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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 433 records · Page 24

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NASA NTRS1991

Simultaneous measurements of temperature and density in air flows using UV laser spectroscopy

The simultaneous measurement of temperature and density using laser-induced fluorescence of oxygen in combination with Q-branch Raman scattering of nitrogen and oxygen is demonstrated in a low-speed air flow. The lowest density and temperature measured in the experiment correspond to the freestream values at Mach 5 in the Ames 3.5-Foot Hypersonic Wind Tunnel for stagnation conditions of 100 atm and 1000 K. The experimental results demonstrate the viability of the optical technique for measurements that support the study of compressible turbulence and the validation of numerical codes in supersonic and hypersonic wind tunnel flows.

Fletcher, D. G.↗

NASA NTRS1991

Optical waveguide formed by cubic silicon carbide on sapphire substrates

Optical confinement in beta silicon carbide (beta-SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin beta-SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far-field mode patterns are shown. It is believed that this is the first step in validating a silicon carbide optoelectronic technology.

Tang, Xiao↗

NASA NTRS1990

Development of a Fabry-Perot interferometer for rocket engine plume monitoring

The development of a lightweight, compact, high-resolution Fabry-Perot interferometer (FPI) based spectrometer capable of detecting the spectral signatures of eroding engine components during test and/or flight operations is discussed. FPI based spectrometers will be designed to be smaller and lighter than grating or prism type devices and to provide greater wavelength resolving capability. The FPI system seeks to combine the features of high line resolution, active background discrimination, smart digital signal processing, and rocket engine flight capability. The design, fabrication, and test of a breadboard FPI spectrometer have been completed and the breadboard instrument has clearly demonstrated the viability of the approach. The breadboard instrument design and test results are also presented.

Bickford, R. L.↗

NASA NTRS1991

Experimental and theoretical comparison of the Probe Thrust Vector Control concept

A concept that offers an alternate method for thrust vector control of liquid or solid propellant rockets is the use of a solid body or probe that is inserted on demand through the wall of the rocket nozzle. This Probe Thrust Vector Control (PTVC) concept is an alternative to that of a gimbaled nozzle or a Liquid Injection Thrust Vector control system. The viability of the PTVC concept can be assessed either experimentally and/or with the use of CFD. A purely experimental assessment is time consuming and expensive, whereas a CFD assessment is time- and cost-effective. Two key requirements of the concept are PTVC vectoring performance and active cooling requirements for the probe to maintain its thermal and structural integrity. The objective of the work reported here is presentation of experimental subscale cold flow tests and comparison of these tests with CFD predictions and the response time of the PTVC system.

Cavalleri, Robert↗

NASA NTRS1991

Simulation of cryogenic liquid flows with vapor bubbles

Liquid flows in rocket engine components (such as bearings, seals, and pumps) often involve the formation of vapor bubbles due to local superheating of the fluid (either boiling or cavitation). Under the present effort, an analysis has been developed for liquid flows with vapor bubbles, based on a combined Eulerian-Lagrangian technique, in which the continuous (liquid) phase is treated by solving a system of Eulerian conservation equations, while the discrete (vapor bubble) phase is dealt with by integrating Lagrangian equations of motion in computational coordinates. Vapor bubbles of changing size can be accommodated easily by this analysis, and models for the simulation of bubble formation, growth, and motion have been included. The effect of bubble motion and other bubble processes on the continuous (liquid) phase has been accounted for by appropriate bubble mass, momentum, and energy interchange source terms in the Eulerian conservation equations. To demonstrate the viability of the resulting procedure, the cavitating flow of liquid oxygen through a simplified model of a labyrinth seal has been successfully calculated.

De Jong, Frederik J.↗

NASA NTRS1991

HSCT designs for reduced sonic boom

The versatility of High Speed Civil Transports (HSCT) will be operationally limited by regulations that prohibit overland supersonic flight. This limitation gives impetus to the study of aerodynamic designs for reduced sonic boom. An HSCT design with an 'acceptable' sonic boom can allow routine overland supersonic cruise that would provide increased productivity and economic viability. During this four-year NASA-sponsored study, several configurations were designed for reduced sonic boom. An iterative technique was used in which the standard linear supersonic and Whitham sonic boom methods are extended. For the most severe sonic boom constraint of 72 dBA sonic boom loudness and 0.75 lb/sq ft shock strength at the ground, an economic benefit for operating at Mach 1.7 overland was not realized because of a decrease in the ratio of payload to takeoff gross weight. Additional design work is required to develop the best compromise between the low-boom requirements and optimum cruise performance.

Haglund, George T.↗

NASA NTRS1991

Generation of Pc 1 waves by the ion temperature anisotropy associated with fast shocks caused by sudden impulses

The high correlation of Pc 1 events with magnetospheric compressions is known. A mechanism is proposed which leads to the generation of Pc 1 waves. The interaction of a dynamic pressure pulse with the earth's bow shock leads to the formation of a weak fast-mode shock propagating into the magnetoshealth. The shock wave can pass right through a tangential discontinuity (magnetopause) and into the magnetosphere, without disturbing either of the structures. In a quasiperpendicular geometry, the shock wave exhibits anisotropic heating. This anisotropy drives unstable ion-cyclotron waves which can contribute to the generation of the Pc 1 waves which are detected. The viability of the mechanism is demonstrated with simulations. This mechanism could explain the peak in the occurrence of observed Pc 1 waves in the postnoon sector where a field-aligned discontinuity in the solar wind would most often be parallel to the magnetopause surface due to the average Parker-spiral magnetic-field configuration.

Mandt, M. E.↗

NASA NTRS1991

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Roth, Don J.↗

NASA NTRS1991

Polynomial optimization techniques for activity scheduling. Optimization based prototype scheduler

Polynomial optimization techniques for activity scheduling (optimization based prototype scheduler) are presented in the form of the viewgraphs. The following subject areas are covered: agenda; need and viability of polynomial time techniques for SNC (Space Network Control); an intrinsic characteristic of SN scheduling problem; expected characteristics of the schedule; optimization based scheduling approach; single resource algorithms; decomposition of multiple resource problems; prototype capabilities, characteristics, and test results; computational characteristics; some features of prototyped algorithms; and some related GSFC references.

Reddy, Surender↗

NASA NTRS1991

Nested ocean models: Work in progress

The ongoing work of combining three existing software programs into a nested grid oceanography model is detailed. The HYPER domain decomposition program, the SPEM ocean modeling program, and a quasi-geostrophic model written in England are being combined into a general ocean modeling facility. This facility will be used to test the viability and the capability of two-way nested grids in the North Atlantic.

Perkins, A. Louise↗

NASA NTRS1991

Space Station Freedom contingency reboost and resupply strategies

The objective of this study was to determine the requirements necessary to ensure a viable Space Station Freedom (SSF) in the event of a delay in the date of the first element launch, and/or in the event that the nominal assembly sequence is interrupted, perhaps due to a delay in the Space Shuttle Launch Schedule. Orbit lifetimes, reboost fuel requirements, and controllability requirements were calculated for each stage of the SSF assuming anywhere from a 6 to 24 month delay/interruption in the baseline SSF assembly sequence. These results were assessed in order to formulate strategies to assure SSF viability in the presence of assembly sequence delays and interruptions.

Troutman, Patrick A.↗

NASA NTRS1992

Visually Coupled Systems (VCS): The Virtual Panoramic Display (VPD) System

The development and impact is described of new visually coupled system (VCS) equipment designed to support engineering and human factors research in the military aircraft cockpit environment. VCS represents an advanced man-machine interface (MMI). Its potential to improve aircrew situational awareness seems enormous, but its superiority over the conventional cockpit MMI has not been established in a conclusive and rigorous fashion. What has been missing is a 'systems' approach to technology advancement that is comprehensive enough to produce conclusive results concerning the operational viability of the VCS concept and verify any risk factors that might be involved with its general use in the cockpit. The advanced VCS configuration described here, was ruggedized for use in military aircraft environments and was dubbed the Virtual Panoramic Display (VPD). It was designed to answer the VCS portion of the systems problem, and is implemented as a modular system whose performance can be tailored to specific application requirements. The overall system concept and the design of the two most important electronic subsystems that support the helmet mounted parts, a new militarized version of the magnetic helmet mounted sight and correspondingly similar helmet display electronics, are discussed in detail. Significant emphasis is given to illustrating how particular design features in the hardware improve overall system performance and support research activities.

Kocian, Dean F.↗

NASA NTRS1992

Eggs: The role of gravity in the establishment of the dorso-ventral axis in the amphibian embryo (7-IML-1)

The purpose of this experiment is to fertilize frog (Xenopus laevis) eggs under microgravity, to perform histological fixations at two different programmed times, and after return to Earth, to determine whether timing and pattern of egg cleavages and axis formation are normal. Because of the limited viability of the gametes, this experiment will be the very first to be activated in the Biorack. Various aspects of this investigation are discussed.

Ubbels, Geertje A.↗

NASA NTRS1992

Growth and sporulation of Bacillus subtilis under microgravity (7-IML-1)

The experiment was aimed at measuring the growth and sporulation of Bacillus subtilis under microgravity. The hardware for the experiment consists of a culture chamber (15 ml) made from titanium and closed by a membrane permeable for gases but not for water. Two variants of this basic structure were built which fit into the standard Biorack container types 1 and 2 respectively. Growth of the bacteria will be monitored by continuously measuring the optical density with a built-in miniaturized photometer. Other parameters (viability, sporulation, fine structure, size distribution of cells and spores, growth kinetics, etc.) will be measured on the fixed samples and on those where metabolism was temporarily halted, respectively.

Mennigmann, Horst-Dieter↗

NASA NTRS1990

Multiple access capacity trade-offs for a Ka-band personal access satellite system

System capability is critical to the economic viability of a personal satellite communication system. Ka band has significant potential to support a high capacity multiple access system because of the availability of bandwidth. System design tradeoffs are performed and multiple access schemes are compared with the design goal of achieving the highest capacity and efficiency. Conclusions regarding the efficiency of the different schemes and the achievable capacities are given.

Dessouky, Khaled↗

NASA NTRS1990

Description and performance of a digital mobile satellite terminal

A major goal of the Mobile Satellite Experiment (MSAT-X) program at the Jet Propulsion Lab (JPL) is the development of an advanced digital terminal for use in land mobile satellite communication. The terminal has been developed to minimize the risk of applying advanced technologies to future commercial mobile satellite systems (MSS). Testing with existing L band satellites was performed in fixed, land mobile and aeronautical mobile environments. JPL's development and tests of its mobile terminal have demonstrated the viability of narrowband digital voice communications in a land mobile environment through geostationary satellites. This paper provides a consolidated description of the terminal architecture and the performance of its individual elements.

Lay, N.↗

NASA NTRS1992

Comparison of epifluorescent viable bacterial count methods

Two methods, the 2-(4-Iodophenyl) 3-(4-nitrophenyl) 5-phenyltetrazolium chloride (INT) method and the direct viable count (DVC), were tested and compared for their efficiency for the determination of the viability of bacterial populations. Use of the INT method results in the formation of a dark spot within each respiring cell. The DVC method results in elongation or swelling of growing cells that are rendered incapable of cell division. Although both methods are subjective and can result in false positive results, the DVC method is best suited to analysis of waters in which the number of different types of organisms present in the same sample is assumed to be small, such as processed waters. The advantages and disadvantages of each method are discussed.

Rodgers, E. B.↗

NASA NTRS1992

High speed research system study. Advanced flight deck configuration effects

In mid-1991 NASA contracted with industry to study the high-speed civil transport (HSCT) flight deck challenges and assess the benefits, prior to initiating their High Speed Research Program (HSRP) Phase 2 efforts, then scheduled for FY-93. The results of this nine-month effort are presented, and a number of the most significant findings for the specified advanced concepts are highlighted: (1) a no nose-droop configuration; (2) a far forward cockpit location; and (3) advanced crew monitoring and control of complex systems. The results indicate that the no nose-droop configuration is critically dependent upon the design and development of a safe, reliable, and certifiable Synthetic Vision System (SVS). The droop-nose configuration would cause significant weight, performance, and cost penalties. The far forward cockpit location, with the conventional side-by-side seating provides little economic advantage; however, a configuration with a tandem seating arrangement provides a substantial increase in either additional payload (i.e., passengers) or potential downsizing of the vehicle with resulting increases in performance efficiencies and associated reductions in emissions. Without a droop nose, forward external visibility is negated and takeoff/landing guidance and control must rely on the use of the SVS. The technologies enabling such capabilities, which de facto provides for Category 3 all-weather operations on every flight independent of weather, represent a dramatic benefits multiplier in a 2005 global ATM network: both in terms of enhanced economic viability and environmental acceptability.

Swink, Jay R.↗