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All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Study of cosmic-ray H and He isotopes at 23 AU

We have measured the spectra of H and He isotopes during the 1987 solar minimum with the cosmic-ray detector system (CRS) on the Voyager 2 spacecraft. By carrying out the measurement near solar minimum and at large heliospheric distances, the effects of solar modulations were reduced. In particular, the adiabatic energy losses were smaller, and these results from 23 AU over the solar minimum period of cycle 21 represent observations at energies not accessible from previous measurements near 1 AU. The modulated spectra with the diffusion coefficient constant k(sub 0) = 3.15 x 10(exp 22) sq cm/s (which corresponds to a solar modulation parameter of 360 MV at 23 AU and 500 MV at 1 AU) agree well with both our data at 23 AU and the previous solar minimum measurements at 1 AU. The measured H-1 and H-2 spectra are both consistent with the calculated spectra, using standard Galactic and heliospheric propagation models without invoking an anomalous hydrogen component. With the fixed modulation parameter of 360 MV, the mean pathlengths, source spectra, and cross sections were varied to study the effects of different input parameters on the spectra and relative abundances. At this stage of our work, we have not found any strong evidence from the low-energy H-2 and He-3 data that H-1 and He-4 should have a different propagation history, or different types of source spectra from the heavier cosmic-ray nuclei.

Seo, E. S.↗
NASA NTRS1993

HZE reactions and data-base development

The primary cosmic rays are dispersed over a large range of linear energy transfer (LET) values and their distribution over LET is a determinant of biological response. This LET distribution is modified by radiation shielding thickness and shield material composition. The current uncertainties in nuclear cross sections will not allow the composition of the shield material to be distinguished in order to minimize biological risk. An overview of the development of quantum mechanical models of heavy ion reactions will be given and computational results compared with experiments. A second approach is the development of phenomenological models from semi-classical considerations. These models provide the current data base in high charge and energy (HZE) shielding studies. They will be compared with available experimental data. The background material for this lecture will be available as a review document of over 30 years of research at Langley but will include new results obtained over the last year.

Townsend, Lawrence W.↗
NASA NTRS1972

Flow field predictions for a slab delta wing at incidence

Theoretical results are presented for the structure of the hypersonic flow field of a blunt slab delta wing at moderately high angle of attack. Special attention is devoted to the interaction between the boundary layer and the inviscid entropy layer. The results are compared with experimental data. The three-dimensional inviscid flow is computed numerically by a marching finite difference method. Attention is concentrated on the windward side of the delta wing, where detailed comparisons are made with the data for shock shape and surface pressure distributions. Surface streamlines are generated, and used in the boundary layer analysis. The three-dimensional laminar boundary layer is computed numerically using a specially-developed technique based on small cross-flow in streamline coordinates. In the rear sections of the wing the boundary layer decreases drastically in the spanwise direction, so that it is still submerged in the entropy layer at the centerline, but surpasses it near the leading edge. Predicted heat transfer distributions are compared with experimental data.

Conti, R. J.↗
NASA NTRSDate not supplied

An Approach to Shape Parameterization Using Laboratory Hypervelocity Impact Experiments

NASA’s Orbital Debris Program Office relies on laboratory-based impact tests to supplement the measurement data of on-orbit events that defines the orbital debris environment. These experiments provide information that is essential to interpreting the radar and optical measurements of orbital fragmentation events into useful metrics, such as characteristic size of the debris, and to providing a better understanding of the distributions of fragment populations in terms of their masses, material constituents, fragment densities, cross-sectional areas, area-to-mass ratios, shapes, etc. The Satellite Orbital Debris Characterization Impact Test (SOCIT) was a notable laboratory impact experiment conducted in 1992 using a surplus U.S. Navy Transit navigation satellite of the 1960s. The data from this ground-based experiment were combined with on-orbit measurements to develop the NASA Standard Satellite Breakup Model (SSBM). To account for advancements in satellite design and construction since, a new impact test series – DebriSat – was conducted in 2014. This test utilized a high-fidelity mock-up spacecraft that better represents the materials and construction techniques used to design and manufacture modern spacecraft. Together, these tests offer valuable data to model an orbital debris environment composed of legacy and modern spacecraft. This paper presents an overview of the two laboratory impact tests, comparing their fragment parameter distributions with each other and with relevant distributions from the NASA SSBM. The categorization and descriptions of fragment shapes are of significant interest for future work, yet there are marked differences in the definitions of shape categories between each dataset. The categorizations of constituent materials, and the measurement techniques employed to populate these two datasets, are also different. New rubrics simplify and equate the categorizations between datasets to aid comparative analyses and to facilitate the potential use of both datasets in tandem with future environmental debris models. A preferred approach to classifying shape across disparate datasets uses the characteristic-length dimensions, and a simplified shape classification based on physical, solid-body dimensions, to mathematically construct an encapsulating right-circular cylinder that represents the fragment. The ratio of cylinder length-to-diameter (L:D) then provides a single continuum value for shape that is strongly correlated with its designated shape and size. This metric can then be used to further assess the distribution of shape with populations of other fragment characteristics within these datasets. The shape parameterization using the L:D ratios of right-circular cylinders is discussed.

John H. Seago↗
NASA NTRSDate not supplied

An Approach to Shape Parameterization Using Laboratory Hypervelocity Impact Experiments

NASA’s Orbital Debris Program Office relies on laboratory-based impact tests to supplement the measurement data of on-orbit events that defines the orbital debris environment. These experiments provide information that is essential to interpreting the radar and optical measurements of orbital fragmentation events into useful metrics, such as characteristic size of the debris, and to providing a better understanding of the distributions of fragment populations in terms of their masses, material constituents, fragment densities, cross-sectional areas, area-to-mass ratios, shapes, etc. The Satellite Orbital Debris Characterization Impact Test (SOCIT) was a notable laboratory impact experiment conducted in 1992 using a surplus U.S. Navy Transit navigation satellite of the 1960s. The data from this ground-based experiment were combined with on-orbit measurements to develop the NASA Standard Satellite Breakup Model (SSBM). To account for advancements in satellite design and construction since, a new impact test series – DebriSat – was conducted in 2014. This test utilized a high-fidelity mock-up spacecraft that better represents the materials and construction techniques used to design and manufacture modern spacecraft. Together, these tests offer valuable data to model an orbital debris environment composed of legacy and modern spacecraft. This paper presents an overview of the two laboratory impact tests, comparing their fragment parameter distributions with each other and with relevant distributions from the NASA SSBM. The categorization and descriptions of fragment shapes are of significant interest for future work, yet there are marked differences in the definitions of shape categories between each dataset. The categorizations of constituent materials, and the measurement techniques employed to populate these two datasets, are also different. New rubrics simplify and equate the categorizations between datasets to aid comparative analyses and to facilitate the potential use of both datasets in tandem with future environmental debris models. A preferred approach to classifying shape across disparate datasets uses the characteristic-length dimensions, and a simplified shape classification based on physical, solid-body dimensions, to mathematically construct an encapsulating right-circular cylinder that represents the fragment. The ratio of cylinder length-to-diameter (L:D) then provides a single continuum value for shape that is strongly correlated with its designated shape and size. This metric can then be used to further assess the distribution of shape with populations of other fragment characteristics within these datasets. The shape parameterization using the L:D ratios of right-circular cylinders is discussed.

John H Seago↗
NASA NTRS1978

Radar backscatter from the ocean - Dependence on surface friction velocity

From the mid 1960s to the present, the normalized radar cross-section (NRCS) of the ocean has been measured using airborne radars operating over a frequency range of 0.4 to 14 GHz. Analyses of these data have shown that the NRCS was proportional to the ocean surface wind speed raised to some power, but the values of the exponent remained in dispute. This paper extends previous work and uses these NRCS measurements to demonstrate that to the first order, the NRCS is a function of only the friction velocity at the ocean's surface. Further analyses characterize the dependence of the NRCS on radar variables such as frequency, incidence angle, polarization, etc. Finally, recommendations are made for using Ku-band radars at large incidence angles for remote sensing of the wind friction velocity vector.

Jones, W. L.↗
NASA NTRS1978

Industrial ion source technology

An analytical model was developed to describe the development of a coned surface texture with ion bombardment and simultaneous deposition of an impurity. A mathematical model of sputter deposition rate from a beveled target was developed in conjuction with the texturing models to provide an important input to that model. The establishment of a general procedure that will allow the treatment of manay different sputtering configurations is outlined. Calculation of cross sections for energetic binary collisions was extened to Ar, Kr.. and Xe with total cross sections for viscosity and diffusion calculated for the interaction energy range from leV to 1000eV. Physical sputtering and reactive ion etching experiments provided experimental data on the operating limits of a broad beam ion source using CF4 as a working gas to produce reactive species in a sputtering beam. Magnetic clustering effects are observed when Al is seeded with Fe and sputtered with Ar(?) ions. Silicon was textured at a micron scale by using a substrate temperature of 600 C.

Kaufman, H. R.↗
NASA NTRS1979

Line-by-line transport calculations for Jupiter entry probes

Line-by-line calculations of the radiative transport for a condition near peak heating for entry of the Galileo probe into the Jovian atmosphere are described. The discussion includes a thorough specification of the atomic and molecular input data used in the calculations that could be useful to others working in the field. The results show that the use of spectrally averaged cross sections for diatomic absorbers such as CO and C2 in the boundary layer can lead to an underestimation (by as much as 29%) of the spectral flux at the stagnation point. On the other hand, for the turbulent region near the cone frustum on the probe, the flow tends to be optically thin, and the spectrally averaged results commonly used in coupled radiative transport-flow field calculations are in good agreement with the present line-by-line results. It is recommended that these results be taken into account in sizing the final thickness of the Galileo's heat shield.

Arnold, J. O.↗
NASA NTRS1980

Theory of twisted nonuniformly heated bars

Nonlineary distributed stresses in twisted nonuniformly heated bars of arbitrary cross section are calculated taking into account various elasticity parameters. The approximate theory is shown to be sufficiently general and accurate by comparison with experimental data.

Shorr, B. F.↗
NASA NTRS1984

s-wave threshold in electron attachment - Results in 2-C4F6 and CFCl3 at ultra-low electron energies

Electron attachment lineshapes and cross sections are reported for the processes 2-C4F6(-)/2-C4F6 and Cl(-)/CFCl3 at electron energies of 0-120 and 0-140 meV, and at resolutions of 6 and 7 meV (FWHM), respectively. As in previous measurements in CCl4 and SF6, the results show resolution-limited narrow structure in the cross section at electron energies below 15 meV. This structure arises from the divergence of the s-wave cross section in the limit of zero electron energy. Comparisons are given with swarm-measured results, and with collisional ionization (high-Rydberg attachment) data in this energy range.

Chutjian, A.↗
NASA NTRS1986

Electromagnetic dissociation effects in galactic heavy-ion fragmentation

Methods for calculating cross sections for the breakup of galactic heavy ions by the Coulomb fields of the interacting nuclei are presented. By using the Weizsacker-Williams method of virtual quanta, estimates of electromagnetic dissociation cross sections for a variety of reactions applicable to galactic cosmic ray shielding studies are presented and compared with other predictions and with available experimental data.

Norbury, J. W.↗
NASA NTRS1986

Vertical drop test of a transport fuselage section located aft of the wing

A 12-foot long Boeing 707 aft fuselage section with a tapering cross section was drop tested at the NASA Langley Research Center to measure structural, seat, and occupant response to vertical crash laods and to provide data for nonlinear finite element modeling. This was the final test in a series of three different transport fuselage sections tested under identical conditions. The test parameters at impact were: 20 ft/s velocity, and zero pitch, roll, and yaw. In addition, the test was an operational shock test of the data acquisition system used for the Controlled Impact Demonstration (CID) of a remotely piloted Boeing 720 that was crash tested at NASA Ames Dryden Flight Research Facility on December 1, 1984. Post-test measurements of the crush showed that the front of the section (with larger diameter) crushed vertically approximately 14 inches while the rear crushed 18 inches. Analysis of the data traces indicate the maximum peak normal (vertical) accelerations at the bottom of the frames were approximately 109 G at body station 1040 and 64 G at body station 1120. The peak floor acceleration varied from 14 G near the wall to 25 G near the center where high frequency oscillations of the floor were evident. The peak anthropomorphic dummy pelvis normal (vertical) acceleration was 19 G's.

Fasanella, E. L.↗
NASA NTRS1986

Bodies with noncircular cross sections and bank-to-turn missiles

An evaluation is made of prospective missile applications for noncircular cross section bodies, and of recent developments in bank-to-turn missile configuration aerodynamics. The discussion encompasses cross-flow analysis techniques, as well as study results obtained for bodies with elliptical and square cross sections and with variable cross sections. Attention is given to both the performance advantages and the stability and control problems of bank-to-turn missile configurations; the aerodynamic data presented for monoplanar configurations extend to those incorporating airbreathing propulsion systems.

Jackson, C. M., Jr.↗
NASA NTRS1993

Al-26 production profile and model comparisons in Canyon Diablo

The large preatmospheric size of the Canyon Diablo meteorite, a radius of about 15 m, makes it especially suitable for systematic studies of cosmogenic nuclide production rates of iron objects in a 2 pi geometry. To reconstruct the exposure history of the meteoroid, Heymann et al. investigated several fragments recovered from known geographic locations around the crater for their shock features and cosmogenic nobel gases. They applied the Signer-Nier noble gas production rate model to establish the preatmospheric depth of the specimens in the meteoroid. Cosmic ray exposure ages suggested a multi-episodic irradiation, with 170 or 540 Ma being inferred for most of the samples studied while two anomalous specimens indicated a possible third exposure age at 940 Ma. Be-10 and Cl-36 have been measured in a number of these same samples by accelerator mass spectrometry (AMS), with use being made of the preatmospheric depths determined in Heymann et al. to construct production profiles. The present study extends the cosmogenic radionuclide data to Al-26 and compares the results with both the production rate model of Reedy and Arnold and production rates determined from the cross sections used by the Reedy-Arnold model (for the major nuclear reactions making Al-26) in combination with differential fluxes calculated using the Los Alamos High Energy Transport (LAHET) Code System. Model calculations for Be-10 and Cl-36 have also been obtained.

Michlovich, E.↗
NASA NTRS1994

Four years of ground-based total ozone measurements by visible spectrometry in Antarctica

Visible spectrometers SAOZ have been developed at Service d'Aeronomie for permanent ground-based ozone monitoring at all latitudes up to the polar circle in winter. Observations are made by looking at the sunlight scattered at zenith in the visible range, twice a day, at sunrise and sunset. Compared to ozone observations in the UV generally in use, visible observations in the small Chappuis bands at twilight have the advantages of being independent of stratospheric temperature, little contaminated by tropospheric ozone and multiple scattering, and of permitting observations even in winter at the polar circle. SAOZ instruments have been installed since 1988 at several stations in the Antarctic and the Arctic. More than four years data at Dumont d'Urville in Terre Adelie (67 deg S) are now available. The station is generally located at the edge of the vortex in spring and therefore the ozone hole is seen there only occasionally. The lowest values (140 DU) were reported in early October 1991. According to these first regular observations throughout the whole winter ozone seems to increase in late autumn and winter. Its decay does not start before the end of August. Although of smaller amplitude than with the previous version five data, the ratio between the groundbased and satellite/TOMS measurements displays a systematic seasonal variation correlated partly to the sun zenith angle of observations from orbit and partly to the temperature of the stratosphere. Since ground-based measurements are always made at 90 deg SZA, the SZA dependence must come from the satellite data interpretation (TOMS observations are between 43 to 88 deg SZA). The temperature dependence could be partly due to variations of ozone absorption cross-sections in the ultraviolet used by the satellite spectrometer, and partly to a systematic seasonal cycle of the air mass factor use in the interpretation of the ground based observations. However, the last contribution appears to be too small to compensate the ozone increase in winter reported by SAOZ, which is then real.

Goutail, F.↗
NASA NTRS1999

Cryogenic Fuel Tank Draining Analysis Model

One of the technological challenges in designing advanced hypersonic aircraft and the next generation of spacecraft is developing reusable flight-weight cryogenic fuel tanks. As an aid in the design and analysis of these cryogenic tanks, a computational fluid dynamics (CFD) model has been developed specifically for the analysis of flow in a cryogenic fuel tank. This model employs the full set of Navier-Stokes equations, except that viscous dissipation is neglected in the energy equation. An explicit finite difference technique in two-dimensional generalized coordinates, approximated to second-order accuracy in both space and time is used. The stiffness resulting from the low Mach number is resolved by using artificial compressibility. The model simulates the transient, two-dimensional draining of a fuel tank cross section. To calculate the slosh wave dynamics the interface between the ullage gas and liquid fuel is modeled as a free surface. Then, experimental data for free convection inside a horizontal cylinder are compared with model results. Finally, cryogenic tank draining calculations are performed with three different wall heat fluxes to demonstrate the effect of wall heat flux on the internal tank flow field.

Greer, Donald↗
NASA NTRS2012

A 40 Year Time Series of SBUV Observations: the Version 8.6 Processing

Under a NASA program to produce long term data records from instruments on multiple satellites (MEaSUREs), data from a series of eight SBUV and SBUV 12 instruments have been reprocessed to create a 40 year long ozone time series. Data from the Nimbus 4 BUV, Nimbus 7 SBUV, and SBUV/2 instruments on NOAA 9, 11, 14, 16, 17, and 18 were used covering the period 1970 to 1972 and 1979 to the present. In past analyses an ozone time series was created from these instruments by adjusting ozone itself, instrument by instrument, for consistency during overlap periods. In the version 8.6 processing adjustments were made to the radiance calibration of each instrument to maintain a consistent calibration over the entire time series. Data for all eight instruments were then reprocessed using the adjusted radiances. Reprocessing is necessary to produce an accurate latitude dependence. Other improvements incorporated in version 8.6 included the use of the ozone cross sections of Brion, Daumont, and Malicet, and the use of a cloud height climatology derived from Aura OMI measurements. The new cross sections have a more accurate temperature dependence than the cross sections previously used. The OMI-based cloud heights account for the penetration of UV into the upper layers of clouds. The consistency of the version 8.6 time series was evaluated by intra-instrument comparisons during overlap periods, comparisons with ground-based instruments, and comparisons with measurements made by instruments on other satellites such as SAGE II and UARS MLS. These comparisons show that for the instruments on NOAA 16, 17 and 18, the instrument calibrations were remarkably stable and consistent from instrument to instrument. The data record from the Nimbus 7 SBUV was also very stable, and SAGE and ground-based comparisons show that the' calibration was consistent with measurements made years laterby the NOAA 16 instrument. The calibrations of the SBUV/2 instruments on NOAA 9, 11, and 14 were more of a problem. The rapidly drifting orbits of these satellites resulted in relative time and altitude dependent differences that are significant. Despite these problems, total column ozone appears to be consistent to better than 1% over the entire time series, while the ozone vertical distribution is consistent to approximately 5%.

McPeters, Richard↗
NASA NTRS2012

Mass Spectrometric Studies of Oxides

Current studies at NASA Glenn on oxide thermodynamics are discussed. Previous studies on the vaporization of B2O3 in reducing atmospheres led to inconsistent studies when B was used as a reductant. It is shown that liquid B2O3 does not wet B and a clear phase separation was noted in the Knudsen cell. This problem was solved by using FeB and Fe2B to supply a different and constant activity of B. The thermodynamic data thus derived are compared to quantum chemical composite calculations. A major problem in high temperature mass spectrometry is the determination of accurate ionization cross sections, particularly for molecules. The method of Deutsch and Mark shows promise and some sample calculations are discussed. Finally current studies on the thermodynamics of rare earth silicates are discussed. Here the problems are obtaining a measurable signal from SiO2 vaporization and non-equilibrium vaporization. The use of a Ta reducing agent provides a stronger signal, which is related to silica activity. The Whitman-Motzfeld relation adapted to KEMS measurements is applied to obtain equilibrium pressures.

Jacobson, Nathan S.↗