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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 109 records · Page 6
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NASA NTRS1990

Compositions of near-Earth asteroids

Observational studies of near-earth asteroids and development of techniques for determining their composition were continued. The analysis techniques were applied to the spectra of several bodies in preparation for their application of near-earth asteroids. In mid-November 1989, near-IR observations of three near-earth atseroids, 1865 Cerberus, 1989 VA, and 1989 VB, were made. These asteroids were observed in six broadband visual and near-IR filters (0.4 to 2.5 microns), and a few narrowband measurements in the IR were obtained, but the asteroids were too faint to measure beyond 2.5 microns. Simultaneous, high-resolution visual CCD spectra were measured for these objects, but the data were not yet reduced to determine their quality. Narrowband spectra of the Martian satellite Deimos in the 1 to 3 micron spectral region were obtained. Simultaneous with the observing project, laboratory studies of meteorites and meteorite analogs which are used in spectral analysis of the telescopic data are continuing to be performed. Extensive work was performed in developing applications of Hapke reflectance theory to compositional analysis. Hapke theory is an adaptation of radiative reflectance theory to particulate surfaces.

Lebofsky, Larry A.↗
NASA NTRS1992

Near-wall reconstruction of higher order moments and length scales using the POD

An analysis of the near-wall behavior of the proper orthogonal decomposition (POD) eigenfunctions derived from direct numerical simulation (DNS) of channel flow is performed. Consistent with previous studies, a low order multi-mode reconstruction of the kinetic energy and Reynolds shear stress suffices. A similar reconstruction of the isotropic dissipation rate is shown to be insufficient, however. An analysis is performed of the multi-mode composition of the dissipation rate in the near-wall region, and it is shown that a significant number of higher-order modes are required to achieve the correct asymptotic consistency in the near-wall region. In an attempt to avoid this problem, a length scale definition is proposed in terms of an integration of the correlation tensor which factors in the presence of the wall. The wall is accounted for by only integrating out to 2y(+) and not over the entire domain. Viscous and inviscid estimates for the dissipation were used in the near-wall and core regions respectively, in conjunction with this length scale representation to obtain an estimate of the dissipation throughout the domain. The resulting dissipation exhibits the proper behavior near the wall and in the inertial layer. A 1 POD mode estimate of the length scale is computed and found to agree quite well with the length scale obtained when the entire correlation tensor is used.

Glauser, Mark N.↗
NASA NTRS1992

Lunar Resources Using Moderate Spectral Resolution Visible and Near-infrared Spectroscopy: Al/si and Soil Maturity

Modern visible and near-infrared detectors are critically important for the accurate identification and relative abundance measurement of lunar minerals; however, even a very small number of well-placed visible and near-infrared bandpass channels provide a significant amount of general information about crucial lunar resources. The Galileo Solid State Imaging system (SSI) multispectral data are an important example of this. Al/Si and soil maturity will be discussed as examples of significant general lunar resource information that can be gleaned from moderate spectral resolution visible and near-infrared data with relative ease. Because quantitative-albedo data are necessary for these kinds of analyses, data such as those obtained by Galileo SSI are critical. SSI obtained synoptic digital multispectral image data for both the nearside and farside of the Moon during the first Galileo Earth-Moon encounter in December 1990. The data consist of images through seven filters with bandpasses ranging from 0.40 microns in the ultraviolet to 0.99 microns in the near-infrared. Although these data are of moderate spectral resolution, they still provide information for the following lunar resources: (1) titanium content of mature mare soils based upon the 0.40/0.56-micron (UV/VIS) ratio; (2) mafic mineral abundance based upon the 0.76/0.99-micron ratio; and (3) the maturity or exposure age of the soils based upon the 0.56-0.76-micron continuum and the 0.76/0.99-micron ratio. Within constraints, these moderate spectral resolution visible and near-infrared reflectance data can also provide elemental information such as Al/Si for mature highland soils.

Fischer, Erich M.↗
NASA NTRS1992

Near term NEP missions and systems

The topics covered are presented in viewgraph form and include the following: Nuclear Propulsion Office Nuclear Electric Propulsion (NEP) goals; near term systems definition, representative near term NEP systems; demonstration missions; primary missions; near term NEP Mars cargo mission; near term NEP Mars mission analysis; and near term NEP mars mission.

Gilland, Jim↗
NASA NTRS1992

The flux of small asteroids near the Earth

Fifteen new EA's (Earth approachers) have been discovered since September, among them the smallest asteroids on record: 1990 UN, 1991 BA, and 1991 JR, which are in the 10 to 100 m size range (Scotti et al. 1991b). For the first time, we can make estimates of the fluxes near the Earth of these small objects, thought to be the immediate parents of meteorites, from direct observation. In this paper, I show that for EA's larger than a few 100 m, the magnitude-frequency dependence we observe is consistent with the cumulative magnitude-frequency relation, m(H), established for the main belt asteroids. Assuming this relation extends to smaller sizes, however, the probability for discovering both 1990 UN and 1991 JR was 15 percent, and for discovering 1991 BA only 1 percent. Objects smaller than approx. 100 m are therefore increasingly overabundant compared to an extrapolation from larger objects, with the excess increasing with decreasing size. Near 10 m, the most probable flux near the Earth is two orders of magnitude higher. This is in agreement with the flux extrapolated from observations of bright meteors and fireballs. It is thus likely that processes other than collisional breakup of asteroidal material begin to supply the population of small objects near the Earth at sizes near 100 m. Tantalizing clues from spectral measurements and orbital associations suggest that these objects may be the debris from extinct, short-period comets.

Rabinowitz, David L.↗
NASA NTRS1992

Composition of near-Earth asteroids

The continuing goal is to determine whether any of the near-Earth asteroids or the satellites of Mars contain hydrated phyllosilicate (clay) minerals. If these minerals are present, they would provide a ready source of water for propellant generation and use in life support systems. Many of the dark main belt asteroids have been shown to contain hydrated phyllosilicate minerals. Some of the near-Earth asteroids are also dark, but telescopic detection of water on these near-Earth asteroids is complicated because of the faintness of these small asteroids and because thermal emission masks the diagnostic spectral features beyond 3 microns due to water of hydration for objects within 2 AU of the Sun. New techniques for asteroid classification based on spectral reflectance and mineralogy will be necessary to determine whether the water absorption features are present on any of the near-Earth asteroids. This past year, better ways to classify 'wet' vs. 'dry' asteroids in the main belt were looked at. This new classification may allow us to determine the presence of water of hydration in the surface minerals of near-Earth asteroids even when we can only observe them at wavelengths that are not affected by thermal emission.

Lebofsky, Larry A.↗
NASA NTRS1992

A near-wall two-equation model for turbulent heat fluxes

A near-wall two-equation model for turbulent heat fluxes is derived from the temperature variance and its dissipation-rate equations and the assumption of gradient transport. Only incompressible flows with non-buoyant heat transfer are considered. The near-wall asymptotics of each term in the exact equations are examined and used to derive near-wall correction functions that render the modeled equations consistent with these behavior. Thus modeled, the equations are used to calculate fully-developed pipe and channel flows with heat transfer. It is found that the proposed two-equation model yields asymptotically correct near-wall behavior for the normal heat flux, the temperature variance and its near-wall budget and correct limiting wall values for these properties compared to direct simulation data and measurements obtained under different wall boundary conditions.

Sommer, T. P.↗
NASA NTRS1993

Near- and mid-infrared imaging of the planetary nebulae BD +30 deg 3639 and IC 418

We present near- and mid-IR images of the planetary nebulae BD +30 deg 3639 and IC 418, with a unique combination of high spatial and spectral resolution. The mid-IR images were obtained with MIRAC, a new IR array camera. For BD +30 deg 3639, the mid-IR images at 10.0, 11.2, 12.4, 12.8, and 13.2 microns have allowed us to separate the various spectral emission components such as the broad UIR features, the 12.8-micron forbidden Ne II emission feature, and continuum emission, to determine the distribution of these components in the nebula. For IC 418, we have obtained high-resolution images in both the near- and mid-IR. The images in the near-IR at J, H, and K are important for determining the source of the IR excess; one component of the excess is located near the central star. We have also imaged the halo emission at H and K, which has been detected in earlier studies, and have determined its spatial extent. The mid-IR images at 9.8 and 11.7 microns show continuum emission coincident with the ionized zone and suggest that SiC emission originates from the region near the central star.

Hora, Joseph L.↗
NASA NTRS1991

Turbulence closure modeling near rigid boundaries

The near-wall region plays an essential role in turbulent boundary layers: it is a region of high shear; the peak rate of production and peak intensity of turbulence occurs there; and the peak rate of dissipation occurs right at the wall. Nevertheless, this region has received less attention from modelers than have more nearly homogeneous flows. One reason for this is that when the boundary layer is near equilibrium, experimental data can be used to prescribe the flow in the wall layer. Another reason is that most turbulence models are developed under assumptions of near homogeneity. This is a poor approximation in the wall region. A single-point moment closure model for the strongly non-homogeneous A turbulent flow near a rigid boundary is developed.

Durbin, Paul A.↗
NASA NTRS1994

Pickup protons and pressure-balanced structures: Voyager 2 observations in merged interaction regions near 35 AU

Five pressure-balanced structures, each with a scale of the order of a few hundredths of an astonomical unit (AU), were identified in two merged interaction regions (MIRs) near 35 AU in the Voyager 2 plasma and magnetic field data. They include a tangential discountinuity, simple and complex magnetic holes, slow correlated variations among the plasma and magnetic field parameters, and complex uncorrelated variations among the parameters. The changes in the magnetic pressure in these events are balanced by changes in the pressure of interstellar pickup protons. Thus the pickup protons probably play a major role in the dynamics of the MIRs. The solar wind proton and electron pressures are relatively unimportant in the MIRs at 35 AU and beyond. The region near 35 AU is transition region: the Sun is the source of the magnetic field, but the interstellar medium in source of pickups protons. Relative to the solar wind proton guyroadius, the thicknesses of the discontinuities and simple magnetic holes observed near 35 AU are at least an order of magnitude greater than those observed at 1 AU. However, the thicknesses of the tangential discontinuity and simple magnetic holes observed near 35 AU (in units of the pickup proton Larmor radius) are comparable to those observed at 1 AU (in units of the solar wind proton gyroradius). Thus the gyroradius of interstellar pickup protons controls the thickness of current sheets near 35 AU. We determine the interstellar pickup proton pressure in the PBSs. Using a model for the pickup proton temperature, we estimate that the average interstellar pickup proton pressure, temperature, and density in the MIRs at 35 AU are (0.53 +/- 0.14) x 10(exp -12) erg/cu cm, (5.8 +/- 0.4) x 10(exp 6) K and (7 +/- 2) x 10(exp -4)/cu cm.

Burlaga, L. F.↗
NASA NTRS1994

Near-infrared (J, H, K) imaging of Herbig Ae/Be stars

Near-infrared (J, H, K) images were obtained for 16 Herbig Ae/Be stars. The primary goal was to determine the contributions by circumstellar nebulae and nearby sources to near-infrared photometry carried out with large beams. Quasi-simultaneous photometric results were obtained with small apertures. The emission toward five Herbig Ae/Be stars is extended, including all four Group II sources in our sample (Hillebrand et al. 1992); 13 objects have nearby sources (within 10 sec separation). However, the extended emission and nearby sources are too faint to affect previous photometry significantly. The surface brightness profiles of most of the nebulae can be explained by reflection nebulae which scatter the light from the central star/disk systems with single, isotropic scattering processes. The exception is Par 21, which may require emission from very small grains. The color-color diagram, making use of our new photometry, essentially agrees with the results of Lada & Adams (1992). The Group II objects in our sample tend to have extended emission more frequently than do Group I objects, supporting the suggestion of Hillebrand et al. that Group II sources are more affected by circumstellar envelopes. However, most of the near-infrared emission comes from the central (less than or = 6 sec) regions. This upper limit is still much larger than the expected size of accretion disks. Possible envelope effects could not be ruled out for most Herbig Ae/Be stars with unresolved emission. The images do not clearly favor very small, thermally emitting grains as the origin of the near-infrared emission. The problem still exists of how to explain the observed peaks near 3 sec in the spectral energy distributions of Herbig Ae/Be stars. The possible effects of envelopes and companions are addressed.

Li, Wenbin↗
NASA NTRS1994

Near-surface ice on Mercury and the Moon: A topographic thermal model

A thermal model that can be easily adapted to craters of arbitrary shape is developed and applied to high-latitude impact craters on Mercury and the Moon, Chao Meng Fu crater at -87.5 deg L on Mercury, an unnamed bowl-shaped crater at 86.7 deg L on Mercury, and Peary crater at 88.6 deg L on the Moon. For an assumed input topography and grid of surface elements, the model computes for each element the irradiation from direct insolation and reflected and emitted radiation from other elements, taking into account shadowing by walls of the crater, partial obscuration of the solar disk near the poles and the diurnal, orbital, and seasonal cycles. Temperatures are computed over the surface grid as functions of depth and time from the surface to a specified depth and over the pertinent astronomical cycles, including the effects of direct and indirect surface irradiation, infrared radiation, heat conduction, and interior heating. Vapor fluxes and ice recession times are computed as functions of ice depth over the surface grid. Temperatures profiles, vapor fluxes, and ice recession times were computed for flat surfaces not associated with craters near the poles of Mercury and the Moon. It was found that water ice could have existed throughout geologic time within the maximum radar detection depth of recent observation of Mercury (J. K. Harmon and M. A. Slade, 1992, Science 258, 640-643) poleward of approximately 87 - 88 deg L on Mercury and poleward of approximately 73 deg L on the Moon. For Chao Meng Fu crater it was found that approximately 40% of the crater floor is permanently shadowed from direct solar insolation, while the remainder of the crater floor is periodically illuminated by a partially obscured Sun. Temperatures at the upper levels of the south wall can slightly exceed 550 K. Surface temperatures in the permanently shadowed region of the crater floor are under approximately 130 K, which could have allowed water ice to exist throughout geologic time within the radar detection depth of recent observation of Mercury. For small bowl-shaped crater on Mercury, it was found that most of the crater is permanently shadowed from direct solar radiation, except for a narrow semicircular band bordering the north rim. However, temperatures in the permanently shadowed region periodically reach a maximum near approximately 315 K due to efficient heating of the small crater by thermal emission and reflection from the small sunlit region, which periodically reaches temperatures exceeding 630 K. Water ice could not have existed throughout geologic time anywhere in this crater within the radar detection depth. For Peary crater on the Moon, the entire crater floor is permanently shadowed from direct solar insolation with maximum temperature under 120 K. The upper level of the north wall periodically reaches a maximum temperature near 310 K. The low temperatures on the crater floor would have allowed water ice to exist near the surface throughout geologic time, provided that the Moon's obliquity was always as low as it is at present.

Salvail, James R.↗
NASA NTRS1995

Biological processes and optical measurements near the sea surface: Some issues relevant to remote sensing

The advent of remote sensing, the develpmemt of new optical instrumentation, and the associated advances in hydrological optics have transformed oceanography; it is now feasible to describe ocean-scale biogeochemical dynamcis from satellite observations, verified and complemented by measurements from optical sensors on profilers, moorings, and drifters. Only near-surface observations are common to both remote sensing and in situ observation, so it is critical to understand processes in the upper euphotic zone. Unfortunately, the biological principles that must be used to interpret optical variability near the sea surface are weaker than we would like, because relatively few experiments and analyses have examined bio-optical relationships under high irradiance characteristic of the upper optical depth. Special consideration of this stratum is justified, because there is good evidence that bio-optical relationships are altered near the surface; (1) the fluorescence yield from chlorophyll declines, leading to bias in the estimation of pigment from fluorometry; (2) the modeled relationship between solar-stimulated fluorecence and photosynthesis seems to deviate significantly from that presented for the lower euphotic zone; and (3) carbon-specific and cellular attenuation cross sections of phytoplankton change substantially during exposures to bright light. Even the measurement of primary productivity is problematic near the sea surface, because vertical mixing is not simulated and artifactual inhibition of photosynthesis can result. These problems can be addressed by focusing more sampling effort, experimental simulation, and analytical consideration on the upper optical depth, and by shortening timescales for the measurement of marine photosynthesis. Special efforts to study near-surface processes are justified, because new bio-optical algorithms will require quantitaitve descriptions of the responses of phytoplankton to bright light.

Cullen, John J.↗
NASA NTRS1999

Preliminary Planning for NEAR's Low-Altitude Operations at 433 Eros

On February 14, 2000, an orbit insertion burn will place NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft (S/C) into orbit around asteroid 433 Eros. NEAR will initially orbit Eros with distances ranging from 500 to 100 km in order to characterize the shape, gravity and spin of Eros. Once the physical parameters of Eros are determined reasonably well, the plan is to establish an orbit of the NEAR S/C with increasingly lower altitudes as the one year orbital mission progresses while further characterizing the gravity and shape of Eros. Towards the end of the NEAR mission, after the shape, gravity and spin of Eros have been well characterized, the scientific interest of obtaining very close observations (< 5 km) can be realized. The navigation during this phase relies on a combination of NASA's Deep Space Network (DSN) radio metric tracking, laser ranging (LIDAR) data from the S/C to the surface of Eros, and onboard optical imaging of landmarks on Eros. This paper will provide preliminary plans for mission design and navigation during the last two months of the orbit phase, where several close passes to the surface will be incorporated to enhance the science return. The culmination of these close passes will result in the eventual landing of the S/C on the surface of Eros. Several considerations for these plans are given by Antreasian, et at. [1998]. The objective for the end of the mission will be to land the S/C autonomously using the surface relative information obtained from the onboard LIDAR instrument. The goal will be to soft land the S/C in such a way as to keep it operational. With the use of an onboard LIDAR landing algorithm as discussed by Antreasian et at. [1998], it is believed that the S/C impact velocity can be kept well under 7 m/s which is a requirement for allowing the S/C to remain operational.

Antreasian, P. G.↗
NASA NTRS2003

Utility of Satellite Magnetic Observations for Estimating Near-Surface Magnetic Anomalies

Regional to continental scale magnetic anomaly maps are becoming increasingly available from airborne, shipborne, and terrestrial surveys. Satellite data are commonly considered to fill the coverage gaps in regional compilations of these near-surface surveys. For the near-surface Antarctic magnetic anomaly map being produced by the Antarctic Digital Magnetic Anomaly Project (ADMAP), we show that near-surface magnetic anomaly estimation is greatly enhanced by the joint inversion of the near-surface data with the satellite observations relative to the conventional technique such as minimum curvature. Orsted observations are especially advantageous relative to the Magsat data that have order-of-magnitude greater measurement errors, albeit at much lower orbital altitudes. CHAMP is observing the geomagnetic field with the same measurement accuracy as the Orsted mission, but at the lower orbital altitudes covered by Magsat. Hence, additional significant improvement in predicting near-surface magnetic anomalies can result as these CHAMP data are available. Our analysis also suggests that considerable new insights on the magnetic properties of the lithosphere may be revealed by a further order-of-magnitude improvement in the accuracy of the magnetometer measurements at minimum orbital altitude.

Kim, Hyung Rae↗
NASA NTRS2003

Detecting Near-Surface Water and Hydrate Minerals on Mars from a Rover, Penetrator, or Borehole: The HYDRA Instrument

One of the major goals of near term NASA Mars exploration is to identify exact locations of near-surface water or hydrated minerals on Mars. Evidence for the existence of recent nearsurface water on Mars underscores the need for developing instrumentation that can identify water or hydrated minerals very near the surface. Further encouraging evidence of surface and near-surface water and hydrate minerals on Mars comes from neutron spectrometer measurements aboard Mars Odyssey. Preliminary results show very large regions of high hydrogen content poleward of 60 deg. latitude, as well as interesting features closer to the equator. However, spatial resolution from orbit is very poor, approx. 400 km. The next logical step is to use in-situ or near-surface investigations to map in detail some of the most interesting features. Relatively simple instrumentation based on He-3 gas proportional counters were shown to be highly successful on the Lunar Prospector mission in identifying even low levels of enhanced hydrogen abundances. Here we discuss HYDRA, a water- and hydrate-sensing instrument currently being developed under the NASA Mars Instrument Development Program (MIDP). HYDRA is based on Lunar Prospector technology, and is intended as a rover body-mounted instrument, or an instrument on an aerobot, penetrator, hard lander on the surface of Mars, or for borehole stratigraphy applications. Our proposed instrument would be ideal for such platforms as it would be small (less than 7 cm diameter by 10 cm long), low mass (less than 500 g), low power (less than 1W), and have a low data volume per measurement. We use neutron spectrometry (a) because of its proven ability to uniquely detect and quantify hydrogen abundance, and (b) because the resources required by this approach (weight, power, size, telemetry bandwidth, and measurement time) are extremely low. This compact neutron spectrometer package, comprised of two small He-3 gas proportional counters, offers superior sensitivity, extensive flight heritage, and inherent ruggedness. These tubes have survived approx. 1500 g's of acceleration in penetrator tests. In a landed application, HYDRA would help address many topics of interest to the Mars Exploration and Astrobiology communities: (a) nature and origin of stratified deposits; (b) water cycle(s) and temporal changes; (c) early water oceans, aquifers, precipitation; (d) current extent/location/state of water; (e) polar cap processes and temporal changes; (f) where extremeophiles could survive on Mars; (g) paleoclimate surface signatures and modeling; (h) strategies for future Mars exploration.

R C Elphic↗
NASA NTRS2003

SMASS Near-Earth Object Survey: An Album of Results

The Small Main-Belt Asteroid Spectroscopic Survey (SMASS) undertaken at MIT has produced and published visible spectra for more than 1300 main-belt asteroids. The infrared extension of this program (SMASSIR) has produced near-infrared spectra for about 200 main-belt asteroids. In this poster we present visible and near-infrared spectral results for more than 300 near-Earth objects (NEOs) measured during the SMASS and SMASSIR programs and through ongoing observations at Kitt Peak, Palomar, IRTF, and Magellan observatories. The scientific goals for this sample are to deduce the compositional distribution of the near-Earth object population. Knowledge of this distribution will allow the origin and relative hazard of the NEO population to be better understood and will provide the basis for gaining further insights to asteroid-meteorite and asteroid-comet relationships. While a portion of our NEO sample has been published, spectral measurements are newly presented here for more than 250 NEOs. All published SMASS spectra are available at our website http://smass.mit.edu/. These new near-Earth object spectra will also be made available at the SMASS website at the time they are submitted for publication.

Binzel, R. P.↗
NASA NTRS2002

Near-Real-Time Detection and Monitoring of Dust Events by Satellite (SeaWIFS, MODIS, and TOMS)

Over the last few years satellites have given us increasingly detailed information on the size, location, and duration of dust events around the world. These data not only provide valuable feedback to the modelling community as to the fidelity of their aerosol models but are also finding increasing use in near real-time applications. In particular, the ability to locate and track the development of aerosol dust clouds on a near real-time basis is being used by scientists and government to provide warning of air pollution episodes over major urban area. This ability has also become a crucial component of recent coordinated campaigns to study the characteristics of tropospheric aerosols such as dust and their effect on climate. One such recent campaign was ACE-Asia, which was designed to obtain the comprehensive set of ground, aircraft, and satellite data necessary to provide a detailed understanding of atmospheric aerosol particles over the Asian-Pacific region. As part of ACE-Asia, we developed a near real-time data processing and access system to provide satellite data from the polar-orbiting instruments Earth Probe TOMS (in the form of absorbing aerosol index) and SeaWiFS (in the form of aerosol optical thickness, AOT, and Angstrom exponent). The results were available via web access. The location and movement information provided by these data were used both in support of the day-to-day flight planning of ACE-Asia and as input into aerosol transport models. While near real-time SeaWiFS data processing can be performed using either the normal global data product or data obtained via direct broadcast to receiving stations close to the area of interest, near real-time MODIS processing of data to provide aerosol retrievals is currently only available using its direct broadcast capability. In this paper, we will briefly discuss the algorithms used to generate these data. The retrieved aerosol optical thickness and Angstrom exponent from SeaWiFS will be compared with those obtained from various AERONET sites over the Asian-Pacific region. The TOMS aerosol index will also be compared with AERONET aerosol optical thickness over different aerosol conditions, and comparisons between the MODIS and SeaWiFS data will also be presented. Finally, we will discuss the climate implication of our studies using the combined satellite and AERONET observations.

Hsu, N. Christina↗