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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

The Effect of Approximating Some Molecular Integrals in Coupled-Cluster Calculations: Fundamental Frequencies and Rovibrational Spectroscopic Constants of Cyclopropenylidene

The singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations, denoted CCSD(T), has been used, in conjunction with approximate integral techniques, to compute highly accurate rovibrational spectroscopic constants of cyclopropenylidene, C3H2. The approximate integral technique was proposed in 1994 by Rendell and Lee in order to avoid disk storage and input/output bottlenecks, and today it will also significantly aid in the development of algorithms for distributed memory, massively parallel computer architectures. It is shown in this study that use of approximate integrals does not impact the accuracy of CCSD(T) calculations. In addition, the most accurate spectroscopic data yet for C3H2 is presented based on a CCSD(T)/cc-pVQZ quartic force field that is modified to include the effects of core-valence electron correlation. Cyclopropenylidene is of great astronomical and astrobiological interest because it is the smallest aromatic ringed compound to be positively identified in the interstellar medium, and is thus involved in the prebiotic processing of carbon and hydrogen. The singles and doubles coupled-cluster method that includes a perturbational estimate of

Lee, Timothy J.↗
NASA NTRS2001

Single-Crystal Elastic Constants of Yttria (Y2O3) Measured to High Temperatures

Yttria, or yttrium sesquioxide (Y2O3), has been considered for use in nuclear applications and has gained interest relatively recently for use in infrared optics. Single crystals of yttria have been grown successfully at the NASA Glenn Research Center using a laser-heated float zone technique in a fiber and rod. Such samples allow measurement of the single-crystal elastic properties, and these measurements provide useful property data for the design of components using single crystals. They also yield information as to what degree the elastic properties of yttria ceramics are a result of the intrinsic properties of the yttria crystal in comparison to characteristics that may depend on processing, such as microstructure and intergranular phases, which are common in sintered yttria. The single-crystal elastic moduli are valuable for designing such optical components. In particular, the temperature derivatives of elastic moduli allow the dimensional changes due to heating under physical constraints, as well as acoustic excitation, to be determined. The single-crystal elastic moduli of yttria were measured by Brillouin spectroscopy up to 1200 C. The room-temperature values obtained were C(sub 11) = 223.6 + 0.6 GPa, C(sub 44) = 74.6 + 0.5 GPa, and C(sub 12) = 112.4 + 1.0 GPa. The resulting bulk and (Voigt-Reuss-Hill) shear moduli were K = 149.5 + 1.0 GPa and G(sub VRH) = 66.3 + 0.8 GPa, respectively. Linear least-squares regressions to the variation of bulk and shear moduli with temperature resulted in derivatives of dK/dT = -17 + 2 MPa/C and dG(sub VRH)/dT = -8 + 2 MPa/ C. Elastic anisotropy was found to remain essentially constant over the temperature range studied.

Sayir, Ali↗
NASA NTRS2005

Application of a Constant Gain Extended Kalman Filter for In-Flight Estimation of Aircraft Engine Performance Parameters

An approach based on the Constant Gain Extended Kalman Filter (CGEKF) technique is investigated for the in-flight estimation of non-measurable performance parameters of aircraft engines. Performance parameters, such as thrust and stall margins, provide crucial information for operating an aircraft engine in a safe and efficient manner, but they cannot be directly measured during flight. A technique to accurately estimate these parameters is, therefore, essential for further enhancement of engine operation. In this paper, a CGEKF is developed by combining an on-board engine model and a single Kalman gain matrix. In order to make the on-board engine model adaptive to the real engine s performance variations due to degradation or anomalies, the CGEKF is designed with the ability to adjust its performance through the adjustment of artificial parameters called tuning parameters. With this design approach, the CGEKF can maintain accurate estimation performance when it is applied to aircraft engines at offnominal conditions. The performance of the CGEKF is evaluated in a simulation environment using numerous component degradation and fault scenarios at multiple operating conditions.

Kobayashi, Takahisa↗
NASA NTRS2006

New Optical Constants for Amorphous and Crystalline H2O-ice and H2O-mixtures.

We will present the products of new laboratory measurements of ices relevant to Trans-Neptunian Objects. We have calculated the real and imaginary indices of refraction for amorphous and crystalline H2O-ice and also H2O-rich ices containing other molecular species. We create ice samples by condensing gases onto a cold substrate. We measure the thickness of the sample by reflecting a He-Ne laser off of the sample and counting interference fringes as it grows. We then collect transmission spectra of the samples in the wavelength range from 0.7-22 micrometers. Using the thickness and the transmission spectra of the ice we calculate the imaginary part of the index of refraction. We then use a Kramers-Kronig calculation to calculate the real part of the index of refraction (Berland et al. 1994; Hudgins et al. 1993). These optical constants can then be used to create model spectra for comparison to spectra from Solar System objects, including TNOs. We will summarize the difference between the amorphous and crystalline H2O-ice spectra. These changes include weakening of features and shifting of features to shorter wavelength. One important result is that the 2 pm feature is stronger in amorphous H2O ice than it is in crystalline H2O-ice. We will also discuss the changes seen when H2O is mixed with other components, including CO2, CH4, HCN, and NH3 (Bernstein et al. 2005; Bernstein et al. 2006).

Mastrapa, Rachel↗
NASA NTRS1995

New Tests for Variations of the Fine Structure Constant

We describe a new test for possible variations of the fine structure constant, by comparisons of rates between clocks based on hyperfine transitions in alkali atomos with different atomic number Z. H- maser, Cs and Hg+ clocks have a different dependence on ia relativistic contributions of order (Z. Recent H-maser vs Hg+ clock comparison data improves laboratory limits on a time variation by 100-fold to giveFuture laser cooled clocks (Be+, Rb, Cs, Hg+, etc.), when compared, will yield the most senstive of all tests for.

Fine Structure↗
NASA NTRS2006

New Optical Constants for Amorphous and Crystalline H2O-ice

We have used the infrared spectra of laboratory ices to calculate the real and imaginary indices of refraction for amorphous and crystalline H2O-ice. We create H2O-ice samples in vacuum (approx. 10(exp ^-8)Torr). We measure the thickness of the sample by reflecting a He-Ne laser off of the sample and counting interference fringes as it grows and then collect transmission spectra of the samples in the wavelength range 1.25-22 micrometers. Using the ice thickness and transmission spectrum we calculate the imaginary part of the index of refraction. A Kramers-Kronig calculation is then used to calculate the real part of the index of refraction (Berland et al. 1994; Hudgins et al. 1993). These optical constants can be used to create model spectra for comparison to spectra from Solar System objects. We will summarize the differences between the amorphous and crystalline H2O-ice spectra. These include weakening of features and shifting of features to shorter wavelength in amorphous H,O-ice spectra. We will also discuss methods of using band area ratios to quickly estimate the fraction of amorphous to crystalline H2O-ice. We acknowledge financial support from the NASA Origins of the Solar System Program, the NASA Planetary Geology and Geophysics Program, and the NASA Postdoctoral Program.

Mastrapa, Rachel↗
NASA NTRS1990

Ballast system for maintaining constant pressure in a glove box

A ballast system for a glove box including a fixed platform on which is mounted an inflatable bag on top of which resides a cover and a weight. The variable gas volume of the inflatable bag communicates with that of the glove box via a valved tube. The weight and gas volume are selected to maintain a relatively constant pressure in the glove box despite variations in the glove box volume while avoiding the use of complicated valving apparatus.

Shlichta, Paul J.↗
NASA NTRS2007

Accurate L-Band Measurements of the Dielectric Constant of Seawater

A new temperature controlled microwave cavity system to measure the complex dielectric constant of seawater at 1.413 GHz is discussed. The system is being developed to measure seawater for temperatures from O C to 30 C and salinities from 10 to 40 psu, The paper discusses the construction of the measurement system and initial stability tests.

Lang, R.H.↗
NASA NTRS2008

Automated Method for Estimating Nutation Time Constant Model Parameters for Spacecraft Spinning on Axis

Calculating an accurate nutation time constant (NTC), or nutation rate of growth, for a spinning upper stage is important for ensuring mission success. Spacecraft nutation, or wobble, is caused by energy dissipation anywhere in the system. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and, if it is in a state of resonance, the NTC can become short enough to violate mission constraints. The Spinning Slosh Test Rig (SSTR) is a forced-motion spin table where fluid dynamic effects in full-scale fuel tanks can be tested in order to obtain key parameters used to calculate the NTC. We accomplish this by independently varying nutation frequency versus the spin rate and measuring force and torque responses on the tank. This method was used to predict parameters for the Genesis, Contour, and Stereo missions, whose tanks were mounted outboard from the spin axis. These parameters are incorporated into a mathematical model that uses mechanical analogs, such as pendulums and rotors, to simulate the force and torque resonances associated with fluid slosh.

Source record↗
NASA NTRS2008

New Optical Constants of Amorphous and Crystalline H2O-ice, 3-20_m

We will present new optical constants forth amorphous and crystalline H2O-ice in the spectral range 3-20 _m. Our new measurements provide high temperature resolution for crystalline H2O-ice, 10 K intervals from 20-150 K, including temperatures relevant to Solar System ices. We have found that the shape of the 3 _m feature in amorphous H2O-ice is strongly dependant on deposition temperature and the high and low density phases of amorphous H2O-ice are not easily distinguishable. We will present methods of measuring the change in band shape with phase and temperature. We acknowledge financial support from the NASA Origins of the Solar System Program and the NASA Planetary Geology and Geophysics Program.

Mastrapa, Rachel Michelle Elizab↗
NASA NTRS2010

Origin of the Central Constant Emission Component of Eta Carinae

The X-ray campaign observation of the wind-wind colliding (WWC) binary system, Eta Carinae, targeted at its periastron passage in 2003, presented a detailed view of the flux and spectral variations of the X-ray minimum phase. One of the discoveries in this campaign was a central constant emission (CCE) component very near the central WWC source (Hamaguchi et al. 2007, ApJ, 663, 522). The CCE component was noticed between 1-3 keY during the X-ray minima and showed no variation on either short timescales within any observation or long timescales of up to ~ 10 years. Hamaguchi et al. (2007) discussed possible origins as collisionally heated shocks from the fast polar winds from Eta Car or the fast moving outflow from the WWC with the ambient gas, or shocked gas that is intrinsic to the wind of Eta Car. During the 2009 periastron passage, we launched another focussed observing campaign of Eta Carinae with the Chandra, XMM-Newton and Suzaku observatories, concentrating on the X-ray faintest phase named the deep X-ray minimum. Thanks to multiple observations during the deep X-ray minimum, we found that the CCE spectrum extended up to 10 keV, indicating presence of hot plasma of kT approx.4-6 keV. This result excludes two possible origins that assume relatively slow winds (v approx. 1000 km/s) and only leaves the possibility that the CCE plasma is wind blown bubble at the WWC downstream. The CCE spectrum in 2009 showed a factor of 2 higher soft band flux as the CCE spectrum in 2003, while the hard band flux was almost unchanged. This variation suggests decrease in absorption column along the line of sight. We compare this result with recent increase in V-band magnitude of Eta Carinae and discuss location of the CCE plasma.

Hamaguchi, Kenji↗
NASA NTRS2010

Empirical Method to Estimate Hydrogen Embrittlement of Metals as a Function of Hydrogen Gas Pressure at Constant Temperature

High pressure Hydrogen (H) gas has been known to have a deleterious effect on the mechanical properties of certain metals, particularly, the notched tensile strength, fracture toughness and ductility. The ratio of these properties in Hydrogen as compared to Helium or Air is called the Hydrogen Environment Embrittlement (HEE) Index, which is a useful method to classify the severity of H embrittlement and to aid in the material screening and selection for safety usage H gas environment. A comprehensive world-wide database compilation, in the past 50 years, has shown that the HEE index is mostly collected at two conveniently high H pressure points of 5 ksi and 10 ksi near room temperature. Since H embrittlement is directly related to pressure, the lack of HEE index at other pressure points has posed a technical problem for the designers to select appropriate materials at a specific H pressure for various applications in aerospace, alternate and renewable energy sectors for an emerging hydrogen economy. Based on the Power-Law mathematical relationship, an empirical method to accurately predict the HEE index, as a function of H pressure at constant temperature, is presented with a brief review on Sievert's law for gas-metal absorption.

Lee, Jonathan A.↗
NASA NTRS2008

Estimation of Nutation Time Constant Model Parameters for On-Axis Spinning Spacecraft

Calculating an accurate nutation time constant for a spinning spacecraft is an important step for ensuring mission success. Spacecraft nutation is caused by energy dissipation about the spin axis. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and can be simulated using a forced motion spin table. Mechanical analogs, such as pendulums and rotors, are typically used to simulate propellant slosh. A strong desire exists for an automated method to determine these analog parameters. The method presented accomplishes this task by using a MATLAB Simulink/SimMechanics based simulation that utilizes the Parameter Estimation Tool.

Schlee, Keith↗
NASA NTRS2014

Vibrational Frequencies and Spectroscopic Constants for 1(sup 3)A' HNC and 1(sup 3)A' HOC+ from High-Accuracy Quartic Force Fields

The spectroscopic constants and vibrational frequencies for the 1(sup 3)A' states of HNC, DNC, HOC+, and DOC+ are computed and discussed in this work. The reliable CcCR quartic force field based on high-level coupled cluster ab initio quantum chemical computations is exclusively utilized to provide the anharmonic potential. Then, second order vibrational perturbation theory and vibrational configuration interaction methods are employed to treat the nuclear Schroedinger equation. Second-order perturbation theory is also employed to provide spectroscopic data for all molecules examined. The relationship between these molecules and the corresponding 1(sup 3)A' HCN and HCO+ isomers is further developed here. These data are applicable to laboratory studies involving formation of HNC and HOC+ as well as astronomical observations of chemically active astrophysical environments.

Astrochemistry↗
NASA NTRS2015

Environmental Effects on Long Term Displacement Data of Woven Fabric Webbings Under Constant Load for Inflatable Structures

An experimental study of the effects of environmental temperature and humidity conditions on long-term creep displacement data of high strength Kevlar and VectranTM woven fabric webbings under constant load for inflatable structures is presented. The restraint layer of an inflatable structure for long-duration space exploration missions is designed to bear load and consists of an assembly of high strength webbings. Long-term creep displacement data of webbings can be utilized by designers to validate service life parameters of restraint layers of inflatable structures. Five groups of high-strength webbings were researched over a two year period. Each group had a unique webbing length, load rating, applied load, and test period. The five groups consisted of 1.) 6K Vectran webbings loaded to 49% ultimate tensile strength (UTS), 2.) 6K Vectran webbings loaded to 55% UTS, 3.) 12.5K Vectran webbings loaded to 22% UTS, 4.) 6K Kevlar webbings loaded to 40% and 43% UTS, and 5.) 6K Kevlar webbings loaded to 48% UTS. Results show that all webbing groups exhibit the initial two stages of three of a typical creep curve of an elastic material. Results also show that webbings exhibit unique local wave patterns over the duration of the test period. Data indicate that the local pattern is primarily generated by daily variations in relative humidity values within the test facility. Data indicate that after a three to six month period, where webbings reach a steady-state creep condition, an annual sinusoidal displacement pattern is exhibited, primarily due to variations in annual mean temperature values. Data indicates that variations in daily temperature values and annual mean humidity values have limited secondary effects on creep displacement behavior. Results show that webbings in groups 2 and 5 do not exhibit well defined annual displacement patterns because the magnitude of the applied loads cause large deformations, and data indicate that material yielding within a webbing tends to neutralize the annual sinusoidal displacement pattern. Study indicates that applied load, environmental effects, mechanical strength, coefficient of thermal expansion, and hygroscopic properties of webbings are fundamental requirements for quantifying accurate creep displacements and behaviors over multiple year time periods. Results from a study of the environmental effects on long-term creep displacement data of Kevlar and Vectran woven webbings are presented to increase the knowledge base of webbing materials and to enhance designs of inflatable space structures for long-duration space missions.

Kenner, WInfred S.↗