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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The SSME HPFTP interstage seals: Analysis and experiments for leakage and reaction-force coefficients

An improved theory for the prediction of the rotordynamic coefficients of turbulent annular seals was developed. Predictions from the theory are compared to the experimental results and an approach for the direct calculation of empirical turbulent coefficients from test data are introduced. An improved short seal solution is shown to do a better job of calculating effective stiffness and damping coefficients than either the original short seal solution or a finite length solution. However, the original short seal solution does a much better job of predicting equivalent added mass coefficient.

Childs, D. W.↗
NASA NTRS1982

The evolution of tectonic features on Ganymede

The bands of bright resurfaced terrain on Ganymede are probably broad grabens formed by global expansion and filled with deposits of ice. Grooves within the bands are thought to be extensional features formed during the same episode of expansion. The crust of Ganymede is modeled as a viscoelastic material subjected to extensional strain. With sufficiently high strain rates and stresses, deep normal faulting will occur, creating broad grabens that may then be filled. Continuing deformation at high strain rates and stresses will cause propagation of deep faults up into the flood deposits and normal faulting at the surface, while lower strain rates and stresses will cause formation of open extension fractures or, if the crustal strength is very low, grabens at the surface. The spacing between adjacent fractures may reflect the geothermal gradient at the time of deformation. Surface topography resulting from fracturing and normal faulting will decay with time as a result of viscous relaxation and mass-wasting.

Squyres, S. W.↗
NASA NTRS1985

Charge and energy dependence of the residence time of cosmic ray nuclei below 15 GeV/nucleon

The relative abundance of nuclear species measured in cosmic rays at Earth has often been interpreted with the simple leaky box model. For this model to be consistent an essential requirement is that the escape length does not depend on the nuclear species. The discrepancy between escape length values derived from iron secondaries and from the B/C ratio was identified by Garcia-Munoz and his co-workers using a large amount of experimental data. Ormes and Protheroe found a similar trend in the HEAO data although they questioned its significance against uncertainties. They also showed that the change in the B/C ratio values implies a decrease of the residence time of cosmic rays at low energies in conflict with the diffusive convective picture. These conclusions crucially depend on the partial cross section values and their uncertainties. Recently new accurate cross sections of key importance for propagation calculations have been measured. Their statistical uncertainties are often better than 4% and their values significantly different from those previously accepted. Here, these new cross sections are used to compare the observed B/C+O and (Sc to Cr)/Fe ratio to those predicted with the simple leaky box model.

Soutoul, A.↗
NASA NTRS1985

Hot coronae around early-type galaxies

The analysis of the X-ray emission from a sample of 55 bright early-type galaxies shows that hot gaseous coronae are a common and perhaps ubiquitous feature of such systems. The X-ray emission can be explained most naturally as thermal bremsstrahlung from hot gas which may be accumulated from mass loss during normal stellar evolution. The presence of these coronae shows that matter previously thought to be expelled in a galactic wind is instead stored in a hot galactic corona which may be heated and powered by supernova explosions. Perhaps the single most important feature of these coronae is that they provide a unique tracer of the gravitational potential in the outer regions of bright early-type galaxies. In this paper the X-ray properties of these coronae and their implications for the presence of massive dark halos around individual early-type galaxies are discussed. Total masses of early-type galaxies up to 5 trillion solar masses are found.

Forman, W.↗
NASA NTRS1987

Resistojet control and power for high frequency ac buses

Resistojets are operational on many geosynchronous communication satellites which all use dc power buses. Multipropellant resistojets were selected for the Initial Operating Capability (IOC) Space Station which will supply 208 V, 20 kHz power. This paper discusses resistojet heater temperature controllers and passive power regulation methods for ac power systems. A simple passive power regulation method suitable for use with regulated sinusoidal or square wave power was designed and tested using the Space Station multipropellant resistojet. The breadboard delivered 20 kHz power to the resistojet heater. Cold start surge current limiting, a power efficiency of 95 percent, and power regulation of better than 2 percent were demonstrated with a two component, 500 W breadboard power controller having a mass of 0.6 kg.

Gruber, Robert P.↗
NASA NTRS1987

Resistojet control and power for high frequency ac buses

Resistojets are operational on many geosynchronous communication satellites which all use dc power buses. Multipropellant resistojets were selected for the Initial Operating Capability (IOC) Space Station which will supply 208 V, 20 kHz power. This paper discusses resistojet heater temperature controllers and passive power regulation methods for ac power systems. A simple passive power regulation method suitable for use with regulated sinusoidal or square wave power was designed and tested using the Space Station multipropellant resistojet. The breadboard delivered 20 kHz power to the resistojet heater. Cold start surge current limiting, a power efficiency of 95 percent, and power regulation of better than 2 percent were demonstrated with a two component, 500 W breadboard power controller having a mass of 0.6 kg.

Gruber, Robert P.↗
NASA NTRS1988

The impact of mass extinctions

In the years since Snowbird an explosive growth of research on the patterns, causes, and consequences of extinction was seen. The fossil record of extinction is better known, stratigraphic sections were scrutinized in great detail, and additional markers of environmental change were discovered in the rock record. However flawed, the fossil record is the only record that exists of natural extinction. Compilations from the primary literature contain a faint periodic signal: the extinctions of the past 250 my may be regulary spaced. The reality of the periodicity remains a subject for debate. The implications of periodicity are so profound that the debate is sure to continue. The greater precision from stratigraphic sections spanning extinction events has yet to resolve controversies concerning the rates at which extinctions occurred. Some sections seem to record sudden terminations, while others suggest gradual or steplike environmental deterioration. Unfortunately, the manner in which the strata record extinctions and compile stratigraphic ranges makes a strictly literal reading of the fossil record inadvisable. Much progress was made in the study of mass extinctions. The issues are more sharply defined but they are not fully resolved. Scenarios should look back to the phenomena they purport to explain - not just an iridium-rich layer, but the complex fabric of a mass extinction.

Flessa, Karl W.↗
NASA NTRS1989

Limits to the radiative decays of neutrinos and axions from gamma-ray observations of SN 1987A

Gamma-ray observations obtained by the SMM gamma-ray spectrometer in the energy range 4.1-6.4 MeV are used to provide limits on the possible radiative decay of neutrinos and axions emitted by SN 1987A. For branching ratio values for the radiative decay modes of less than about 0.0001, the present limits are more stringent than those based upon the photon flux from decaying relic neutrinos. The data are also used to set an axion mass limit.

Kolb, Edward W.↗
NASA NTRS1989

Response of a chemically reacting shear layer to streamwise vorticity

A series of Direct Numerical Simulations are performed of a temporally evolving shear layer subject to both harmonic (2D) and streamwise (3D) forcing. The interaction and coupling of these various 2D and 3D modes is shown to significantly alter the development of the flow. The scale of the 3D modes is quite important to the coupling process with greatly enhanced mixing and product formation resulting from 3D modes that are rapidly amplified by the spanwise vorticity. In general, the longer wavelength 3D modes are found to be highly efficient at increasing the momentum transport while the shorter wavelengths increase mass transport.

Claus, R. W.↗
NASA NTRS1989

Life sciences and space research XXIII(2): Planetary biology and origins of life; Proceedings of the Topical Meeting and Workshops XX, XXI and XXIII of the 27th COSPAR Plenary Meeting, Espoo, Finland, July 18-29, 1988

This volume includes chapters on exobiology in space, chemical and early biochemical evolution, life without oxygen, potential for chemical evolution in the early environment of Mars, planetary protection issues and sample return missions, and the modulation of biological evolution by astrophysical phenomena. Papers are presented on the results of spaceflight missions, the action of some factors of space medium on the abiogenic synthesis of nucleotides, early peptidic enzymes, microbiology and biochemistry of the methanogenic archaeobacteria, and present-day biogeochemical activities of anaerobic bacteria and their relevance to future exobiological investigations. Consideration is also given to the development of the Alba Patera volcano on Mars, biological nitrogen fixation under primordial Martian partial pressures of dinitrogen, the planetary protection issues in advance of human exploration of Mars, and the difficulty with astronomical explanations of periodic mass extinctions.

Schwartz, A. W.↗
NASA NTRS1989

Experimental investigation into passive damping enhancement for space structures

This work presents experiments which were conducted to verify kinetic and strain energy damping enhancement schemes for large/precision space structures. Two types of damping mechanisms were applied to a 5 meter long, 10 bay aluminum box truss with a quasi free-free three-dimensional suspension. Tuneable proof mass dampers (PMDs) were implemented with space realizable linear electromechanical drivers. Tuneable piezoelectric truss members were designed and constructed for the demonstration of resonant shunted piezoelectric damping concepts. The truss damping was measured and compared to analytical predictions obtained from a frequency domain system modeling technique. The proof mass damper implementation was found to increase first mode damping from 0.6 percent of critical to 6.4 percent of critical with a system mass increase of 2.7 percent. The resonant shunted piezoelectrics increased first mode damping to 6.0 percent with a similar mass penalty.

Hagood, Nesbitt W.↗
NASA NTRS1989

Response of a chemically reacting layer to streamwise vorticity

A series of Direct Numerical Simulations of a temporally evolving shear layer subject to both harmonic (2D) and streamwise (3D) forcing were performed. The interaction and coupling of these various 2D and 3D modes is shown to significantly alter the development of the flow. The scale of the 3D modes is quite important to the coupling process with greatly enhanced mixing and product formation resulting from 3D modes that are rapidly amplified by the spanwise vorticity. In general, the longer wavelength 3D modes are found to be highly efficient at increasing the momentum transport while the shorter wavelengths increase mass transport.

Claus, Russell W.↗
NASA NTRS1995

On-line access to weather satellite imagery and image manipulation software

Advanced Very High Resolution Radiometer and Geostationary Operational Environmental Satellite imagery, received by antennas located at the University of Colorado, are made available to the Internet users through an on-line data access system. Created as a 'test bed' system for the National Aeronautics and Space Administration's future Earth Observing System Data and Information System, this test bed provides an opportunity to test both the technical requirements of an on-line data system and the different ways in which the general user community would employ such a system. Initiated in December 1991, the basic data system experiment four major evolutionary changes in response to user requests and requirements. Features added with these changes were the addition of on-line browse, user subsetting, and dynamic image processing/navigation. Over its lifetime the system has grown to a maximum of over 2500 registered users, and after losing many of these users due to hardware changes, the system is once again growing with its own independent mass storage system.

Emery, W.↗
NASA NTRS1996

Disruption of Helmet Streamers by Current Emergence

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting field and the newly emerging field have opposite polarities. Thus magnetic reconnection will occur at the flanks of the emerged structure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnection will promptly disrupt the streamer. If the emerging current is small, the streamer will experience a stage of slow evolution. In this stage, slow magnetic reconnection occurring at the flanks of the emerged structure leads to the degeneration of the emerged current to a neutral point. Above this point, a new magnetic bubble will form. The resulting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure will either remain in situ, forming a quasi-static structure, or move upward, forming a coronal transient similar to coronal jets. The numerical method used in this paper can be used to construct helmet streamers containing a detached magnetic structure in their closed field region. The quasi-static solution may serve as a preevent corona for studying coronal mass ejection initiation.

Guo, W. P.↗
NASA NTRS1996

Disruption of Helmet Streamers by Current Emergence

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting field and the newly emerging field have opposite polarities. Thus magnetic reconnection will occur at the flanks of the emerged structure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnection will promptly disrupt the streamer. If the emerging current is small, the streamer will experience a stage of slow evolution. In this stage, slow magnetic reconnection occurring at the flanks of the emerged structure leads to the degeneration of the emerged current to a neutral point. Above this point, a new magnetic bubble will form. The resulting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure will either remain in situ, forming a quasi-static structure, or move upward, forming a coronal transient similar to coronal jets. The numerical method used in this paper can be used to construct helmet streamers containing a detached magnetic structure in their closed field region. The quasi-static solution may serve as a preevent corona for studying coronal mass ejection initiation.

Guo, W. P.↗
NASA NTRS2004

In-Situ Measurements of Aerosol Optical Properties using New Cavity Ring-Down and Photoacoustics Instruments and Comparison with more Traditional Techniques

Carbonaceous species (BC and OC) are responsible for most of the absorption associated with aerosol particles. The amount of radiant energy an aerosol absorbs has profound effects on climate and air quality. It is ironic that aerosol absorption coefficient is one of the most difficult aerosol properties to measure. A new cavity ring-down (CRD) instrument, called Cadenza (NASA-ARC), measures the aerosol extinction coefficient for 675 nm and 1550 nm light, and simultaneously measures the scattering coefficient at 675 nm. Absorption coefficient is obtained from the difference of measured extinction and scattering within the instrument. Aerosol absorption coefficient is also measured by a photoacoustic (PA) instrument (DRI) that was operated on an aircraft for the first time during the DOE Aerosol Intensive Operating Period (IOP). This paper will report on measurements made with this new instrument and other in-situ instruments during two field recent field studies. The first field study was an airborne cam;oaign, the DOE Aerosol Intensive Operating Period flown in May, 2003 over northern Oklahoma. One of the main purposes of the IOP was to assess our ability to measure extinction and absorption coefficient in situ. This paper compares measurements of these aerosol optical properties made by the CRD, PA, nephelometer, and Particle Soot Absorption Photometer (PSAP) aboard the CIRPAS Twin-Otter. During the IOP, several significant aerosol layers were sampled aloft. These layers are identified in the remote (AATS-14) as well as in situ measurements. Extinction profiles measured by Cadenza are compared to those derived from the Ames Airborne Tracking Sunphotometer (AATS-14, NASA-ARC). The regional radiative impact of these layers is assessed by using the measured aerosol optical properties in a radiative transfer model. The second study was conducted in the Caldecott Tunnel, a heavily-used tunnel located north of San Francisco, Ca. The aerosol sampled in this study was characterized by fresh automobile and diesel exhaust. Measurements from Cadenza and from an aethalometer are presented. The aethalometer is a filter-based photometer and the infrared channel is calibrated to produce a measure of BC mass loading.

Strawa, A. W.↗