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NASA NTRS1994

SI (Metric) handbook

This guide provides information for an understanding of SI units, symbols, and prefixes; style and usage in documentation in both the US and in the international business community; conversion techniques; limits, fits, and tolerance data; and drawing and technical writing guidelines. Also provided is information of SI usage for specialized applications like data processing and computer programming, science, engineering, and construction. Related information in the appendixes include legislative documents, historical and biographical data, a list of metric documentation, rules for determining significant digits and rounding, conversion factors, shorthand notation, and a unit index.

Artusa, Elisa A.↗

NASA NTRS2003

The Magnetic Structure of H-Alpha Macrospicules in Solar Coronal Holes

Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic flux of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of H-alpha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar-coronal holes in 6 days of image-processed full-disk H-alpha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single-column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events, and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions and corona are driven by explosive reconnection events in the magnetic network.

Yamauchi, Y.↗

NASA NTRS2012

Mapping the Upper Subsurface of MARS Using Radar Polarimetry

Future human exploration of Mars will require detailed knowledge of the surface and upper several meters of the subsurface in potential landing sites. Likewise, many of the Planetary Science Decadal Survey science goals, such as understanding the history of Mars climate change, determining how the surface was altered through processes like volcanism and fluvial activity, and locating regions that may have been hospitable to life in the past, would be significantly advanced through mapping of the upper meters of the surface. Synthetic aperture radar (SAR) is the only remote sensing technique capable of penetrating through meters of material and imaging buried surfaces at high (meters to tens-of-meters) spatial resolution. SAR is capable of mapping the boundaries of buried units and radar polarimetry can provide quantitative information about the roughness of surface and subsurface units, depth of burial of stratigraphic units, and density of materials. Orbital SAR systems can obtain broad coverage at a spatial scale relevant to human and robotic surface operations. A polarimetric SAR system would greatly increase the safety and utility of future landed systems including sample caching.

Carter, L. M.↗

NASA NTRS1991

Isotopic constraints on the origin of meteoritic organic matter

Salient features of the isotopic distribution of H, C and N in the organic material found in carbonaceous meteorites are noted. Most organic fractions are strongly enriched in D with respect to the D/H ratio characteristic of H2 in the protosolar system; substantial variations in C-13/C-12 ratio are found among different molecular species, with oxidised species tending to be C-13 enriched relative to reduced species; some homologous series reveal systematic decrease in C-13/C-12 with increasing C number; considerable variation in N-15/N-14 ratio is observed within organic matter, though no systematic pattern to its distribution has yet emerged; no interelement correlations have been observed between isotope enrichments for the different biogenic elements. The isotopic complexity echoes the molecular diversity observed in meteoritic organic matter and suggests that the organic matter was formed by multiple processes and/or from multiple sources. However, existence of a few systematic patterns points towards survival of isotopic signatures characteristic of one or more specific processes. The widespread D enrichment implies either survival of many species of interstellar molecule or synthesis from a reservoir containing a significant interstellar component. Several of the questions raised above can be addressed by more detailed determination of the distribution of the H, C and N isotopes among different well-characterized molecular fractions. Thus, the present study is aimed at discovering whether the different amino acids have comparable D enrichments, which would imply local synthesis from a D-enriched reservoir, or very viable D enrichments, which would imply survival of some interstellar amino acids. The same approach is also being applied to polycyclic aromatic hydrocarbons. Because the analytical technique employed (secondary ion mass spectrometry) can acquire data for all three isotopic systems from each molecular fraction, any presently obscured interelement isotopic correlation should also be revealed, which will aid in identifying pertinent synthetic processes.

Kerridge, J. F.↗

NASA NTRS2011

Sources of Variation in Creep Testing

Creep rupture is an important material characteristic for the design of rocket engines. It was observed during the characterization of GRCop-84 that the complete data set had nearly 4 orders of magnitude of scatter. This scatter likely confounded attempts to determine how creep performance was influenced by manufacturing. It was unclear if this variation was from the testing, the material, or both. Sources of variation were examined by conducting tests on identically processed specimens at the same specified stresses and temperatures. Significant differences existed between the five constant-load creep frames. The specimen temperature was higher than the desired temperature by as much as 43 C. It was also observed that the temperature gradient was up to 44 C. Improved specimen temperature control minimized temperature variations. The data from additional tests demonstrated that the results from all five frames were comparable. The variation decreased to 1/2 order of magnitude from 2 orders of magnitude for the baseline data set. Independent determination of creep rates in a reference load frame closely matched the creep rates determined after the modifications. Testing in helium tended to decrease the sample temperature gradient, but helium was not a significant improvement over vacuum.

Loewenthal, William S.↗

NASA NTRS1994

Two-sample discrimination of Poisson means

This paper presents a statistical test for detecting significant differences between two random count accumulations. The null hypothesis is that the two samples share a common random arrival process with a mean count proportional to each sample's exposure. The model represents the partition of N total events into two counts, A and B, as a sequence of N independent Bernoulli trials whose partition fraction, f, is determined by the ratio of the exposures of A and B. The detection of a significant difference is claimed when the background (null) hypothesis is rejected, which occurs when the observed sample falls in a critical region of (A, B) space. The critical region depends on f and the desired significance level, alpha. The model correctly takes into account the fluctuations in both the signals and the background data, including the important case of small numbers of counts in the signal, the background, or both. The significance can be exactly determined from the cumulative binomial distribution, which in turn can be inverted to determine the critical A(B) or B(A) contour. This paper gives efficient implementations of these tests, based on lookup tables. Applications include the detection of clustering of astronomical objects, the detection of faint emission or absorption lines in photon-limited spectroscopy, the detection of faint emitters or absorbers in photon-limited imaging, and dosimetry.

Lampton, M.↗

NASA NTRS1993

Performance evaluation of the JPL TOPSAR system: An across-track interferometric SAR system for topographic mapping

An across-track interferometric (XTI) SAR has the capability of determining the three dimensional target location from the recorded radar echos thus providing high spatial resolution both horizontally and vertically. The output of an XTI SAR will typically include both a radar backscatter map and a digital elevation model (DEM). The accuracy of the derived DEM is determined by factors such as data acquisition geometry, signal-to-noise ratio, knowledge of platform position and attitude as well as the accuracy of the processing system. In the summer of 1992 the authors acquired TOPSAR data over the Ft. Irwin area in California, a desert area with significant relief (height standard deviation 150 m). Very accurate DEM's have been derived for this area by the Topographic Engineering Center (TEC) using digital correlation methods on 1:20,000 scale digitized photographs. Corner reflectors were deployed in the area, and their locations were determined to cm accuracies by the Defense Mapping Agency (DMA) using differential GPS techniques. DEM's generated from the acquired radar data have been rotated and translated to overlay the reference DEM's provided by TEC. A detailed description of the errors and their characteristics will be given. The standard deviations of the radar data sets we acquired measured over a 5.6 by 7 km area were 1.9 and 2.3 m. The corresponding numbers for flat areas were 1.1 and 2.0 m and for mountain areas 3.3 and 2.2 m.

Madsen, Soren N.↗

NASA NTRS1982

The possible role of heterogeneous aerosol processes in the chemistry of CH4 and CO in the troposphere

The effect of particle-gas interactions on the CH4 to CO oxidation sequence in the troposphere is investigated by developing rate expressions for the heterogeneous removal of gaseous species based on the absorption of the species by aerosol particles. The results of this analysis indicate that the homogeneous models describe the tropospheric chemistry of CO and CH4 more accurately than heterogeneous models, which suggests that heterogeneous processes may not be significant in this sequence of chemical reactions. Estimates of the CO and CH4 emission rates are not found to provide a conclusive basis on which to compare the significance of the homogeneous and heterogeneous processes. In addition, the time period during which an aerosol particle is effective in removing a trace gaseous species from the troposphere is determined to vary according to the tropospheric concentration and solubility of the particular gaseous species.

Luther, C. J.↗

NASA NTRS1991

Thermal and solutal conditions at the tips of a directional dendritic growth front

The line-of-sight averaged, time-dependent dendrite tip concentrations for the diffusion dominated vertical directional solidification of a metal model (ammonium chloride and water) were obtained by extrapolating exponentially fit diffusion layer profiles measured using a laser interferometer. The tip concentrations were shown to increase linearly with time throughout the diffusion dominated growth process for an initially stagnant dendritic array. The process was terminated for the cases chosen by convective breakdown suffered when the conditionally stable diffusion layer exceeded the critical Rayleigh criteria. The transient tip concentrations were determined to significantly exceed the values predicted for steady state, thus producing much larger constitutional undercoolings. This has ramifications for growth speeds, arm spacings and the dendritic structure itself.

Mccay, T. D.↗

NASA NTRS1993

Digital mammography, cancer screening: Factors important for image compression

The use of digital mammography for breast cancer screening poses several novel problems such as development of digital sensors, computer assisted diagnosis (CAD) methods for image noise suppression, enhancement, and pattern recognition, compression algorithms for image storage, transmission, and remote diagnosis. X-ray digital mammography using novel direct digital detection schemes or film digitizers results in large data sets and, therefore, image compression methods will play a significant role in the image processing and analysis by CAD techniques. In view of the extensive compression required, the relative merit of 'virtually lossless' versus lossy methods should be determined. A brief overview is presented here of the developments of digital sensors, CAD, and compression methods currently proposed and tested for mammography. The objective of the NCI/NASA Working Group on Digital Mammography is to stimulate the interest of the image processing and compression scientific community for this medical application and identify possible dual use technologies within the NASA centers.

Clarke, Laurence P.↗

NASA NTRS1998

A Study of Undercooling Behavior Of Immiscible Metal Alloys in the Absence of Crucible-Induced Nucleation

The purpose of this study is to investigate the question: Would eliminating the crucible eliminate the wall-induced nucleation of one of the liquid phases in an immiscible alloy and result in undercooling of the liquid into the metastable region thereby producing significant differences in the separation process and the microstructure upon solidification. Another primary objective of this research is to study systems with a metastable miscibility gap and to directly determine the metastable liquid miscibility gap by undercooling experiments. Nucleation and growth of droplets in these undercooled metallic liquid-liquid mixtures is also being studied. Results of this investigation indicate that containerless processing of immiscibles may not promote the undercooling of the single-phase liquid into the metastable region. Although no recalescence event was observed for this liquid-liquid transition, undercooling did occur across the miscibility gap for the solidification of the Ti phase that eventually separated.

Robinson, Michael B.↗

NASA NTRS2015

Evaluation of Solid Rocket Motor Component Data Using a Commercially Available Statistical Software Package

Commercially available software packages today allow users to quickly perform the routine evaluations of (1) descriptive statistics to numerically and graphically summarize both sample and population data, (2) inferential statistics that draws conclusions about a given population from samples taken of it, (3) probability determinations that can be used to generate estimates of reliability allowables, and finally (4) the setup of designed experiments and analysis of their data to identify significant material and process characteristics for application in both product manufacturing and performance enhancement. This paper presents examples of analysis and experimental design work that has been conducted using Statgraphics®(Registered Trademark) statistical software to obtain useful information with regard to solid rocket motor propellants and internal insulation material. Data were obtained from a number of programs (Shuttle, Constellation, and Space Launch System) and sources that include solid propellant burn rate strands, tensile specimens, sub‐scale test motors, full‐scale operational motors, rubber insulation specimens, and sub‐scale rubber insulation analog samples. Besides facilitating the experimental design process to yield meaningful results, statistical software has demonstrated its ability to quickly perform complex data analyses and yield significant findings that might otherwise have gone unnoticed. One caveat to these successes is that useful results not only derive from the inherent power of the software package, but also from the skill and understanding of the data analyst.

Stefanski, Philip L.↗

NASA NTRSDate not supplied

Responses of Microbes to Modeled Space Radiation

The built environment of spaceships is host to a microbial community that affects crew and craft alike. While the static composition of this community has been characterized and its temporal dynamics examined, the mechanisms controlling its make-up and evolutionary trajectory are not understood. Systematic analyses of microbial diversity show consistent patterns in community composition and function. Understanding these patterns' ecological origins remains a significant challenge, as it requires connecting processes at varying temporal and spatial scales. However, it is clear that the state and trajectories of microbial communities are in-part determined by their physical environment. In this regard, the spaceflight environment includes numerous interacting factors that differentiate it from Earth environments, including an altered atmospheric composition, reduced gravity (and thus altered fluid dynamics), and increased ionizing radiation. These factors impart selective pressures on microbial communities that affect their evolutionary trajectories and thus the risks and benefits these communities represent to crew and craft. The radiation environment of space leads to chronic exposure to low doses and is difficult to mimic on Earth. Thus, little is known about how microbial communities in spacecraft will respond and evolve. Therefore, given the limitations of existing studies, we aim to empirically determine how exposure to low doses of ionizing radiation for thousands of cell divisions affects rates of mutation accumulation in bacteria and the trajectory of their evolution. In this way, we will provide a critical set of data for designing safe and robust space missions. Here we discuss our progress towards this aim, including the construction of exposure facilities, our culturing and analysis approach, and preliminary data.

radiation↗

NASA NTRS1980

The polarization and directivity of solar-flare hard X-ray bremsstrahlung from a thermal source

The polarization and directivity of hard X-ray bremsstrahlung from a thermal source consisting of a region in which a thermal flux drives a pair of steel collisionless conduction fronts were evaluated. The conduction fronts are symmetrically driven from a central region, heated by the flare energy dissipation process. By comparing results with similar calculations based on a nonthermal thick-target electron beam model of the source, it was aimed to determine the degree to which the observed polarization and directivity of solar flare hard X-rays favor either model. Results which exhibit significant polarization and directivity of the hard X-ray radiation emitted by the source are produced by using Maxwellian electron-phase-space distribution functions modified to take into account a directional heat flux and a steady direct current in the X-ray source, and a fully relativistic treatment of the bremsstrahlung emission process. The results are consistent with solar hard X-ray anisotropy and polarization observations to date, although these observations are too crude to be conclusive.

Emslie, A. G.↗

NASA NTRS1995

Accelerated aging test results for aerospace wire insulation constructions

Several wire insulation constructions were evaluated with and without continuous glow discharges at low pressure and high temperature to determine the aging characteristics of acceptable wire insulation constructions. It was known at the beginning of the test program that insulation aging takes several years when operated at normal ambient temperature and pressure of 20 C and 760 torr. Likewise, it was known that the accelerated aging process decreases insulation life by approximately 50% for each 10 C temperature rise. Therefore, the first phases of the program, not reported in these test results, were to select wire insulation constructions that could operate at high temperature and low pressure for over 10,000 hours with negligible shrinkage and little materials' deterioration.The final phase of the program was to determine accelerated aging characteristics. When an insulation construction is subjected to partial discharges the insulation is locally heated by the bombardment of the discharges, the insulation is also subjected to ozone and other deteriorating gas particles that may significantly increase the aging process. Several insulation systems using either a single material or combinations of teflon, kapton, and glass insulation constructions were tested. All constructions were rated to be partial discharge and/or corona-free at 240 volts, 400 Hz and 260 C (500 F) for 50, 000 hours at altitudes equivalent to the Paschen law. Minimum partial discharge aging tests were preceded by screening tests lasting 20 hours at 260 C. The aging process was accelerated by subjecting the test articles to temperatures up to 370 C (700 F) with and without partial discharges. After one month operation with continuous glow discharges surrounding the test articles, most insulation systems were either destroyed or became brittle, cracked, and unsafe for use. Time with space radiation as with partial discharges is accumulative.

Dunbar, William G.↗

NASA NTRS2000

Marangoni Effects on Near-Bubble Microscale Transport During Boiling of Binary Fluid Mixtures

In earlier investigations, Marangoni effects were observed to be the dominant mechanism of boiling transport in 2-propanol/water mixtures under reduced gravity conditions. In this investigation we have examined the mechanisms of binary mixture boiling by exploring the transport near a single bubble generated in a binary mixture between a heated surface and cold surface. The temperature field created in the liquid around the bubble produces vaporization over the portion of its interface near the heated surface and condensation over portions of its interface near the cold surface. Experiments were conducted using different mixtures of water and 2-propanol under 1g conditions and under reduced gravity conditions aboard the KC135 aircraft. Since 2-propanol is more volatile than water, there is a lower concentration of 2-propanol near the hot surface and a higher concentration of 2-propanol near the cold plate relative to the bulk quantity. This difference in interface concentration gives rise to strong Marangoni effects that move liquid toward the hot plate in the near bubble region for 2-propanol and water mixtures. In the experiments in this study, the pressure of the test system was maintained at about 5 kPa to achieve the full spectrum of boiling behavior (nucleate boiling, critical heat flux and film boiling) at low temperature and heat flux levels. Heat transfer data and visual documentation of the bubble shape were extracted from the experimental results. In the 1-g experiments at moderate to high heat flux levels, the bubble was observed to grow into a mushroom shape with a larger top portion near the cold plate due to the buoyancy effect. The shape of the bubble was somewhat affected by the cold plate subcooling and the superheat of the heated surface. At low superheat levels for the heated surface, several active nucleation sites were observed, and the vapor stems from them merged to form a larger bubble. The generation rate of vapor is moderate in this regime and the bubble shape is cylindrical in appearance. In some instances, the bubble interface appeared to oscillate. At higher applied heat flux levels, the top of the bubble became larger, apparently to provide more condensing interface area adjacent to the cold plate. Increasing the applied heat flux ultimately led to dry-out of the heated surface, with conditions just prior to dryout corresponding to the maximum heat flux (CHF). A more stable bubble was observed when the system attained the minimum heat flux (for film boiling). In this regime, most of the surface under the bottom of the bubble was dry with nucleate boiling sometimes occuring around the contact perimeter of the bubble at heated surface. Different variations (e.g. gap between two plates, molar concentration of the liquid mixture) of the experiments were examined to determine parametric effects on the boiling process and to determine the best conditions for the KC135 reduced gravity tests. Variation of the gap was found to have a minor impact on the CHF. However, reducing the gap between the hot and cold surface was observed to significantly reduce the minimum heat flux for fixed molar concentration of 2-propanol. In the reduced gravity experiments aboard the KC135 aircraft, the bubble formed in the 6.4 mm gap was generally cylindrical or barrel shaped and it increased its extent laterally as the surface superheat increased. In reduced gravity experiments, dryout of the heated surface under the bubble was observed to occur at a lower superheated temperature than for 1g conditions. Observed features of the boiling process and heat transfer data under reduced gravity will be discussed in detail. The results of the reduced gravity experiments will also be compared to those obtained in comparable 1g experiments. In tandem with the experiments we are also developing a computational model of the transport in the liquid surrounding the bubble during the boiling process. The computational model uses a level set method to model motion of the interface. It will incorporate a macroscale treatment of the transport in the liquid gap between the surfaces and a microscale treatment of transport in the regions between the bubble interface and the solid surfaces. The features of the model will be described in detail. Future research directions suggested by the results to date will also be discussed.

V. Carey↗

NASA NTRS1975

A preliminary investigation of the potential applicability of the IPAD system to non-aerospace industry

A study of the applicability of the planned Integrated Programs for Aerospace-Vehicle Design (IPAD) system to the design activities of non-aerospace industries was carried out. It was determined that IPAD could be of significant benefit to a number of industries, with the most likely users being the heavy construction and automotive industries. Two additional short studies were initiated to investigate the possible impact of IPAD on a national energy program and on urban and regional planning activities of local and state governments. These initial studies indicated the possibility of significant payoff in these areas and the need for further investigations. It was also determined that utilization of IPAD by non-aerospace industries will probably involve a long stepwise process, since these industries maintain a policy of gradual introduction of new technology.

Hulbert, L. E.↗

NASA NTRS1981

Further SEASAT SAR coastal ocean wave analysis

Analysis techniques used to exploit SEASAT synthetic aperture radar (SAR) data of gravity waves are discussed and the SEASAT SAR's ability to monitor large scale variations in gravity wave fields in both deep and shallow water is evaluated. The SAR analysis techniques investigated included motion compensation adjustments and the semicausal model for spectral analysis of SAR wave data. It was determined that spectra generated from fast Fourier transform analysis (FFT) of SAR wave data were not significantly altered when either range telerotation adjustments or azimuth focus shifts were used during processing of the SAR signal histories, indicating that SEASAT imagery of gravity waves is not significantly improved or degraded by motion compensation adjustments. Evaluation of the semicausal (SC) model using SEASAT SAR data from Rev. 974 indicates that the SC spectral estimates were not significantly better than the FFT results.

Kasischke, E. S.↗