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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Geometric programming prediction of design trends for OMV protective structures

The global optimization trends of protective honeycomb structural designs for spacecraft subject to hypervelocity meteroid and space debris are presented. This nonlinear problem is first formulated for weight minimization of the orbital maneuvering vehicle (OMV) using a generic monomial predictor. Five problem formulations are considered, each dependent on the selection of independent design variables. Each case is optimized by considering the dual geometric programming problem. The dual variables are solved for in terms of the generic estimated exponents of the monomial predictor. The primal variables are then solved for by conversion. Finally, parametric design trends are developed for ranges of the estimated regression parameters. Results specify nonmonotonic relationships for the optimal first and second sheet mass per unit areas in terms of the estimated exponents.

Mog, R. A.↗
NASA NTRS1990

A study of sonic boom overpressure trends with respect to weight, altitude, Mach number, and vehicle shaping

This paper presents and discusses trends in nose shock overpressure generated by two conceptual Mach 2.0 configurations. One configuration was designed for high aerodynamic efficiency, while the other was designed to produce a low boom, shaped-overpressure signature. Aerodynamic lift, sonic boom minimization, and Mach-sliced/area-rule codes were used to analyze and compute the sonic boom characteristics of both configurations with respect to cruise Mach number, weight, and altitude. The influence of these parameters on the overpressure and the overpressure trends are discussed and conclusions are given.

Needleman, Kathy E.↗
NASA NTRS1990

Stratospheric constituent trends from ER-2 profile data

Trend analysis of the Airborne Arctic Stratospheric Expedition's ER-2 profile data reveals an average decrease in N2O on potential temperature isentropes which can be attributed to diabatic cooling of inner vortex air. This conclusion is independently supported by radiative transfer computations. Trends in ozone and water vapor over the same period are not consistent with the magnitude of the diabatic descent. After accounting for the diabatic motion (estimated from N2O), an additional 0.44 + or - 0.3 percent/day average anomalous O3 decrease above 440 K (about 20 km) is needed to balance the continuity equation. This ozone decrease suggests additional photochemical destruction of ozone in the presence of the high amounts of ClO observed during the mission. A 0.4 + or - 0.3 percent/day average anomalous increase in H2O is also observed near 420 K (about 18 km) which may be due to the evaporation of ice crystals falling from higher, colder stratospheric layers.

Schoeberl, Mark R.↗
NASA NTRS1990

Analysis of the eight-year trend in ozone depletion from empirical models of solar backscattered ultraviolet instrument degradation

Arguments are presented showing that the basic empirical model of the solar backscatter UV (SBUV) instrument degradation used by Cebula et al. (1988) in their analysis of the SBUV data is likely to lead to an incorrect estimate of the ozone trend. A correction factor is given as a function of time and altitude that brings the SBUV data into approximate agreement with the SAGE, SME, and Dobson network ozone trends. It is suggested that the currently archived SBUV ozone data should be used with caution for periods of analysis exceeding 1 yr, since it is likely that the yearly decreases contained in the archived data are too large.

Herman, J. R.↗
NASA NTRS1990

Long-term trends in the concentrations of SF6, CHClF2, and COF2 in the lower stratosphere from analysis of high-resolution infrared solar occultation spectra

Long-term trends in the concentrations of SF6, CHClF2 in the lower stratosphere are derived using results from analyses of the 1980 and of several more recently obtained IR solar occultation spectra. Results show that the increase rates of SF6 and CHClF2 were about 7.4/yr and 9.4/yr, respectively, which correspond to cumulative increases by factors of about 1.7 and 2.0 in the concentrations of these gases over the 7.2 yr measurement period. The average increase rate for COF2 was 10.3/yr over the same time period. The present results are compared with previously reported observations and trends and with one-dimensional model calculations.

Rinsland, C. P.↗
NASA NTRS1989

Reference model for CH4 and N2O and trends

Data from the Stratospheric and Mesospheric Sounder on Nimbus 7 were used as the basis for a model of the abundances of nitrous oxide and methane in the stratosphere. A version of this was produced two years ago (Taylor, Dudhia, and Rodgers - hereafter called the original paper) and in this new paper some of the possible error sources and long term trends are considered in more detail. The principle source of error in the SAMS retrievals is thought to be the use of climatological ozone profiles to invert the temperature profile data. However, it was found that the effect is too small, and of the opposite sign, to explain the discrepancies between satellite and in situ measurements, noted in the original paper. As expected, no systematic trends which exceed the estimated error in the data are found in either methane or nitrous oxide.

Taylor, F. W.↗
NASA NTRS1989

Remote sensing of geobotanical trends in East Africa

The spatial and phenological distribution of vegetation was examined in a remote sensing geobotanical study of the East Africa Rift region. Six normalized difference vegetation index (NDVI) AVHRR (advanced very high resolution radiometer) scenes (February, June, and September of both 1984 and 1987) were used as a measure of vegetation presence. NOAA ETOPO-5 elevation and geographic coordinate data were coregistered with the multitemporal NDVI images. Univariate and multivariate statistics indicate that the NDVI values are significantly associated with elevation, latitude, and longitude. This supports the concept of quantifiable, regional gradients that affect large-scale geobotanical studies. A quadratic regression line was fitted to the NDVI, elevation, latitude, and longitudinal data. In this way a regional trend, as affected by elevation, was determined. The deviation of the actual data from this regional trend was displayed as an image, and shows the local climatic and geological influences.

Warner, Timothy A.↗
NASA NTRS1990

An approach to the detection of long-term trends in upper stratospheric ozone from space

A central problem in the detection of long-term trends in the upper stratospheric ozone from orbiting remote sensors involves the separation of instrument drifts from true geophysical changes. Periodic flights of a Solar Backscatter Ultraviolet radiometer (SSBUV) on the Space Shuttle will allow the detection of drifts in optically identical sensors (SBUV/2) carried on operational satellites. A detailed simulation of the SSBUV and SBUV/2 datasets defines the accuracy that can be attained by the in-orbit calibration procedure. The repeatability of the SSBUV calibration from one flight to the next is the most critical variable in the analysis. A repeatability near + or - 1.0 percent is essential for detection and correction of drifts in the SBUV/2 radiance measurements. The simulations show that true geophysical trends in backscattered radiance can be inferred to an accuracy of approximately + or - 1.0 percent per decade when SSBUV flies approximately once per year and provides a precise calibration correction to the SBUV/2 dataset over a full decade.

Frederick, John E.↗
NASA NTRS1989

Ozone trends in Atlanta, Georgia - Have emission controls been effective?

Nine years of summertime ozone data from the Atlanta metropolitan area are analyzed and compared to local emissions of volatile organic carbon and nitrogen oxides. Trends from 1979 to 1987 were studied for the number of days per year ozone exceeded the NAAQS standard, the second-highest ozone level observed per year, and the first quartile summertime average ozone observed, as well as the mean difference between the ozone level observed downwind and upwind of the city. Because this last parameter is sensitive to chemical factors but relatively insensitive to the number of days each year with meteorological conditions conducive to ozone formation, its trend may be best suited for determining how effective emission controls have been in reducing O3 in the Atlanta area. In spite of the fact that sizeable reductions have been claimed for volatile organic carbon emissions over the past several years, the data give no indication that ozone levels have decreased and in fact, imply that summertime ozone production may have increased. The results imply that either emissions have not decreased as much as has been claimed or that ozone is not sensitive to anthropogenic volatile organic carbon emissions.

Lindsay, Ronald W.↗
NASA NTRS1991

Lithium in the most extreme halo stars - Trends with metallicity

A grid of extremely metal-poor stellar evolutionary tracks (Z = 0.00001) is constructed to compare the predicted lithium abundance depletion to observations of the lithium abundance in correspondingly metal-poor stars (Fe/H = -3.3), and, combined with an earlier work to investigate trends of lithium isochrones with metal abundance. Lithium abundances in the most extreme halo stars hint at the possibility of small downward slope toward lower T(eff) in the flat Li-T(eff) relation (the Spite lithium plateau) observed in slightly less extreme stars; the models also predict this. In the cool star region of the Li-T(eff) plane, higher metallicity lithium isochromes are cooler at fixed lithium abundance, consistent with the observations. Current data thus agree well with the lithium trends from standard model.

Deliyannis, Constantine P.↗
NASA NTRS1990

STARS - Supportability Trend Analysis and Reporting System for the National Space Transportation System

The concept, implementation, and long-range goals of a Supportability Trend Analysis and Reporting System (STARS) for the National Space Transportation System (NSTS) are discussed. The requirement was established as a direct result of the recommendations of the Rogers Commission investigation of the circumstances of the Space Shuttle Challenger accident. STARS outlines the requirements for the supportability-trend data collection, analysis, and reporting requirements that each of the project offices supporting the Space Shuttle are required to provide to the NSTS program office. STARS data give the historic and predictive logistics information necessary for all levels of NSTS management to make safe and cost-effective decisions concerning the smooth flow of Space Shuttle turnaround.

Graham, Leroy J.↗
NASA NTRS1991

Seasonal cycle and secular trend of the total and tropospheric column abundance of ethane above the Jungfraujoch

The secular trend and the seasonal cycle of the total and the tropospheric column abundances of C2H6 over the Jungfraujoch Station (Switzerland) were deduced from infrared solar spectra recorded in 1951 and from 1984 to 1988. Results show a definite seasonal variation in the total vertical column abundance of C2H6, with a maximum of (1.43 + or - 0.03) x 10 to the 16th molecules/sq cm during March and April and a minimum in the fall; the ratio between the maximum and the minimum column abundances was found to be 1.62 + or - 0.11. The secular trend in the tropospheric burden above the Jungfraujoch was found to be (0.85 + or - 0.3) percent/yr.

Ehhalt, D. H.↗
NASA NTRS1991

Preliminary assessment of possible aerosol contamination effects on SAGE ozone trends in the lower stratosphere

An investigation of the validity of long-term ozone trends in the lower stratosphere derived from SAGE I and II measurements is described. At altitudes below approximately 20 km, it is important to separate the ozone and aerosol contributions to SAGE extinction at 600 nm. The correlation between SAGE II measurements of ozone and aerosols indicates that most of the variability in these parameters is associated with physically induced variations resulting from quasi-horizontal motions of air parcels. The SAGE ozone measurements are however found to be as much as 20 percent larger than coincident ozonesonde measurements between 15 and 20 km altitude. A sudden change in the difference at approximately 14.5 km altitude for which there is a change in the SAGE aerosol retrieval procedure suggests that SAGE ozone trends below 20 km altitude may be more sensitive to aerosol variations. Between 20 and 25 km altitude, however, both SAGE and the ozonesondes indicate a reduction in ozone of approximately 0.5 percent/year over the period 1979 to 1989 at midlatitudes of the Northern Hemisphere.

Cunnold, Derek M.↗
NASA NTRS1989

Report of the International Ozone Trends Panel 1988, volume 1

Chapters on the following topics are presented: spacecraft instrument calibration and stability; information content of ozone retrieval algorithms; trends in total column ozone measurements; and trends in ozone profile measurement.

Source record↗
NASA NTRS1989

Trends in total column ozone measurements

It is important to ensure the best available data are used in any determination of possible trends in total ozone in order to have the most accurate estimates of any trends and the associated uncertainties. Accordingly, the existing total ozone records were examined in considerable detail. Once the best data set has been produced, the statistical analysis must examine the data for any effects that might indicate changes in the behavior of global total ozone. The changes at any individual measuring station could be local in nature, and herein, particular attention was paid to the seasonal and latitudinal variations of total ozone, because two dimensional photochemical models indicate that any changes in total ozone would be most pronounced at high latitudes during the winter months. The conclusions derived from this detailed examination of available total ozone can be split into two categories, one concerning the quality and the other the statistical analysis of the total ozone record.

Rowland, F. S.↗
NASA NTRS1989

Trends in source gases

Source gases are defined as those gases that, by their breakdown, introduce into the stratosphere halogen, hydrogen, and nitrogen compounds that are important in stratospheric ozone destruction. Given here is an update of the existing concentration time series for chlorocarbons, nitrous oxide, and methane. Also reviewed is information on halogen containing species and the use of these data for establishing trends. Also reviewed is evidence on trends in trace gases that influence tropospheric chemistry and thus the tropospheric lifetimes of source gases, such as carbon dioxide, carbon monoxide, or nitrogen oxides. Much of the information is given in tabular form.

Ehhalt, D. H.↗
NASA NTRS1992

Trends in aeropropulsion research and their impact on engineering education

This presentation is concerned with the trends in aeropropulsion both in the U.S. and abroad and the impact of these trends on the educational process in our universities. In this paper, we shall outline the new directions for research which may be of interest to educators in the aeropropulsion field. Awareness of new emphases, such as emission reductions, noise control, maneuverability, speed, etc., will have a great impact on engineering educators responsible for restructuring courses in propulsion. The information presented herein will also provide some background material for possible consideration in the future development of propulsion courses. In describing aeropropulsion, we are concerned primarily with air-breathing propulsion; however many observations apply equally as well to rocket engine systems. Aeropropulsion research needs are primarily motivated by technologies required for advanced vehicle systems and frequently driven by external requirements such as economic competitiveness, environmental concern and national security. In this presentation, vehicle based research is first described, followed by a discussion of discipline and multidiscipline research necessary to implement the vehicle-focused programs. The importance of collaboration in research and the training of future researchers concludes this presentation.

Povinelli, Louis A.↗
NASA NTRS1991

Recent trends in stratospheric total ozone - Implications of dynamical and El Chichon perturbations

The recently reprocessed Nimbus-7 TOMS total ozone data from 1979 to 1989 are analyzed to assess the global impact of the El Chichon volcanic eruption on stratospheric total ozone. An apparent decrease in total ozone of 5 to 6 percent is present during the winter of 1982-1983 following the eruption of El Chichon. A regression analysis of total ozone with the equatorial zonal wind at 30 mb indicates that response to the quasi-biennial oscillation can explain much of the observed ozone anomaly, and that the total ozone decrease which can be attributed to El Chichon is at most 2 to 4 percent. This study also suggests that the interannual variability caused by the quasi-biennial oscillation and planetary wave activity may introduce apparent seasonal trends in total ozone and temperature in the lower stratosphere, particularly if the length of the data record is not very long. Such trends may affect the assessment of total ozone changes caused by chemical perturbations.

Chandra, S.↗