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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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NASA NTRS1995

Gaussian statistics of the cosmic microwave background: Correlation of temperature extrema in the COBE DMR two-year sky maps

We use the two-point correlation function of the extrema points (peaks and valleys) in the Cosmic Background Explorer (COBE) Differential Microwave Radiometers (DMR) 2 year sky maps as a test for non-Gaussian temperature distribution in the cosmic microwave background anisotropy. A maximum-likelihood analysis compares the DMR data to n = 1 toy models whose random-phase spherical harmonic components a(sub lm) are drawn from either Gaussian, chi-square, or log-normal parent populations. The likelihood of the 53 GHz (A+B)/2 data is greatest for the exact Gaussian model. There is less than 10% chance that the non-Gaussian models tested describe the DMR data, limited primarily by type II errors in the statistical inference. The extrema correlation function is a stronger test for this class of non-Gaussian models than topological statistics such as the genus.

Kogut, A.↗

NASA NTRS1996

Repeat Pass Aircraft Interferometry Results at Portage Lake, Maine and Innisfail, Australia

The NASA/JPL AIRSAR/TOPSAR instruments have the capability of collecting fully polarimetric radar data at three wavelengths (C, L, and P-bands) and dual antenna interferometry at C-band, and more recently, L-band. In order to understand frequency and baseline dependent scattering effects in vegetated regions, repeat pass interferometry data was collected for two vegetated regions in 1993. Portage Lake, Maine is a primarily coniferous forested region with some clear cutting from logging activities in the region. The second site at Innisfail, Australia borders a tropical rain forest and is situated adjacent to some major clear cut regions and banana plantations. Preliminary analysis of repeat pass data collected in these areas shows that the smaller the wavelength the greater the temporal decorrelation between passes, the longer the wavelength the greater the penetration depth for some types of vegetation canopy, yet for some vegetation canopy types, in particular for a banana plantation, there appears to be no frequency dependent penetration into the canopy.

Hensley, Scott↗

NASA NTRS1996

Repeat Pass Aircraft Interferometry Results at Portage Lake, Maine and Innisfail, Australia

The NASA/JPL AIRSAR/TOPSAR instruments have the capability of collecting fully polarimetric radar data at three wavelengths (C, L and P-Bands) and dual antenna interferometry at C-Band, and more recently L-Band. In order to understand frequency and baseline dependent scattering effects in vegetated regions repeat pass interferometry data was collected for two vegetated regions in 1993. Portage Lake, Maine is a primarily coniferous forested region with some clear cutting from logging activities in the region. The second site at Innisfail, Australia borders a tropical rain forest and is situated adjacent to some major clear cut regions and banana plantations. Preliminary analysis of repeat pass data collected in these areas shows that the smaller the wavelength the greater the temporal decorrelation between passes, the longer the wavelength the greater the penetration depth for some types of vegetation canopy, yet for some vegetation canopy types, in particular for a banana plantation there appears to be no frequency dependent penetration into the canopy.

Hensley, Scott↗

NASA NTRS2000

A High Resolution Survey of the Disk of M31

This report describes research activities funded for SAO Proposal P3481-5-95, "Monitoring the Center of M31". Related activities for SAO Proposal P3486- 5-95, "A High-Resolution Survey of the Disk of M31" are also described. The research involved the data analysis and interpretation of eleven separate ROSAT (Roentgen Satellite) HRI (High Resolution Imager) observations of the center and inner disk of M31, obtained between July, 1990 and January, 1997. A log of the individual data sets is given. All proposed observations were successfully carried out by the ROSAT Observatory, and standard data products were successfully generated for each observation. There were two basic thrusts to the research. First, we wished to monitor the x-ray source nearest the nucleus of M31, to search for anti-correlated radio/x-ray variability predicted by theoretical models for the source. We would also be able to assess the degree and range of variability of other x-ray sources in the central bulge of M31 and to estimate rates of transients. Secondly, we wished to survey the entire inner disk of M31, and in particular the region covered by the recent MIT wide-band and narrow-band surveys to identify x-ray counterparts to supernova remnants, OB associations, and young blue stars, in areas in which the ROSAT PSPC survey was confused. Results of each research project are summarized. Papers describing the results in more detail are in preparation.

Primini, Francis A.↗

NASA NTRS2013

Evaluation of Low-Gravity Smoke Particulate for Spacecraft Fire Detection

Tests were conducted on the International Space Station to evaluate the smoke particulate size from materials and conditions that are typical of those expected in spacecraft fires. Five different materials representative of those found in spacecraft (Teflon, Kapton, cotton, silicone rubber and Pyrell) were heated to temperatures below the ignition point with conditions controlled to provide repeatable sample surface temperatures and air flow. The air flow past the sample during the heating period ranged from quiescent to 8 cm/s. The effective transport time to the measurement instruments was varied from 11 to 800 seconds to simulate different smoke transport conditions in spacecraft. The resultant aerosol was evaluated by three instruments which measured different moments of the particle size distribution. These moment diagnostics were used to determine the particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment). These statistics were combined to determine the diameter of average mass and the count mean diameter and by assuming a log-normal distribution, the geometric mean diameter and the geometric standard deviations were also calculated. Smoke particle samples were collected on TEM grids using a thermal precipitator for post flight analysis. The TEM grids were analyzed to determine the particle morphology and shape parameters. The different materials produced particles with significantly different morphologies. Overall the majority of the average smoke particle sizes were found to be in the 200 to 400 nanometer range with the quiescent cases and the cases with increased transport time typically producing with substantially larger particles. The results varied between materials but the smoke particles produced in low gravity were typically twice the size of particles produced in normal gravity. These results can be used to establish design requirements for future spacecraft smoke detectors.

Fire Safety↗

NASA NTRS2013

Evaluation of Low-Gravity Smoke Particulate for Spacecraft Fire Detection

Fire↗

NASA NTRS1979

Robustness properties of discrete time regulators, LOG regulators and hybrid systems

Robustness properites of sample-data LQ regulators are derived which show that these regulators have fundamentally inferior uncertainty tolerances when compared to their continuous-time counterparts. Results are also presented in stability theory, multivariable frequency domain analysis, LQG robustness, and mathematical representations of hybrid systems.

Stein, G.↗

NASA NTRS2015

X-Raying the Coronae of HD 155555

We present an analysis of the high-resolution Chandra observation of the multiple system, HD 155555 (an RS CVn type binary system, HD 155555 AB, and its spatially resolved low-mass companion HD 155555 C). This is an intriguing system which shows properties of both an active pre-main sequence star and a synchronised (main sequence) binary. We obtain the emission measure distribution, temperature structures, plasma densities, and abundances of this system and compare them with the coronal properties of other young/active stars. HD 155555 AB and HD 155555 C produce copious X-ray emission with log L(sub x) of 30.54 and 29.30, respectively, in the 0.3-6.0 kiloelectronvolt energy band. The light curves of individual stars show variability on timescales of few minutes to hours. We analyse the dispersed spectra and reconstruct the emission measure distribution using spectral line analysis. The resulting elemental abundances exhibit inverse first ionisation potential effect in both cases. An analysis of He-like triplets yields a range of coronal electron densities 1010 − 1013 per cubic centimeter. Since HD 155555 AB is classified both as an RS CVn and a PMS star, we compare our results with those of other slightly older active main-sequence stars and T Tauri stars, which indicates that the coronal properties of HD 155555 AB closely resemble that of an older RS CVn binary rather than a younger PMS star. Our results also suggests that the properties of HD 155555 C is very similar to those of other active M dwarfs.

stars: coronae↗

NASA NTRS1974

Method for remotely sensing turbulence of planetary atmospheres

Based on variances of log-amplitude and phase fluctuations of radio occultation data received from orbital and fly-by missions, structure constant for Venusian planetary atmosphere has been estimated with high-confidence factor. Analysis indicates that effects of inhomogeneity, finite size, and superrefractivity of atmospheric turbulence cannot be ignored.

Woo, R. T.↗

NASA NTRS1975

Are clear-cut areas estimated from LANDSAT imagery reliable?

The reliability of LANDSAT imagery for estimation of clear-cut areas was evaluated by comparison with data obtained from high-altitude photos and logging historical map and from field inspections. A mature forest was selected as a test site because of its continuous clear-cut operation. The forest is about 50 km northwest of Victoria, British Columbia, Canada, and consists of 9092 ha. Areas clear-cut within the past year were overestimated by 12.9%, those clear-cut 1-year or more by 2.2%, whereas uncut mature timber was underestimated by 3.6%. Three clear-cut areas were missed in the logging map and two in the LANDSAT enhancement. The difference between area estimates was significant when all 26 areas were included but not when 2 overestimated areas were excluded from the analysis. The study indicates that LANDSAT imagery color enhancement is a useful tool in up-dating clear-cut areas for long-term planning in forest management.

Lee, Y. J.↗

NASA NTRS2012

Very Massive Stars in the Primitive Galaxy, IZw 18

IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9) Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties and evolutionary status of very massive stars in IZw 18, based on UV photometry of individual stars in I Zw 18 and analysis of unresolved ultraviolet spectra of IZw 18-NW obtained with HST.

Heap, Sara↗

NASA NTRS2019

The Weather Analysis Display (WAND) Tool: Developing a Meteorological Data Display Tool for Situational Awareness During Day-Of-Launch of Space Launch Vehicles Using Python

Atmospheric conditions are an important driver in the design and operation of space launch vehicles. The Profile Envision and Splicing Tool (PRESTO) was developed by NASA’s Marshall Space Flight Center (MSFC) Natural Environments Branch (NE) to generate vertically complete atmospheric profiles from various data sources at NASA’s Kennedy Space Center (KSC), co-located on the United States Air Force (USAF) Eastern Range (ER), for NASA’s Space Launch System (SLS) day-of-launch (DOL) loads and trajectory analysis. PRESTO was designed solely to generate a vertically complete atmospheric profile (Orcutt et al., 2017). However, NE has also been tasked to provide a quality assessment of meteorological data examined on DOL, which goes beyond PRESTO’s utility. Thus, NE developed the Weather Analysis Display (WAND) to visualize data from all available observation systems in conjunction with climatological databases. WAND can display data from various sources in multiple ways, including Skew-T Log-P plots, time-height cross sections, and time series. WAND was developed in Python 3 taking advantage of common packages, such as NumPy for data handling, SciPy for mathematical functions, Matplotlib for data visualization, and Tkinter for the execution of the Graphical User Interface (GUI).

Orcutt, John M.↗

NASA NTRS2019

Template Matching Used for Small Body Optical Navigation with Poorly Detailed Objects

Object and template matching becomes difficult when an image lacks detail. This is particularly worrisome when typical matching techniques, cross-correlation, log-polar mapping, and key point matching fail. Work herein describes a formulation that identifies objects of interest, estimates the affine transformation between a template object and scene using Principal Component Analysis (PCA), and provides a fit value for the objects and template incorporating Hu's Moments. The algorithm presented is tested on synthetic images and images obtained from the OSIRIS-REx mission while the spacecraft was approaching its target, Bennu. Results for the current formulation show that, with the presence of large-scale variations and rotation, the fitting scheme performs well when compared with other techniques.

Lyzhoft, Joshua R.↗

NASA NTRS1979

Development of procedures for calculating stiffness and damping of elastomers in engineering applications. Part 5: Elastomer performance limits and the design and test of an elastomer damper

Tests were performed on elastomer specimens of the material polybutadiene to determine the performance limitations imposed by strain, temperature, and frequency. Three specimens were tested: a shear specimen, a compression specimen, and a second compression specimen in which thermocouples were embedded in the elastomer buttons. Stiffness and damping were determined from all tests, and internal temperatures were recorded for the instrumented compression specimen. Measured results are presented together with comparisons between predictions of a thermo-viscoelastic analysis and the measured results. Dampers of polybutadiene and Viton were designed, built, and tested. Vibration measurements were made and sensitivity of vibration to change in unbalance was also determined. Values for log decrement were extracted from the synchronous response curves. Comparisons were made between measured sensitivity to unbalance and log decrement and predicted values for these quantities.

Tecza, J. A.↗

NASA NTRS1991

A critical analysis of the ultraviolet temperature scale of the helium-dominated DB and DBV white dwarfs

The temperatures of the hottest of the DB and of some of the variable DBV white dwarfs have been reanalyzed, using a new helium-rich model atmosphere grid and archival IUE data. The grid covers variations in the effective temperature, surface gravity, and trace hydrogen abundance. Significantly lower temperatures than those found by earlier investigations are found. This has influence on the issue of which mixing-length theory is the best one for treatment of convection in DB white dwarfs. The prototype of the DBV stars, GD 358, is given particular attention in view of the recently reported HE II 1640-A line. The sensitivity of the new results to input physics is analyzed. It is found that uncertainties in Stark broadening parameters, convective efficiency, and equation of state and the assumptions of a fixed gravity (log g = 8) and a negligible abundance of hydrogen can at most give an error in the effective temperature of 400 K for a typical DB star. The uncertainty on the absolute calibration of the IUE cameras and the effect of small interstellar reddening dominate the error analysis.

Thejll, Peter↗

NASA NTRS2006

Discerning Trends in Performance Across Multiple Events

Mass Data is a computer program that enables rapid, easy discernment of trends in performance data across multiple flights and ground tests. The program can perform Fourier analysis and other functions for the purposes of frequency analysis and trending of all variables. These functions facilitate identification of past use of diagnosed systems and of anomalies in such systems, and enable rapid assessment of related current problems. Many variables, for computation of which it is usually necessary to perform extensive manual manipulation of raw downlist data, are automatically computed and made available to all users, regularly eliminating the need for what would otherwise be an extensive amount of engineering analysis. Data from flight, ground test, and simulation are preprocessed and stored in one central location for instantaneous access and comparison for diagnostic and trending purposes. Rules are created so that an event log is created for every flight, making it easy to locate information on similar maneuvers across many flights. The same rules can be created for test sets and simulations, and are searchable, so that information on like events is easily accessible.

Slater, Simon↗

NASA NTRS2016

Degradation of Leakage Currents and Reliability Prediction for Tantalum Capacitors

Two types of failures in solid tantalum capacitors, catastrophic and parametric, and their mechanisms are described. Analysis of voltage and temperature reliability acceleration factors reported in literature shows a wide spread of results and requires more investigation. In this work, leakage currents in two types of chip tantalum capacitors were monitored during highly accelerated life testing (HALT) at different temperatures and voltages. Distributions of degradation rates were approximated using a general log-linear Weibull model and yielded voltage acceleration constants B = 9.8 +/- 0.5 and 5.5. The activation energies were Ea = 1.65 eV and 1.42 eV. The model allows for conservative estimations of times to failure and was validated by long-term life test data. Parametric degradation and failures are reversible and can be annealed at high temperatures. The process is attributed to migration of charged oxygen vacancies that reduce the barrier height at the MnO2/Ta2O5 interface and increase injection of electrons from the MnO2 cathode. Analysis showed that the activation energy of the vacancies' migration is ~ 1.1 eV.

acceleration factors↗

NASA NTRS1979

Maintenance cost study of rotary wing aircraft, phase 2

The Navy's maintenance and materials management data base was used in a study to determine the feasibility of predicting unscheduled maintenance costs for the dynamic systems of military rotary wing aircraft. The major operational and design variables were identified and the direct maintenance man hours per flight hour were obtained by step-wise multiple regression analysis. Five nonmilitary helicopter users were contacted to supply data on which variables were important factors in civil applications. These uses included offshore oil exploration and support, police and fire department rescue and enforcement, logging and heavy equipment movement, and U.S. Army military operations. The equations developed were highly effective in predicting unscheduled direct maintenance man hours per flying hours for military aircraft, but less effective for commercial or public service helicopters, probably because of the longer mission durations and the much higher utilization of civil users.

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