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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Investigation of upwind, multigrid, multiblock numerical schemes for three dimensional flows. Volume 1: Runge-Kutta methods for a thin layer Navier-Stokes solver

A state-of-the-art computer code has been developed that incorporates a modified Runge-Kutta time integration scheme, upwind numerical techniques, multigrid acceleration, and multi-block capabilities (RUMM). A three-dimensional thin-layer formulation of the Navier-Stokes equations is employed. For turbulent flow cases, the Baldwin-Lomax algebraic turbulence model is used. Two different upwind techniques are available: van Leer's flux-vector splitting and Roe's flux-difference splitting. Full approximation multi-grid plus implicit residual and corrector smoothing were implemented to enhance the rate of convergence. Multi-block capabilities were developed to provide geometric flexibility. This feature allows the developed computer code to accommodate any grid topology or grid configuration with multiple topologies. The results shown in this dissertation were chosen to validate the computer code and display its geometric flexibility, which is provided by the multi-block structure.

Cannizzaro, Frank E.↗
NASA NTRS1992

Daily quality assurance software for a satellite radiometer system

Six Differential Microwave Radiometers (DMR) on COBE (Cosmic Background Explorer) measure the large-angular-scale isotropy of the cosmic microwave background (CMB) at 31.5, 53, and 90 GHz. Quality assurance software analyzes the daily telemetry from the spacecraft to ensure that the instrument is operating correctly and that the data are not corrupted. Quality assurance for DMR poses challenging requirements. The data are differential, so a single bad point can affect a large region of the sky, yet the CMB isotropy requires lengthy integration times (greater than 1 year) to limit potential CMB anisotropies. Celestial sources (with the exception of the moon) are not, in general, visible in the raw differential data. A 'quicklook' software system was developed that, in addition to basic plotting and limit-checking, implements a collection of data tests as well as long-term trending. Some of the key capabilities include the following: (1) stability analysis showing how well the data RMS averages down with increased data; (2) a Fourier analysis and autocorrelation routine to plot the power spectrum and confirm the presence of the 3 mK 'cosmic' dipole signal; (3) binning of the data against basic spacecraft quantities such as orbit angle; (4) long-term trending; and (5) dipole fits to confirm the spacecraft attitude azimuth angle.

Keegstra, P. B.↗
NASA NTRS1992

Observation of meteors by MST radar

The observation of meteor trails by a vertical mesosphere - stratosphere - troposphere (MST) radar beam has the advantage of good height resolution and an approximate knowledge of the zenith angle since the trails are horizontal or near-horizontal. An extension of the ablation theory of meteors was developed for near horizontal trails which takes into account the curvature of the earth. Observations of the Geminid meteor shower by MST radar reveal the 'diffusion heights' to be in fair agreement with the true height, but with some discrepancies that can amount to 4 km. The true heights are almost entirely confined to the range 87-91 km, although the upper limit is attributed to the coherent integration time of the existing MST radar processing.

Jones, William↗
NASA NTRS1992

How to get on board Space Station Freedom

Space Station Freedom will accommodate researchers with interests in science, technology and commercial applications. NASA sponsors will be responsible for selecting the U.S. researchers for Space Station Freedom. The four NASA sponsors are: Office of Space Science and Applications (OSSA), Office of Aeronautics and Space Technology (OAST), Office of Commercial Programs (OCP), and the Office of Space Flight (OSF). The areas of research responsibility for each sponsor are presented. The researcher solicitation vehicles used by OSSA and OAST and the methodology for researchers seeking sponsorship from OCP and OSF as well as the pricing policy are discussed. Descriptions of flight planning, payload integration and operations functions are presented. Three categories of payloads and their respective payload integration times are discussed. Researchers are advised to contact a NASA sponsor and a source which lists the points of contact for the NASA sponsors is noted.

Bartoe, John-David↗
NASA NTRS1993

Investigation of serendipitious WFC sources

The serendipitious WFC sources under investigation, i.e., those which just happened to lie in the field of view while another object was being studied, were disappointing. The integration times were chosen to suit the primary target not the serendipitous targets. UX UMa, CZ Ori, BI Ori, WX Cet and AR And were not detected. A long (approximately 17 ksec) pointed observation of UX Uma (PI Wood) has since been carried out (February 1993) and the data is expected shortly. The other observations were much more successful. V471 Tau was observed with the WFC for 6.5 hrs with the S1 filter and 1.1 hrs with the S2b filter. It was easily detected with a count rate of 0.03 cps in the S1 filter and 0.15 cps in the S2b filter. The oscillations were seen, even before the data was folded, as was expected from preliminary results from the survey (Barstow et al. 1992). The pointed observations provide a much better phase coverage of the oscillations than did the survey data where the coverage was sparse. These data will be presented in a paper with the PSPC data (PI's Robinson and Shipman) and the pulse profiles in the different wavelengths will be compared.

Robinson, Edward L.↗
NASA NTRS1993

Using AI/expert system technology to automate planning and replanning for the HST servicing missions

This paper describes a knowledge-based system that has been developed to automate planning and scheduling for the Hubble Space Telescope (HST) Servicing Missions. This new system is the Servicing Mission Planning and Replanning Tool (SM/PART). SM/PART has been delivered to the HST Flight Operations Team (FOT) at Goddard Space Flight Center (GSFC) where it is being used to build integrated time lines and command plans to control the activities of the HST, Shuttle, Crew and ground systems for the next HST Servicing Mission. SM/PART reuses and extends AI/expert system technology from Interactive Experimenter Planning System (IEPS) systems to build or rebuild time lines and command plans more rapidly than was possible for previous missions where they were built manually. This capability provides an important safety factor for the HST, Shuttle and Crew in case unexpected events occur during the mission.

Bogovich, L.↗
NASA NTRS1992

A 492 GHz cooled Schottky receiver for radio-astronomy

We developed a 492 GHz cooled GaAs Schottky receiver driven by a solid state local oscillator with a DSB noise temperature of 550 K measured at the telescope. The receiver-bandwidth is approx. equal to 1.0 GHz. Quasi-optical mirrors focus the sky and local oscillator radiation into the mixer. Stability analysis via the Allan variance method shows that the total system including a 1 GHz bandwidth acousto-optical spectrometer built in Cologne allows integration times up to 100 sec per half switching cycle. We successfully used the receiver at the KOSMA 3 m telescope on Gornergrat (3150m) located in the central Swiss Alps near Zermatt during January-February 1992 for observations of the 492 GHz, (CI) (3)P1 to (3)P0 fine structure line in several galactic sources. These observations confirm that Gornergrat is an excellent winter submillimeter site in accordance with previous predictions based on the atmospheric opacity from KOSMA 345 GHz measurements.

Hernichel, J.↗
NASA NTRS1991

On the effect of grain burnback on STS-SRM fragment velocity

Concerns raised during the Ulysses Final Safety Analysis Review (FSAR) process called the solid rocket motor (SRM) fragment velocity prediction model into question. The specific area of concern was that there was a section of the SRM casing which was exposed to SRM chamber pressure as the grain (fuel) was consumed. These questions centered on the velocity of fragments which originated from the field joint region given that failure occurred between 37 and 72 seconds mission elapsed time (MET). Two dimensional coupled Eulerian-Lagrangian calculations were performed to assess the hot gas flow field which resulted from SRM casing fragmentation. The fragment to gas interface-pressure time-history obtained from these analyses was reduced to a boundary condition algorithm which was applied to an explicit-time-integration, finite element, three dimensional shell model of the SRM casing and unburned fuel. The results of these calculations showed that the velocity of fragments originating in the field joint was adequately described by the range of velocities given in the Shuttle Data Book (1988). Based on these results, no further analyses were required, and approval was obtained from the Launch Abort Subpanel of the Interagency Nuclear Safety Review Panel to use the SRM fragment velocity environments presented in the Ulysses FSAR (1990).

Eck, Marshall B.↗
NASA NTRS1992

The energy spectra of solar flare hydrogen, helium, oxygen, and iron - Evidence for stochastic acceleration

The time-integrated differential energy spectra of H, He, O, and Fe measured in 10 large flare events observed at 1 AU over the energy range of 0.3-80 MeV/nucleon showed consistent patterns in their spectral shapes: particles with larger mean mass-to-charge ratios were generally less abundant at higher energies. A steady state model of stochastic particle acceleration with rigidity-dependent diffusion coefficients fit the spectra best; spectra representative of diffusive shock acceleration also described the spectra of some events with the same number of free parameters, but often fell off faster in energy above 30 MeV per nucleon than the observations. The two model predictions differed most at energies near 0.1 MeV per nucleon, below the lowest energies observed in this study. The stochastic model quantitatively described the observed spectral ordering with less efficient acceleration of species with larger mean mass-to-charge ratios.

Mazur, J. E.↗
NASA NTRS1992

Characteristics of bursts observed by the SMM Gamma-Ray Spectrometer

The Gamma Ray Spectrometer (GRS) on the SMM completed close to 10 years of highly successful operation when the spacecraft reentered the atmosphere on December 2, 1989. During this period the GRS detected 177 events above 300 keV which have been classified as cosmic gamma-ray bursts. A catalog of these events is in preparation which will include time profiles and spectra for all events. Visual inspection of the spectra indicates that emission typically extends into the MeV range, without any evidence for a high-energy cutoff; 17 of these events are also observed above 10 MeV. We find no convincing evidence for line-like emission features in any of the time-integrated spectra.

Share, G. H.↗
NASA NTRS1993

High accuracy computation of fluid-structure interaction in transonic cascades

A coupling strategy for simulating fluid-structure interaction phenomena is formulated and applied to the prediction of flutter in transonic cascades. The flow is governed by the Euler equations and discretized using a finite volume flux-splitting scheme. The structure is modeled using an isoparametric finite element formulation. The coupling strategy successfully reconciles these two formulations at the fluid-structure interface by enforcing both kinematic and kinetic boundary conditions. In particular, the conservation laws applicable to the combined fluid-structure system are preserved across the interface. Since the primary mechanism driving aeroelastic phenomena involves energy exchange occurring at the interface, this highly accurate coupling mechanism is believed to improve the predictive capability of the scheme. The coupled equations are advanced simultaneously in time using an implicit time integration method. Results obtained using the coupling method are presented for cascade geometries operating in transonic flow.

Boschitsch, Alexander↗
NASA NTRS1992

Imaging solar flares in hard X-rays using Fourier telescopes

The sun emits hard X-rays (above 10 keV) during solar flares. Imaging hard X-ray sources on the sun with spatial resolutions on the order of 1-5 arcsec and integration times of 1 sec will provide greater insight into the energy release processes during a solar flare. In these events, tremendous amounts of energy stored in the solar magnetic field are rapidly released leading to emission across the electromagnetic spectrum. Two Fourier telescope designs, a spatial modulation collimator and a rotating modulation collimator, were developed to image the full sun in hard X-rays (10-100 keV) in an end-to-end simulation. Emission profiles were derived for two hard X-ray solar flare models taken from the current solar theoretical literature and used as brightness distributions for the telescope simulations. Both our telescope models, tailored to image solar sources, were found to perform equally well, thus offering the designer significant flexibility in developing systems for space-based platforms. Given sufficient sensitive areas, Fourier telescopes are promising concepts for imaging solar hard X-rays.

Campbell, Jonathan W.↗
NASA NTRS1993

Sensitivity analysis of flutter response of a typical section and a wing in transonic flow

A sensitivity analysis of flutter response of a two-degree of freedom airfoil with plunging and pitching degrees of freedom in transonic flow was performed using a state-space representation of the unsteady aerodynamic behavior. The structural equations of motion of the airfoil with bending and torsional degrees of freedom are coupled to the unsteady airloads, and the aeroelastic system so modeled is solved as an eigenvalue problem to determine the stability. The results of eigenanalysis showed good agreement with flutter calculations performed using a time-integration of the aeroelastic equations. The sensitivities of the flutter speed with respect to the mass and stiffness parameters wee computed by both the analytical and finite difference methods, showing excellent agreement.

Kapania, Rakesh K.↗
NASA NTRS1993

Orbiting stellar interferometer for astrometry and imaging

The orbiting stellar interferometer (OSI) is a concept for a first-generation space interferometer with astrometric and imaging goals. The OSI is a triple Michelson interferometer with articulating siderostats and optical delay lines. Two point designs for the instrument are described. The 18-m design uses an 18-m maximum baseline and aperture diameters of 40 cm; the targeted astrometric performance is a wide-field accuracy of 10 microarsec for 16-mag objects in 100 s of integration time and for 20-mag objects in 1 h. The instrument would also be capable of synthesis imaging with a resolution of 5 marcsec, which corresponds to the diffraction limit of the 18-m base line. The design uses a deployed structure, which would fold to fit into an Atlas IIAS shroud, for insertion into a 900-km sun-synchronous orbit. In addition to the 18-m point design, a 7-m point design that uses a shorter base line in order to simplify deployment is also discussed. OSI's high performance is made possible by utilizing laser metrology and controlled-optics technology.

Colavita, M. M.↗
NASA NTRS1993

Data processing and calibration for tunable diode laser harmonic absorption spectrometers

Data processing and calibration methods are described for tunable diode laser absorption spectrometers which produce harmonic absorption spectra as raw data for measuring gas mixing ratios down to parts-per-trillion levels at a variety of pressures. The methods, which take advantage of modern computer speed, memory, and data storage capabilities, are applicable to the detection of weakly absorbing gases in quantitative industrial monitoring, in addition to aircraft and balloon atmospheric measurements for which they were designed. Algorithms for calibration and data analysis, including rejection of erroneous spectra, variation of effective integration time, spectral alignment prior to averaging, and plotting and archiving of results, have been tested on actual stratospheric laser spectra recorded by the Aircraft Laser Infrared Absorption Spectrometer (ALIAS) spectrometer in numerous flights of NASA's ER-2 aircraft.

May, Randy D.↗
NASA NTRS1993

Modeling Titan's thermal infrared spectrum for high-resolution space observations

The observability of minor species in Titan's atmosphere in its infrared thermal range is systematically studied and modeled to generate synthetic spectra. The model results on methane, water vapor, benzene, allene, and other heavier trace molecules are used to illustrate the capabilities of instruments aboard the Infrared Space Observatory, in particular a high-resolution composite infrared spectrometer, to determine vertical distributions of the molecules in a few hours of integration time.

Coustenis, A.↗
NASA NTRS1992

Rain rate statistics and fade distributions at 20 and 30 GHz derived from a network of rain gauges in the Mid-Atlantic coast over a five year period

A network of ten tipping bucket rain gauges located within a grid 70 km north-south and 47 km east-west in the Mid-Atlantic coast of the United States was used to analyze rain rate and modeled slant path attenuation distributions at 20 and 30 GHz. It was shown that, for realistic fade margins at 20 GHz and above, the variable integration times results are adequate to estimate slant path attenuations using models which require 1 min averages. Crane's Global Model was used to derive fade distributions at 20 and 30 GHz.

Goldhirsh, Julius↗
NASA NTRS1993

A discrete momentum-conserving explicit algorithm for rigid body dynamics analysis

A discrete momentum-conserving explicit time integration is presented. The accurate feature and simplicity of the present algorithm are realized by a mid-point implicit formula for integrating the Euler parameters and a second-order discrete momentum-conserving form of the central difference algorithm, respectively. The accuracy and robustness of the algorithm is demonstrated by example problems which exhibit large overall rigid motions under holonomic constraints.

Park, K. C.↗