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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A relationship between peak temperature drop and velocity differential in a microburst

Results from numerical microburst simulations using the Terminal Area Simulation System (Proctor, 1987) are used to develop a relationship between wind velocity differential and peak temperature drop. The numerical model and the relationships derived from the model are described. The relationship between peak temperature drop and differential wind velocity is shown to be valid during microburst development, for all precipitation shaft intensities and diameters. It is found that the relationship is not valid for low-reflectivity microburst events or in the presence of ground-based stable layers. The use of the relationship in IR wind shear detection systems is considered.

Proctor, Fred H.↗
NASA NTRS2011

Sodium Velocity Maps on Mercury

The objective of the current work was to measure two-dimensional maps of sodium velocities on the Mercury surface and examine the maps for evidence of sources or sinks of sodium on the surface. The McMath-Pierce Solar Telescope and the Stellar Spectrograph were used to measure Mercury spectra that were sampled at 7 milliAngstrom intervals. Observations were made each day during the period October 5-9, 2010. The dawn terminator was in view during that time. The velocity shift of the centroid of the Mercury emission line was measured relative to the solar sodium Fraunhofer line corrected for radial velocity of the Earth. The difference between the observed and calculated velocity shift was taken to be the velocity vector of the sodium relative to Earth. For each position of the spectrograph slit, a line of velocities across the planet was measured. Then, the spectrograph slit was stepped over the surface of Mercury at 1 arc second intervals. The position of Mercury was stabilized by an adaptive optics system. The collection of lines were assembled into an images of surface reflection, sodium emission intensities, and Earthward velocities over the surface of Mercury. The velocity map shows patches of higher velocity in the southern hemisphere, suggesting the existence of sodium sources there. The peak earthward velocity occurs in the equatorial region, and extends to the terminator. Since this was a dawn terminator, this might be an indication of dawn evaporation of sodium. Leblanc et al. (2008) have published a velocity map that is similar.

Potter, A. E.↗
NASA NTRS1987

Optimal time free nodal transfers between elliptical orbits

The paper presents the necessary conditions for the minimum fuel, time-free transfer between two noncoplanar elliptical orbits. It is shown that the solution is obtained by solving a system of three nonlinear equations for three unknowns. The case where the impulses are applied along the line of nodes is discussed. In general, this nodal transfer is nonoptimal, but the characteristic velocity for the best nodal transfer, called the minimizing nodal transfer, is reasonably close to the one for the optimal transfer for it to be useful as a substitute for a practical transfer. Furthermore, when the relative position of the two terminal orbits is varied, the two characteristic velocities, for the minimizing nodal transfer and the optimal transfer, exhibit the same trend in the sense that they pass through their maxima and minima at nearly the same relative position. This makes the set of explicit formulas for computing the minimizing nodal transfer, as presented in this paper, a useful tool for designing a minimum fuel transfer between several orbits.

Vinh, Nguyen X.↗
NASA NTRS1978

The energy balance of the nighttime thermosphere

Energy balance considerations for the thermosphere are affected by the uncertainty of the solar EUV flux. The problem is simplified by investigating only the nighttime thermosphere. Vapor trail measurements provide wind data at the sunset and sunrise terminators and near the polar cap boundary. Temperature and density profiles were obtained from incoherent scatter and Ogo 6 measurements. Based on the available data the energy losses are estimated to be 8 times 10 to the 10th W due to downward conduction at 120 km and 3 times 10 to the 10th W due to infrared radiation. The energy carried by the measured winds from the polar cap is found to be 4.6 times 10 to the 10th W and that transported across the mid- and low-latitude terminators, 7.6 to 11 times 10 to the 10th W. The greatest uncertainty in this analysis was in the estimates of the differences in the densities and temperatures in the lower thermosphere at the dawn and dusk terminators. Because of the large rotational velocity of the earth, small differences in these parameters correspond to large amounts of energy transported to the night hemisphere.

Glenar, D. A.↗
NASA NTRS1987

Sound radiation from single and annular stream nozzles, with modal decomposition of in-duct acoustic power

An experimental program was carried out to study the acoustic characteristics of single and annular stream duct-nozzle systems at various flow conditions by using a refined acoustic impulse technique. In this technique, signal synthesis and signal averaging processes are incorporated to generate a desired impulsive signal from acoustic driver(s) and to eliminate background noise (flow noise) from in-duct and far field signals, respectively. The contribution of higher order modes to incident reflected and transmitted acoustic powers is accounted for by using a modal decomposition process. The annular stream terminations were tested statically at various annular stream flow velocities with no inner stream flow. The results derived from the experiments include in-duct acoustic powers, termination reflection coefficients, transmission coefficients, far field power, and acoustic dissipation.

Salikuddin, M.↗
NASA NTRS1992

Computation of near-minimum-time maneuvers of flexible structures by parameter optimization

Near-minimum-time attitude maneuvers of space structures as well as ground based test articles are considered. Switching nature of the controls for rigid body maneuvers are illustrated using a control-cube and a critical control axis of rotation. The presence of torque smoothing and where appropriate, gravitational effects and connections to other bodies are explicitly included in the mathematical models of the systems to be optimized. A maximum fuel consumption constraint is included besides the required terminal conditions on attitude and angular velocities. The switch times, maximum thrust magnitudes, and smoothing parameters are determined using the Sequential Quadratic Programming method for parameter optimization. Results indicating attitude and angular velocity histories, thruster forces, and structural vibrations are presented for three, four, and five switch maneuvers, as well as maneuvers that involve large coasting arcs.

Vadali, S. R.↗
NASA NTRS1992

Shuttle entry guidance revisited

The Shuttle entry guidance concept is reviewed which is aimed at tracking a reference drag trajectory that leads to the specified range and velocity for the initiation of the terminal energy management phase. An approximate method of constructing the domain of attraction is proposed, and its validity is ascertained by simulation. An alternative guidance law yielding global exponential tracking in the absence of control saturation is derived using a feedback linearization method. It is noted that the alternative guidance law does not improve on the stability and performance of the current guidance law, for the operating domain and control capability of the Shuttle. It is suggested that the new guidance law with a larger operating domain and increased lift-to-drag capability would be superior.

Mease, Kenneth D.↗
NASA NTRS1998

Evidence for Asteroidal Origin of the Tunguska Object

The progress in the understanding of the Tunguska object is reviewed in the light of evidence presented in numerous recent investigations, which appeared following the publication of my 1983 paper on the object's proposed asteroidal nature. The issues addressed extensively in the present review involve: (i) the fundamental characteristics of the event, such as the object's energy, altitude and velocity at the time of its terminal explosion and the dynamic pressure involved; (ii) the problem of atmospheric fragmentation of very massive impactors and the implications for their ablation and deceleration; (iii) new analysis of the orientation of the Tunguska object's heliocentric orbit based on the best data on the apparent radiant of the fireball's atmospheric trajectory; and (iv) comparison with the findings of other recent investigations, including compositional studies. Also employed in the arguments are the results now available on the impacts of comet Shoemaker-Levy 9's fragments into Jupiter and the findings of a recent comparative study of two huge fireballs (one cometary, one stony, both involving impactors several meters across) observed with the cameras of the European Network of fireball monitoring. It is concluded that hypotheses based on presumed cometary origin of the Tunguska object encounter unsurmountable difficulties and that the interpretation of the event as a fall of a small stony or carbonaceous asteroid is not only plausible, but virtually certain.

Sekanina, Z.↗
NASA NTRS2005

Planar Laser-Induced Iodine Fluorescence Measurements in Rarefied Hypersonic Flow

A planar laser-induced fluorescence (PLIF) technique is discussed and applied to measurement of time-averaged values of velocity and temperature in an I(sub 2)-seeded N(sub 2) hypersonic free jet facility. Using this technique, a low temperature, non-reacting, hypersonic flow over a simplified model of a reaction control system (RCS) was investigated. Data are presented of rarefied Mach 12 flow over a sharp leading edge flat plate at zero incidence, both with and without an interacting jet issuing from a nozzle built into the plate. The velocity profile in the boundary layer on the plate was resolved. The slip velocity along the plate, extrapolated from the velocity profile data, varied from nearly 100% down to 10% of the freestream value. These measurements are compared with results of a DSMC solution. The velocity variation along the centerline of a jet issuing from the plate was measured and found to match closely with the correlation of Ashkenas and Sherman. The velocity variation in the oblique shock terminating the jet was resolved sufficiently to measure the shock wave thickness.

Cecil, Eric↗
DOE OSTI2025

Surface acoustic waves and lattice vibrations in two-dimensional Ti 3 ⁢C 2 ⁢𝑇 𝑥 (𝑇 =O, F) MXene films

We investigated surface acoustic wave (SAW) propagation and lattice vibrations in two-dimensional (2D) titanium carbide (Ti 3 ⁢C 2 ⁢𝑇 x ) MXene films as a function of surface termination and layer stacking, using atomistic simulations. We found that SAW propagation velocity is highly sensitive to both single-layer properties and interlayer bonding. Surface terminations significantly modulate wave behavior, with oxygen and fluorine terminations producing distinct effects on wave propagation, with oxygen-terminated monolayers exhibiting 20% higher wave speeds than fluorine counterparts due to strengthened intralayer bonds. Key observations include the transition from one to two layers causing wave speed variations, and the development of interlayer modes that generate more dispersed lattice vibrations. As the film layer thickness increases, SAW propagation becomes predominantly confined to the upper surface, with coherence of vibrational modes diminishing in multilayer structures. These findings suggest MXene terminations and layer stacking are crucial parameters for controlling SAW behavior, offering promising avenues for novel acoustic wave device applications.

2-dimensional systems↗
NASA NTRS2011

FPGA Sequencer for Radar Altimeter Applications

A sequencer for a radar altimeter provides accurate attitude information for a reliable soft landing of the Mars Science Laboratory (MSL). This is a field-programmable- gate-array (FPGA)-only implementation. A table loaded externally into the FPGA controls timing, processing, and decision structures. Radar is memory-less and does not use previous acquisitions to assist in the current acquisition. All cycles complete in exactly 50 milliseconds, regardless of range or whether a target was found. A RAM (random access memory) within the FPGA holds instructions for up to 15 sets. For each set, timing is run, echoes are processed, and a comparison is made. If a target is seen, more detailed processing is run on that set. If no target is seen, the next set is tried. When all sets have been run, the FPGA terminates and waits for the next 50-millisecond event. This setup simplifies testing and improves reliability. A single vertex chip does the work of an entire assembly. Output products require minor processing to become range and velocity. This technology is the heart of the Terminal Descent Sensor, which is an integral part of the Entry Decent and Landing system for MSL. In addition, it is a strong candidate for manned landings on Mars or the Moon.

Berkun, Andrew C.↗
NASA NTRS1973

On local inflexional instability in boundary-layer flows.

Development of a linearized theory of the two- and three-dimensional incompressible viscous flows ensuing from locally unstable velocity profiles. Indications of the theory with respect to the instability of the two-dimensional separation bubble and the mechanisms underlying formation of the turbulence wedge behind a fixed roughness element are pointed out. In connection with the aforementioned mechanisms, a theoretically based argument is advanced that, as a result of local inflectional instability of the velocity profile in a succession of skewed planes, a corresponding succession of stationary vortices is induced, the induction process terminating at the boundaries of the turbulence wedge when the velocity profiles along the boundaries themselves become unstable. It is suggested that a rational method of predicting the occurrence of roughness-induced turbulence wedges might be possible if a theory were available for the steady laminar flow caused by the roughness at a stage just prior to transition.

Tobak, M.↗
NASA NTRS1975

Is the four-day 'rotation' of Venus illusory

An overlooked systematic error exists in the apparent radial velocities of solar lines reflected from regions of Venus near the terminator, owing to a combination of the finite angular size of the sun and its large equatorial velocity of rotation. This error produces an apparent, but fictitious, retrograde component of planetary rotation, typically on the order of 40 m/sec. Spectroscopic, photometric, and radiometric evidence against a 4-day atmospheric rotation is reviewed. The bulk of the somewhat contradictory evidence seems to favor slow motions, on the order of 5 m/sec, in the atmosphere of Venus; the 4-day 'rotation' may be due to a traveling wavelike disturbance, not bulk motions, driven by the UV albedo differences.

Young, A. T.↗
DOE OSTI2021

Time-resolved Rotational Velocities in the Upper Atmosphere of WASP-33 b

While steady empirical progress has been made in understanding the structure and composition of hot-planet atmospheres, direct measurements of velocity signatures, including winds, rotation, and jets, have lagged behind. Quantifying atmospheric dynamics of hot planets is critical for a complete understanding of their atmospheres, and such measurements may even illuminate other planetary properties, such as magnetic field strengths. In this manuscript we present the first detection of the Balmer lines Hα and Hβ in the atmosphere of the ultra-hot Jupiter WASP-33 b. Using atmospheric models that include the effects of atmospheric dynamics, we show that the shape of the average Balmer line transmission spectrum is consistent with rotational velocities in the planet’s thermosphere of v{sub rot}=10.1{sub −1.0}{sup +0.8} km s{sup −1}. We also measure a low-significance day- to nightside velocity shift of −4.6{sub −3.4}{sup +3.4} km s{sup −1} in the transmission spectrum, which is naturally explained by a global wind across the planet’s terminator. In a separate analysis the time-resolved velocity centroids of individual transmission spectra show unambiguous evidence of rotation, with a best-fit velocity of 10.0{sub −2.0}{sup +2.4} km s{sup −1}, consistent with the value of v {sub rot} derived from the shape of the average Balmer line transmission spectrum. Our observations and analysis confirm the power of time-resolved transmission spectra with a high signal-to-noise ratio to measure the velocity structures in exoplanet atmospheres. The high rotational and wind velocities we measure highlight the need for more detailed 3D global climate simulations of the rarefied upper atmospheres of ultra-hot gas giants.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1983

Dual measurement terminal fall speeds and multiple Doppler winds

It is shown that radar-derived terminal fall speed measurements can be useful in determining vertical air velocity in the middle troposphere by means of a network of Doppler radars. The theoretical principles of the dual measurement technique are described, and the relationship between measurement accuracies and theoretical estimates of terminal fall speeds is discussed. It is demonstrated that the use of differential reflectivity to estimate terminal fall speeds can reduce the standard error of vertical velocity estimates by 40-50 percent.

Grosh, R. C.↗
NASA NTRS1974

Is the four-day rotation of Venus illusory?

An overlooked systematic error exists in the apparent radial velocities of solar lines reflected from regions of Venus near the terminator, owing to a combination of the finite angular size of the Sun and its large (2 km/sec) equatorial velocity of rotation. This error produces an apparent, but fictitious, retrograde component of planetary rotation, typically on the order of 40 meters/sec. Spectroscopic, photometric, and radiometric evidence against a 4-day atmospheric rotation is also reviewed. The bulk of the somewhat contradictory evidence seems to favor slow motions, on the order of 5 m/sec, in the atmosphere of Venus; the 4-day rotation may be due to a traveling wave-like disturbance, not bulk motions, driven by the UV albedo differences.

Young, A. T.↗
NASA NTRS1984

Spokes in Saturn's rings - Dynamical and reflectance properties

The results and implications of dynamical and reflectance studies of spokes in the Voyager 2 low-resolution ring movie are presented. The spoke of greater interest (Spoke 1) can be traced from its first appearance on the morning and to its terminal dispersion on the evening side. Orbital velocities, reflectances, and reflectance profiles are reported. The behavior of Spoke 1 conforms to the plasma cloud model of spoke formation and evolution proposed by Goertz and Morfill (1983). A second spoke observed in the ring movie provides corroborating support for the observed behavior of Spoke 1.

Eplee, R. E., Jr.↗