SEARCH · Search NASA

Results for “surface shape fitting”

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.

SourceResearch connectionFrom yearThrough year

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

At least 73 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1978

A time dependent model of the Jovian current sheet

Analysis of vector helium magnetometer measurements during the Pioneer 10 outbound pass through the Jovian magnetosphere reveals that the average location of the near-equatorial current sheet is a surface whose shape is determined by the velocity at which the magnetic perturbations produced by a rotating tilted dipole propagate to large radial distances. A model is presented which is a surface encircling the planet and rotating rigidly with it. Based on a linear fit to the times of the current sheet crossings, a formula is derived for the surface representing the average position of the near-equatorial current sheet in the Jovian magnetosphere.

Kivelson, M. G.↗

NASA NTRS1994

Retrieval of sizes and total masses of particles in volcanic clouds using AVHRR bands 4 and 5

The advanced very high resolution radiometer (AVHRR) sensor on polar orbiting NOAA satellites can discriminate between volcanic clouds and meteorological clouds using two-band data in the thermal infrared. This paper is aimed at developing a retrieval of the particle sizes, optical depth, and total masses of particles from AVHRR two-band data of volcanic clouds. Radiative transfer calculations are used with a semi-transparent cloud model that is based on assumptions of spherical particle shape, a homogeneous underlying surface, and a simple thin cloud parallel to the surface. The model is applied to observed AVHRR data from a 13-hour old drifting cloud from the August 19, 1992, eruption of Crater Peak/Spurr Volcano, Alaska. The AVHRR data fit in the range of results calculated by the model, which supports its credibility. According to the model results, the average of effective particle radius in the test frame of this cloud is in the range of 2 to 2.5 micrometer, the optical depth at 12 micrometer is about 0.60 - 0.65. The total estimated mass of ash in the air amounts to 0.24 - 0.31 x 10(exp 6) tons, which is about 0.7-0.9% of the mass measured in the ashfall blanket. Sensitivity tests show that the mass estimate is more sensitive to the assumed ash size distribution than it is to the ash composition.

Wen, Shiming↗

NASA NTRS2012

The Near-Earth Encounter of Asteroid 308635 (2005 YU55): Thermal IR Observations

The near-Earth approach (0.00217 AU, or 0.845 lunar distances) of the C-type asteroid 308635 (2005 YU55) in November 2011 presented a rare opportunity for detailed observations of a low-albedo NEA in this size range. As part of a multi-telescope campaign to measure visible and infrared spectra and photometry, we obtained mid-infrared (approx. 8 to 22 micron) photometry and spectroscopy of 2005 YU55 using Michelle on the Gemini North telescope on UT November 9 and 10,2011. An extensive radar campaign together with optical light-curves established the rotation state of YU55. In addition, the radar imaging resulted in a shape model for the asteroid, detection of numerous boulders on its surface, and a preliminary estimate of its equatorial diameter at 380 +/- 20 m. In a preliminary analysis, applying the radar and lightcurve-derived parameters to a rough-surface thermophysical model fit to the Gemini/Michelle thermal emission photometry results in a thermal inertia range of approximately 500 to 1500 J/sq m/0.5s/K, with the low-thermal-inertia solution corresponding to the small end of the radar size range and vice versa. Updates to these results will be presented and modeling of the thermal contribution to the measured near-infrared spectra from Palomar/Triplespec and IRTF/SpeX will also be discussed.

Lim, Lucy F.↗

NASA NTRS1982

A porous flow model for the geometrical form of volcanoes - Critical comments

A critical evaluation is presented of the assumptions on which the mathematical model for the geometrical form of a volcano arising from the flow of magma in a porous medium of Lacey et al. (1981) is based. The lack of evidence for an equipotential surface or its equivalent in volcanoes prior to eruption is pointed out, and the preference of volcanic eruptions for low ground is attributed to the local stress field produced by topographic loading rather than a rising magma table. Other difficulties with the model involve the neglect of the surface flow of lava under gravity away from the vent, and the use of the Dupuit approximation for unconfined flow and the assumption of essentially horizontal magma flow. Comparisons of model predictions with the shapes of actual volcanoes reveal the model not to fit lava shield volcanoes, for which the cone represents the solidification of small lava flows, and to provide a poor fit to composite central volcanoes.

Wadge, G.↗

NASA NTRS2012

SE-FIT

The mathematical theory of capillary surfaces has developed steadily over the centuries, but it was not until the last few decades that new technologies have put a more urgent demand on a substantially more qualitative and quantitative understanding of phenomena relating to capillarity in general. So far, the new theory development successfully predicts the behavior of capillary surfaces for special cases. However, an efficient quantitative mathematical prediction of capillary phenomena related to the shape and stability of geometrically complex equilibrium capillary surfaces remains a significant challenge. As one of many numerical tools, the open-source Surface Evolver (SE) algorithm has played an important role over the last two decades. The current effort was undertaken to provide a front-end to enhance the accessibility of SE for the purposes of design and analysis. Like SE, the new code is open-source and will remain under development for the foreseeable future. The ultimate goal of the current Surface Evolver Fluid Interface Tool (SEFIT) development is to build a fully integrated front-end with a set of graphical user interface (GUI) elements. Such a front-end enables the access to functionalities that are developed along with the GUIs to deal with pre-processing, convergence computation operation, and post-processing. In other words, SE-FIT is not just a GUI front-end, but an integrated environment that can perform sophisticated computational tasks, e.g. importing industry standard file formats and employing parameter sweep functions, which are both lacking in SE, and require minimal interaction by the user. These functions are created using a mixture of Visual Basic and the SE script language. These form the foundation for a high-performance front-end that substantially simplifies use without sacrificing the proven capabilities of SE. The real power of SE-FIT lies in its automated pre-processing, pre-defined geometries, convergence computation operation, computational diagnostic tools, and crash-handling capabilities to sustain extensive computations. SE-FIT performance is enabled by its so-called file-layer mechanism. During the early stages of SE-FIT development, it became necessary to modify the original SE code to enable capabilities required for an enhanced and synchronized communication. To this end, a file-layer was created that serves as a command buffer to ensure a continuous and sequential execution of commands sent from the front-end to SE. It also establishes a proper means for handling crashes. The file layer logs input commands and SE output; it also supports user interruption requests, back and forward operation (i.e. undo and redo), and others. It especially enables the batch mode computation of a series of equilibrium surfaces and the searching of critical parameter values in studying the stability of capillary surfaces. In this way, the modified SE significantly extends the capabilities of the original SE.

Chen, Yongkang↗

NASA NTRS2000

Surface Change Detection Using Large Footprint Laser Altimetry

Laser altimeters provide a precise and accurate method for mapping topography at fine horizontal and vertical scales. A laser altimeter provides range by measuring the roundtrip flight time of a short pulse of laser light from the laser altimeter instrument to the target surface. The range is then combined with laser beam pointing knowledge and absolute position knowledge to provide an absolute measurement of the surface topography. Newer generations of laser altimeters measure the range by recording the shape and time of the outgoing and received laser pulses. The shape of the return pulse can also provide unique information about the vertical structure of material such as vegetation within each laser footprint. Distortion of the return pulse is caused by the time-distributed reflections adding together and representing the vertical distribution of surfaces within the footprint. Larger footprints (10 - 100m in diameter) can support numerous target surfaces and thus provide the potential for producing complex return pulses. Interpreting the return pulse from laser altimeters has evolved from simple timing between thresholds, range-walk corrections, constant-fraction discriminators, and multi-stop time interval units to actual recording of the time varying return pulse intensity - the return waveform. Interpreting the waveform can be as simple as digitally thresholding the return pulse, calculating a centroid, to fitting one or more gaussian pulse-shapes to the signal. What we present here is a new technique for using the raw recorded return pulse as a raw observation to detect centimeter-level vertical topographic change using large footprint airborne and spaceborne laser altimetry. We use the correlation of waveforms from coincident footprints as an indication of the similarity in structure of the waveforms from epoch to epoch, and assume that low correlation is an indicator of vertical structure or elevation change. Thus, using vertically and horizontally geolocated waveforms as raw observables (i.e., waveforms tied to a common reference ellipsoid), we assess whether epoch-to-epoch vertical ground motion results in a decrease in the correlation of coincident waveforms over time, and whether this can be used to quantify the magnitude of the deformation. Results of computer models and an example over an area of eroded beachfront will be presented.

Blair, J. Bryan↗

NASA NTRS1991

Fuzzy set methods for object recognition in space applications

Progress on the following tasks is reported: (1) fuzzy set-based decision making methodologies; (2) feature calculation; (3) clustering for curve and surface fitting; and (4) acquisition of images. The general structure for networks based on fuzzy set connectives which are being used for information fusion and decision making in space applications is described. The structure and training techniques for such networks consisting of generalized means and gamma-operators are described. The use of other hybrid operators in multicriteria decision making is currently being examined. Numerous classical features on image regions such as gray level statistics, edge and curve primitives, texture measures from cooccurrance matrix, and size and shape parameters were implemented. Several fractal geometric features which may have a considerable impact on characterizing cluttered background, such as clouds, dense star patterns, or some planetary surfaces, were used. A new approach to a fuzzy C-shell algorithm is addressed. NASA personnel are in the process of acquiring suitable simulation data and hopefully videotaped actual shuttle imagery. Photographs have been digitized to use in the algorithms. Also, a model of the shuttle was assembled and a mechanism to orient this model in 3-D to digitize for experiments on pose estimation is being constructed.

Keller, James M.↗

NASA NTRS1996

Scattering and the Point Spread Function of the New Generation Space Telescope

Preliminary design work on the New Generation Space Telescope (NGST) is currently under way. This telescope is envisioned as a lightweight, deployable Cassegrain reflector with an aperture of 8 meters, and an effective focal length of 80 meters. It is to be folded into a small-diameter package for launch by an Atlas booster, and unfolded in orbit. The primary is to consist of an octagon with a hole at the center, and with eight segments arranged in a flower petal configuration about the octagon. The comers of the petal-shaped segments are to be trimmed so that the package will fit atop the Atlas booster. This mirror, along with its secondary will focus the light from a point source into an image which is spread from a point by diffraction effects, figure errors, and scattering of light from the surface. The distribution of light in the image of a point source is called a point spread function (PSF). The obstruction of the incident light by the secondary mirror and its support structure, the trimmed corners of the petals, and the grooves between the segments all cause the diffraction pattern characterizing an ideal point spread function to be changed, with the trimmed comers causing the rings of the Airy pattern to become broken up, and the linear grooves causing diffraction spikes running radially away from the central spot, or Airy disk. Any figure errors the mirror segments may have, or any errors in aligning the petals with the central octagon will also spread the light out from the ideal point spread function. A point spread function for a mirror the size of the NGST and having an incident wavelength of 900 nm is considered. Most of the light is confined in a circle with a diameter of 0.05 arc seconds. The ring pattern ranges in intensity from 10(exp -2) near the center to 10(exp -6) near the edge of the plotted field, and can be clearly discerned in a log plot of the intensity. The total fraction of the light scattered from this point spread function is called the total integrated scattering (TIS), and the fraction remaining is called the Strehl ratio. The angular distribution of the scattered light is called the angle resolved scattering (ARS), and it shows a strong spike centered on a scattering angle of zero, and a broad , less intense distribution at larger angles. It is this scattered light, and its effect on the point spread function which is the focus of this study.

Schreur, Julian J.↗

NASA NTRS2021

Retrieval Algorithm for the Column CO2 Mixing Ratio from Pulsed Multi-Wavelength Lidar Measurements

The retrieval algorithm for the column mixing ratio of CO2 from the measurements of a pulsed multi-wavelength integrated path differential absorption (IPDA) lidar is described. The lidar samples the shape of the 1572.33 nm CO2 absorption line at 15 or 30 wavelengths. The algorithm uses a least-squares fit between the CO2 line shape computed from a layered 10 atmosphere model to that sampled by the lidar. In addition to the column average CO2 dry air mole fraction (XCO2), several other parameters are also solved simultaneously from the fit. These include the Doppler shift in the received laser signal wavelengths, the product of the surface reflectivity and atmospheric transmission and a linear trend in the lidar receiver’s spectral response. The algorithm can also be used to solve for the average water vapor mixing ratio, which causes a secondary absorption in the wings of the CO2 absorption line under high humidity conditions. The least-squares fit is linearized about the 15 expected XCO2 value which allows the use of a standard linear least-squares fitting method and software tools. The standard deviation of the retrieved XCO2 is obtained from covariance matrix of the fit. An averaging kernel is defined similarly to that used for passive trace-gas sounding. Examples are presented of using the algorithm to retrieve XCO2 from the measurements from NASA Goddard’s airborne CO2 Sounder lidar made at a constant altitude and during spiral-down maneuvers.

Xiaoli Sun↗

NASA NTRSDate not supplied

Laser Beam Welding Advancements for In-Space Servicing, Assembly, and Manufacturing

NASA is currently working to develop in-space servicing, assembly, and manufacturing (ISAM) capabilities for low Earth orbit and the lunar surface. One crucial technology for this effort is laser beam welding. Laser systems can perform joining, cleaning, cutting, and repair activities, which will enable the construction of large in-space structures that could not fit on a single launch vehicle, such as trusses for solar panels, radiators, or communications infrastructure. Multiple projects studying laser welding for space applications are currently underway at NASA Marshall Space Flight Center. One of these, the DIsk-Shaped Configurable and Modular vAcuum uNit (DISCMAN), is a compact vacuum chamber designed to support parameter development for laser welding in microgravity. It contains a rotating platen with weld samples made from aluminum, steel, and titanium, a high-power infrared laser, and integrated pumps for pulling vacuum inside the sample cartridge. The DISCMAN payload is planned to launch to the International Space Station, where welds will be performed under sustained microgravity inside the Bishop Airlock. Another effort underway at Marshall is the Lunar Assembly and Servicing by Autonomous Robotics (LASAR) initiative. This project uses a space-rated robotic arm equipped with a laser weld head, wire feeder, and multiple cameras to perform welds in a thermal vacuum chamber simulating the lunar surface environment. Some of these welds are done on snowflake joints, which are specially designed to slot together to join segments of trussN structures, allowing for the construction of tall surface infrastructure. DISCMAN, LASAR, and other projects are being carried out to advance the technological maturity of in-space laser beam welding, collect data to inform computational models, and learn reliable processes for creating weld joints in space. This work supports NASA’s greater goals to expand humanity’s presence in low Earth orbit, establish a permanent moon base, and eventually send crewed missions to Mars and beyond.

Manufacturing↗

NASA NTRSDate not supplied

Laser Beam Welding Advancements for In-Space Servicing, Assembly, and Manufacturing

Robotics↗

NASA NTRS1973

Approximations to the mean surface of Mars and Mars atmosphere using Mariner 9 occultations

When the Mariner 9 spacecraft passed behind Mars in its orbiting phase, the radio beam was cut off by some physical feature. These occultations occurred during the months of November and December 1971 and again in April and May 1972. The fairly good global spread of these data was used to estimate the shape of the Martian globe, as definable by mathematical shapes (ellipsoidal and spherical harmonic). The refraction profiles allowed the estimation of pressure near the occultation point; these, corrected back to an arbitrary fixed value of pressure, chosen to be 6.1 mb, were used as radii to an isobaric surface. Preliminary results showed a figure displacement from the mass center with a best fit southeast by 2.85 km. There was also an equatorial displacement in the direction of about 100 deg W. Atmospheric approximations for the mass center to 6.1-mb pressure distances were fit to an ellipsoid.

Cain, D. L.↗

NASA NTRS1982

Effects of body shape on disk-integrated spectral reflectance

The effects of scattering geometry on the spectral reflectance curves of various powdered substances representing possible planetary surfaces are examined. Reflectance measurements were made as a function of incidence angle and emission angle for ground samples of a slightly oxidized basalt, the C3 carbonaceous chondrite Allende, and the ordinary chondrite Bruderheim, and compared with various photometric functions. The best fit to the observations is obtained with the photometric function of Goguen (1981) and Hapke (1981), and with a simpler function representing a linear combination of a Hapke-Irvine law and Lambert's law. The wavelength dependence of the adopted functions implies that the spherical reflectance of a flat sample will differ from that of a spherical planet of the same material, and that there will be a difference between the spectral reflectance curves of spherical and elliptical planets.

Gradie, J.↗

NASA NTRS1991

Observations of Scorpius X-1 with IUE - Ultraviolet results from a multiwavelength campaign

IUE UV results are presented for the low-mass X-ray binary Sco X-1. Models that predict UV continuum emission from the X-ray-heated surface from the companion star and from an X-ray illuminated accretion disk are adjusted for parameters intrinsic to Sco X-1, and fitted to the data. X-ray heating is found to be the dominant source of UV emission; the mass-accretion rate increases monotonically along the 'Z-shaped' curve in an X-ray color-color diagram. UV emission lines from He, C, N, O, and Si were detected; they all increase in intensity from the HB to the FB state. A model in which emission lines are due to outer-disk photoionization by the X-ray source is noted to give good agreement with line fluxes observed in each state.

Vrtilek, S. D.↗

NASA NTRS2010

Enhanced Modeling of First-Order Plant Equations of Motion for Aeroelastic and Aeroservoelastic Applications

A methodology is described for generating first-order plant equations of motion for aeroelastic and aeroservoelastic applications. The description begins with the process of generating data files representing specialized mode-shapes, such as rigid-body and control surface modes, using both PATRAN and NASTRAN analysis. NASTRAN executes the 146 solution sequence using numerous Direct Matrix Abstraction Program (DMAP) calls to import the mode-shape files and to perform the aeroelastic response analysis. The aeroelastic response analysis calculates and extracts structural frequencies, generalized masses, frequency-dependent generalized aerodynamic force (GAF) coefficients, sensor deflections and load coefficients data as text-formatted data files. The data files are then re-sequenced and re-formatted using a custom written FORTRAN program. The text-formatted data files are stored and coefficients for s-plane equations are fitted to the frequency-dependent GAF coefficients using two Interactions of Structures, Aerodynamics and Controls (ISAC) programs. With tabular files from stored data created by ISAC, MATLAB generates the first-order aeroservoelastic plant equations of motion. These equations include control-surface actuator, turbulence, sensor and load modeling. Altitude varying root-locus plot and PSD plot results for a model of the F-18 aircraft are presented to demonstrate the capability.

Pototzky, Anthony S.↗

NASA NTRS1982

A technique for measuring magnetic fields on solar-type stars

A method is developed and tested by which magnetic-field strengths and area filling-factors of magnetic regions on late-type stars may be inferred from high-resolution, absorption-line profiles that have been broadened by the Zeeman effect. The technique involves fitting such profiles with a triplet of components, the shape of which is derived from profiles of lines of low Zeeman sensitivity. Tests of the systematic and random errors indicate that such magnetic flux measurements have an uncertainty of 20% for stars with field strengths of 2000 gauss if at least 10% of the stellar surface contains magnetic regions.

Marcy, G. W.↗

NASA NTRS1991

Hoop column soil moisture spacecraft in low Earth orbit for global change monitoring

A subset of the total Global Change Technology Initiative instruments are required to be in low Earth, sunsynchronous orbits. There is one instrument, however, that requires its own specialized spacecraft; the Soil Moisture Microwave Radiometer (SMMR). The characteristic structure of the instrument is the 118 m hoop column support structure. The hoop is supported by an axially placed column. Tension cables support and shape an electromagnetically reflective mesh surface. The instrument is capable of detecting frequencies in the 1.4 GHz range (Soil Moisture and Sea Salinity). Three apertures are used to reduce the degree of paraboloid offset and improve the beam quality. The spacecraft configuration is determined by the instrument support requirements and the requirement that it can fit into the Titan IV cargo bay. The configuration is derived by cross referencing the instrument performance requirements with the performance of the spacecraft. The spacecraft design is similar with the Multi-mission Modular Spacecraft in terms of size and packaging. A description of the spacecraft's features will yield a summary of the technologies needed for the SMMR spacecraft.

Ferebee, Melvin J., Jr.↗

NASA NTRS1992

Probability distributions for the magnification of quasars due to microlensing

Gravitational microlensing can magnify the flux of a lensed quasar considerably and therefore possibly influence quasar source counts or the observed quasar luminosity function. A large number of distributions of magnification probabilities due to gravitational microlensing for finite sources are presented, with a reasonable coverage of microlensing parameter space (i.e., surface mass density, external shear, mass spectrum of lensing objects). These probability distributions were obtained from smoothing two-dimensional magnification patterns with Gaussian source profiles. Different source sizes ranging from 10 exp 14 cm to 5 x 10 exp 16 cm were explored. The probability distributions show a large variety of shapes. Coefficients of fitted slopes for large magnifications are presented.

Wambsganss, Joachim↗