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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 289 records · Page 16
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NASA NTRS1992

Rings of earth

Small particles moving at an orbital velocity of 7.6 kilometers per second can present a considerable hazard to human activity in space. For astronauts outside of the protective shielding of their space vehicles, such particles can be lethal. The powerful radar at NASA's Goldstone Deep Communications Complex was used to monitor such orbital debris. This radar can detect metallic objects as small as 1.8 mm in diameter at 600 km altitude. The results of the preliminary survey show a flux (at 600 km altitude) of 6.4 objects per square kilometer per day of equivalent size of 1.8 mm or larger. Forty percent of the observed particles appear to be concentrated into two orbits. An orbital ring with the same inclination as the radar (35.1 degrees) is suggested. However, an orbital band with a much higher inclination (66 degrees) is also a possibility.

Goldstein, Richard M.↗
NASA NTRS1992

Capacitive skin characterization

NASA is currently involved in research that utilizes a capacitive sensor that is used for proximity detection of objects. This sensor is sensitive to conductive and dielectric materials including metal objects and humans. The range of the sensor has been found to be about twelve inches. It is the goal of this research project to further characterize the sensor so that it can be tailored to specific requirements. The characterization of the sensor should be with respect to shield size, sensor size, object size, and object distance. The method of finite elements to calculate the capacitance of the sensor while varying different parameters was used. Each of the parameters was varied in turn, often by selecting data points from different runs. The plotted results are shown and an apparent functionality developed for each.

Mcconnell, Robert↗
NASA NTRS1992

Spacewatch discovery of near-Earth asteroids

Our overall scientific goal is to survey the solar system to completion - that is, to find the various populations and to study their statistics, interrelations, and origins. The practical benefit to SERC is that we are finding Earth-approaching asteroids that are accessible for mining. Our system can detect Earth-approachers in the 1-km size range even when they are far away, and can detect smaller objects when they are moving rapidly past Earth. Until Spacewatch, the size range of 6-300 meters in diameter for the near-Earth asteroids was unexplored. This important region represents the transition between the meteorites and the larger observed near-Earth asteroids. One of our Spacewatch discoveries, 1991 VG, may be representative of a new orbital class of object. If it is really a natural object, and not man-made, its orbital parameters are closer to those of the Earth than we have seen before; its delta V is the lowest of all objects known thus far. We may expect new discoveries as we continue our surveying, with fine-tuning of the techniques.

Gehrels, Tom↗
NASA NTRS1992

The equilibrium of atmospheric sodium

We now have four examples of planetary objects with detectable sodium (and potassium) in their atmospheres: Earth, Io, Mercury and the moon. After a summary of the observational data, this survey discusses proposed sources and sinks. It appears that Io's surface material is rich in frozen SO2, but with around 1 percent of some sodium compound. The Io plasma torus contains ions of S, O and Na, also with at least one molecular ion containing Na. In turn, impact by these ions probably sustains the torus, as well as an extended neutral corona. A primary source for the Earth, Mercury and the moon is meteoroidal bombardment; at Mercury and perhaps the moon it may be supplemented by degassing of atoms from the regolith. Photoionization is important everywhere, although hot electrons are dominant at Io.

Hunten, Donald M.↗
NASA NTRS1994

Reduction procedures for accurate analysis of MSX surveillance experiment data

Technical challenges of the Midcourse Space Experiment (MSX) science instruments require careful characterization and calibration of these sensors for analysis of surveillance experiment data. Procedures for reduction of Resident Space Object (RSO) detections will be presented which include refinement and calibration of the metric and radiometric (and photometric) data and calculation of a precise MSX ephemeris. Examples will be given which support the reduction, and these are taken from ground-test data similar in characteristics to the MSX sensors and from the IRAS satellite RSO detections. Examples to demonstrate the calculation of a precise ephemeris will be provided from satellites in similar orbits which are equipped with S-band transponders.

Gaposchkin, E. Mike↗
NASA NTRS1993

Hubble Space Telescope observations of the galactic center region at 1.02 micron

We present HST observations of the galactic center region using the Planetary Camera with the F1042M filter at an effective wavelength of 1.02 micron. We detect several infrared sources seen at this wavelength before but with angular resolution better than previous observations. Our data reveal the source GZ A which was first seen by Rosa et al. (1992) at 1 micron. However, our astrometry identifies this source as IRS 16C, not Sgr A*. We marginally detect an object at 2- to 3-sigma, coincident with the position of Sgr A* to within 0.2 arcsec. This object has unphysical continuum colors which are bluer than an infinite temperature blackbody. If the source is real and associated with Sgr A*, 1 micron line emission is a possible explanation. The possibility of this object being a foreground star or an HST artifact cannot be ruled out.

Liu, T.↗
NASA NTRS1994

Infrared spectroscopy of Seyfert 2 galaxies: A look through the obscuring Torus?

We present both high-resolution (R = 1260) and low-resolution (R = 345 and 425) J-band spectra of a sample of 15 Seyfert 2 galaxies. Our goal is to look for broad Pa beta lines, indicating broad-line regions which are hidden by dust from our view at optical wavelengths. Of the 15 objects studied here, three have broad Pa beta lines: MCG-05.23.16, Mrk 463E, and NGC 2992. Mrk 176 and NGC 5728 may also have weak broad lines. In NGC 5506, previously reported to have broad Pa beta and hydrogen alpha lines, we find that the Pa beta line profile is continuous and has the same shape as the nearby line (Fe II) lambda 1.2567, which should not have a broad component. We interpret these observations as gas from the narrow-line region (NLR) with no broad component. In NGC 5506, however, the NLR profiles become broader with increasing wavelength, indicating that highly reddened wings are becoming more readily visible at the longer wavelengths. We confirm the correlation of (O I) lambda 6300/hydrogen alpha and (Fe II) lambda 1.644/Br gamma (the latter transformed to (Fe II) lambda 1.2567/Pa beta to compare with our data) found by previous authors when comparing active galactic nuclei (AGNs), supernova remnants, starbursts, and H II regions. The correlation confirms that in all of these objects both (O I) lambda 6300 and the (Fe II) lines come from partially ionized regions in which hydrogen is mostly neutral. Comparison of the infrared optical depths with column depths determined from X-ray data show a general tendency for the objects with detected broad Pa beta to have lower X-ray columns.

Goodrich, Robert W.↗
NASA NTRS1995

Optical and infrared observations of SGR 1806-20

The soft gamma-ray repeater (SGR) 1806-20 is associated with the center-brightened nonthermal nebula G10.0-0.3, thought to be a plerion. As in other plerions, a steady X-ray source, AX 1805.7-2025, has been detected coincident with the peak of the nebular radio emission. Vasisht et al. have shown that the radio peak has a core-jet appearance and argue that the core marks the true position of the SGR. At optical wavelengths, we detect three objects in the vicinity of the radio core. Only for the star closest to the core, barely visible in the optical but bright in the infrared (K-8.4 mag), the reddening is consistent with the high extinction (A(sub V) is approximately equal to 30 mag) that has been inferred for AX 1805.7 - 2025. From the absence of CO band absorption, we infer that the spectral type of this star is earlier than late-G/early-K. The large extinction probably arises in a molecular cloud located at a distance of 6 kpc, which means that the star, just like AX 1805.7-2025, is in or behind this cloud. This implies that the star is a supergiant. Since supergiants are rare, a chance coincidence with the compact radio core is very unlikely. To our knowledge, there are only three other examples of luminous stars embedded in nonthermal radio nebulae: SS 433, Cir X-1, and G70.7+1.2. Given this and the low coincidence probability, we suggest that the bright star is physically associated with SGR 1806-20, making it the first stellar indentification of a high-energy transient.

Kulkarni, S. R.↗
NASA NTRS1997

Three-Centimeter Doppler Radar Observations of Wingtip-Generated Wake Vortices in Clear Air

This report documents a high risk, high pay-off experiment with the objective of detecting, for the first time, the presence of aircraft wake vortices in clear air using X-band Doppler radar. Field experiments were conducted in January 1995 at the Wallops Flight Facility (WFF) to demonstrate the capability of the 9.33 GHz (I=3 cm) radar, which was assembled using an existing nine-meter parabolic antenna reflector at VVTT and the receiver/transmitter from the NASA Airborne Windshear Radar-Program. A C-130-aircraft, equipped with wingtip smoke generators, created visually marked wake vortices, which were recorded by video cameras. A C-band radar also observed the wake vortices during detection attempts with the X-band radar. Rawinsonde data was used to calculate vertical soundings of wake vortex decay time, cross aircraft bearing wind speed, and water vapor mixing ratio for aircraft passes over the radar measurement range. This experiment was a pathfinder in predicting, in real time, the location and persistence of C-130 vortices, and in setting the flight path of the aircraft to optimize X-band radar measurement of the wake vortex core in real time. This experiment was conducted in support of the NASA Aircraft Vortex Spacing System (AVOSS).

Marshall, Robert E.↗
NASA NTRS1999

The Rondonia Lightning Detection Network: Network Description, Science Objectives, Data Processing/Archival Methodology, and First Results

A four station Advanced Lightning Direction Finder (ALDF) network was recently established in the state of Rondonia in western Brazil through a collaboration of U.S. and Brazilian participants from NASA, INPE, INMET, and various universities. The network utilizes ALDF IMPACT (Improved Accuracy from Combined Technology) sensors to provide cloud-to-ground lightning observations (i.e., stroke/flash locations, signal amplitude, and polarity) using both time-of-arrival and magnetic direction finding techniques. The observations are collected, processed and archived at a central site in Brasilia and at the NASA/Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Initial, non-quality assured quick-look results are made available in near real-time over the internet. The network will remain deployed for several years to provide ground truth data for the Lightning Imaging Sensor (LIS) on the Tropical Rainfall Measurement Mission (TRMM) satellite which was launched in November 1997. The measurements will also be used to investigate the relationship between the electrical, microphysical and kinematic properties of tropical convection. In addition, the long-term observations from this network will contribute in establishing a regional lightning climatological data base, supplementing other data bases in Brazil that already exist or may soon be implemented. Analytic inversion algorithms developed at NASA/MSFC are now being applied to the Rondonian ALDF lightning observations to obtain site error corrections and improved location retrievals. The processing methodology and the initial results from an analysis of the first 6 months of network operations will be presented.

Blakelee, Richard↗
NASA NTRS1999

The Rondonia Lightning Detection Network: Network Description, Science Objectives, Data Processing/Archival Methodology, and First Results

A four station Advanced Lightning Direction Finder (ALDF) network was recently established in the state of Rondonia in western Brazil through a collaboration of U.S. and Brazilian participants from NASA, INPE, INMET, and various universities. The network utilizes ALDF IMPACT (Improved Accuracy from Combined Technology) sensors to provide cloud-to-ground lightning observations (i.e., stroke/flash locations, signal amplitude, and polarity) using both time-of-arrival and magnetic direction finding techniques. The observations are collected, processed and archived at a central site in Brasilia and at the NASA/ Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Initial, non-quality assured quick-look results are made available in near real-time over the internet. The network will remain deployed for several years to provide ground truth data for the Lightning Imaging Sensor (LIS) on the Tropical Rainfall Measuring Mission (TRMM) satellite which was launched in November 1997. The measurements will also be used to investigate the relationship between the electrical, microphysical and kinematic properties of tropical convection. In addition, the long-term observations from this network will contribute in establishing a regional lightning climatological data base, supplementing other data bases in Brazil that already exist or may soon be implemented. Analytic inversion algorithms developed at NASA/Marshall Space Flight Center (MSFC) are now being applied to the Rondonian ALDF lightning observations to obtain site error corrections and improved location retrievals. The processing methodology and the initial results from an analysis of the first 6 months of network operations will be presented.

Blakeslee, Rich↗
NASA NTRS2002

Chandra Discovery of Luminous Supersoft X-Ray Sources in M81

A Chandra ACIS-S imaging observation of the nearby galaxy M81 (NGC 3031) reveals 9 luminous soft X-ray sources. The local environments, X-ray spectral properties, and X-ray light curves of the sources are presented and discussed in the context of prevailing physical models for supersoft sources. It is shown that the sample falls within expectations based on population synthesis models taken from the literature though the high observed luminosities (L approx.2e36 to approx.3e38 ergs in the 0.2--2.0-keV band) and equivalent blackbody temperatures (T approx.40 to 80 eV) place the brightest detected M81 objects at the high luminosity end of the class of supersoft sources defined by previous ROSAT and Einstein studies of nearby galaxies. This is interpreted as a natural consequence of the higher sensitivity of Chandra to hotter and more luminous systems. Most of the sources can be explained as canonical supersoft sources, secreting white dwarfs powered by steady surface nuclear burning, with X-ray spectra well-fit by hot white dwarf local thermodynamic equilibrium atmosphere models. An exceptionally bright source is scrutinized in greater detail as its estimated barometric luminosity, L approx. 1.5e39 ergs, greatly exceeds theoretical estimates for supersoft sources. This source may be beyond the stability limit and undergoing a phase of mass outflow under extreme conditions. Alternatively, a model in which the observed X-ray spectrum arises from an accretion disk around a blacklists of mass approx.1200/sqrt(cosi) solar masses (viewed at an inclination angle 1) cannot be excluded.

Swartz, Douglas A.↗
NASA NTRS2005

Coronal Dynamics and Complete Flare Energy Budget for the M Dwarf AD Leo

This grant supported the observing and data analysis for FUSE Cycle 3 project C114 to observe the flare star AD Leo for 50 ksec coordinated with HST (Hubble Space Telescope) STIS ultraviolet spectroscopy and Chandra X-ray spectroscopy. Unfortunately, it was impossible to obtain the planned FUSE observations because AD Leo is a low declination target (delta approximately 20 degrees) and was rendered unobservable by restrictions in the sky coverage for FUSE observations. In April 2002 another M dwarf star, EV Lac, which is at significantly higher declination, was substituted for this project. EV Lac was observed by FUSE for a cumulative exposure of 35 ksec on 2002 July 1. The observation used the large LWRS aperture and collected data in time-tagged mode. The LWRS aperture is large enough that the target should remain within the aperture despite the normal level of pointing jitter and target drift experienced during FUSE observing. Our examination of the stellar signal showed that the target was well within the aperture throughout the observation. The data were split into night-time and day-time data so that the effects of airglow emission were recognizable. No obvious flaring, the primary science objective, was detected during the observation. The only stellar lines detected are 0 VI 1031.9, 1037.6 Angstrom, and the C III 1175 Angstrom, UV multiplet and the 977 Angstrom, resonance line. A comparison of the day-time and night-time spectra show that the 0 VI lines and the C III intersystem multiplet are unaffected by airglow features. The day-time data 977 Angstrom profile shows the presence of significant scattered solar C III photons, which should not be present in the night time spectrum. Emission fluxes for these lines were measured by direct summation of the emission lines. No continuum signal was detected in the region of these lines. The cleanest emission line profiles are for the O VI lines and we performed Gaussian fitting for these profiles. Both lines are clearly skewed with the emission peak shifted shortward of the line centroid and with emission extending further in the longward wing than for the shortward wing. A single Gaussian fits the 1032 Angstrom line profile reasonably and gives a line flux similar to that from direct integration with a line width (FWHM) of 0.16 Angstrom, (46 kilometers per second).

Brown, Alexander↗
NASA NTRS1994

DDC Systems for Searching for Near-Earth Asteroids

Large format CCD systems are superior to photographic systems in terms of quantum efficiency and that they yield digital output directly, which can be computer analyzed to detect moving objects and to obtain astrometric measurements.

telescopes↗
NASA NTRS2010

Method and apparatus for shadow aperture backscatter radiography (SABR) system and protocol

A shadow aperture backscatter radiography (SABR) system includes at least one penetrating radiation source for providing a penetrating radiation field, and at least one partially transmissive radiation detector, wherein the partially transmissive radiation detector is interposed between an object region to be interrogated and the radiation source. The partially transmissive radiation detector transmits a portion of the illumination radiation field. A shadow aperture having a plurality of radiation attenuating regions having apertures therebetween is disposed between the radiation source and the detector. The apertures provide illumination regions for the illumination radiation field to reach the object region, wherein backscattered radiation from the object is detected and generates an image by the detector in regions of the detector that are shadowed by the radiation attenuation regions.

Shedlock, Daniel↗
NASA NTRS2012

Validation of Satellite-Based Objective Overshooting Cloud-Top Detection Methods Using CloudSat Cloud Profiling Radar Observations

Two satellite infrared-based overshooting convective cloud-top (OT) detection methods have recently been described in the literature: 1) the 11-mm infrared window channel texture (IRW texture) method, which uses IRW channel brightness temperature (BT) spatial gradients and thresholds, and 2) the water vapor minus IRW BT difference (WV-IRW BTD). While both methods show good performance in published case study examples, it is important to quantitatively validate these methods relative to overshooting top events across the globe. Unfortunately, no overshooting top database currently exists that could be used in such study. This study examines National Aeronautics and Space Administration CloudSat Cloud Profiling Radar data to develop an OT detection validation database that is used to evaluate the IRW-texture and WV-IRW BTD OT detection methods. CloudSat data were manually examined over a 1.5-yr period to identify cases in which the cloud top penetrates above the tropopause height defined by a numerical weather prediction model and the surrounding cirrus anvil cloud top, producing 111 confirmed overshooting top events. When applied to Moderate Resolution Imaging Spectroradiometer (MODIS)-based Geostationary Operational Environmental Satellite-R Series (GOES-R) Advanced Baseline Imager proxy data, the IRW-texture (WV-IRW BTD) method offered a 76% (96%) probability of OT detection (POD) and 16% (81%) false-alarm ratio. Case study examples show that WV-IRW BTD.0 K identifies much of the deep convective cloud top, while the IRW-texture method focuses only on regions with a spatial scale near that of commonly observed OTs. The POD decreases by 20% when IRW-texture is applied to current geostationary imager data, highlighting the importance of imager spatial resolution for observing and detecting OT regions.

Bedka, Kristopher M.↗
NASA NTRS2016

Interpreting The Unresolved Intensity Of Cosmologically Redshifted Line Radiation

Intensity mapping experiments survey the spectrum of diffuse line radiation rather than detect individual objects at high signal-to-noise ratio. Spectral maps of unresolved atomic and molecular line radiation contain three-dimensional information about the density and environments of emitting gas and efficiently probe cosmological volumes out to high redshift. Intensity mapping survey volumes also contain all other sources of radiation at the frequencies of interest. Continuum foregrounds are typically approximately 10(sup 2)-10(Sup 3) times brighter than the cosmological signal. The instrumental response to bright foregrounds will produce new spectral degrees of freedom that are not known in advance, nor necessarily spectrally smooth. The intrinsic spectra of fore-grounds may also not be well known in advance. We describe a general class of quadratic estimators to analyze data from single-dish intensity mapping experiments and determine contaminated spectral modes from the data themselves. The key attribute of foregrounds is not that they are spectrally smooth, but instead that they have fewer bright spectral degrees of freedom than the cosmological signal. Spurious correlations between the signal and foregrounds produce additional bias. Compensation for signal attenuation must estimate and correct this bias. A successful intensity mapping experiment will control instrumental systematics that spread variance into new modes, and it must observe a large enough volume that contaminant modes can be determined independently from the signal on scales of interest.

INTERPRETING↗
NASA NTRS2013

Parasitic Interference in Nulling Interferometry

Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental perturbations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental effect impairs the performance of a Bracewell interferometer. A simple formalism is developed to derive the corresponding modified intensity response of the interferometer, as a function of the two parameters of interest: the crosstalk level (or contamination rate) and the phase shift between the primary and secondary - parasitic - beams. We then apply our mathematical approach to a few scientific cases, both analytically and using the GENIESIM simulation software, adapted to handle coherent crosstalk. Our results show that a coherent crosstalk level of about 1 per cent implies a 20 per cent drop of the signal-to-noise ratio at most. Careful attention should thus be paid to reduce the crosstalk level inside an interferometric instrument and ensure an instrumental stability that provides the necessary sensitivity through calibration procedures.

circumstellar matter↗