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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Practical methods for near-term piloted Mars missions

An evaluation is made of ways of using near-term technologies for direct and semidirect manned Mars missions. A notable feature of the present schemes is the in situ propellant production of CH4/O2 and H2O on the Martian surface in order to reduce surface consumable and return propellant requirements. Medium-energy conjunction class trajectories are shown to be optimal for such missions. Attention is given to the backup plans and abort philosophy of these missions. Either the Russian Energia B or U.S. Saturn VII launch vehicles may be used.

Zubrin, Robert M.↗
NASA NTRS1992

Environmental effects on long term behavior of composite laminates

Model equations are presented for approximate methods simulating the long-term behavior of composite materials and structures in hot/humid service environments. These equations allow laminate property upgradings with time, and can account for the effects of service environments on creep response. These methodologies are illustrated for various individual and coupled temperature/moisture, longitudinal/transverse, and composite material type cases. Creep deformation is noted to rise dramatically for cases of matrix-borne, but not of fiber-borne, loading in hot, humid environments; the coupled influence of temperature and moisture is greater than a mere combination of their individual influences.

Singhal, S. N.↗
NASA NTRS1993

Long-term containment of energetic particles in coronal loops

Recent observation from the Compton Gamma-Ray Observatory shows that gamma-ray emission after a solar flare can last for as long as 8 hours. There is also evidence that electrons and protons are accelerated only during the impulsive phase of the flare and are subsequently mirror trapped in coronal magnetic loops. This poses the following dilemma: if the magnetic field lines in the loop are simple plane arches, the protons will drift across the cross section of the loop in seconds to minutes, rather than hours. To solve the dilemma, we use guiding center theory to show that long-term containment of energetic protons in a coronal loop is possible if magnetic field lines have enough twist. We also find that in the trapped region of the loop, the twist angle of field lines between the mirror points of a bounce orbit is approximately 2 pi.

Lau, Yun-Tung↗
NASA NTRS1945

Analysis of wind-tunnel stability and control tests in terms of flying qualities of full-scale airplanes

The analysis of results of wind-tunnel stability and control tests of powered airplane models in terms of the flying qualities of full-scale airplanes is advocated. In order to indicated the topics upon which comments are considered desirable in the report of a wind-tunnel stability and control investigation and to demonstrate the nature of the suggested analysis, the present NACA flying-qualities requirements are discussed in relation to wind-tunnel tests. General procedures for the estimation of flying qualities from wind-tunnel tests are outlined.

Kayten, Gerald G↗
NASA NTRS1993

CO2 lidar observations of Mount Pinatubo debris: FIRE 2 and longer-term measurements

The volcanic debris in the stratosphere from the June 1991 eruption of Mt. Pinatubo first appeared over the NOAA Wave Propagation Laboratory (WPL) field site near Boulder, Colorado (40.15 N, 105.23 W), in July of 1991. The presence of the Pinatubo cloud has allowed us to characterize both the tropospheric and stratospheric aerosol backscatter using the NOAA/WPL CO2 Doppler lidar. The lidar has measured vertical backscatter profiles at lambda = 10.59 mu m for over a decade. Analysis of this dense set of profiles reveals the effects of atmospheric and microphysical processes during the buildup and decay of Mt. Pinatubo's clouds. Further information on the NOAA lidar, specifically calibrations using a hard target, can be found in Post and Cupp (1990). We present results of those measurements for June 15, 1991, through December 31, 1992. During that period of longer-term measurements, WPL took part in FIRE II (First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment II), from November 12 through December 8, 1991, measuring vertical backscatter profiles almost daily. One of the mechanisms for purging stratospheric aerosols is tropopause folding, which occurs in cold-core extratropical cyclones. Tropospheric mass loading occurs during folding events which can substantially increase the amount of ice nuclei in the upper troposphere, and may affect the formation of cirrus in that region. Spring and fall are prominent times for tropopause folding events because of the migration of the subtropical and polar jet streams during the transition seasons. Sassen has suggested that the volcanic aerosols from Pinatubo played a role in the formation of cirrus during FIRE II, particularly during a period of moist subtropical flow on December 5-6, 1991.

Levinson, David H.↗
NASA NTRS1993

Long term trending of engineering data for the Hubble Space Telescope

A major goal in spacecraft engineering analysis is the detection of component failures before the fact. Trending is the process of monitoring subsystem states to discern unusual behaviors. This involves reducing vast amounts of data about a component or subsystem into a form that helps humans discern underlying patterns and correlations. A long term trending system has been developed for the Hubble Space Telescope. Besides processing the data for 988 distinct telemetry measurements each day, it produces plots of 477 important parameters for the entire 24 hours. Daily updates to the trend files also produce 339 thirty day trend plots each month. The total system combines command procedures to control the execution of the C-based data processing program, user-written FORTRAN routines, and commercial off-the-shelf plotting software. This paper includes a discussion the performance of the trending system and of its limitations.

Cox, Ross M.↗
NASA NTRS1992

Advances in modeling the pressure correlation terms in the second moment equations

In developing turbulence models, various model constraints were proposed in an attempt to make the model equations more general (or universal). The most recent of these are the realizability principle, the linearity principle, the rapid distortion theory, and the material indifference principle. Several issues are discussed concerning these principles and special attention is payed to the realizability principle. Realizability (defined as the requirement of non-negative energy and Schwarz' inequality between any fluctuating quantities) is the basic physical and mathematical principle that any modeled equation should obey. Hence, it is the most universal, important and also the minimal requirement for a model equation to prevent it from producing unphysical results. The principle of realizability is described in detail, the realizability conditions are derived for various turbulence models, and the model forms are proposed for the pressure correlation terms in the second moment equations. Detailed comparisons of various turbulence models with experiments and direct numerical simulations are presented. As a special case of turbulence, the two dimensional two-component turbulence modeling is also discussed.

Shih, Tsan-Hsing↗
NASA NTRS1994

Looking at Earth from space. Glossary of terms

This glossary is one of a series of NASA publications designed to familiarize educators with global change issues and Mission to Planet Earth. The series enables teachers to enhance classroom studies with hands-on activities, including satellite images. Concepts and terms related to the global environment and the impact of human activities on the planet are presented.

Source record↗
NASA NTRS1994

A new method for monitoring long term calibration of the SBUV and TOMS instruments

A new method has been developed to monitor the long-term calibration of the Solar Backscatter Ultraviolet (SBUV) and Total Ozone Mapping Spectrometer (TOMS) instruments. It is based on the fact that the radiance in one channel can be expressed as a linear sum of the radiances in neighboring channels. Using simulated radiances for the SBUV and TOMS instruments, various scenarios of changes in instrument calibration are investigated. Results from sample processing of SBUV data are also presented.

Ahmad, Z.↗
NASA NTRS1994

Time-dependent variational approach in terms of squeezed coherent states: Implication to semi-classical approximation

A general framework for time-dependent variational approach in terms of squeezed coherent states is constructed with the aim of describing quantal systems by means of classical mechanics including higher order quantal effects with the aid of canonicity conditions developed in the time-dependent Hartree-Fock theory. The Maslov phase occurring in a semi-classical quantization rule is investigated in this framework. In the limit of a semi-classical approximation in this approach, it is definitely shown that the Maslov phase has a geometric nature analogous to the Berry phase. It is also indicated that this squeezed coherent state approach is a possible way to go beyond the usual WKB approximation.

Tsue, Yasuhiko↗
NASA NTRS1994

The long-term forecast of station view periods

Using dynamical systems theory, a definite integral is obtained that gives the average view period of a ground station for spacecraft in circular orbits. Minor restrictions exist on the class of circular orbits to which this method can be applied. This method avoids the propagation of the orbit, which requires a lot of resources, and simplifies the algorithm used to compute the mean station view period. The integral is used for long-term station load forecast studies. It also provides a quantitative measure of the effectiveness of a ground station as a function of its latitude.

Lo, M. W.↗
NASA NTRS1995

Long term variability of B supergiant winds

The object of this observing proposal was to sample wind variability in B supergiants on a daily basis over a period of several days in order to determine the time scale with which density variability occurs in their winds. Three stars were selected for this project: 69 Cyg (B0 Ib), HD 164402 (B0 Ib), and HD 47240 (B1 Ib). Three grey scale representations of the Si IV lambda lambda 1400 doublet in each star are attached. In these figures, time (in days) increases upward, and the wavelength (in terms of velocity relative to the rest wavelength of the violet component of the doublet) is the abscissa. The spectra are normalized by a minimum absorption (maximum flux) template, so that all changes appear as absorptions. As a result of these observations, we can now state with some certainty that typical B supergiants develop significant wind inhomogeneities with recurrence times of a few days, and that some of these events show signs of strong temporal coherence.

Massa, Derck L.↗
NASA NTRS1995

Probabilistic simulation of long term behavior in polymer matrix composites

A methodology to compute cumulative probability distribution functions (CDF) of fatigue life for different ratios, r of applied stress to the laminate strength based on first ply failure criteria has been developed and demonstrated. Degradation effects due to long term environmental exposure and mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation/aging of material properties due to cyclic loads. Fast probability integration method is used to perform probabilistic simulation of uncertainties. Sensitivity of fatigue life reliability to uncertainties in the primitive random variables are computed and their significance in the reliability based design for maximum life is discussed. The results show that the graphite/epoxy (0/+45/90) deg laminate with ply thickness 0.125 in. has 500,000 cycles life for applied stress to laminate strength ratio of 0.6 and a reliability of 0.999. Also, the fatigue life reliability has been found to be most sensitive to the ply thickness and matrix tensile strength. Tighter quality controls must therefore be enforced on ply thickness and matrix strength in order to achieve high reliability of the structure.

Shah, A. R.↗
NASA NTRS1992

Design prediction for long term stress rupture service of composite pressure vessels

Extensive stress rupture studies on glass composites and Kevlar composites were conducted by the Lawrence Radiation Laboratory beginning in the late 1960's and extending to about 8 years in some cases. Some of the data from these studies published over the years were incomplete or were tainted by spurious failures, such as grip slippage. Updated data sets were defined for both fiberglass and Kevlar composite stand test specimens. These updated data are analyzed in this report by a convenient form of the bivariate Weibull distribution, to establish a consistent set of design prediction charts that may be used as a conservative basis for predicting the stress rupture life of composite pressure vessels. The updated glass composite data exhibit an invariant Weibull modulus with lifetime. The data are analyzed in terms of homologous service load (referenced to the observed median strength). The equations relating life, homologous load, and probability are given, and corresponding design prediction charts are presented. A similar approach is taken for Kevlar composites, where the updated stand data do show a turndown tendency at long life accompanied by a corresponding change (increase) of the Weibull modulus. The turndown characteristic is not present in stress rupture test data of Kevlar pressure vessels. A modification of the stress rupture equations is presented to incorporate a latent, but limited, strength drop, and design prediction charts are presented that incorporate such behavior. The methods presented utilize Cartesian plots of the probability distributions (which are a more natural display for the design engineer), based on median normalized data that are independent of statistical parameters and are readily defined for any set of test data.

Robinson, Ernest Y.↗
NASA NTRS1993

A comparison of three-dimensional nonequilibrium solution algorithms applied to hypersonic flows with stiff chemical source terms

Three solution algorithms, explicit underrelaxation, point implicit, and lower upper symmetric Gauss-Seidel (LUSGS), are used to compute nonequilibrium flow around the Apollo 4 return capsule at 62 km altitude. By varying the Mach number, the efficiency and robustness of the solution algorithms were tested for different levels of chemical stiffness. The performance of the solution algorithms degraded as the Mach number and stiffness of the flow increased. At Mach 15, 23, and 30, the LUSGS method produces an eight order of magnitude drop in the L2 norm of the energy residual in 1/3 to 1/2 the Cray C-90 computer time as compared to the point implicit and explicit under-relaxation methods. The explicit under-relaxation algorithm experienced convergence difficulties at Mach 23 and above. At Mach 40 the performance of the LUSGS algorithm deteriorates to the point it is out-performed by the point implicit method. The effects of the viscous terms are investigated. Grid dependency questions are explored.

Palmer, Grant↗
NASA NTRS1993

NASA assurance terms and definitions

This publication provides a compendium of commonly used safety, reliability, maintainability, and quality assurance (SRM&QA) definitions to ensure standardized assurance communications among NASA Field Installations, Headquarters, and contractors. This list of standard assurance terms and definitions shall be utilized by all NASA organizations and contractors. Program/project tailoring of these definitions may be permitted for specific program applications.

Source record↗
NASA NTRS1995

Long-term variation of Saturn H2 emission

The goal of this research effort was to analyze the long-term IUE database of Saturn images for the possible presence of diffuse H2 emissions, using techniques originally developed for analysis of Jupiter images. The poor S/N ratio in many of the Saturn images proved to be a significant limitation to the possible detection of H2 emission. The creation of a satisfactory background atmosphere model was also limited by difficulties in reproducing the observed C2H2 band structure at long wavelengths. The results currently available suggest that diffuse H2 emission is present on Saturn on some occasions. However, the IUE data are not able to indicate whether H2 emission is present at all times with a magnitude proportional to solar activity, as was shown for Jupiter.

DeLand, Matthew T.↗