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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Yawed-Rolling Tire Mechanical Properties Testing of the Navy T-45 Aircraft Tires

The T-45 Goshawk is a United States Navy Jet aircraft used primarily as a trainer. The aircraft design makes use of "off the shelf" hardware as much as possible and was found to have unusual directional control issues during around operations. The aircraft was involved in numerous pilot-induced-oscillation incidents as well as observed to have unusual directional control reactions to failed main gear tires, a condition that is normally handled relatively easily by conventional aircraft steering control techniques. The behavior of the aircraft's tires had previously been modeled in simulators as a result of approximations provided in 40-year-old reference publications. Since knowledge of the true tire cornering and braking behavior is essential to modeling, understanding, and fixing directional control problems, the United States Navy requested assistance from the NASA Langley Research Center's (LARC) Aircraft Landing Dynamics Facility (ALDF) to define the yawed-rolling mechanical properties of the T-45 aircraft tires. The purpose of this report is to document the results of testing the subject tires at the NASA LaRC ALDF in September 1998. Brief descriptions of the Instrumented Tire Test Vehicle (ITTV) are included to familiarize the reader with the ITTV capabilities, data acquisition system, test and measurement techniques, data accuracy, and analysis and presentation of the testing results.

Daugherty, Robert H.↗
NASA NTRS1991

Atomic oxygen interaction with solar array blankets at protective coating defect sites

Atomic oxygen in the low-Earth-orbital environment oxidizes SiOx protected polyimide Kapton solar array blankets at sites which are not protected such as pin windows or scratches in the protective coatings. The magnitude and shape of the atomic oxygen undercutting which occurs at these sites is dependent upon the exposure environment details such as arrival direction and reaction probability. The geometry of atomic oxygen undercutting at defect sites exposed to atomic oxygen in plasma asher was used to develop a Monte Carlo model to simulate atomic oxygen erosion processes at defect sites in protected Kapton. Comparisons of Monte Carlo predictions and experimental results are presented for plasma asher atomic oxygen exposures for large and small defects as well as for protective coatings on one or both sides of Kapton. The model is used to predict in-space exposure results at defect sites for both directed and sweeping atomic oxygen exposure. A comparison of surface textures predicted by the Monte Carlo model and those experimentally observed from both directed space ram and laboratory plasma asher atomic oxygen exposure indicate substantial agreement.

Banks, Bruce A.↗
NASA NTRS1972

Photochemistry of unsaturated polymers.

The mechanisms of the direct photochemical reactions which occur in unsaturated polymers when irradiated as thin films in vacuo are reviewed. Important reactions in 1,4-polyisoprene and 1,4-polybutadiene are cis-trans isomerization, loss of 1,4-unsaturation, formation of new external double bonds (vinylidene and/or vinyl units) and cyclopropyl formation. In 1,2-polybutadiene and 3,4-polyisoprene, on the other hand, the main reaction is consumption of the external double bonds through cyclization. Recent work on the photoinduced microstructural changes in cis and trans polypentenamers is also discussed.

Golub, M. A.↗
NASA NTRS1972

Solvent effects on enzymes - Implications for extraterrestrial life.

Review of several studies on the alterations taking place in the structure, catalytic activity, specificity, and stability of an enzyme when some or all of the water in the medium is replaced by another solvent. These studies show the utility of solvents as a tool for probing enzyme function. They also suggest that solvents other than water should be investigated as media for controlling and directing enzyme reactions.

Heinrich, M. R.↗
NASA NTRS1977

Inorganic chemistry: Direct syntheses from pure liquid SO3 and from trivalent and pentavalent nitrogen derivatives

From pure liquid SO3 direct synthesis reactions were carried out with N2O5, NO2Cl, NOCl which yielded N2O54SO3, 3SO3, 2SO3-NO2Cl2SO3-NOCl2SO3 and NOCl2SO3, the latter being obtained for the first time in the pure state. In all cases the crystallized product was obtained by separating the constituents of the mixture and then going through a single viscous liquid phase.

Vandorpe, B.↗
NASA NTRS1983

Transient nucleation in condensed systems

Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.

Kelton, K. F.↗
NASA NTRS1992

Upper limit on the steady emission of the 2.223 MeV neutron capture gamma-ray line from the sun

A search for steady emission of the 2.223 MeV gamma-ray line arising from the direct capture reaction 1H(n, gamma)2H is presented on the basis of an analysis of SMM data. The upper limits for continuous 2.223 MeV gamma-ray line emission from the active and inactive sun, as established in the present work, are about two orders of magnitude less than previously published results. These findings for inactive periods also suggest that small flares (or a continuous acceleration mechanism) are unlikely to be the source of the heating of the quiet solar corona. It is concluded that the power in accelerated nuclei during inactive periods falls short of the coronal heating requirement by about four orders of magnitude unless there is a large and as yet unobserved population of nuclei at energies below 1 MeV. The energy release in other forms associated with the acceleration process falls short of the heating requirement by about two orders of magnitude if this energy release is in the same proportion to the power in accelerated nuclei as is estimated from observed flares.

Harris, M. J.↗
NASA NTRS1996

Laboratory studies of stratospheric aerosol chemistry

In this report we summarize the results of the two sets of projects funded by the NASA grant NAG2-632, namely investigations of various thermodynamic and nucleation properties of the aqueous acid system which makes up stratospheric aerosols, and measurements of reaction probabilities directly on ice aerosols with sizes corresponding to those of polar stratospheric cloud particles. The results of these investigations are of importance for the assessment of the potential stratospheric effects of future fleets of supersonic aircraft. In particular, the results permit to better estimate the effects of increased amounts of water vapor and nitric acid (which forms from nitrogen oxides) on polar stratospheric clouds and on the chemistry induced by these clouds.

Molina, Mario J.↗
NASA NTRS1950

Theoretical Investigations on the Efficiency and the Conditions for the Realization of Jet Engines

Contents: Preliminary notes on the efficiency of propulsion systems; Part I: Propulsion systems with direct axial reaction rockets and rockets with thrust augmentation; Part II: Helicoidal reaction propulsion systems; Appendix I: Steady flow of viscous gases; Appendix II: On the theory of viscous fluids in nozzles; and Appendix III: On the thrusts augmenters, and particularly of gas augmenters

Roy, Maurice↗
NASA NTRS1980

Product distribution for the reaction of HO2 with ClO

The paper reports the direct measurement of the reaction product HOCl from the reaction of H2O with ClO, and sets an upper limit for the possible product O3, using a discharge flow/mass spectrometry/resonance fluorescence apparatus. The upper limits of the reaction channel producing HCl + O3 are 1.5% at 298 K and 3.0% at 248 K. It is seen that the HCl production rate from the HO2 + ClO reaction could be as large as that from the Cl + CH4 reaction in the lower and middle stratosphere. Thus, this reaction may possibly increase the HCl production rate appreciably and thereby reduce the calculated O3 destruction by chlorofluoromethanes.

Leu, M.-T.↗
NASA NTRS1992

Reactive collision terms for fluid transport theory

A modified Bhatnagar-Gross-Krook (BGK) collision method is used for the derivation of reactive collision terms to allow for complete higher-moment approximations in fluid transport theory. The general reactive collision terms for the 8-, 10- and 13-moment approximation for binary reactions are derived. Then, reactive collision terms for specific chemistry are derived with the assumptions: (1) all reactants and products have 13-moment distribution functions; (2) simple, classical assumptions provide sufficient models for reaction dynamics; and (3) the reaction rate is energy-independent. The derived specific formulas reflect two extremes in reactive collision dynamics: direct and indirect reaction mechanisms. Finally, considerations for correct use of the reactive collision terms are discussed in the context of space plasma environments.

Eccles, J. V.↗
NASA NTRS1977

Semiclassical dynamics on multiple electronic surfaces - Three-dimensional treatment of reactive F + H2

The role of electron transitions in collisions is studied for the F + H2 reaction by combining quasi-classical Monte Carlo trajectories with a semiclassical decoupling approximation for the electron transitions. Attention is directed at the reaction of excited state F atoms reacting to form ground state products; the reactants are initiated in either of two spin-orbit states of the atom with the diatom in the ground vibrational state and the lowest four rotational states, at relative translational energies of 0.1, 0.2 and 0.3 eV. Even if the reactants are initiated on the excited state surface, the reactive cross sections (which are classically forbidden) are significant. The major dynamical effects of the excited state reaction are the flow of reactant electronic energy into product internal energy.

Komornicki, A.↗
NASA NTRS1992

Spacecraft momentum unloading using controlled magnetic torques

A method for maintaining the attitude of a three-axis controlled satellite by use of magnetic torquers includes using magnetometers for measuring the direction of the ambient geomagnetic field. The direction of the net reaction wheel momentum is also determined. The angle between the direction of the geomagnetic field and the net reaction wheel momentum is determined. The angle is compared with a threshold value. Magnetic torquer power consumption is reduced by operating the magnetic torquers only when the angle exceeds the threshold value.

Linder, David M.↗
NASA NTRS1990

Heterogeneous reactions on nitric acid trihydrate

The first direct measurements are reported of the reaction probabilities at stratospheric temperatures for two important heterogeneous reactions on nitric acid trihydrate (NAT), the compound which makes up the predominant, type I form of polar stratospheric cloud (PSC). Sticking coefficients and solubilities of HCl and NAT, which are important in modeling physicochemical processes in the stratosphere, are also reported. The results show that the conversion of the chlorine reservoir species in the stratosphere to photochemically active forms can occur within a few days of the first appearance of type I PSCs during the polar winter.

Moore, S. B.↗
NASA NTRS1993

The ultraviolet photochemistry of diacetylene - Direct detection of primary products of the metastable C4H2* + C4H2 reaction

The products of diacetylene's ultraviolet photochemistry over the 245-220 nm region were directly determined in experiments where C4H2 was excited within a small reaction tube attached to a pulsed nozzle. The products formed in the collisions of C4H2* with C4H2 were subsequently ionized by vacuum UV radiation (at 118 nm) in the ion source of a time-of-flight mass spectrometer. It was found that the reaction of C4H2* with C4H2 produces C6H2 (+C2H2), C8H2 (+2H,H2), and C8H3 (+H), confirming the results of Glicker and Okabe (1987). Under certain conditions, secondary products were observed. Mechanisms for the observed reactions are proposed.

Bandy, Ralph E.↗
NASA NTRS2012

In-Flight Position Calibration of the Cassini Articulated Reaction Wheel Assembly

NASA's long-lived Cassini-Huygens spacecraft is currently in its 14th year of flight and in the midst of its second, and final, extended mission. Cassini is a massive interplanetary spacecraft that is three axis stabilized and can maintain attitude control using either its reaction control system thrusters or using reaction wheel control. Cassini has four identical reaction wheels, of which three are mutually orthogonal and have a fixed orientation. The fourth reaction wheel has an articulation motor that allows this reaction wheel to be aligned with the momentum direction of any of the other three fixed reaction wheels. The articulation motor allows this reaction wheel to be used as a replacement for any of the other three wheels without any performance degradation. However, due to limitations in the design of this backup system, there are few telemetric indications of the orientation of this reaction wheel following an articulation. This investigation serves to outline the procedures that have been developed by the Cassini Attitude and Articulation Control Subsystem to calibrate the position of the articulated reaction wheel assembly in the event that the momentum direction of this reaction wheel must be reoriented.

Brown, Todd S.↗
NASA NTRS1985

Template-directed synthesis of novel, nucleic acid-like structures

In studying the origins of life, it is important to examine reactions of substrate mixtures that could plausibly have accumulated on the primitive earth. Nucleoside diphosphates would probably have been synthesized along with the standard nucleotides under prebiotic conditions. For these reasons, the template-directed reactions of activated derivatives of these diphosphates, alone or mixed with activated nucleotides, were investigated. An activated derivative of deoxyguanosine 3',5'-didphosphate condensed efficiently on a polycytidylate template to give oligonucleotide analogous in which each 3,5'ophosphodiester bond was replaced by a pyrophosphate linkage. Oligomers were formed even in the absence of a template, but much more slowly. Template-directed condensation occurred also with an analogous deoxadenosine derivative on polyuridylic acid and with an analogous acycloguanosine derivative on polycytidylic acid.

Schwartz, A. W.↗
NASA NTRS1978

Direct nuclear-pumped lasers using the He-3/n,p/H-3 reaction

A description is presented of experimental results concerning a specific class of direct nuclear-pumped lasers classified as 'volumetric nuclear lasers'. In the considered laser system a fissioning gas, He-3, is mixed with the lasing gas to form a homogeneous mixture, resulting in uniform volume excitation. In typical volumetric nuclear lasers a fast-burst reactor is used as a source of neutrons which penetrate a polyethylene moderator. Here the fast neutrons are thermalized. After thermalization, neutrons scatter into the laser cell. Nuclear reactions produce a proton of 0.56 MeV and a tritium ion of 0.19. These ions produce secondary electrons which pump the laser medium creating a population inversion. The results reported demonstrate direct nuclear pumping of He-3-Ar, Xe, Kr, and Cl with the considered system.

Deyoung, R. J.↗