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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 343 records · Page 19

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NASA NTRS1981

Chaotic behavior and fluid dynamics

It is shown that while fluids are very complicated systems having many degrees of freedom, the basic mechanism underlying the observed chaotic behavior of fluid turbulence may not require the consideration of many degrees of freedom. Simple dynamical systems display erratic and chaotic behavior reminiscent of turbulence, the key to which is the 'sensitivity to initial conditions' introduced by Ruelle (1978). Simple models which are sensitive to initial data and have permitted workers to study chaotic behavior are described, with attention to the Lorenz equations, Landau's idea of a continuous transition to turbulence via an infinite cascade of bifurcations, and one-dimensional maps.

Yorke, J. A.↗

NASA NTRS1982

End-to-end imaging information rate advantages of various alternative communication systems

The efficiency of various deep space communication systems which are required to transmit both imaging and a typically error sensitive class of data called general science and engineering (gse) are compared. The approach jointly treats the imaging and gse transmission problems, allowing comparisons of systems which include various channel coding and data compression alternatives. Actual system comparisons include an advanced imaging communication system (AICS) which exhibits the rather significant advantages of sophisticated data compression coupled with powerful yet practical channel coding. For example, under certain conditions the improved AICS efficiency could provide as much as two orders of magnitude increase in imaging information rate compared to a single channel uncoded, uncompressed system while maintaining the same gse data rate in both systems. Additional details describing AICS compression and coding concepts as well as efforts to apply them are provided in support of the system analysis.

Rice, R. F.↗

NASA NTRS1985

QCD-motivated description of very high energy particle interactions

Cross sections for the production of secondaries with large transverse momentum can become comparable to the total cross section in the TeV energy range. It is argued that the onset of this effect is observed at sub TeV energies via an increase of the rapidity distribution near y = 0, an increase of p sub T with energy and, most directly, via a correlation between p sub T and multiplicity. If indeed scaling violations are associated with the hard scattering of partons, then scaling violations are largely confined to the central region and have little effect on cosmic ray data which are sensitive to the forward fragmentation region.

Gaisser, T. K.↗

NASA NTRS1984

High-temperature fiber optic pressure sensor

Attention is given to a program to develop fiber optic methods to measure diaphragm deflection. The end application is intended for pressure transducers capable of operating to 540 C. In this paper are reported the results of a laboratory study to characterize the performance of the fiber-optic microbend sensor. The data presented include sensitivity and spring constant. The advantages and limitations of the microbend sensor for static pressure measurement applications are described. A proposed design is presented for a 540 C pressure transducer using the fiber optic microbend sensor.

Berthold, J. W.↗

NASA NTRS1988

Booster propulsion/vehicle impact study

The use of hydrogen RP-1, propane, and methane as fuels for booster engines of launch vehicles is discussed. An automated procedure for integrated launch vehicle, engine sizing, and design optimization was used to define two stage and single stage concepts for minimum dry weight. The two stage vehicles were unmanned and used a flyback booster and partially reusable orbiter. The single stage designs were fully reusable, manned flyback vehicles. Comparisons of these vehicle designs, showing the effects of using different fuels, as well as sensitivity and trending data, are presented. In addition, the automated design technique utilized for the study is described.

Weldon, Vincent↗

NASA NTRS1988

Summary of booster propulsion/vehicle impact study results

Hydrogen, RP-1, propane, and methane were identified by propulsion technology studies as the most probable fuel candidates for the boost phase of future launch vehicles. The objective of this study was to determine the effects of booster engines using these fuels and coolant variations on representative future launch vehicles. An automated procedure for integrated launch vehicle, engine sizing, and design optimization was used to optimize two stage and single stage concepts for minimum dry weight. The two stage vehicles were unmanned and used a flyback booster and partially reusable orbiter. The single stage designs were fully reusable, manned flyback vehicles. Comparisons of these vehicle designs, showing the effects of using different fuels, as well as sensitivity and trending data, are presented. In addition, the automated design technique is described.

Weldon, Vincent A.↗

NASA NTRS1990

Telescopic limiting magnitudes

The prediction of the magnitude of the faintest star visible through a telescope by a visual observer is a difficult problem in physiology. Many prediction formulas have been advanced over the years, but most do not even consider the magnification used. Here, the prediction algorithm problem is attacked with two complimentary approaches: (1) First, a theoretical algorithm was developed based on physiological data for the sensitivity of the eye. This algorithm also accounts for the transmission of the atmosphere and the telescope, the brightness of the sky, the color of the star, the age of the observer, the aperture, and the magnification. (2) Second, 314 observed values for the limiting magnitude were collected as a test of the formula. It is found that the formula does accurately predict the average observed limiting magnitudes under all conditions.

Schaefer, Bradley E.↗

NASA NTRS1990

Interactive effects of nutrition, environment, and rat-strain on cortical and vertebral bone geometry and biomechanics

An investigation was conducted to generate comparative data on the sensitivity of cortical- and vertebral-bone adaptations in two different rat strains maintained at conditions typical for spaceborne experiments conducted by U.S.A. and USSR. The effects of cage environment, diet, and rat-strain on the cortical (humerus) and vertebral (T7) bones of male Taconic-Sprague-Dawley and Czechoslovakian-Wistar rats were investigated using different flight-simulation cages (one rat/cage for U.S.A.; ten rats/cage for USSR conditions) and fed either U.S.A. or USSR diet. The results showed significant effects of these factors on the humeral and vertebral geometry and mechanical properties, as well as significant interactive effects on the mechanical properties of the humerus.

Zernicke, R. F.↗

NASA NTRS1991

Applications of low lift to drag ratio aerobrakes using angle of attack variation for control

Several applications of low lift to drag ratio aerobrakes are investigated which use angle of attack variation for control. The applications are: return from geosynchronous or lunar orbit to low Earth orbit; and planetary aerocapture at Earth and Mars. A number of aerobrake design considerations are reviewed. It was found that the flow impingement behind the aerobrake and the aerodynamic heating loads are the primary factors that control the sizing of an aerobrake. The heating loads and other loads, such as maximum acceleration, are determined by the vehicle ballistic coefficient, the atmosphere entry conditions, and the trajectory design. Several formulations for defining an optimum trajectory are reviewed, and the various performance indices that can be used are evaluated. The 'nearly grazing' optimal trajectory was found to provide the best compromise between the often conflicting goals of minimizing the vehicle propulsive requirements and minimizing vehicle loads. The relationship between vehicle and trajectory design is investigated further using the results of numerical simulations of trajectories for each aerobrake application. The data show the sensitivity of the trajectories to several vehicle parameters and atmospheric density variations. The results of the trajectory analysis show that low lift to drag ratio aerobrakes, which use angle of attack variation for control, can potentially be used for a wide range of aerobrake applications.

Mulqueen, J. A.↗

NASA NTRS1991

Measurement of self-broadening of the ozone nu(3) transitions

Self-broadening coefficients have been measured for a number of rovibrational lines in the nu(3) band of ozone, in the frequency range 1015-1058/cm, with J values between 0 and 27, and over a range of K(a) values. A multiparameter nonlinear least-squares fitting procedure is used to reduce the data, and the sensitivity of the procedure to instrument line width, weak satellite features, and absolute intensity has been examined. The retrieved coefficients are compared with millimeter-wave broadening coefficients, direclty measured rotational relaxation times, and recently suggested empirical representations.

Flannery, C.↗

NASA NTRS1992

Cockpit weather information needs

The primary objective is to develop an advanced pilot weather interface for the flight deck and to measure its utilization and effectiveness in pilot reroute decision processes, weather situation awareness, and weather monitoring. Identical graphical weather displays for the dispatcher, air traffic control (ATC), and pilot crew should also enhance the dialogue capabilities for reroute decisions. By utilizing a broadcast data link for surface observations, forecasts, radar summaries, lightning strikes, and weather alerts, onboard weather computing facilities construct graphical displays, historical weather displays, color textual displays, and other tools to assist the pilot crew. Since the weather data is continually being received and stored by the airborne system, the pilot crew has instantaneous access to the latest information. This information is color coded to distinguish degrees of category for surface observations, ceiling and visibilities, and ground radar summaries. Automatic weather monitoring and pilot crew alerting is accomplished by the airborne computing facilities. When a new weather information is received, the displays are instantaneously changed to reflect the new information. Also, when a new surface or special observation for the intended destination is received, the pilot crew is informed so that information can be studied at the pilot's discretion. The pilot crew is also immediately alerted when a severe weather notice, AIRMET or SIGMET, is received. The cockpit weather display shares a multicolor eight inch cathode ray tube and overlaid touch panel with a pilot crew data link interface. Touch sensitive buttons and areas are used for pilot selection of graphical and data link displays. Time critical ATC messages are presented in a small window that overlays other displays so that immediate pilot alerting and action can be taken. Predeparture and reroute clearances are displayed on the graphical weather system so pilot review of weather along the route can be accomplished prior to pilot acceptance of the clearance. An ongoing multiphase test series is planned for testing and modifying the graphical weather system. Preliminary data shows that the nine test subjects considered the graphical presentation to be much better than their current weather information source for situation awareness, flight safety, and reroute decision making.

Scanlon, Charles H.↗

NASA NTRS1992

A search for anisotrophy in the cosmic microwave background on intermediate angular scales

The results of a search for anisotropy in the cosmic microwave background on angular scales near 1 deg are presented. Observations were simultaneously performed in bands centered at frequencies of 6, 9, and 12 per cm with a multifrequency bolometric receiver mounted on a balloon-borne telescope. The statistical sensitivity of the data is the highest reported to date at this angular scale, which is of critical importance for understanding the formation of structure in the universe. Signals in excess of random were observed in the data. The experiment, data analysis, and interpretation are described.

Alsop, D. C.↗

NASA NTRS1992

Effects of habitat map generalization in biodiversity assessment

Species richness is being mapped as part of an inventory of biological diversity in California (i.e., gap analysis). Species distributions are modeled with a GIS on the basis of maps of each species' preferred habitats. Species richness is then tallied in equal-area sampling units. A GIS sensitivity analysis examined the effects of the level of generalization of the habitat map on the predicted distribution of species richness in the southern Sierra Nevada. As the habitat map was generalized, the number of habitat types mapped within grid cells tended to decrease with a corresponding decline in numbers of species predicted. Further, the ranking of grid cells in order of predicted numbers of species changed dramatically between levels of generalization. Areas predicted to be of greatest conservation value on the basis of species richness may therefore be sensitive to GIS data resolution.

Stoms, David M.↗

NASA NTRS1993

Cosmic background radiation anisotropy at degree angular scales - Further results from the South Pole

We report further results from the University of California at Santa Barbara program to measure anisotropy in the cosmic background radiation at angular scales near 1 deg, an angular range corresponding to the largest scales where structure is observed. A 30 GHz high electron mobility transistor amplifier-based detector was coupled to the Advanced Cosmic Microwave Explorer, a 1 m off-axis Gregorian telescope. We present data that represent 64 of the total of 500 hr acquired with this system during the 1990-1991 season. The data have a statistical error of 13.5/micro-K/pixel. These are the smallest error bars of any data set of this type published to date. The data contain a significant signal with a maximum likelihood Delta T/T roughly 1 x 10 exp -5. The spectrum of the signal seen in slightly less than 2 sigma away from the thermal spectrum expected of primordial fluctuations in the cosmic background radiation. If the source of the fluctuations is primordial, then the data are consistent with cold dark matter scenarios when normalized to the large-scale anisotropy observed by COBE, while if the origin of the signal is foreground emission or another form of contaminant then the data are marginally inconsistent with standard cold dark matter models. In either case, the data are sufficiently sensitive to provide a crucial test of many models.

Schuster, Jeffrey↗

NASA NTRS1990

River and lake ice conditions as determined from AIRSAR imagery

Synthetic aperture radar (SAR) imagery data can provide information on types and distribution of river and lake ice needed for studying river ice processes and dynamics, monitoring ice during winter navigation, and formulating ice control strategies. Visible and IR remote sensing systems cannot provide such data and present field methods are inadequate for characterizing ice conditions over long river reaches. Our ongoing analysis of JPL's AIRSAR imagery data and concurrent ground truth of ice conditions on the Tanana River and surrounding lakes near Fairbanks, Alaska, in March 1988, has resulted in several findings: hummocked ice covers and zones of variable ice surface roughness within them can be differentiated; C- and L-band data are more sensitive than P-band to the range of surface roughnesses encountered; smooth, level ice that is clear or contains small bubbles produces little backscatter; snow-covered river ice, whether rough or smooth, is distinguishable from snow-covered river sediments on exposed river beds and unvegetated bars; and open water leads are readily distinguished.

Melloh, Rae A.↗

NASA NTRS1995

Regional mapping of forest canopy water content and biomass using AIRSAR images over BOREAS study area

In recent years, monitoring vegetation biomass over various climate zones has become the primary focus of several studies interested in assessing the role of the ecosystem responses to climate change and human activities. Airborne and spaceborne Synthetic Aperture Radar (SAR) systems provide a useful tool to directly estimate biomass due to its sensitivity to structural and moisture characteristics of vegetation canopies. Even though the sensitivity of SAR data to total aboveground biomass has been successfully demonstrated in many controlled experiments over boreal forests and forest plantations, so far, no biomass estimation algorithm has been developed. This is mainly due to the fact that the SAR data, even at lowest frequency (P-band) saturates at biomass levels of about 200 tons/ha, and the structure and moisture information in the SAR signal forces the estimation algorithm to be forest type dependent. In this paper, we discuss the development of a hybrid forest biomass algorithm which uses a SAR derived land cover map in conjunction with a forest backscatter model and an inversion algorithm to estimate forest canopy water content. It is shown that unlike the direct biomass estimation from SAR data, the estimation of water content does not depend on the seasonal and/or environmental conditions. The total aboveground biomass can then be derived from canopy water content for each type of forest by incorporating other ecological information. Preliminary results from this technique over several boreal forest stands indicate that (1) the forest biomass can be estimated with reasonable accuracy, and (2) the saturation level of the SAR signal can be enhanced by separating the crown and trunk biomass in the inversion algorithm. We have used the JPL AIRSAR data over BOREAS southern study area to test the algorithm and to generate regional scale water content and biomass maps. The results are compared with ground data and the sources of errors are discussed. Several SAR images in synoptic modes are used to generate the parameter maps. The maps are then combined to generate mosaic maps over the BOREAS modeling grid.

Saatchi, Sasan↗

NASA NTRS1994

Relationship of ozone and carbon monoxide over North America

Observations at sites in eastern North America show a strong correlation between O3 and CO concentrations in summer, with a consistent slope DeltaO3/DeltaCO approximately = 0.3. Observations in the aged Denver plume at Niwot Ridge, Colorado, also show a strong correlation but with DeltaO3/DeltaCO = 0.15. These data offer a sensitive test for evaluating the ability of photochemical models to simulate production of O3 over North America and its export to the global atmosphere. Application to the Harvard/Goddard Institute for Space Studies three-dimensional, continental-scale model shows that the model gives a good simulation of the observed O3-CO correlations and of the associated DeltaO3/DeltaCO. This successful simulation lends support to model estimates of 6 Gmol/d for the net O3 production in the U.S. boundary layer in summer (corresponding to a net O3 production efficiency of 5.5, which is the number of O3 molecules produced per molecule of NOx consumed) and 70% for the fraction of the net production that is exported to the global atmosphere. Export of U.S. pollution appears to make a significant contribution to total tropospheric O3 over the northern hemisphere in summer. Simple interpretation of observed DeltaO3/DeltaCO as an O3/CO anthropogenic enhancement ratio is shown to underestimate substantially anthropogenic O3 production, because O3 and CO concentrations are negatively correlated in the absence of photochemistry. It is also shown that concurrent observations of DeltaO3/DeltaCO and DeltaO3/Delta(NO(y)-NO(x)) ratios can be used to impose lower and upper limits on the net O3 production efficiency.

Chin, Mian↗

NASA NTRS1998

Reciprocal Space Mapping of Macromolecular Crystals in the Laboratory

The technique of reciprocal space mapping applied to the physical measurement of macromolecular crystals will be described. This technique uses a triple axis diffractometer setup whereby the monochromator is the first crystal, the sample is the second and the third crystal (of the same material as the monochromator) analyzes the diffracted beam. The geometry is such that it is possible to separate mosaic volume effects from lattice strain effects. The deconvolution of the instrument parameters will also be addressed. Results from measurements at Brookhaven National Synchrotron Radiation Source carried out on microgravity and ground-grown crystals will be presented. The required beam characteristics for reciprocal space mapping are also ideal for topographic studies and the first topographs ever recorded from microgravity protein crystal samples will be shown. We are now working on a system which will enable reciprocal space mapping, mosaicity and topography studies to be carried out in the home laboratory. This system uses a rotating anode X-ray source to provide an intense beam then a Bartels double crystal, four reflection monochromator to provide the spectral and geometric beam conditioning necessary such that the instrument characteristics do not mask the measurement. This is coupled to a high precision diffractometer and sensitive detector. Commissioning data and first results from the system will be presented.

Snell, Edward H.↗