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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

On the Role of Surface Friction in Tropical Intraseasonal Oscillation

The Madden-Julian oscillation (MJO), or the tropical intraseasonal oscillation, has attracted much attention, ever since its discovery in the early seventies for reasons of both scientific understanding and practical forecasts. Among the theoretical interpretations of the MJO, the wave-CISK (conditional instability of the second kind) mechanism is the most popular. The basic idea of the wave-CISK interpretation is that the cooperation between the low-level convergence associated with the eastward moving Kelvin wave and the cumulus convection generates an eastward moving Kelvin-wave-like mode. Later it was recognized that the MJO has an important Rossby-wave-like component. However linear analysis and numerical simulations based on it (even when conditional heating is used) have revealed two problems with the wave-CISK interpretation; i.e., excessive speed and the most preferred scale being zero or grid scale. Chao (1995) presented a discussion of these problems and attributed these problems to the particular type of expression for the cumulus heating used in the linear analyses and numerical studies (i.e., the convective heating is proportional to low-level convergence and a fixed vertical heating profile). It should be pointed out that in the relatively successful simulation of MJO with general circulation models the problem of grid scale being the most preferred scale does not appear and die problem of excessive speed is not as severe as in the linear analysis.

Chao, Winston C.↗
NASA NTRS1999

Remote X-Ray Diffraction and X-Ray Fluorescence Analysis on Planetary Surfaces

The legacy of planetary X-ray Diffraction (XRD) and X-ray Fluorescence (XRF) began in 1960 when W. Parish proposed an XRD instrument for deployment on the moon. The instrument was built and flight qualified, but the Lunar XRD program was cancelled shortly before the first human landing in 1969. XRF chemical data have been collected in situ by surface landers on Mars (Viking 1 & 2, Pathfinder) and Venus (Venera 13 & 14). These highly successful experiments provide critical constraints on our current understanding of surface processes and planetary evolution. However, the mineralogy, which is more critical to planetary surface science than simple chemical analysis, will remain unknown or will at best be imprecisely constrained until X-ray diffraction (XRD) data are collected. Recent progress in X-ray detector technology allows the consideration of simultaneous XRD (mineralogic analysis) and high-precision XRF (elemental analysis) in systems miniaturized to the point where they can be mounted on fixed landers or small robotic rovers. There is a variety of potential targets for XRD/XRF equipped landers within the solar system, the most compelling of which are the poles of the moon, the southern highlands of Mars and Europa.

Blake, David F.↗
NASA NTRS2000

Experimental Replication of an Aeroengine Combustion Instability

Combustion instabilities in gas turbine engines are most frequently encountered during the late phases of engine development, at which point they are difficult and expensive to fix. The ability to replicate an engine-traceable combustion instability in a laboratory-scale experiment offers the opportunity to economically diagnose the problem (to determine the root cause), and to investigate solutions to the problem, such as active control. The development and validation of active combustion instability control requires that the causal dynamic processes be reproduced in experimental test facilities which can be used as a test bed for control system evaluation. This paper discusses the process through which a laboratory-scale experiment was designed to replicate an instability observed in a developmental engine. The scaling process used physically-based analyses to preserve the relevant geometric, acoustic and thermo-fluid features. The process increases the probability that results achieved in the single-nozzle experiment will be scalable to the engine.

Cohen, J. M.↗
NASA NTRS2001

Longitudinal Mode Aeroengine Combustion Instability: Model and Experiment

Combustion instabilities in gas turbine engines are most frequently encountered during the late phases of engine development, at which point they are difficult and expensive to fix. The ability to replicate an engine-traceable combustion instability in a laboratory-scale experiment offers the opportunity to economically diagnose the problem more completely (to determine the root cause), and to investigate solutions to the problem, such as active control. The development and validation of active combustion instability control requires that the casual dynamic processes be reproduced in experimental test facilities which can be used as a test bed for control system evaluation. This paper discusses the process through which a laboratory-scale experiment and be designed to replicate an instability observed in a developmental engine. The scaling process used physically-based analyses to preserve the relevant geometric, acoustic, and thermo-fluid features, ensuring that results achieved in the single-nozzle experiment will be scalable to the engine.

Cohen, J. M.↗
NASA NTRS1999

The Mean Curvature of the Influence Surface of Wave Equation With Sources on a Moving Surface

The mean curvature of the influence surface of the space-time point (x, t) appears in linear supersonic propeller noise theory and in the Kirchhoff formula for a supersonic surface. Both these problems are governed by the linear wave equation with sources on a moving surface. The influence surface is also called the Sigma - surface in the aeroacoustic literature. This surface is the locus, in a frame fixed to the quiescent medium, of all the points of a radiating surface f(x, t) = 0 whose acoustic signals arrive simultaneously to an observer at position x and at the time t. Mathematically, the Sigma- surface is produced by the intersection of the characteristic conoid of the space-time point (x, t) and the moving surface. In this paper, we derive the expression for the local mean curvature of the Sigma - space of the space-time point for a moving rigid or deformable surface f(x, t) = 0. This expression is a complicated function of the geometric and kinematic parameters of the surface f(x, t) = 0. Using the results of this paper, the solution of the governing wave equation of high speed propeller noise radiation as well as the Kirchhoff formula for a supersonic surface can be written as very compact analytic expression.

Farassat, F.↗
NASA NTRS2012

Error Reduction Methods for Integrated-path Differential-absorption Lidar Measurements

We report new modeling and error reduction methods for differential-absorption optical-depth (DAOD) measurements of atmospheric constituents using direct-detection integrated-path differential-absorption lidars. Errors from laser frequency noise are quantified in terms of the line center fluctuation and spectral line shape of the laser pulses, revealing relationships verified experimentally. A significant DAOD bias is removed by introducing a correction factor. Errors from surface height and reflectance variations can be reduced to tolerable levels by incorporating altimetry knowledge and "log after averaging", or by pointing the laser and receiver to a fixed surface spot during each wavelength cycle to shorten the time of "averaging before log".

averging before log↗
NASA NTRS1980

Grid evolution in time asymptotic problems

A technique for generating systems of coordinates for solving time asymptotic problems is described which provides a simple way of moving the mesh points in physical space and reduces the error in the solution relative to that obtained using a fixed mesh. First order partial differential equations are formulated for the grid point velocity in transient problems. Local flow information and boundary motion are used to determine the interior grid point motion.

Rai, M. M.↗
NASA NTRS2016

eLISA Telescope In-field Pointing and Scattered Light Study

The orbital motion of the three spacecraft that make up the eLISA Observatory constellation causes long-arm line of sight variations of approximately ± one degree over the course of a year. The baseline solution is to package the telescope, the optical bench, and the gravitational reference sensor (GRS) into an optical assembly at each end of the measurement arm, and then to articulate the assembly. An optical phase reference is exchanged between the moving optical benches with a single mode optical fiber (“backlink” fiber). An alternative solution, referred to as in-field pointing, embeds a steering mirror into the optical design, fixing the optical benches and eliminating the backlink fiber, but requiring the additional complication of a two-stage optical design for the telescope. We examine the impact of an in-field pointing design on the scattered light performance.

Livas, J↗
NASA NTRS2018

In-Flight Characterization of the Lunar Orbiter Laser Altimeter Instrument Pointing and Far-Field Pattern

The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) has collected nearly seven billion measurements of surface height on the Moon with an absolute accuracy of ∼1 m and a precision of ∼10 cm. Converting time-of-flight laser altimeter measurements to topographic elevations requires accurate knowledge of the laser pointing with respect to the spacecraft body-fixed coordinate system. To that end, we have utilized altimetric crossovers from LOLA, as well as bidirectional observations of the LOLA laser and receiver boresight via an Earth-based laser tracking ground station. Based on a sample of ∼780,000 globally distributed crossovers from the circular-orbit phase of LRO's mission (∼27 months), we derive corrections to the LOLA laser boresight. These corrections improve the cross-track and along-track agreement of the crossovers by 24% and 33%, respectively, yielding RMS residuals of ∼10 m. Since early in the LRO mission, the bidirectional laser tracking experiments have confirmed a pointing anomaly when the LOLA instrument is facing toward deep space or the night side of the Moon and have allowed the reconstruction of the laser far-field pattern and receiver telescope pointing. By conducting such experiments shortly after launch and nearly eight years later, we have directly measured changes in the laser characteristics and obtained critical data to understand the laser behavior and refine the instrument pointing model. The methods and results presented here are also relevant to the design, fabrication, and operation of future planetary laser altimeters and their long-term behavior in the space environment.

Barker, M. K.↗
NASA NTRS1999

Inlet Noise Reduction by Shielding for the Blended-Wing-Body Airplane

Noise shielding benefits associated with an advanced unconventional subsonic transport concept, the Blended-Wing-Body, were studied using a 4- percent scale, 3-engine nacelle model. The study was conducted in the Anechoic Noise Research Facility at NASA Langley Research Center. A high- frequency, wideband point source was placed inside the nacelles of the center engine and one of the side engines in order to simulate broadband engine noise. The sound field of the model was measured with a rotating microphone array that was moved to various stations along the model axis and with a fixed array of microphones that was erected behind the model. Ten rotating microphones were traversed a total of 22 degrees in 2-degree increments. Seven fixed microphones covered an arc that extended from a point in the exhaust exit plane of the center engine (and directly below its centerline) to a point 30 degrees above the jet centerline. While no attempt was made to simulate the noise emission characteristics of an aircraft engine, the model source was intended to radiate sound in a frequency range encompassing 1, 2, and 3 times the blade passage of a typical full-scale engine. In this study, the Blended-Wing-Body model was found to provide significant shielding of inlet noise. In particular, noise radiated downward into the forward sector was reduced by 20 to 25 dB overall in the full-scale frequencies from 2000 to 4000 Hz, decreasing to 10 dB or less at the lower frequencies. Also, it was observed that noise associated with the exhaust radiates into the sector directly below the model downstream to reduce shielding efficiency.

Clark, Lorenzo R.↗
NASA NTRS1975

Some results of the hydrodynamic theory of finite-amplitude waves

Standing waves can be interpreted as free waves between two vertical walls; for a standing wave in an unlimited container there is no transport of liquid mass in the horizontal direction. Standing waves of finite amplitude also possess the following properties not possessed by the waves of the linear theory: (1) there are no motionless points, (2) the points of maximum amplitude (crests and troughs) are fixed, and coincide with the antinodes of the original linear wave, (3) the ordinates of the wave crests are greater in absolute magnitude than the ordinates of the troughs; the wave is similar to a trochoid curve; (4) the wave profile never becomes straight; and (5) the frequency of the oscillations depends not only on the wave length but also on the amplitude.

Sekerzh-Zenkovich, Y. I.↗
NASA NTRS1975

A high-precision CdS photodetector for sun sensor applications

A sun detector developed for the Mariner Jupiter/Saturn mission is described. Redundant photopotentiometers for both pitch and yaw axes, positioned below slit apertures, provide spacecraft stabilization and biased operation over plus or minus 20-deg fields of view. The biased (off-sun) operation is required for pointing the 366-cm-diameter (spacecraft-fixed) radio antenna toward earth. Configuration and fabrication processes are presented, along with a summary of development history. Particular attention is given to the properties of cadmium sulfide as these affect adaptation to this application.

Chamberlain, F. R.↗
NASA NTRS1977

Performance tests of two precision attitude determination systems

Results of laboratory performance tests of two satellite attitude determination systems are given. One system employed a strapdown star tracker and gyro assembly, the other a single axis, gimballed star tracker and a gyro assembly. The laboratory tests simulated those orbit conditions which would be experienced on a three axis stabilized, earth pointed satellite in geosynchronous orbit. A ground-fixed laboratory test was performed in which system axes remained stationary in the laboratory coordinates while revolving star beams stimulated the star trackers. The laboratory instrumentation techniques used to meet the stringent accuracy requirements are described. Results are presented which show both systems met the performance goal of 3.6 arc seconds. Comparative analyses of both systems are also discussed.

Mcaloon, K. J.↗
NASA NTRS1981

Stratospheric trace constituent profile retrievals using laser heterodyne radiometer IR limb sensing spectra

A retrieval technique for high resolution IR solar occultation limb sensing data is described for profiling stratospheric trace constituents. Remote measurement of ClO during sunset in the 24-45-km region with a 2-km height resolution is chosen as an example. Two types of instruments are considered: a laser heterodyne radiometer with line resolving spectral resolution and an interferometer spectrometer with a fixed slit width of 0.02/cm. It is pointed out that a multichannel approach is necessary with the heterodyne instrument for improved retrieval accuracy. The error analysis indicates the relative sizes of instrument noise and other sources of error in the retrieval of altitude profiles with high (2-km) vertical resolution.

Majumdar, A. K.↗
NASA NTRS1981

Galileo maneuver analysis

In the maneuver analysis of the Galileo spacecraft, analytic models have been developed to assess the performance of an interplanetary dual spin spacecraft. These models take into account all the important effects of dual spin and flexible body dynamics to determine the spacecraft capability to achieve precise velocity changes for a variety of maneuver modes, as dictated by the requirements and as are tested and verified by computer simulation. Proportional velocity change magnitude accuracies as small as 0.34%, proportional velocity change pointing accuracies as little as 10 milliradians and fixed velocity change accuracies as precise as 0.015 m/sec are indicative of the stringency of these requirements. Error sources considered in the statistical analysis include probabilistic uncertainties due to wobble, plume impingement, nutation, thruster and accelerometer misalignments and radial offsets, gyro drift, burn timing, mass properties and algorithm errors. With its twelve thrusters, the versatility of the spacecraft to maneuver among the Galilean moons for eleven encounters after delivering a probe into the Jovian atmosphere provides a new level of challenge in the area of maneuver analysis.

Longuski, J. M.↗
NASA NTRS1982

The use of solution adaptive grids in solving partial differential equations

The grid point distribution used in solving a partial differential equation using a numerical method has a substantial influence on the quality of the solution. An adaptive grid which adjusts as the solution changes provides the best results when the number of grid points available for use during the calculation is fixed. Basic concepts used in generating and applying adaptive grids are reviewed in this paper, and examples illustrating applications of these concepts are presented.

Anderson, D. A.↗
NASA NTRS1984

Remote sensing of biomass and annual net aerial primary productivity of a salt marsh

Net aerial primary productivity is the rate of storage of organic matter in above-ground plant issues exceeding the respiratory use by the plants during the period of measurement. It is pointed out that this plant tissue represents the fixed carbon available for transfer to and consumption by the heterotrophic organisms in a salt marsh or the estuary. One method of estimating annual net aerial primary productivity (NAPP) required multiple harvesting of the marsh vegetation. A rapid nondestructive remote sensing technique for estimating biomass and NAPP would, therefore, be a significant asset. The present investigation was designed to employ simple regression models, equating spectral radiance indices with Spartina alterniflora biomass to nondestructively estimate salt marsh biomass. The results of the study showed that the considered approach can be successfully used to estimate salt marsh biomass.

Hardisky, M. A.↗