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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Characterizing Young Giant Planets with the Gemini Planet Imager: An Iterative Approach to Planet Characterization

After discovery, the first task of exoplanet science is characterization. However experience has shown that the limited spectral range and resolution of most directly imaged exoplanet data requires an iterative approach to spectral modeling. Simple, brown dwarf-like models, must first be tested to ascertain if they are both adequate to reproduce the available data and consistent with additional constraints, including the age of the system and available limits on the planet's mass and luminosity, if any. When agreement is lacking, progressively more complex solutions must be considered, including non-solar composition, partial cloudiness, and disequilibrium chemistry. Such additional complexity must be balanced against an understanding of the limitations of the atmospheric models themselves. For example while great strides have been made in improving the opacities of important molecules, particularly NH3 and CH4, at high temperatures, much more work is needed to understand the opacity of atomic Na and K. The highly pressure broadened fundamental band of Na and K in the optical stretches into the near-infrared, strongly influencing the spectral shape of Y and J spectral bands. Discerning gravity and atmospheric composition is difficult, if not impossible, without both good atomic opacities as well as an excellent understanding of the relevant atmospheric chemistry. I will present examples of the iterative process of directly imaged exoplanet characterization as applied to both known and potentially newly discovered exoplanets with a focus on constraints provided by GPI spectra. If a new GPI planet is lacking, as a case study I will discuss HR 8799 c and d will explain why some solutions, such as spatially inhomogeneous cloudiness, introduce their own additional layers of complexity. If spectra of new planets from GPI are available I will explain the modeling process in the context of understanding these new worlds.

exoplanets↗
NASA NTRS2024

Analyses of the MISSE 9-15 Polymers and Composites Experiment 1-4 (PCE 1-4) Contamination Samples

Spacecraft in low Earth orbit (LEO) are subjected to harsh environmental conditions, including radiation (cosmic rays, ultraviolet (UV), x-ray and charged particle radiation), micrometeoroids and orbital debris, temperature extremes, thermal cycling, and atomic oxygen (AO). These environmental exposures can result in erosion, embrittlement and optical property degradation of susceptible materials threatening spacecraft performance and durability. To increase our understanding of environmental effects such as AO erosion and radiation induced embrittlement of spacecraft materials, NASA Glenn Research Center developed a series of experiments that were flown as part of the Materials International Space Station Experiment (MISSE) missions on the exterior of the International Space Station (ISS). Recently, four Glenn experiments with 365 flight samples were flown on ISS’s MISSE-Flight Facility (MISSE-FF). These experiments are the Polymers and Composites Experiment-1 (PCE-1) flown as part of the MISSE-9 mission, the PCE-2 flown as part of the MISSE-10 mission, the PCE-3 flown as part of the MISSE-12 and MISSE-15 missions, and the PCE-4 flown as part of the MISSE-13 mission. Each of these experiments included passive contamination witness samples in each flight direction for post-flight molecular contamination analyses. A total of 13 contamination flight samples were flown. The post-flight analyses of the PCE 1-4 contamination samples include X-ray Photoelectron Spectroscopy (XPS) analyses (surface and ion sputter depth analyses) and optical properties (total reflectance, total transmittance and solar absorptance). This paper provides results of post-flight analyses of the PCE 1-4 contamination samples and their corresponding control samples. Knowledge of on-orbit contamination is important for the PCE 1-4 flight data interpretation.

Atomic Oxygen↗
NASA NTRS1978

Metastable oxygen emission bands

Recombination of ground-state oxygen atoms populates six different bound electronic states of molecular oxygen. Of the six optical transitions expected between the three upper states at 4 to 4.5 electron volts and the two lowest states, five have been observed in the afterglow of a conventional helium-oxygen microwave discharge in both (O-16)2 and (O-18)2, three of them for the first time in gas-phase spectra. Generation of these emissions from oxygen atoms in a system free of molecular oxygen establishes that atom recombination is the production mechanism.

Slanger, T. G.↗
NASA NTRS2006

Optical Coatings and Surfaces in Space: MISSE

The space environment presents some unique problems for optics. Components must be designed to survive variations in temperature, exposure to ultraviolet, particle radiation, atomic oxygen and contamination from the immediate environment. To determine the importance of these phenomena, a series of passive exposure experiments have been conducted which included, among others, the Long Duration Exposure Facility (LDEF, 1985- 1990), the Passive Optical Sample Assembly (POSA, 1996- 1997) and most recently, the Materials on the International Space Station Experiment (MISSE, 2001 - 2005). The MISSE program benefited greatly from past experience so that at the conclusion of this 4 year mission, samples which remained intact were in remarkable condition. This study will review data from different aspects of this experiment with emphasis on optical properties and performance.

Stewart, Alan F.↗
NASA NTRS2023

Advancing Solar and Heliospheric Science Through the Ongoing Development and Support of Atomic and Laboratory Plasma Physics

This paper outlines the necessity for the availability, accessibility, and expansion of atomic physics data and analysis tools for the meaningful interpretation of spectroscopic and polarimetric observations. As we move towards observing the Sun at higher spatio-temporal resolutions, and near-continuously at a range of wavelengths, it becomes critical to develop the appropriate atomic data and physics tools to facilitate scientific progress. We recommend the continued improvement and expansion of current databases to support the development of optically-thick/radiative transfer models, evaluate non-thermal and non-equilibrium ionization effects, and quantify uncertainties in atomic and molecular values. A critical longterm goal will require extending and strengthening collaborations across the atomic, solar/heliospheric, and laboratory plasma physics communities through the participation and training of early career scientists. We also recommend establishing funding for a centralized atomic physics resource made up of a comprehensive and user-oriented atomic database and modeling framework.

Y J Rivera↗
NASA NTRS1986

Partial analysis of experiment LDEF A-0114

Due to delays in manifesting the return of the Long Duration Exposure Facility from space, attention was concentrated on extracting the maximum information from the EIOM-2 (oxygen interaction with materials experiment) flown on STS-8 in September 1983. An analysis was made of the optical surfaces exposed during that flight and an assessment made of the effect of the 5 eV atomic oxygen upon their physical and chemical properties. The surfaces studied were of two types: high-purity thin films sputtered or evaporated onto 2.54-cm diam lambda/20 fused silica optical flats, and highly polished bulk samples. Rapid etching of carbon and carbonaceous surfaces was observed with polycarbonate CR-39 showing the largest etch of any substrate flown and measured. Of the metals tested, only osmium and silver showed large effects, the former being heavily etched and the later forming a very thick layer of oxide. The first measurable effects on iridium, aluminum, nickel, tungsten and niobium thin films are reported.

Gregory, J. C.↗
NASA NTRS2003

Stabilized Fiber-Optic Distribution of Reference Frequency

An optoelectronic system distributes a reference signal of low noise and highly stabilized phase and frequency (100 MHz) from an atomic frequency standard to a remote facility at a distance up to tens of kilometers. The reference signal is transmitted to the remote station as amplitude modulation of an optical carrier signal propagating in an optical fiber. The stabilization scheme implemented in this system is intended particularly to suppress phase and frequency fluctuations caused by vibrations and by expansion and contraction of the optical fiber and other components in diurnal and seasonal heating and cooling cycles. The system (see figure) comprises several subsystems, the main one being (1) a hydrogen-maser or linear-ion-trap frequency standard in an environmentally controlled room in a signal-processing center (SPC), (2) a stabilized fiber-optic distribution assembly (SFODA), (3) a compensated sapphire oscillator (CSO) in an environmentally controlled room in the remote facility, (4) thermally stabilized distribution amplifiers and cabling from the environmentally controlled room to end users, and (5) performance- measuring equipment.

Calhoun, Malcolm↗
NASA NTRS1981

The X-ray spectrum of a hot interstellar plasma

The soft X-ray spectrum of a hot, low density, optically thin plasma in collisional ionization equilibrium is calculated using current atomic data. Many Fe collision strengths differ from previous calculations. The spectra from individual elements are presented for use in abundance determinations from X-ray observations. Collision strengths and line energies, sorted both according to energy and according to ion, are tabulated.

Shull, J. M.↗
NASA NTRS1994

Discovery of the double Doppler-shifted emission-line systems in the X-ray spectrum of SS 433

We have used the CCD X-ray spectrometers on ASCA and resolved the X-ray emission line from the jet of SS 433 both into Doppler-shifted components with two distinct velocities, and into emission from different ionization states of iron, i.e., Fe XXV and Fe XXVI. This is the first direct detection of the two Doppler shifted beams in the X-ray spectra of SS 433 and allows the radial velocity of the jet along the line of sight to be determined with an accuracy comparable to the optical spectroscopy. We also found pairs of emission lines from other atomic species, such as ionized silicon and sulfur, with the Doppler shifts consistent with each other. This confirms the origin of the X-ray emission in the high temperature plasma in the jets.

Kotani, Taro↗
NASA NTRS1996

Spectroscopic Diagnostics and an Arc Jet Heated Air Plasma

Spectral radiation measurements were made in the range of 200 to 900 nm across a section of the plenum of an arc jet wind tunnel using a series of optical fibers. The spectra contained line radiation from Oxygen and Nitrogen atoms and molecular radiation from N2(+), N2, and NO. Abel inversion technique is used to obtain radial distribution of the spectra. The analysis yielded radial profiles of the electronic excitation, vibrational and rotational temperatures of the flow field. Spectral fitting yielded branching ratios for different vibrational and rotational bands. Relatively mild flow conditions, i.e. enthalpy and mass flow rate, were used for prolonged measurements of up to and over two hours to establish the best experimental methods of temperature determinations. Signal to noise was improved by at least an order of magnitude enabling the molecular vibrational band heads of N2(+) (first negative system), N2 (second positive system), and NO (beta, gamma, delta, and epsilon systems) to be resolved in the lower ultraviolet wavelength regions. The increased signal to noise ratio also enabled partial resolution of the rotational lines of N2(+) and N2 in certain regions of minimal overlap. Comparison of the spectra with theoretical models such as the NEQAIR2 code are presented and show potential for fitting the spectra when reliable calibration is performed for the complete wavelength range.

Mack, Larry Howard, Jr.↗
NASA NTRS2002

Techniques for Measuring Low Earth Orbital Atomic Oxygen Erosion of Polymers

Polymers such as polyimide Kapton and Teflon FEP (fluorinated ethylene propylene) are commonly used spacecraft materials due to their desirable properties such as flexibility, low density, and in the case of FEP, a low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low Earth orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen reaction with polymers causes erosion, which is a threat to spacecraft durability. It is therefore important to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. The most common technique for determining E is through mass loss measurements. For limited duration exposure experiments, such as shuttle experiments, where the atomic oxygen fluence is often so low that mass loss measurements can not produce acceptable uncertainties, recession measurements based on atomic force microscopy analyses can be used. Equally necessary to knowing the mass loss or recession depth for determining the erosion yield of polymers is the knowledge of the atomic oxygen fluence that the polymers were exposed to in space. This paper discusses the procedures and relevant issues for mass loss and recession depth measurements for passive atomic oxygen erosion yield characterization of polymers, along with techniques for active atomic oxygen fluence and erosion characterization. One active atomic oxygen erosion technique discussed is a new technique based on optical measurements. Details including the use of both semi-transparent and opaque polymers for active erosion measurement are reviewed.

deGroh, Kim K.↗
NASA NTRSDate not supplied

Flame Structure Comparison using Jet-A and an isoparaffinic fuel in a lean direct injection flame tube combustor

This paper offers a first look at some recently acquired optical data. The effect of reference velocity on flame thickness, fuel atomization, and relative speciation of OH, CH, C2, and soot for two National Jet Fuel Combustion Program (NJFCP) fuels are explored in this paper. The NJFCP fuels are an average Jet-A, designated A-2 with a derived cetane number (DCN) of 49, and an isoparaffinic kerosene, C-4. C-4 fuel is made up primarily of C9 - C13, and C16 isoparaffins and is a combination of 60% Sasol IPK and 40% GEVO alcohol-to-jet (ATJ). C-4 has a DCN of 28. Both fuels begin distillation at about the same temperature, but C-4 completes about 30 degrees Celsius lower than A-2. Chemiluminescence images were acquired in a 5-atm gas turbine flame tube combustor using the NASA 7-point lean direct injector (LDI). The flame characteristics were determined through imaging with three scientific cameras. OH*, CH*, and C2* chemiluminescence were collected through narrow bandpass filters centered at 313nm, 430nm and 515nm onto an intensified high-speed camera framed at 8-kHz. A second high-speed camera collected color flame images at rates between 40 and 50 kHz. An ICCD camera framed at 20 Hz was used to record planar laser scatter from liquid fuel. Differences in speciation for the chemiluminescent species was observed between the two fuels. Some reasons for the differences are explored in this paper.

gas turbine combustion↗
NASA NTRS2005

Magnetometer Based on Optoelectronic Microwave Oscillator

proposed instrument, intended mainly for use as a magnetometer, would include an optoelectronic oscillator (OEO) stabilized by an atomic cell that could play the role of a magnetically tunable microwave filter. The microwave frequency would vary with the magnetic field in the cell, thereby providing an indication of the magnetic field. The proposed magnetometer would offer a combination of high accuracy and high sensitivity, characterized by flux densities of less than a picotesla. In comparison with prior magnetometers, the proposed magnetometer could, in principle, be constructed as a compact, lightweight instrument: It could fit into a package of about 10 by 10 by 10 cm and would have a mass <0.5 kg. As described in several prior NASA Tech Briefs articles, an OEO is a hybrid of photonic and electronic components that generates highly spectrally pure microwave radiation, and optical radiation modulated by the microwave radiation, through direct conversion between laser light and microwave radiation in an optoelectronic feedback loop. As used here, "atomic cell" signifies a cell containing a vapor, the constituent atoms of which can be made to undergo transitions between quantum states, denoted hyperfine levels, when excited by light in a suitable wavelength range. The laser light must be in this range. The energy difference between the hyperfine levels defines the microwave frequency. In the proposed instrument (see figure), light from a laser would be introduced into an electro-optical modulator (EOM). Amplitude-modulated light from the exit port of the EOM would pass through a fiber-optic splitter having two output branches. The light in one branch would be sent through an atomic cell to a photodiode. The light in the other branch would constitute the microwave-modulated optical output. Part of the light leaving the atomic cell could also be used to stabilize the laser at a frequency in the vicinity of the desired hyperfine or other quantum transition. The microwave signal from the output of the photodiode would be amplified (if necessary, as explained below) and fed back into the EOM. This system would oscillate if the amplification in the closed loop exceeded the linear absorption of the loop. The microwave amplifier may be unnecessary to sustain stable oscillations, depending on the power of the laser radiation at the photodetector and on particular features of the modulator and optical delay line.

Maleki, Lute↗
NASA NTRS1992

Optical luminescence spectroscopy as a probe of the surface mineralogy of Mars

Optical luminescence (OpL) spectroscopy is an attractive use of a visible-near-IR spectrometer on a Mars lander because mineral products of atmosphere-surface interactions on Mars will probably have characteristic OpL spectra. Optical luminescence spectra would be taken at night, when a spectrometer might otherwise sit idle. Also needed would be a source of exciting radiation, which could be shared with other experiments. Optical luminescence is emission of nonthermal optical photons (near-UV through near-IR) as a response to energy input. On absorption of energy, an atom (or ion) will enter an excited state. The favored decay of many such excited states involving valence-band electrons is emission of an optical photon. Optical luminescence spectra can be useful in determining mineralogy and mineral composition. Optical luminescence in crystals can arise from essential elements (or ions), trace-element substituents (activators), or defects. Common activators in salts of alkali and alkaline earth elements include Mn(2+)(VI), other transition metals, the rare earths, and the actinides. Trace substituents of other species can enhance or quench OpL (e.g., Pb(2+) vs. Fe(3+)). Optical luminescence can also arise from defects in crystal structures, including those caused by radiation and shock.

Treiman, A. H.↗
NASA NTRS2003

A New Fitting Procedure for the Blended He I 1083 nm Multiplet

The He I 1083 nm multiplet is a powerful tool for observing the outer solar atmosphere but is difficult to analyze because the lines are weak, highly variable, and spectrally blended, both internally and with other neighboring solar and telluric lines. After separation from nearby spectral features, two components of the He I multiplet are resolved. Fitting these lines with two unconstrained Gaussian profiles always gives a ratio of major to minor component of less than half the value which would be expected for optically thin lines. One possibility for explaining the discrepancy between the weakness of the lines and the ratio of the spectral components is to assume that the line formation regions are concentrated in laterally unresolved, optically thick structures with small filling factor. However, we present here a least-squares fitting technique using cubic splines with fixed breakpoints with the constraint that the blend is the sum of three identically shaped profiles shifted in wavelength according to the atomic structure of the blend and weighted by the corresponding statistics weights, in agreement with optically thin line formation. The basis functions for the fitting procedure have no built-in spectral symmetry or shape. The resulting underlying profiles tend to be asymmetric with excess absorption to the blue, consistent with formation by "hot" and "cool" spatial elements within the observed volume, with the hotter regions having differential motion toward the observer. The results agree well with NASA/XSO Spectromagnetograph observations in quiet sun and coronal holes. Partial funding of this research was provided through the NASA Sun-Earth Connection SR&T program.

Jones, H. P.↗
NASA NTRS2018

Materials International Space Station Experiment-9 (MISSE-9) Polymers and Composites Experiment

Spacecraft in low Earth orbit (LEO) are subjected to harsh environmental conditions, including radiation (cosmic rays, ultraviolet, x-ray, and charged particle radiation), micrometeoroids and orbital debris, temperature extremes, thermal cycling, and atomic oxygen (AO). These environmental exposures can result in erosion, embrittlement and optical property degradation, threatening spacecraft performance and durability. To increase our understanding of effects such as AO erosion and radiation induced embrittlement of spacecraft materials, NASA Glenn has developed a series of experiments flown as part of the Materials International Space Station Experiment (MISSE) missions on the exterior of the International Space Station (ISS). These experiments have provided critical LEO space environment durability data such as AO erosion data for many materials and mechanical properties changes after long term space exposure. In continuing these studies, a new experiment called the Polymers and Composites Experiment has been selected for flight on the MISSE-Flight Facility (MISSE-FF). The Polymers and Composites Experiment will be flown as part of the MISSE-9 mission, the inaugural mission of MISSE-FF manifested on SpaceX-14. This experiment includes 138 samples being flown in ram, wake or zenith orientations for space environmental durability assessment. The primary objective is to determine the LEO AO erosion yield, Ey (the volume loss per incident oxygen atom (cm3/atom)), of polymers, composites, and coated samples, as a function of solar irradiation and AO fluence. In addition, epoxy samples with varying levels of ZnO powder are included to study the effect of filler quantity on AO erosion. An AO Scattering Chamber is included to help improve the understanding of AO scattering mechanisms for improved AO undercutting modeling. Indium tin oxide (ITO) coated samples are included to validate the durability of ITO conductive coatings in LEO. Tensile samples of Teflon fluorinated ethylene propylene (FEP) of varying thicknesses and back-surface coatings will be flown in wake and zenith orientations to study radiation embrittlement versus thickness, and the effect of heating on FEP embrittlement. Finally, shape memory composite and cosmic ray shielding samples will be flown for LEO durability assessment. This paper presents an overview of the MISSE-9 Polymers and Composites Experiment.

Embrittlement↗
NASA NTRS1992

Atomic oxygen effects on thermal control and mirror coatings: Evaluation of experiment A0034

Evaluation of the degradation attributed to contamination of the collector mirrors in Experiment A0034, which were exposed to an earth orbital environment while on the leading and trailing edges of the LDEF, has provided some evidence for outgassing of coatings stimulated by atomic oxygen. Effects of the natural space environment on the coatings and mirrors, including the effects of incident and re-directed atomic oxygen flux, were investigated. The effects of exposure on the coatings and mirrors were evaluated by optical, surface profiling, chemical, and scanning electron microscopy (SEM) measurements. Preliminary results of these analyses are discussed for application to both the issues of mirror and coating stability and the specific issue of atomic oxygen stimulated outgassing.

Linton, Roger C.↗
NASA NTRS1977

Measurement of the Specific Refractivities of CF4 and C2F6

In order to relate the measured fringe shift of an interferometer to density, the relation between density rho and refractive index n must be known. For gases where the refractive index is close to unity, this relation between density and refractive index is very closely approximated by (n - 1) = K rho where K is the specific refractivity, or the Gladstone-Dale constant. The specific refractivity, which is weakly dependent on wavelength and temperature, is readily available for a number of common test gases such as N2 and air. For more unique test gases such as CF4 and C2F6 for which refractive index data at optical wavelengths is not readily available, the constants can be estimated from the atomic refractivities of carbon and fluorine. In order to verify this estimation, a two-beam interferometer was used to experimentally determine the specific refractivities of CF4 and C2F6. This data was required for holographic interferometric measurements made at the Langley Hypersonic CF4 Tunnel. A Twyman-Green interferometer with a He-Ne laser light source of vacuum wavelength lambda equal to 633 nm was used to measure the constants. One beam of the two-beam interferometer passed through an optical cell of known inside length l which could be evacuated and slowly filled with the test gas to a density of 7.2 kg/cu m for CF4 or 5.7 kg/cu m for C2F6. If the refractive index (and hence density) is constant along the optical path through the cell, the fringe shift M and density change Delta rho are related M = 2Kl Delta rho/lambda for the double pass interferometer. Thus K can be determined by measuring the fringe shift as the density is changed. The output of a photodiode used to detect the fringe shift was recorded on a strip chart recorder. The rate of pressure increase of the test gas in the cell was controlled such that the fringes shifted at a rate of 0.5 to 1 fringe per sec. The pressure in the test cell was measured with a high accuracy quartz crystal pressure transducer and recorded approximately every 20 fringe peaks. The temperature of the cell was measured with a thermocouple and recorded at the start, midpoint, and end of each test.

Burner, A. W.↗