Search NASA⌕ Search

SEARCH · Search NASA

Results for “phase object approximation”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Growth in the Number of SSN Tracked Orbital Objects

The number of objects in earth orbit tracked by the US Space Surveillance Network (SSN) has experienced unprecedented growth since March, 2003. Approximately 2000 orbiting objects have been added to the "Analyst list" of tracked objects. This growth is primarily due to the resumption of full power/full time operation of the AN/FPS-108 Cobra Dane radar located on Shemya Island, AK. Cobra Dane is an L-band (23-cm wavelength) phased array radar which first became operational in 1977. Cobra Dane was a "Collateral Sensor" in the SSN until 1994 when its communication link with the Space Control Center (SCC) was closed. NASA and the Air Force conducted tests in 1999 using Cobra Dane to detect and track small debris. These tests confirmed that the radar was capable of detecting and maintaining orbits on objects as small as 5-cm diameter. Subsequently, Cobra Dane was reconnected to the SSN and resumed full power/full time space surveillance operations on March 4, 2003. This paper will examine the new data and its implications to the understanding of the orbital debris environment and orbital safety.

Stansbery, Eugene G.↗
NASA NTRS2023

Wind Profiling With the Airborne Doppler Aerosol Wind Lidar During the 2022 Convective Processes Experiment

The 2017 Decadal Survey for Earth Science and Applications from Space (ESAS 2017) identifies a critical need for improving our understanding of Planetary Boundary Layer (PBL) processes and air-surface fluxes as well as why clouds, convection, and heavy precipitation occur when and where they do. Lidars are uniquely capable of collecting high precision and high spatio-temporal observations that have been used for atmospheric process studies from the ground, aircraft, and space. The wind lidar team at the NASA Langley Research Center (LaRC) started the development of Doppler wind lidar more than a decade ago to demonstrate technologies required for an Earth-orbiting system to globally measure wind profiles. Since then, an airborne Doppler Aerosol WiNd (DAWN) lidar system has been developed and participated in a series of field campaigns. The Doppler Aerosol WiNd (DAWN) lidar uses atmospheric aerosol motion to derive vertical profiles of horizontal wind speed and direction beneath the aircraft. In September 2022, DAWN, along with a suite of other instruments, was flown on a NASA DC-8 as part of The Convective Processes EXperiment – Cabo Verde (CPEX-CV) field campaign. A main objective of CPEX was to obtain a comprehensive set of temperature, humidity and, particularly, wind observations over tropical waters in undisturbed conditions, Saharan dust outbreaks, and in the vicinity of scattered through organized deep convection in all phases of the convective life cycle. DAWN collected data for approximately 90 hours across 13 CPEX-CV science flights. Airborne Vertical Atmospheric Profiling System (AVAPS) dropsondes were dropped throughout the flight for profiling the atmosphere and validating the DAWN instrument. DAWN had co-located data with 347 AVAPS NRD41 dropsondes, providing 32,117 vertical levels for a comprehensive validation of DAWN wind retrievals. DAWN showed very good agreement with dropsondes of ~0.2 m/s bias and ~1.8 m/s RMS. Given this agreement, DAWN is considered to be a worthy reference dataset, and its retrievals have been compared to winds derived from GOES Atmospheric Motion Vectors (AMVs), Advanced Scatterometer winds (ASCAT), and model data from GFS, GEOS, and MERRA-2 to better understand the quality of our current models and satellite wind observations. The proposed presentation will provide a brief description of the DAWN instrument, discuss the synergistic observations collected across a wide range of atmospheric conditions sampled during the CPEX-CV flights, and a summary of comparisons between DAWN, GOES AMV, ASCAT, and model analyses/predictions, with an emphasis on the PBL.

DAWN↗
DOE OSTI2026

Measurement and feedback-driven adaptive dynamics in the classical and quantum kicked top

In classical dynamical systems, stochastic feedback can stabilize otherwise unstable periodic orbits, giving rise to distinct controlled and uncontrolled phases as the rate of control application is varied. In this work, we apply these control protocols in classical, semiclassical, and quantum regimes to the kicked top, a paradigmatic model of quantum chaos. The quantum kicked top, modeled as the dynamics of a spin-S object, naturally interpolates between these regimes with the spin size S acting as an effective Planck constant. We show that the dynamics of the kicked top in classical, semiclassical, and fully quantum limits can all be controlled using stochastic feedback protocols. Comparing the full quantum dynamics to a truncated Wigner approximation that captures quantum noise but neglects interference beyond the Ehrenfest time, we find that low-moment observables are largely accounted for semiclassically, while the remaining discrepancy in higher moments is consistent with contributions from interference and possibly nonlinearities in rare trajectories that explore the compact phase space. We also find rapid purification in the numerics studied for all rates of control considered, suggesting that control quenches the top's ability to encode a qubit of quantum information even in the uncontrolled phase.

Prasad, Mahaveer [Tata Inst.; Singapore U. Tech. D↗
NASA NTRS1982

IUE observations of reflection nebulae

Low-resolution IUE spectra in the SWP and LWR ranges were obtained of several reflection nebulae in the vicinity of their respective illuminating stars. Data for NGC 7023 (HD200775), NGC 1435 (Merope, 23 Tau), NGC 1432 (Maia, 20 Tau) and the Electra (17 Tau) nebula were found to display significant differences in the shape of their normalized nebular spectra. If the dust in these nebulae is similar from one object to the next, these differences can be most readily explained by differences in the line-of-sight dust distribution, coupled with a wavelength-dependent phase function, changing from a strongly forward throwing form (g = 0.6-0.7) in the visible to a more nearly isotropic shape (g approximately 0.25) at 1400A.

Witt, A. N.↗
NASA NTRS1984

Radial velocity studies of cataclysmic binaries. II - The ultrashort period dwarf nova T Leonis

Spectroscopic and photometric observations of T Leo which reveal the object to be an ultrashort period dwarf nova are presented. In particular, the analysis indicates that T Leo has an orbital period of 84.69936 (plus or minus 0.00068) minutes, which is the third shortest orbital period of any known cataclysmic variable and the shortest known for any U Gem type dwarf nova. These observations enable the placement of upper limits of 0.19 and 0.4 solar mass on the mass of the red dwarf and white dwarf, respectively. The overall energy distribution is relatively flat (f-sub-lambda approximately constant) which is consistent with a low mass accretion rate. The models of Williams and Ferguson (1982) suggest that the mass accretion rate is about 10 to the -10th solar mass/yr. A narrow peak component of H-alpha is observed, the phasing of which cannot be explained by the canonical hot spot model. Possible explanations for its origin are presented and discussed. It is predicted that future observations of T Leo may reveal the object to be a SU UMa type dwarf nova.

Shafter, A. W.↗
NASA NTRS1995

Analysis of Gaspra lightcurves using Galileo shape and photometric models

Galileo-based models for the shape of 951 Gaspra and the global-average photometric behavior of its surface have been used to model a representative subset of the asteroid's telescopic lightcurves. Fitting the synthetic lightcurves to the observed timing of lightcurve extrema, and knowing the orientation of Gaspra's axes at the time of the Galileo flyby, leads to a sidereal rotation period for the asteroid of 7.042024 +/- 0.000020 hr, a slight change from the period reported by Magnusson et al. (1992). Initially, the shapes, amplitudes, and absolute photometry of the synthetic and observed lightcurves agree with each other to within 0.05-0.1 mag. Small modifications to the Gaspra shape model on sides of the asteroid poorly imaged by Galileo (changes of 700 m or less in the southern hemisphere at longitudes 90 deg-270 deg W) reduce the typical discrepancies to approximately 0.05 mag in lightcurve shape and less than 0.03 mag in absolute photometry. The result demonstrates that Earth-based lightcurves can be used to refine the shape of a spacecraft-imaged irregular object in areas that are poorly constrained by the spacecraft observations. The consistency and phase-angle dependence of the Galileo-based model for Gaspra photometry, supports the accuracy of the absolute calibration of the Galileo SSI camera, and confirms the Earth-based determination of the V-filter geometric albedo of the asteroid (0.22 +/- 0.03; Tholen et al., submitted for publication). Remaining discrepancies between the synthetic and observed lightcurves show no indication of systematic latitudinal variations in albedo and also cannot be explained entirely by isolated albedo spots. These discrepancies are most likely caused by (1) small, remaining, hard-to-constrain errors in the Gaspra shape model and/or (2) moderate variations in macroscopic roughness across the asteroid's surface, in particular making longitudes 130 deg to 300 deg W moderately rougher than the opposite hemisphere.

Simonelli, Damon P.↗
DOE OSTI2016

Automatic software correction of residual aberrations in reconstructed HRTEM exit waves of crystalline samples

Abstract We develop an automatic and objective method to measure and correct residual aberrations in atomic-resolution HRTEM complex exit waves for crystalline samples aligned along a low-index zone axis. Our method uses the approximate rotational point symmetry of a column of atoms or single atom to iteratively calculate a best-fit numerical phase plate for this symmetry condition, and does not require information about the sample thickness or precise structure. We apply our method to two experimental focal series reconstructions, imaging a β-Si 3 N 4 wedge with O and N doping, and a single-layer graphene grain boundary. We use peak and lattice fitting to evaluate the precision of the corrected exit waves. We also apply our method to the exit wave of a Si wedge retrieved by off-axis electron holography. In all cases, the software correction of the residual aberration function improves the accuracy of the measured exit waves.

36 MATERIALS SCIENCE↗
NASA NTRS1992

High-pressure melting of carbonaceous chondrite

Phase equilibria experiments investigating the melting and differentiation of the primordial Earth require a realistic 'initial' chemical composition. Carbonaceous chondrites are good analogues for the initial bulk chemical composition of an accreting early Earth because they contain approximately solar abundances of the non-volatile elements and are the most primitive objects yet sampled in the solar system.

Agee, Carl B.↗
NASA NTRS2021

Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE)

NASA has partnered with Advanced Space to develop and build the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission which will serve as a pathfinder for Near Rectilinear Halo Orbit (NHRO) operations around the Moon. The NHRO, (Perilune = 3,200 km; Apolune = 70,000 km) will be the intended orbit for the NASA’s Artemis Gateway lunar orbital platform. The CAPSTONE mission will validate simulations and confirm operational planning for Gateway while also validating performance of navigation and station-keeping requirements for the Power and Propulsion Element. Thus, this mission will provide operational experience to NASA, commercial, and international missions for operations in a demanding orbital regime. The baseline for CAPSTONE is to fly a 12U cubesat developed, integrated, and tested by Tyvak Nanosatellite Systems carrying a payload communications system capable of cross-link ranging with the Lunar Reconnaissance Orbiter (LRO), a dedicated payload flight computer for software demonstration, and a camera. The launch, coordinated by NASA Launch Services Program, will be provided by a Rocket Lab launch vehicle utilizing their new Proton upper stage to deploy the CAPSTONE spacecraft into the lunar orbit. The CAPSTONE mission is targeting a launch no earlier than September 23, 2021. Upon launch, the spacecraft will traverse a highly efficient transfer taking approximately three months to enter a primary demonstration phase in an NRHO for six months followed by a twelve month technology enhancement operations phase. The CAPSTONE Project is lead by Advanced Space, LLC of Boulder Colorado. Spacecraft development and mission operations will be conducted by Tyvak Nanosatellite Systems of Irvine, California. Noted objectives for the CAPSTONE mission will be to demonstrate the accessibility of NHROs, validate key operational concepts in the NHRO environment, lay a foundation for commercial support of future lunar operations and accelerate the availability of peer-to-peer navigation capabilities provided by the Cislunar Autonomous Positioning System (CAPS). The CAPSTONE mission is funded through NASA's Small Spacecraft Technology Program (SSTP), which is one of several programs in NASA’s Space Technology Mission Directorate. SSTP is chartered to develop and demonstrate technologies to enhance and expand the capabilities of small spacecraft with a particular focus on enabling new mission architectures through the use of small spacecraft, expanding the reach of small spacecraft to new destinations, and augmenting future missions with supporting small spacecraft. The launch for the CAPSTONE Mission is provided by Human Exploration & Operations Missions Directorate Advanced Exploration Systems Division. Coordination and Acquisition of the Launch is managed by NASA’s Launch Services Program. The CAPSTONE Mission and project status will be presented.

CAPSTONE↗
NASA NTRS2021

Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) Mission

NASA has partnered with Advanced Space to develop and build the Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) mission which will serve as a pathfinder for Near Rectilinear Halo Orbit (NHRO) operations around the Moon. The NHRO, (Perilune = 3,200 km; Apolune = 70,000 km) will be the intended orbit for the NASA’s Artemis Gateway lunar orbital platform. The CAPSTONE mission will validate simulations and confirm operational planning for Gateway while also validating performance of navigation and station-keeping requirements for the Power and Propulsion Element. Thus, this mission will provide operational experience to NASA, commercial, and international missions for operations in a demanding orbital regime. The baseline for CAPSTONE is to fly a 12U cubesat developed, integrated, and tested by Tyvak Nanosatellite Systems carrying a payload communications system capable of cross-link ranging with the Lunar Reconnaissance Orbiter (LRO), a dedicated payload flight computer for software demonstration, and a camera. The launch, coordinated by NASA Launch Services Program, will be provided by a Rocket Lab launch vehicle utilizing their new Proton upper stage to deploy the CAPSTONE spacecraft into the lunar orbit. The CAPSTONE mission is targeting a launch no earlier than September 23, 2021. Upon launch, the spacecraft will traverse a highly efficient transfer taking approximately three months to enter a primary demonstration phase in an NRHO for six months followed by a twelve month technology enhancement operations phase. The CAPSTONE Project is lead by Advanced Space, LLC of Boulder Colorado. Spacecraft development and mission operations will be conducted by Tyvak Nanosatellite Systems of Irvine, California. Noted objectives for the CAPSTONE mission will be to demonstrate the accessibility of NHROs, validate key operational concepts in the NHRO environment, lay a foundation for commercial support of future lunar operations and accelerate the availability of peer-to-peer navigation capabilities provided by the Cislunar Autonomous Positioning System (CAPS). The CAPSTONE mission is funded through NASA's Small Spacecraft Technology Program (SSTP), which is one of several programs in NASA’s Space Technology Mission Directorate. SSTP is chartered to develop and demonstrate technologies to enhance and expand the capabilities of small spacecraft with a particular focus on enabling new mission architectures through the use of small spacecraft, expanding the reach of small spacecraft to new destinations, and augmenting future missions with supporting small spacecraft. The launch for the CAPSTONE Mission is provided by Human Exploration & Operations Missions Directorate Advanced Exploration Systems Division. Coordination and Acquisition of the Launch is managed by NASA’s Launch Services Program. The CAPSTONE Mission and project status will be presented.

CAPSTONE↗
DOE OSTI2017

Near-field limitations of Fresnel-regime coherent diffraction imaging

Coherent diffraction imaging (CDI) is a rapidly developing form of imaging that offers the potential of wavelength-limited resolution without image-forming lenses. In CDI, the intensity of the diffraction pattern is measured directly by the detector, and various iterative phase retrieval algorithms are used to “invert” the diffraction pattern and reconstruct a high-resolution image of the sample. But, there are certain requirements in CDI that must be met to reconstruct the object. Although most experiments are conducted in the “far-field”—or Fraunhofer—regime where the requirements are not as stringent, some experiments must be conducted in the “near field” where Fresnel diffraction must be considered. According to the derivation of Fresnel diffraction, successful reconstructions can only be obtained when the small-angle number, a derived quantity, is much less than one. We show, however, that it is not actually necessary to fulfill the small-angle condition. The Fresnel kernel well approximates the exact kernel in regions where the phase oscillates slowly, and in regions of fast oscillations, indicated by large A n , the error between kernels should be negligible due to stationary-phase arguments. Finally we verify, by experiment, this conclusion with a helium neon laser setup and show that it should hold at x-ray wavelengths as well.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1988

On nonsteady accretion in stellar wind-fed X-ray sources

The paper reports on the results of hydrodynamical simulations of nonaxisymmetric gas flow past a finite-sized gravitating object. The asymmetry in the flow is assumed to be due to a transverse density gradient. The solutions are found to be highly time-dependent and exhibit phases in which a disk forms. The direction of circulation of the disk alternates between the direct and counter sense on time scales of approximately 1 hr. While the disk is present, the specific angular momentum is high, and the mass accretion rate, low. The angular momentum capture oscillates about a mean which secularly increases. Such temporal behavior may be relevant to those X-ray pulsing systems (e.g., Vela X-1) which exhibit fluctuations in the X-ray luminosity and pulse period on time scales much shorter than the orbital period of the binary system.

Taam, Ronald E.↗
NASA NTRS1995

Micron Accuracy Deployment Experiment (MADE), phase A. Volume 1

This report documents a Phase A In-STEP flight experiment development effort. The objective of the experiment is to deploy a portion of a segmented reflector on the Shuttle and study its micron-level mechanics. Ground test data are presented which projects that the on-orbit precision of the test article should be approximately 5 microns. Extensive hardware configuration development information is also provided.

Peterson, Lee D.↗
NASA NTRS2004

Spectral Index and Quasi-Periodic Oscillation Frequency Correlation in Black Hole Sources: Observational Evidence of Two Phases and Phase Transition in Black Holes

Recent studies have shown that strong correlations are observed between the low frequencies (1-10 Hz) of quasi-periodic oscillations (QPOs) and the spectral power law index of several black hole (BH) candidate sources, in low (hard) states, steep power law (soft) states, and transitions between these states. The observations indicate that the X-ray spectra of such state (phases) show the presence of a power-law component and are sometimes related to simultaneous radio emission, indicating the probable presence of a jet. Strong QPOs (>20% rms) are present in the power density spectrum in the spectral range where the power-law component is dominant (i.e., 60%90%). This evidence contradicts the dominant, long-standing interpretation of QPOs as a signature of the thermal accretion disk. We present the data from the literature and our own data to illustrate the dominance of power-law index-QPO frequency correlations. We provide a model that identifies and explains the origin of the QPOs and how they are imprinted on the properties of the power-law flux component. We argue for the existence of a bounded compact coronal region that is a natural consequence of the adjustment of the Keplerian disk flow to the innermost sub-Keplerian boundary conditions near the central object and that ultimately leads to the formation of a transition layer (TL) between the adjustment radius and the innermost boundary. The model predicts two phases or states dictated by the photon upscattering produced in the TL: (1) a hard state, in which the TL is optically thin and very hot (kT approximately greater than 50 keV), producing photon upscattering via thermal Comptonization (the photon spectrum index Gamma approximates 1.7 for this state is dictated by gravitational energy release and Compton cooling in an optically thin shock near the adjustment radius), and (2) a soft state that is optically thick and relatively cold (kT approximately less than 5 keV the index for this state, Gamma approximates 2.8, is determined by soft-photon upscattering and photon trapping in a converging flow into the BH). In the TL model for the corona, the QPO frequency V(sub high) is related to the gravitational (close to Keplerian) frequency V(sub K) at the outer (adjustment) radius and v(sub low) is related to the TL's normal mode (magnetoacoustic) oscillation frequency v(sub MA) . The observed correlations between index and low and high QPO frequencies are readily explained in terms of this model. We also suggest a new method for evaluation of the BH mass using the index-frequency correlation.

Titarchuk, Lev↗
NASA NTRS2019

NASA’s Next Generation Surface Deformation and Change Observing System Architecture

The United States National Aeronautics and Space Administration (NASA) has initiated a five-year study of a Surface Deformation and Change Observing System Architecture. The goal of the study is to define an observing system that would meet the recommendations of the 2017 US National Academy of Sciences, Engineering, and Medicine Decadal Survey for developing an affordable synthetic aperture radar-based system or systems that can address fundamental scientific questions about the nature of hazards, disasters, landscape change, and serve applications communities as well. The study is to consider the existing international constellation of SAR systems, both civil and commercial, as well as new technologies that could be employed to address scientific and applications objectives and to improve affordability. The study will be conducted in four phases: 1) expanding the architectural trade space; 2) assessing the science and applications value of each identified architecture; 3) down selecting to three final candidates and performing detailed assessments; 4) final reporting and preparation for mission formulation. The first phase is approximately 2 years in duration, and will concentrate on the scope of research and application areas to be addressed, defining the possible architectures to consider, and beginning the assessment of their performance. The study team comprises five NASA centers. Broad participation from the research, applications, technology, and commercial sectors is planned.

Paul A Rosen↗
DOE OSTI2023

Shock-induced transformation of nitinol shape memory alloy: Effect of stress state on transformation

Due to its numerous practical applications and intriguing phase transformation behavior, shape memory alloys (SMAs) have garnered significant research and development interests. In the past, most studies on the mechanical behavior of SMAs have been conducted under uniaxial stress loadings. Limited research on SMAs under shock loading has not provided conclusive results regarding their transformation behavior and transformation stress under such loading. Additionally, there is a lack of comprehensive understanding regarding the effects of different stress states on transformation behavior. The main objectives of this study are to address these issues. To achieve these objectives, a series of shock wave experiments were designed and conducted. Additionally, quasi-static and dynamic uniaxial stress experiments were carried out to establish a baseline for comparison. The results revealed that the transformation stress under dynamic uniaxial strain shock loading was approximately 1.92 GPa in contrast to 0.5 GPa (quasi-static) to 0.8 GPa (dynamic) observed in uniaxial stress loading. The transformation behavior exhibited noticeable rate sensitivity for both types of loading. There appeared to be a critical strain rate above which the austenite phase was driven to a metastable state. This estimated critical axial strain rate along the loading direction was approximately 2 × 10 3 /s–4 × 10 3 /s for uniaxial stress loading and approximately 2 × 10 6 /s for uniaxial strain loading. The apparent high transformation stress for uniaxial strain loading can likely be attributed to a combination of high-pressure confinement and high strain rate. Furthermore, determining their relative contributions remains an open issue.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Observational studies of the clearing phase in proto-planetary disk systems

Progress in this study is summarized for its second year. An extensive program of high dispersion UV spectral studies using the IUE (International Ultraviolet Explorer) has resulted in acquisition of 40 Herbig Ae/Be star and related object spectra. We find that accreting, circumstellar gas is detected with velocities consistent with material in free-fall toward the stars in approximately 38% of the sample. With acquisition of optical measurements of the projected stellar rotational velocities, we find that the systems with accreting gas exhibit systematically higher projected rotational velocities than the systems showing signatures of outflowing material only. When combined with polarimetric and photometric data, the IUE spectra for these stars indicate that accretion in intermediate-mass pre-main sequence stars is confined to the plane of the circumstellar dust disk. This is in contrast to lower-mass PMS stars where accretion, persumably along magnetic field lines, is seen at polar latitudes. Our data also support significant clearing of the central regions of these circumstellar disks, as originally suggested. The model which most closely matches the observational data is accretion from a disk envelope, as developed by Calvet et al. (1994).

Grady, Carol A.↗
DOE OSTI2019

Adaptive correction of the image of an incoherent source object

The paper examines the operation of an optical system forming an image of an incoherent source object under conditions of atmospheric noise. The effect of atmospheric turbulence is considered. The calculations are performed in the Fresnel – Huygens approximation. The characteristics of the image for ‘long’ and ‘short’ exposures are investigated. The issues related to the adaptive correction of the general light wavefront slopes are discussed. The limits of applicability of phase adaptive correction using a reference source are shown. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗