacturing large arrays. Perovskites have also demonstrated some of the lowest temperature coefficients and highest defect tolerance, which make them excellent candidates for aerospace applications. However, MHPs must demonstrate durability in space which presents different challenges than terrestrial operating environments. To decisively test the viability of perovskites being used in space, a perovskite thin film is positioned in low earth orbit for 10 months on the International Space Station, which was the first long-duration study of an MHP in space. Postflight high-resolution ultrafast spectroscopic characterization and comparison with control samples reveal that the flight sample exhibits superior photo-stability, no irreversible radiation damage, and a suppressed structural phase transition temperature by nearly 65 K, broadening the photovoltaic operational range. Further, significant photo-annealing of surface defects is shown following prolonged light-soaking postflight. These results emphasize that methylammonium lead iodide can be packaged adequately for space missions, affirming that space stressors can be managed as theorized.

William Delmas↗
NASA NTRS2012

Seismic Imager Space Telescope

A concept has been developed for a geostationary seismic imager (GSI), a space telescope in geostationary orbit above the Pacific coast of the Americas that would provide movies of many large earthquakes occurring in the area from Southern Chile to Southern Alaska. The GSI movies would cover a field of view as long as 300 km, at a spatial resolution of 3 to 15 m and a temporal resolution of 1 to 2 Hz, which is sufficient for accurate measurement of surface displacements and photometric changes induced by seismic waves. Computer processing of the movie images would exploit these dynamic changes to accurately measure the rapidly evolving surface waves and surface ruptures as they happen. These measurements would provide key information to advance the understanding of the mechanisms governing earthquake ruptures, and the propagation and arrest of damaging seismic waves. GSI operational strategy is to react to earthquakes detected by ground seismometers, slewing the satellite to point at the epicenters of earthquakes above a certain magnitude. Some of these earthquakes will be foreshocks of larger earthquakes; these will be observed, as the spacecraft would have been pointed in the right direction. This strategy was tested against the historical record for the Pacific coast of the Americas, from 1973 until the present. Based on the seismicity recorded during this time period, a GSI mission with a lifetime of 10 years could have been in position to observe at least 13 (22 on average) earthquakes of magnitude larger than 6, and at least one (2 on average) earthquake of magnitude larger than 7. A GSI would provide data unprecedented in its extent and temporal and spatial resolution. It would provide this data for some of the world's most seismically active regions, and do so better and at a lower cost than could be done with ground-based instrumentation. A GSI would revolutionize the understanding of earthquake dynamics, perhaps leading ultimately to effective warning capabilities, to improved management of earthquake risk, and to improved public safety policies. The position of the spacecraft, its high optical quality, large field of view, and large field of regard will make it an ideal platform for other scientific studies. The same data could be simply reused for other studies. If different data, such as multi-spectral data, is required, additional instruments could share the telescope.

Sidick, Erkin↗
NASA NTRS1975

Two high resolution velocity vector analyzers for cosmic dust particles

Two new methods are described to measure velocities and angles of incidence of charged cosmic dust particles with precisions of about 1% and 1 deg, respectively. Both methods employ four one-dimensional position-sensitive detectors in series. The first method utilizes a charge-dividing technique while the second utilizes a time-of-flight technique for determining the position of a particle inside the instrument. The velocity vectors are measured although mechanical interaction between the particle and the instrument is completely avoided. Applications to cosmic dust composition and collection experiments are discussed. The range of radii of measurable particles is from about 0.01 to 100 microns at velocities from 1 to 80 km/sec.

Auer, S.↗
NASA NTRS2015

A High Performance Computing Approach to Tree Cover Delineation in 1-m NAIP Imagery Using a Probabilistic Learning Framework

Tree cover delineation is a useful instrument in deriving Above Ground Biomass (AGB) density estimates from Very High Resolution (VHR) airborne imagery data. Numerous algorithms have been designed to address this problem, but most of them do not scale to these datasets, which are of the order of terabytes. In this paper, we present a semi-automated probabilistic framework for the segmentation and classification of 1-m National Agriculture Imagery Program (NAIP) for tree-cover delineation for the whole of Continental United States, using a High Performance Computing Architecture. Classification is performed using a multi-layer Feedforward Backpropagation Neural Network and segmentation is performed using a Statistical Region Merging algorithm. The results from the classification and segmentation algorithms are then consolidated into a structured prediction framework using a discriminative undirected probabilistic graphical model based on Conditional Random Field, which helps in capturing the higher order contextual dependencies between neighboring pixels. Once the final probability maps are generated, the framework is updated and re-trained by relabeling misclassified image patches. This leads to a significant improvement in the true positive rates and reduction in false positive rates. The tree cover maps were generated for the whole state of California, spanning a total of 11,095 NAIP tiles covering a total geographical area of 163,696 sq. miles. The framework produced true positive rates of around 88% for fragmented forests and 74% for urban tree cover areas, with false positive rates lower than 2% for both landscapes. Comparative studies with the National Land Cover Data (NLCD) algorithm and the LiDAR canopy height model (CHM) showed the effectiveness of our framework for generating accurate high-resolution tree-cover maps.

Segments↗
NASA NTRS2011

The Catalog of Positions of Optically Bright Extragalactic Radio Sources OBRS-1

It is expected that the European Space Agency mission Gaia will make it possible to determine coordinates in the optical domain of more than 500,000 quasars. In 2006, a radio astrometry project was launched with the overall goal of making comparisons between coordinate systems derived from future space-born astrometry instruments and the coordinate system constructed from analysis of global very long baseline interferometry (VLBI) more robust. Investigation of the rotation, zonal errors, and non-alignment of the radio and optical positions caused by both radio and optical structures is needed to validate both techniques. In order to support these studies, the densification of the list of compact extragalactic objects that are bright in both radio and optical ranges is desirable. A set of 105 objects from the list of 398 compact extragalactic radio sources with decl. > -10deg was observed with the Very Long Baseline Array and European VLBI Network (EVN) with the primary goal of producing images with milliarcsecond resolution. These sources are brighter than 18 mag in the V band, and they were previously detected by the EVN. In this paper, coordinates of observed sources have been derived with milliarcsecond accuracies from analysis of these VLBI observations using an absolute astrometry method. The catalog of positions for 105 target sources is presented. The accuracies of source coordinates are in the range of 0.3.7 mas, with a median of 1.1 mas.

Petrov, L.↗
NASA NTRS1974

Errors induced in the measurement and azimuth directions of morphological features imaged on oblique Lunar Orbiter photographs

Many quantitative lunar studies, e.g., the morphology and dimensions of craters, crater density and distribution, have been performed using oblique Lunar Orbiter photographs. If the inherent change in scale and azimuth direction of features imaged on these photographs are not corrected, the measurement can be in considerable error and the resulting statistical inferences may be invalid. The magnitude of this error is dependent upon: the depression angle of the camera, the flight height of the spacecraft, the focal length of the camera, and the position and orientation of the object on the ground. The errors introduced by using unrectified oblique photographs as though they were vertical photographs are examined for several Lunar Orbiter high resolution NASA LRC Enhancement photographic prints taken at various depression angles.

Siegal, B. S.↗