Search NASA⌕ Search

SEARCH · Search NASA

Results for “relative phase angle”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Fluctuations and massive separation in three-dimensional shock-wave/boundary-layer interactions

Shock-wave unsteadiness was observed in rapidly compressed supersonic turbulent boundary layer flows with significant separation. A Mach 2.85 shock-wave/turbulent boundary layer flow was set up over a series of cylinder-flare bodies in the High Reynolds Number Channel 1. The transition from fully attached to fully separated flow was studied using axisymmetric flares with increasing compression angles. In the second phase, the 30-deg flare was inclined relative to the cylinder axis, so that the effect on a separated flow of increasing three-dimensionality could be observed. Two 3-D separated cases are examined. A simple conditional sampling technique is applied to the data to group them according to an associated shock position. Mean velocities and turbulent kinetic energies, computed from the conditionally sampled data, are compared to those from the unsorted data and to computed values. Three basic questions were addressed: can conditional sampling be used to provide snapshots of the flow; are averaged turbulence quantities dominated by the bimodal nature of the interaction; and is the shock unsteadiness really important to computational accuracy.

Kussoy, M. I.↗
NASA NTRS1999

IMF Length Scales and Predictability: The Two Length Scale Medium

We present preliminary results from a systematic study using simultaneous data from three spacecraft, Wind, IMP 8 (Interplanetary Monitoring Platform) and Geotail to examine interplanetary length scales and their implications on predictability for magnetic field parcels in the typical solar wind. Time periods were selected when the plane formed by the three spacecraft included the GSE (Ground Support Equipment) x-direction so that if the parcel fronts were strictly planar, the two adjacent spacecraft pairs would determine the same phase front angles. After correcting for the motion of the Earth relative to the interplanetary medium and deviations in the solar wind flow from radial, we used differences in the measured front angle between the two spacecraft pairs to determine structure radius of curvature. Results indicate that the typical radius of curvature for these IMF parcels is of the order of 100 R (Sub E). This implies that there are two important IMF (Interplanetary Magnetic Field) scale lengths relevant to predictability: (1) the well-established scale length over which correlations observed by two spacecraft decay along a given IMF parcel, of the order of a few tens of Earth radii and (2) the scale length over which two spacecraft are unlikely to even observe the same parcel because of its curvature, of the order of a hundred Earth radii.

Collier, Michael R.↗
NASA NTRS1987

Titania's opposition effect - Analysis of Voyager observations

Voyager 2 obtained images of Titania over phase angles ranging from 0.8 to 150 deg and at sufficient resolution to investigate the photometric behavior of different surface units. The large, relatively narrow opposition surge detected from earth was confirmed and can be successfully modeled with Hapke's (1986) photometric theory. Opposition effects do not vary greatly between bright areas (craters and ejecta) and dark areas, but the brightness of the brighter areas decreases more slowly with increasing phase angle than that of the dark areas. Thus the fresher craters and their ejecta become less prominent in relation to the background as opposition is approached. This effect is best explained by a modest difference in single-scattering albedo.

Thomas, P. C.↗
NASA NTRS2010

Phase-Array Approach to Optical Whispering Gallery Modulators

This technology leverages the well-defined orbital number of a whispering gallery modulator (WGM) to expand the range of applications for such resonators. This property rigidly connects the phase variation of the field in this mode with the azimuthal angle between the coupling locations. A WGM with orbital momentum L has exactly L instant nodes around the circumference of the WGM resonator supporting such a mode. Therefore, in two locations separated by the arc alpha, the phase difference of such a field will be equal to phi= alpha L. Coupling the field out of such locations, and into a balanced interferometer, once can observe a complete constructive or distractive interference (or have any situation in between) depending on the angle alpha. Similarly, a mode L + delta L will pick up the phase phi + alpha delta L. In all applications of a WGM resonator as a modulator, the orbital numbers for the carrier and sidebands are different, and their differences delta L are known (usually, but not necessarily, delta L = 1). Therefore, the choice of the angle alpha, and of the interferometer arms difference, allows one to control the relative phase between different modes and to perform the conversion, separation, and filtering tasks necessary.

Strekalov, Dmitry↗
NASA NTRS2005

The Atmospheres of Saturn and Titan in the Near-Infrared: First Results of Cassini/VIMS

The wide spectral coverage and extensive spatial, temporal, and phase-angle mapping capabilities of the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens Orbiter are producing fundamental new insights into the nature of the atmospheres of Saturn and Titan. For both bodies, VIMS maps over time and solar phase angles provide information for a multitude of atmospheric constituents and aerosol layers, providing new insights into atmospheric structure and dynamical and chemical processes. For Saturn, salient early results include evidence for phosphine depletion in relatively dark and less cloudy belts at temperate and mid-latitudes compared to the relatively bright and cloudier Equatorial Region, consistent with traditional theories of belts being regions of relative downwelling. Additional Saturn results include (1) the mapping of enhanced trace gas absorptions at the south pole, and (2) the first high phase-angle, high-spatial-resolution imagery of CH4 fluorescence. An additional fundamental new result is the first nighttime near-infrared mapping of Saturn, clearly showing discrete meteorological features relatively deep in the atmosphere beneath the planet's sunlit haze and cloud layers, thus revealing a new dynamical regime at depth where vertical dynamics is relatively more important than zonal dynamics in determining cloud morphology. Zonal wind measurements at deeper levels than previously available are achieved by tracking these features over multiple days, thereby providing measurements of zonal wind shears within Saturn's troposphere when compared to cloudtop movements measured in reflected sunlight. For Titan, initial results include (1) the first detection and mapping of thermal emission spectra of CO, CO2, and CH3D on Titan's nightside limb, (2) the mapping of CH4 fluorescence over the dayside bright limb, extending to approximately 750 km altitude, (3) wind measurements of approximately 0.5 ms(exp -1), favoring prograde, from the movement of a persistent (multiple months) south polar cloud near 88 deg S latitude, and (4) the imaging of two transient mid-southern-latitude cloud features.

Cassini Mission↗
NASA NTRS1986

Stress waves in transversely isotropic media: The homogeneous problem

The homogeneous problem of stress wave propagation in unbounded transversely isotropic media is analyzed. By adopting plane wave solutions, the conditions for the existence of the solution are established in terms of phase velocities and directions of particle displacements. Dispersion relations and group velocities are derived from the phase velocity expressions. The deviation angles (e.g., angles between the normals to the adopted plane waves and the actual directions of their propagation) are numerically determined for a specific fiber-glass epoxy composite. A graphical method is introduced for the construction of the wave surfaces using magnitudes of phase velocities and deviation angles. The results for the case of isotropic media are shown to be contained in the solutions for the transversely isotropic media.

Marques, E. R. C.↗
NASA NTRS1989

Physical analysis and second-order modelling of an unsteady turbulent flow - The oscillating boundary layer on a flat plate

The turbulent boundary layer under a freestream whose velocity varies sinusoidally in time around a zero mean is computed using two second order turbulence closure models. The time or phase dependent behavior of the Reynolds stresses are analyzed and results are compared to those of a previous SPALART-BALDWIN direct simulation. Comparisons show that the second order modeling is quite satisfactory for almost all phase angles, except in the relaminarization period where the computations lead to a relatively high wall shear stress.

Ha Minh, H.↗
NASA NTRS1995

Technologies for Maintaining Animals in Space: Lighting, Air Quality, Noise, Food and Water

In the terrestrial environment multiple time cues exist. Zeitgebers have been identified and studied for their ability to convey temporal information to various physiological systems, In the microgravity experiment it is necessary to define time cues within the flight hardware prior to flight. During flight if changes in the Circadian System (e.g., mean, phase angle, period) occur this would indicate that the gravity vector is important relative to biological timing. This presentation is concerned with the environmental parameters to support rodent experiments in microgravity. The Animal Enclosure Module (AEM) provides solid food bars and water via lixits ad libitum. Flight animals (Sprague-Dawley rats, 60 - 300g) when compared to ground controls show similar growth (mean growth per day, g +/- SD; flight 5.4 +/- 2.0, ground 5.9 +/- 2.1). Current AEMs use incandescent lighting (approx. 5 Lux). Light emitting diode (LED) arrays are being developed that provide a similar light environment as cool-white fluorescent sources (40 Lux). In ground based tests (12L:12D), these arrays show normal circadian entrainment (Tau = 24.0) with respect to the behavioral responses. measured (drinking, eating, gross locomotor activity). A newly developed ultra high efficiency filter system can entrap all feces, urine and odors from 6 rats for 24 days. Maximum sound level exposure limits (per octave band 22 Hz - 179 kHz) have been established. The AEM will effectively support animal experiments in microgravity.

Winget, C. M.↗
NASA NTRS1995

Technologies For Maintaining Animals In Space: Lighting, Air Quality, Noise, Food And Water

In the terrestrial environment multiple time cues exist. Zeitgebers have been identified and studied for their ability to convey temporal information to various physiological systems. In the microgravity experiment it is necessary to define time cues within the flight hardware prior to flight. During flight if changes in the Circadian System (e.g., mean, phase angle, period) occur this would indicate that the gravity vector is important relative to biological timing. This presentation is concerned with the environmental parameter: to support rodent experiments in microgravity. The Animal Enclosure Module (AEM) provides solid food bars and water via lixits and ad libitum. Flight animals (Sprague-Dawley rats, 60 - 300g) when compared to ground controls show similar growth (mean growth per day g, plus or minus SD; flight 5.4 plus or minus 2.0, ground 5.9 plus or minus 2.1). Current AEMs use incandescent lighting (approx. 5 Lux). Light emitting diode (LED) arrays are being developed that provide a similar light environment as cool-white fluorescent sources (40 Lux). In ground based tests (12L:12D), these arrays show normal circadian entrainment (Tau = 24.0) with respect to the behavioral responses, measured (drinking, eating, gross locomotor activity). A newly developed ultra high efficiency filter system can entrap all feces, urine and odors from 6 rats for 24 days. Maximum sound level exposure limits (per octave band 22 Hz - 179 kHz) have been established. The AEM will effectively support animal experiments in microgravity.

Winget, C. M.↗
NASA NTRSDate not supplied

Rocket Lab Venus - Enabling Low-Cost Interplanetary Missions

Rocket Lab’s mission to Venus [1], launching in January 2025, aims to demonstrate that small launch vehicles, such as Electron, and high-energy small spacecraft, such as Photon, can enable a new paradigm of regular, low-cost interplanetary missions. The Electron launch vehicle will deliver the Photon spacecraft carrying the entry probe into low earth orbit, at which point Photon will take over and put both itself and the attached probe on an Earth-Venus transfer trajectory, with assistance from a Lunar flyby. The primary science objective of the mission is to sample the Venusian cloud layers between atitudes of 45 and 60 km above the surface with an autofluorescing nephelometer. The ~1kg scientific instrument will be carried by a small ~17 kg direct entry probe which will separate from the Photon spacecraft approximately 30 minutes prior to atmospheric entry. The probe outer mould line is a scaled down version of the Deep Space 2 probes [2]. NASA’s newly developed 3D Woven Carbon Phenolic, a derivative of the Heatshield for Extreme Entry Environment Technology (HEEET) material [3], is an enabling technology for this mission, and it will comprise the probe forebody heat shield.The probe will communicate directly back to the Earth during its descent via a small on-board radio frequency (RF) antenna. The hyperbolic Venus encounter will see the probe enter the Venusia atmosphere at approximately 11 km/s with an entry flight path angle (EFPA) of about 10°. This relatively low entry angle was selected to increase the duration of the descent phase, reduce the peak deceleration, and reduce the sensitivity of the nominal entry environments to navigational errors. For reference, the Pioneer Venus probes entered at EFPAs varying from about 25° to 70°, resulting in peak decelerations between around 220 and 450 g’s and peak stagnation point heat fluxes ranging from about 40 to 75 MW/m2 [4]. In comparison, the Rocket Lab Venus probe will experience a lower preak deceleration of around 60 g’s and a lower peak stagnation point heat flux of about 15 MW/m2, at the cost of a greater total heat load and correspondingly higher thermal protection system (TPS) mass fraction. This paper recounts the development history of the TPS for the Rocket Lab Venus probe, with a focus on the unique requirements of the mission. In particular, the effect on the TPS design of the mission’s tight budget, short development timeline, slim mass and RF link margins, and mild but long duration entry heating. Rocket Lab’s initial investigations into a ‘hybrid’ TPS [5] based on a scaled version of the Pioneer Venus full-density carbon phenolic forebody shield, and the abandonment of this approach in favour of NASA’s 3D Woven Carbon Phenolic is presented. Additionally, the leveraging of previous testing under the HEEET project at higher conditions and the associated TPS margining strategy that was adopted to avoid the need for extensive mission-specific arc jet testing is discussed. Finally, this paper concludes with a brief consideration of the feasibility of a future low-cost aerocapture technology demonstrator mission based on the 2025 Rocket Lab Venus mission and entry probe.

Lyle Campbell↗
NASA NTRS1991

Instantaneous heat transfer coefficient based upon two-dimensional analyses of Stirling space engine components

Twelve different cases of multidimensional models of Stirling engine components for space applications have been numerically investigated for oscillating, incompressible laminar flow with heat transfer. The cases studied covered wide ranges of Valensi number (from 44 to 700), Re(max) number (from 8250 to 60,000), and relative amplitude of fluid motion of 0.686 and 1.32. The Nusselt numbers obtained from the present study indicate a very complex shape with respect to time and axial location in the channel. The results indicate that three parameters can be used to define the local Nusselt number variation, namely: time average, amplitude, and phase angle. These parameters could be correlated respectively using: Re(max), Va and Re(max), and the relative amplitude of fluid motion.

Ibrahim, Mounir↗
NASA NTRS1977

Venus - On the phase variation of CO2 line profiles

The shapes of Venus' CO2 profiles are found to vary with solar phase angle. High-resolution spectra of the P16 and P14 lines in the 8689- and 7820-A bands, respectively, are presented for phase angles ranging from 6 to 158 deg. The scattering mean free path at 80 mbar, approximately the effective pressure, is 1.7 km. Use of the van de Hulst (1974) similarity relations with simple parametric scattering models is inadequate to separate effects due to the scattering phase function from those due to inhomogeneities in depth when one attempts to determine the atmospheric structure by fitting a family of such models over a wide range of phase angles.

Macy, W., Jr.↗
NASA NTRS1984

Lightcurves and phase relations of the asteroids 82 Alkmene and 444 Gyptis

The asteroids 82 Alkmene and 444 Gyptis were observed photoelectrically at Table Mountain Observatory and at Torino Observatory during their 1979 opposition in order to determine their rotation periods and phase relations. The observations of 82 Alkmene yielded a rotation period of 12.999 h + or 0.002 h and an amplitude of variation of 0.55. The measured and corrected absolute magnitudes, when plotted against phase angle, is the best fit Lumme and Bowell (1981) theoretical phase function. The rotation period and amplitude of variation for 444 Gyptis are 6.214 h and 0.15, respectively. The phase relation of this asteroid is poorly fit by the Lumme and Bowell theory when only the multiple scattering parameter and the zero phase angle are treated as variables. A good fit can be obtained by adjusting some of the other parameters of their theory, but the physical interpretation is ambiguous.

Harris, A. W.↗
NASA NTRS2003

A Study of the Opposition Phase Curve in Low Albedo Media

The Opposition Effect, the pronounced non-linear intensity increase in the reflectance phase curve with decreasing phase angle,theta , has long been observed in solar system bodies and in laboratory investigations of the angular scattering properties of particulate media. The size and shape of the phase curve, and the change in linear polarization with theta, have been related to the physical properties of planetary regolith scattering materials. Near zero degrees the increase in reflectance with decreasing phase angle has been attributed to two distinct processes. The first is the elimination of shadows cast between the regolith grains as the phase angle decreases. This is called the shadow hiding opposition effect (SHOE). The second is coherent constructive interference between rays of light traveling along identical but opposite paths in multiply scattering media. This is called the coherent backscattering opposition effect (CBOE).

Nelson, R. M.↗
NASA NTRS2011

Toward Realistic Dynamics of Rotating Orbital Debris, and Implications for Lightcurve Interpretation

Optical observations of rotating space debris near GEO contain important information on size, shape, composition, and rotational states, but these aspects are difficult to extract due to data limitations and the high number of degrees of freedom in the modeling process. For tri-axial rigid debris objects created by satellite fragmentations, the most likely initial rotation state has a large component of initial angular velocity directed along the intermediate axis of inertia, leading to large angular reorientations of the body on the timescale of the rotation period. This lends some support to the simplest possible interpretation of light curves -- that they represent sets of random orientations of the objects of study. However, effects of internal friction and solar radiation are likely to cause significant modification of rotation states within a time as short as a few orbital periods. In order to examine the rotational dynamics of debris objects under the influences of these effects, a set of seven first-order coupled equations of motion were assembled in state form: three are Euler equations describing the rates of change of the components of angular velocity in the body frame, and four describe the rates of change of the components of the unit quaternion. Quaternions are a four-dimensional extension of complex numbers that form a seamless, singularity-free representation of body orientation on S3. The Euler equations contain explicit terms describing torque from solar radiation in terms of spherical harmonics, and terms representing effects of a prescribed rate of internal friction. Numerical integrations of these equations of motion are being performed, and results will be presented. Initial tests show that internal friction without solar radiation torque leads to rotation about the maximum principal axis of inertia, as required, and solar radiation torque is expected to lead to spin-up of objects. Because the axis of maximum rotational inertia tends to be roughly coincident with the normal to the largest projected cross-sectional area, internal friction is expected to lead to reduced variation of light curve amplitudes at a given phase angle, but a large dependence of the same on phase angle. At a given phase angle, databases are generated which contain reflected intensities for comprehensive sets of equally-likely orientations, represented as unit quaternions. When projected onto three dimensions (S2) and color-coded by intensity, the set is depicted as points within a solid, semi-transparent unit sphere, within which all possible reflected intensities for an object at a given phase angle may be inspected simultaneously. Rotational sequences are represented by trajectories through the sphere. Databases are generated for each of a set of phase angles separately, forming a comprehensive dataset of reflected intensities spanning all object orientations and solar phase angles. Symmetries in the problem suggest that preferred rotation states are likely, defined relative to the object-sun direction in inertial space and relative to the maximum principal axis of inertia in the body coordinate system. Such rotation states may greatly simplify the problem of light curve interpretation by reducing the number of degrees of freedom in the problem.

Ojakangas, Gregory W.↗
NASA NTRS1972

The atom-molecule reaction D plus H2 yields HD plus H studied by molecular beams

Collisions between deuterium atoms and hydrogen molecules were studied in a modulated crossed beam experiment. The relative signal intensity and the signal phase for the product HD from reactive collisions permitted determination of both the angular distribution and HD mean velocity as a function of angle. From these a relative differential reactive scattering cross section in center-of-mass coordinates was deduced. The experiment indicates that reactively formed HD which has little or no internal excitation departs from the collision anisotropically, with maximum amplitude 180 deg from the direction of the incident D beam in center-of-mass coordinates, which shows that the D-H-H reacting configuration is short-lived compared to its rotation time. Non reactive scattering of D by H2 was used to assign absolute values to the differential reactive scattering cross sections.

Geddes, J.↗
NASA NTRS1972

Minor planets and related objects. VIII - Deimos.

Evaluation of 12 polarization measurements of Deimos in blue light were obtained at phase angles between 5 and 31 deg. A well-developed negative branch, with minimum polarization approximately -1.5% near phase angle 11 deg, indicates that Deimos is not bare rock but has a particulate surface layer of dark dust or powder. The phase angle of inversion is 19.5 deg, and the slope of the positive branch is 0.26 plus or minus 0.01% per degree. On the basis of the slope-albedo law for the moon and the major asteroids, the geometrical albedo of Deimos in blue light should be 0.07 plus or minus 0.01, and the radius 5.4 plus or minus 0.8 km. These values are in good agreement with preliminary Mariner 9 data.

Zellner, B.↗
NASA NTRS1976

Martian albedo feature variations with season - Data of 1971 and 1973

A qualitative and quantitative study of some recent seasonal and secular albedo variations on Mars is presented, based on improved red-filter photographs obtained during the 1971 and 1973 apparitions. The measurement of albedo features showing significant changes and uncommonly bright areas is described in detail. Photographic differential photometry of 21 albedo features in three longitude regions is also discussed. The major findings are: (1) seasonal differences of the mean brightness ratios for most features were consistent with contrast changes shown on photographic maps, (2) seasonal variations of brightness with latitude and region occurred, (3) most albedo features were more variable during southern spring than summer, (4) a general loss of relative contrast was experienced during southern summer, and (5) no systematic dependence on solar phase angle was detected within the range spanned by both sets of photographs. Possible causes of the variations are considered.

Capen, C. F., Jr.↗