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NASA NTRS1971

Photoionization and absorption spectrum of formaldehyde in the vacuum ultraviolet.

The measurements have been conducted in the spectral range from 600 to 2000 A. Integrated oscillator strengths were determined for a number of strong Rydberg transitions above 1200 A. From the photoionization curve the first adiabatic ionization potential was found to be 10.87 plus or minus 0.01 eV. As an aid in interpreting the absorption spectrum, theoretical calculations were made using a single-configuration self-consistent field procedure for the Rydberg states and a model which included mixing between the Rydberg and valence states.

Mentall, J. E.↗

NASA NTRS1993

A normal stress subgrid-scale eddy viscosity model in large eddy simulation

The Smagorinsky subgrid-scale eddy viscosity model (SGS-EVM) is commonly used in large eddy simulations (LES) to represent the effects of the unresolved scales on the resolved scales. This model is known to be limited because its constant must be optimized in different flows, and it must be modified with a damping function to account for near-wall effects. The recent dynamic model is designed to overcome these limitations but is compositionally intensive as compared to the traditional SGS-EVM. In a recent study using direct numerical simulation data, Horiuti has shown that these drawbacks are due mainly to the use of an improper velocity scale in the SGS-EVM. He also proposed the use of the subgrid-scale normal stress as a new velocity scale that was inspired by a high-order anisotropic representation model. The testing of Horiuti, however, was conducted using DNS data from a low Reynolds number channel flow simulation. It was felt that further testing at higher Reynolds numbers and also using different flows (other than wall-bounded shear flows) were necessary steps needed to establish the validity of the new model. This is the primary motivation of the present study. The objective is to test the new model using DNS databases of high Reynolds number channel and fully developed turbulent mixing layer flows. The use of both channel (wall-bounded) and mixing layer flows is important for the development of accurate LES models because these two flows encompass many characteristic features of complex turbulent flows.

Horiuti, K.↗

NASA NTRS2007

SMART-COMMIT Observations and Deep-Blue Retrievals of Saharan Dust Properties during NAMMA

Monsoon rainfalls sustain the livelihood of more than half of the world's population. The interaction between natural/anthropogenic aerosols, clouds, and precipitation is a critical mechanism that drives the water cycle and fresh water distribution. Analyses of the longterm trend of July-August precipitation anomaly for the last 50 years in the 20" century depict that the largest regional precipitation deficit occurs over the Sahel, where the monsoon water cycle plays an important role. Thus, it is of paramount importance to study how dust aerosols, as well as air pollution and smoke, influence monsoon variability. The NASA African Monsoon Multidisciplinary Activities (NAMMA) was conducted during the international AMMA Special Observation Period (SOP-3) of September 2006 to better comprehend the key attributes of the Saharan Air Layer (SAL) and how they evolve from the source regions to the Atlantic Ocean. The SAL occurs during the late spring through early fall and originates as a result of low-level convergence induced by heat lows over the Sahara that lifts hot, dry, dust laden air aloft into a well mixed layer that extends up to 500mb. This is crucial for understanding the impact of SAL on the key atmospheric processes that determine precipitation over West Africa and tropical cyclogenesis. Results obtained from the synergy of satellite (Deep- Blue) and surface (SMART-COMMIT) observations will be presented and discussed how the physical, optical and radiative properties of the dust in the SAL evolve from the continental to the marine environment.

Tsay, Si-Chee↗

NASA NTRS2018

Instability and Target Design in a Z-Pinch Driven Pulsed Fission / Fusion Engine

Advanced forms of propulsion are required to drastically improve upon the limits of existing technology and enable deep space exploration. Nuclear reactors, both fission and fusion, have great potential as systems with high energy density for spacecraft propulsion. There are a variety of nuclear propulsion concepts that have been proposed over the last several decades. Some of these rely on the confinement of plasmas by both magnetic and inertial means. When discussing the plasma confinement one must consider the stability of the system. The conditions of the plasma dictate the burn rate of the nuclear fuel; therefore, the plasma must maintain a minimum set of conditions in order to achieve an adequate burn. Instabilities limit plasma confinement through growing fluctuations in density and pressure. This results in turbulent mixing and loss of confinement. Thus it is desirable to find ways of managing the impact of instabilities that arise in order for a sufficient burn of the fuel such that surplus energy can be converted into a propulsive force. Note that the same instabilities plague the confinement of plasmas for terrestrial power generation. Over the last several years there has been research relating to the development of a Pulsed Fission-Fusion Engine (PuFF) conducted by the authors and others at their respective institutions. The propulsion system concept centers on the use of a z-pinch to compress a plasma in order to induce nuclear reactions. The plasma along with the additional energy released by the fission and fusion processes is expanded with a magnetic nozzle to produce thrust. The concept, if developed, is expected to have an improvement in specific impulse of several orders of magnitude in comparison with chemical propulsion systems. The z-pinch has been explored in the past as a method to confine a plasma via magnetic confinement fusion (MCF) for power generation. It suffers; however, from instabilities that so far have prevented break even conditions.

Taylor, Brian↗

NASA NTRS1971

Quenching of vibrationally excited hydroxyl /v = 9/ with oxygen.

In the experiment discussed molecular oxygen was allowed to mix with atomic hydrogen and ozone at the entrance to a 3-m flow tube. A rate equation for the decay of the vibrationally excited hydroxyl is derived, taking into consideration the reaction with ozone, radiative decay, wall quenching, and interaction with molecular oxygen. It is pointed out that molecular oxygen might be important as a quencher for the hydroxyl airglow in the upper atmosphere in spite of negative results obtained in fast-flow experiments conducted in the laboratory.-

Worley, S. D.↗

NASA NTRS2006

Aircraft Conceptual Design and Risk Analysis Using Physics-Based Noise Prediction

An approach was developed which allows for design studies of commercial aircraft using physics-based noise analysis methods while retaining the ability to perform the rapid trade-off and risk analysis studies needed at the conceptual design stage. A prototype integrated analysis process was created for computing the total aircraft EPNL at the Federal Aviation Regulations Part 36 certification measurement locations using physics-based methods for fan rotor-stator interaction tones and jet mixing noise. The methodology was then used in combination with design of experiments to create response surface equations (RSEs) for the engine and aircraft performance metrics, geometric constraints and take-off and landing noise levels. In addition, Monte Carlo analysis was used to assess the expected variability of the metrics under the influence of uncertainty, and to determine how the variability is affected by the choice of engine cycle. Finally, the RSEs were used to conduct a series of proof-of-concept conceptual-level design studies demonstrating the utility of the approach. The study found that a key advantage to using physics-based analysis during conceptual design lies in the ability to assess the benefits of new technologies as a function of the design to which they are applied. The greatest difficulty in implementing physics-based analysis proved to be the generation of design geometry at a sufficient level of detail for high-fidelity analysis.

Olson, Erik D.↗

NASA NTRS2019

The 3D Printing of Polyimide Aerogels

Polyimide aerogels are a nanoporous material made by extracting the liquid portion of a wet gel and replacing it with air, while still maintaining the porous solid internal architecture. This results in a material with extremely low densities, low thermal conductivities, high internal surfaces areas, and low dielectric constants. Currently, complex aerogel forms are not possible, since they require molds in order to be shaped. To overcome this challenge, we are attempting to use various additive manufacturing techniques to produce complex architectures. Three different approaches are being studied to accomplish this. One is to print using a viscous wet gel and have the structure solidify at the end of the print, another is to use a mixing tip, where a less viscous gel and the final chemical that causes gelation will be mixed as it is printing, allowing it to gel layer by layer, and the third is to use a UV curable aerogel with a UV light following behind to solidify the gel as it prints. To have these approaches be successful, the printing parameters and the aerogel's chemical formulation need to be optimized. The more harmonious these two factors can be made, the more defined and complex the resulting structure can be. Preliminary results show that 3D printing polyimide aerogels are a viable option, but further optimization must occur for reliable printing.

Nosel, Theresa↗

NASA NTRS1985

An intercomparison of carbon monoxide measurement techniques

Results from an intercomparison of techniques to measure tropospheric levels of carbon monoxide (CO) are discussed. The intercomparison was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment (GTE) and was held at Wallops Island, VA, in July 1983. Instruments intercompared included a laser differential absorption method and three grab sample/gas chromatograph methods. The intercomparison consisted of simultaneous measurements of ambient levels of CO and controlled injections of CO from a common manifold. Results from the techniques exhibited a high degree of correlation among themselves and with changes in the CO mixing ratio. The results suggested a level of agreement among the techniques of about 15 percent. However, a day-to-day bias between the techniques was observed, which resulted in differences between techniques as large as 38 percent.

Hoell, J. M., Jr.↗

NASA NTRS2011

The Impact of Traffic Prioritization on Deep Space Network Mission Traffic

A select number of missions supported by NASA's Deep Space Network (DSN) are demanding very high data rates. For example, the Kepler Mission was launched March 7, 2009 and at that time required the highest data rate of any NASA mission, with maximum rates of 4.33 Mb/s being provided via Ka band downlinks. The James Webb Space Telescope will require a maximum 28 Mb/s science downlink data rate also using Ka band links; as of this writing the launch is scheduled for a June 2014 launch. The Lunar Reconnaissance Orbiter, launched June 18, 2009, has demonstrated data rates at 100 Mb/s at lunar-Earth distances using NASA's Near Earth Network (NEN) and K-band. As further advances are made in high data rate space telecommunications, particularly with emerging optical systems, it is expected that large surges in demand on the supporting ground systems will ensue. A performance analysis of the impact of high variance in demand has been conducted using our Multi-mission Advanced Communications Hybrid Environment for Test and Evaluation (MACHETE) simulation tool. A comparison is made regarding the incorporation of Quality of Service (QoS) mechanisms and the resulting ground-to-ground Wide Area Network (WAN) bandwidth necessary to meet latency requirements across different user missions. It is shown that substantial reduction in WAN bandwidth may be realized through QoS techniques when low data rate users with low-latency needs are mixed with high data rate users having delay-tolerant traffic.

prioritization↗

NASA NTRS2011

The Impact of Traffic Prioritization on Deep Space Network Mission Traffic

quality of service↗

NASA NTRS1976

Mach wave emission from supersonic jets

An experimental investigation has been conducted on supersonic jets at a Mach number of 1.43 over a temperature range from about 420 K to 1370 K (300 F to 2000 F) in which it was found that the noise in the far field was dominated by eddy Mach waves. It is shown that the strength of the Mach waves is determined by the product of the mean shear and the density fluctuations of the jet. Thus, the source of sound arises from the mixing of hot and cold streams as well as from those compressions and expansions that are intuitively associated with sound generation. For the temperature range investigated, the Mach waves were emitted at angles between 37 deg and 59 deg with respect to the jet axis. These values represent those in the region of the jet where the Mach angle was constant.

Parthasarathy, S. P.↗

NASA NTRS1977

Effect of Flame Stabilizer Design on Performance and Exhaust Pollutants of a Two-Row Swirl-Can Combustor Operated to Near-Stoichiometric Conditions

Emissions and performance characteristics were determined for two full annulus modular combustors operated to near stoichiometric fuel air ratios. The tests were conducted to obtain stoichiometric data at inlet air temperatures from 756 to 894 K and to determine the effects of a flat plate circular flame stabilizer with upstream fuel injection and a contraswirl flame stabilizer with downstream fuel injection. Levels of unburned hydrocarbons were below 0.50 gram per kilogram of fuel for both combustors and thus there was no detectable difference in the two methods of fuel injection. The contraswirl flame stabilizer did not produce the level of mixing obtained with a flat plate circular flame stabilizer. It did produce higher levels of oxides of nitrogen, which peaked at a fuel air ratio of 0.037. For the flat plate circular flame stabilizer, oxides of nitrogen emission levels were still increasing with fuel air ratio to the maximum tested value of 0.045.

Biaglow, James A.↗

NASA NTRS1990

Flight tests of a helmet-mounted display synthetic visibility system

A short flight test program was conducted using the NASA Langley Research Center's B737 Advanced Transport Operating Systems (ATOPS) research airplane to determine if pilots could land a transport category airplane under visual meteorological conditions (VMC) by reference to a synthetic visibility system. No external guidance was to be used. The program was undertaken jointly by NASA and the McDonnel-Douglas Corporation. The airplane was fitted with forward-looking television cameras fixed in the nose. Inputs from the television cameras were mixed with internally generated symbology and displayed to the pilot on helmet-mounted eyepieces. The pilot task was to execute a visual approach and landing. Two NASA and two McDonnel-Douglas engineering test pilots participated in the program completing over 200 landings in a 32-hour test program. Landings accomplished with the helmet-mounted display (HMD) were compared with visual landings for each pilot.

Yenni, Kenneth R.↗

NASA NTRS1993

Experimental and numerical study of a turbulent boundary layer with pressure gradients

Results are presented of an experimental and numerical study of a turbulent boundary layer with pressure gradients conducted using the recent 'fringe method' with its numerical advantages and good inflow quality. After an inflow transient good agreement is observed; the differences, of up to 13 percent, are discussed. Moderate deviations from the law of the wall are found in the velocity profiles of the simulation. They are fully correlated with the pressure gradient, are in fair quantitative agreement with the experimental results of Nagano et al. (1992), and are roughly the opposite of uncorrected mixing-length-model predictions. Large deviations from the wall scaling are observed for other quantities, notably for the turbulence dissipation rate. The a(1) structure parameter drops mildly in the upper layer with adverse pressure gradient.

Spalart, Philippe R.↗

NASA NTRS1999

The Effect of Cathode Composition on the Thermal Characteristics of Lithium-Ion Cells

The specific thermal capacity and heat dissipation rate for lithium ion cells containing LiNiO2 and mixed oxide (75%LiCoO2+ 25%LiNiO2) as cathode materials are compared. The experimental measurements were made using a radiative calorimeter consisting of a copper chamber maintained at -168 C by circulating liquid nitrogen and enclosed in a vacuum bell jar. The specific thermal capacity was determined based on warm-up and cool-down transients. The heat dissipation rate was calculated from the values measured for heat radiated and stored, and the resulting values were corrected for conductive heat dissipation through the leads. The specific heat was 1.117 J/ C-g for the LiNiO2 cell and 0.946 J/ C-g for the 75%LiCoO2,25%LiNiO2 cell. Endothermic cooling at the beginning of charge was very apparent for the cell containing 75%LiCoO2,25%LiNiO2 as the cathode. Exothermic heating began at a higher state of charge for the cell with the 75%LiCoO2,25%LiNiO2 cathode compared to the LiNiO2 cathode cell. During discharge, the rate of heat dissipation increased with increase in the discharge current for both types of cells. The maximum heat dissipated at C/5 discharge was 0.065 W and 0.04 W for the LiNiO2 and 75%LiCoO2,25%LiNiO2 cells, respectively, The thermoneutral potential showed variability toward the end of discharge. The plateau region of the curves was used to calculate average thermoneutral potentials of 3.698 V and 3.837 V for the LiNiO2 cell and the 75%LiCoO2,25%LiNiO2 cell, respectively.

Vaidyanathan, Hari↗

NASA NTRS1996

A Comparison of Aircraft and Ground-Based Measurements at Mauna Loa Observatory, Hawaii, During GTE PEM-West and MLOPEX 2

During October 19-20, 1991, one flight of the NASA Global Tropospheric Experiment (GTE) Pacific Exploratory Mission (PEM-West A) mission was conducted near Hawaii as an intercomparison with ground-based measurements of the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2) and the NOAA Climate Modeling and Diagnostics Laboratory (CMDL). Ozone, reactive nitrogen species, peroxides, hydrocarbons, and halogenated hydrocarbons were measured by investigators aboard the DC-8 aircraft and at the ground site. Lidar cross sections of ozone revealed a complex air mass structure near the island of Hawaii which was evidenced by large variation in some trace gas mixing ratios. This variation limited the time and spatial scales for direct measurement intercomparisons. Where differences occurred between measurements in the same air masses, the intercomparison suggested that biases for some trace gases was due to different calibration scales or, in some cases, instrumental or sampling biases. Relatively large uncertainties were associated with those trace gases present in the low parts per trillion by volume range. Trace gas correlations were used to expand the scope of the intercomparison to identify consistent trends between the different data sets.

Atlas, E.↗

NASA NTRS2016

Comparison of Structural and Functional Ocular Outcomes Between 14- and 70 Day Bed Rest

Purpose: To compare structural and functional ocular outcomes in healthy human subjects undergoing 14- and/or 70-day head-down-tilt bed rest (HDTBR). We hypothesized the amount of HDTBR-induced ocular changes be affected by the HDTBR duration. Methods: The studies were conducted at the NASA Flight Analogs Research Unit, The University of Texas Medical Branch at Galveston, Galveston, TX. Participants were selected using NASA standard screening procedures. Standardized NASA screening procedures and bed rest conditions (e.g., strict sleep-wake cycle, standardized diet, continuous video monitoring) were implemented in both studies. Participants maintained a 6deg HDTBR position for 14 and/or 70 consecutive days and did not engage in exercise. Weekly ophthalmological examinations were conducted in the sitting (pre/post-bed rest only) and HDT positions. Ocular outcomes of interest included: near best-corrected visual acuity (BCVA); spherical equivalent, as determined by cycloplegic autorefraction; Goldmann applanation tonometry and iCare (Icare Finland Oy, Espoo, Finland) intraocular pressure (IOP) measurement; color vision; red dot test; modified Amsler grid test; confrontational visual field; stereoscopic color fundus photography; Spectralis OCT (Heidelberg Engineering, GmbH, Heidelberg, Germany) retinal nerve fiber layer thickness (RNFLT), peripapillary and macular retinal thicknesses. Mixed-effects linear models were used to compare pre- and post-HDTBR observations between 14- and 70-day HDTBR for our continuously scaled outcomes.

Cromwell, R. L.↗

NASA NTRS1980

Rocket observations of the vertical distribution of ozone in the polar night and during a mid-winter stratospheric warming

Rocket ozone soundings have been conducted in the stratosphere and lower mesosphere at high latitudes during winter. The collection of soundings show a high degree of variability when compared to ozone distributions measured during summer and at lower latitudes. The concurrently observed temperature and winds also show large variations which can be qualitatively related to the ozone profiles. Two most unusual ozone profiles were observed in January 1979 over Alaska during a stratospheric warming event. Both ozone profiles were consistent in showing the measured mixing ratios to be higher at 50 km than those measured at 40 km, a feature never reported before. This feature is related to the concurrently observed wind and temperature distributions and the NMC analyses of pressure height fields. The polar night ozone observations in the upper stratosphere and lower mesosphere suggest some temperature dependence, but transports seem to play an important role.

Hilsenrath, E.↗