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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Molecular beam simulation of planetary atmospheric entry: Some recent results

Molecular beam sources for producing fast beams containing CO2 and atomic oxygen are discussed. Results pertinent to the design and calibration of mass spectrometer ion source for measurement of the Martian atmosphere during the free molecule portion of the entry trajectory are also presented. The shortcomings and advantages of the simulation technique are discussed. It is shown that an open cavity configuration retains sensitivity to atomic oxygen, provides reasonable signal enhancement from the stagnation effect, is not highly sensitive to pitch and yaw effects, and presents no unforeseen problems in measuring CO2 or atomic oxygen. The simulation techniques used provide assistance in designing, developing, and (potentially) in testing and calibrating the required flight instrument.

French, J. B.↗
NASA NTRS2008

The ALI-ARMS Code for Modeling Atmospheric non-LTE Molecular Band Emissions: Current Status and Applications

The Accelerated Lambda Iteration (ALI) technique was developed in stellar astrophysics at the beginning of 1990s for solving the non-LTE radiative transfer problem in atomic lines and multiplets in stellar atmospheres. It was later successfully applied to modeling the non-LTE emissions and radiative cooling/heating in the vibrational-rotational bands of molecules in planetary atmospheres. Similar to the standard lambda iterations ALI operates with the matrices of minimal dimension. However, it provides higher convergence rate and stability due to removing from the iterating process the photons trapped in the optically thick line cores. In the current ALI-ARMS (ALI for Atmospheric Radiation and Molecular Spectra) code version additional acceleration of calculations is provided by utilizing the opacity distribution function (ODF) approach and "decoupling". The former allows replacing the band branches by single lines of special shape, whereas the latter treats non-linearity caused by strong near-resonant vibration-vibrational level coupling without additional linearizing the statistical equilibrium equations. Latest code application for the non-LTE diagnostics of the molecular band emissions of Earth's and Martian atmospheres as well as for the non-LTE IR cooling/heating calculations are discussed.

Kutepov, A. A.↗
NASA NTRSDate not supplied

The Search for New Molecular Species in the Atmosphere of Titan

The atmosphere of Saturn’s moon, Titan, contains a vast array of minor molecular constituents originating from the dissociation of its primary compounds, N2and CH4. The extent of Titan’s photochemical network was revealed by ionospheric measurements from the Cassini orbiter, leaving substantial gaps in the corresponding neutral inventory typically probed through infrared spectroscopy. Utilizing the unprecedented sensitivity and high spectral resolution of the Atacama Large Millimeter/submillimeter Array (ALMA) at longer wavelengths, we searched for additional trace gases in Titan’s atmosphere during 2016, 2017,and 2019to further characterize Titan’s atmospheric and surface composition. These observations have resulted in the spectroscopic detections of the small cyclic molecule, cyclopropenylidene (c-C3H2), and the largest nitrile to date, methyl cyanoacetylene (CH3C3N), for the first time in Titan’s atmosphere –or anywhere else in the Solar System. We employed radiative transfer models to determine the volume mixing ratio of both species in Titan’s middle and upper atmosphere (altitudes > 350 km)and constrained the total column densities for the incorporation into future photochemical models of Titan’s atmosphere. Discrepancies between these results and current models necessitates the need for dedicated laboratory and modeling studies regarding the production pathways for trace complex organics in Titan’s atmosphere. Additionally, the measurement of previously undetected molecular species provides further incentive for the study of planetary atmospheres in the (sub)millimeter regime with facilities such as ALMA.

A E Thelen↗
NASA NTRS1970

Visible region remote spectroscopy of polluted water

The use of an airborne spectrometer for measuring the amount of pollutants under the surface of a body of water is discussed. Difficulties created by high water absorption, atmospheric absorption, molecular scattering by water, and atmospheric scattering for the range of wavelengths from 0.2 to 20.0 microns are described. It was determined that some form of quantitative measurement of subsurface pollutants is possible using an airborne spectrometer.

White, P. G.↗
NASA NTRS1987

Molecular line parameters for the atmospheric trace molecule spectroscopy experiment

During its first mission in 1985 onboard Spacelab 3, the ATMOS (atmospheric trace molecule spectroscopy) instrument, a high speed Fourier transform spectrometer, produced a large number of high resolution infrared solar absorption spectra recorded in the occultation mode. The analysis and interpretation of these data in terms of composition, chemistry, and dynamics of the earth's upper atmosphere required good knowledge of the molecular line parameters for those species giving rise to the absorptions in the atmospheric spectra. This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results. With over 400,000 entries, the linelist catalogs parameters of 46 minor and trace species in the 1-10,000/cm region.

Brown, L. R.↗
NASA NTRS2020

Interpreting Exo-Planetary Atmospheres with the Next Generation Space-Based Telescope

We will soon have the technological capability to measure the atmospheric composition of temperate Earth-sized planets orbiting nearby stars. Interpreting these atmospheric signals poses a new challenge to planetary science. In contrast to jovian-like atmospheres, whose bulk compositions consist of hydrogen and helium, terrestrial planet atmospheres are likely comprised of high mean molecular weight secondary atmospheres, which have gone through a high degree of evolution. In order to understand the processes which affect a planetary atmosphere, I use early Mars as a case study. I leverage a combination of one-dimensional climate, photochemical and energy balance models in order to create one self-consistent model that closely matches currently available climate data. However, unlike in-situ observations from our own solar system, remote sensing techniques need to be developed and understood in order to accurately characterize exo-atmospheres. I describe the models used to create synthetic transit transmission observations, which includes models of transit spectroscopy and instrumental noise. Using these, I lay the framework for an information content-based approach to optimize our observations and maximize the retrievable information from exo-atmospheres. First I test the method on observing strategies of the well-studied, low-mean-molecular weight atmospheres of warm-Neptunes and hot Jupiters. Upon verifying the methodology, I finally address optimal observing strategies for temperate, high-mean-molecular weight atmospheres (Earths/super-Earths).

Batalha, Natasha↗
NASA NTRS1973

Mariner 9 ultraviolet spectrometer experiment - Morning terminator observations of Mars

Mariner 9 ultraviolet morning terminator data indicate the presence of a high, optically thin scattering layer in the equatorial region of Mars extending to 50S. This is consistent with the afternoon terminator results, which showed the presence of a scattering layer for latitudes as far north as 50N. For both types of terminator observations, the magnitude of the reflectivity for large shadow heights and the apparent scale height of the signal are too large to be explained by a homogeneous atmosphere. The terminator observations poleward of 50S were modeled by a homogeneous atmosphere of molecular and particulate scatterers. As the lower atmosphere began to clear from the dust storm, a progressive change was noted in the magnitude of the terminator reflectivity which is attributed to a changing albedo for single scattering. The shape of the morning terminator reflectivity measured as a function of shadow height indicates larger apparent scale heights than were observed in the afternoon. The difference is attributed to an increase in thickness of the scattering layer during the night.

Ajello, J. M.↗
NASA NTRS1973

On ultraviolet absorption by molecular hydrogen in stellar atmospheres.

The total LTE opacity expected for a variety of temperatures and pressures has been calculated for a mixture of solar composition. The absorption coefficient for the H2 singlet transition between 1300 and 2000 A was obtained from computations at 5000 K by Sando and Dalgarno (1971). It is found that a correct estimate of the resonance broadening in Lyman-alpha wings leads to important modifications of the UV opacity.

Praderie, F.↗
NASA NTRS1975

Formation of molecular lines in stellar atmospheres

Statistical equilibrium of electronic states of diatomic molecules in stellar atmospheres is examined. Atmospheres discussed are representative of the sun, Arcturus (K-giant) and Betelgeuse (M-supergiant). A comparison of the relative collisional and radiative contributions to the equilibrium of the ground electronic state shows that this state is collisionally controlled and that the line source function for vibration-rotation transitions within this state is equivalent to the Planck function. Examination of the equilibrium for excited electronic states demonstrates that the exchange between these states and the ground electronic state is most probably determined by radiative excitation. This result implies that scattering rather than pure absorption is the appropriate mechanism for the formation of lines belonging to these electronic transitions. The scattering hypothesis is given a preliminary check against solar observations. Areas for future investigations are outlined.

Hinkle, K. H.↗
NASA NTRS1976

Diurnal and seasonal variations in atomic and molecular oxygen inferred from Atmosphere Explorer-C

Mass-spectrometer measurements of O and N2, obtained with the Atmosphere Explorer-C satellite during December 1974 and January 1975, are used to derive the O2 concentration near 250 km from several ionization reactions. In order to separate temperature effects from diffusion effects, the measured O and inferred O2 concentrations are employed to determine, under the assumption of diffusive equilibrium, the O/N2 and O2/N2 ratios at 120 km. It is found that the latitudinal and diurnal variations in the O concentration at 120 km are consistent with previous results obtained with OGO 6 and that the O2 concentration in the Northern (winter) Hemisphere is about twice as high as that in the Southern (summer) Hemisphere. The possible importance of photodissociation in the diurnal O2 variations is discussed.

Mayr, H. G.↗
NASA NTRS2005

Ion Neutral Mass Spectrometer Measurements from Titan

Introduction: The Ion Neutral Mass Spectrometer (INMS) aboard the Cassini orbiter has obtained the first in situ composition measurements of the neutral densities of molecular nitrogen, methane, argon, and a host of stable carbon-nitrile compounds in its first flyby of Titan. The bulk composition and thermal structure of the moon s upper atmosphere do not appear to be changed since the Voyager flyby in 1979. However, the more sensitive techniques provided by modern in-situ mass spectrometry also give evidence for large-spatial-scale large-amplitude atmospheric waves in the upper atmosphere and for a plethora of stable carbon-nitrile compounds above 1174 km. Furthermore, they allow the first direct measurements of isotopes of nitrogen, carbon, and argon, which provide interesting clues about the evolution of the atmosphere. The atmosphere was first accreted as ammonia and ammonia ices from the Saturn sub-nebula. Subsequent photochemistry likely converted the atmosphere into molecular nitrogen. The early atmosphere was 1.5 to 5 times more substantial and was lost via escape over the intervening 4.5 billion years due to the reduced gravity associated with the relatively small mass of Titan. Carbon in the form of methane has continued to outgas over time from the interior with much of it being deposited in the form of complex hydrocarbons on the surface and some of it also being lost to space.

Waite, J. H., Jr.↗