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NASA NTRSDate not supplied

New Tools for Automating Arcjet Sample Recession Tracking and Analysis

Arcjet Computer Vision (arcjetCV) has been significantly upgraded to enhance accuracy and performance in tracking material recession and shock-material standoff in test videos. These improvements include integrating new machine learning models, developing a specialized edge detection class, and incorporating a more comprehensive training dataset. These upgrades have refined the software’s ability to automate time-resolved recession tracking, making it more precise and reliable for analyzing complex physical processes. In parallel, a new tool called STARscan (Spatial Targeting and Alignment Rig for Scanning) is being developed to capture detailed 3D surface data before and after testing. By comparing these pre- and post-test scans with arcjetCV’s automated video analysis results, users can achieve a more comprehensive assessment of material recession. This method enables cross-validation of results, improving confidence in the analysis of tested materials. The expanded capabilities of arcjetCV have been successfully demonstrated on videos from various facilities, including the NASA Ames arcjets, UIUC’s PlasmatronX, and the VKI Plasmatron. It has been adopted as a new standard for in-situ recession tracking by the Mars Sample Return Project and Orion. ArcjetCV’s improved efficiency and accuracy are critical for reducing testing uncertainties and validating heatshield material performance under extreme conditions. The software’s user-friendly graphical interface ensures ease of use, enabling seamless processing and precise analysis of arcjet videos, providing deeper insights into material behavior in hypersonic environments. ArcjetCV is now available on both PyPI and Conda, allowing easy installation via "pip install arcjetCV" or through the Conda package manager, ensuring broad accessibility and streamlined deployment for users across various platforms.

Ablation↗
NASA NTRS1979

LACIE registration processing

The basic requirements for the LACIE processing system are to extract specified test sites (sample segments) from LANDSAT MSS data, and to apply geometric corrections and perform correlations to ensure registration between successive data acquisitions to within 1 pixel (root mean square). The general flow within the LACIE processing system is described with emphasis on (1) determination of line and pixel location of a search area within an MSS frame; (2) determination of the geometric correction coefficient and the application of geometric corrections; (3) edge detection; and (4) correlation by coincidence of edges.

Grebowsky, G. J.↗
NASA NTRS1984

Is There a Speed Limit?

Fundamental barriers limiting the rate of the growth of crystals suitable for processing into cost efficient effective solar cells are discussed. The physical conditions which permit the growth of sheet directly from the melt are explored to identify the factors which control the growth rate. These criteria are edge defined film fed growth, free meniscus growth and inclined interface growth with specific reference to the effects that increase of speed has on those aspects of the resulting material that bear on the quality of the solar cells made from it. Useful directions for future research are indicated.

Chalmers, B.↗
NASA NTRS1990

On diamond, graphitic and amorphous carbons in primitive extraterrestrial solar system materials

Carbon is among the most abundant elements in the universe and carbon chemistry in meteorites and comets is an important key to understanding many Solar System and interstellar processes. Yet, the mineralogical properties and interrelations between various structural forms of elemental carbon remain ambiguous. Crystalline elemental carbons include rhombohedral graphite, hexagonal graphite, cubic diamond, hexagonal diamond (i.e., lonsdaleite or carbon-2H) and chaoite. Elemental carbon also occurs as amorphous carbon and poorly graphitized (or turbostratic) carbon but of all the forms of elemental carbon only graphite is stable under physical conditions that prevail in small Solar System bodies and in the interstellar medium. The recent discovery of cubic diamond in carbonaceous chondrites and hexagonal diamond in chondritic interplanetary dust particles (IDPs) have created a renewed interest in the crystalline elemental carbons that were not formed by shock processes on a parent body. Another technique, Raman spectroscopy, confirms a widespread occurrence of disordered graphite in the Allende carbonaceous chondrite and in chondritic IDPs. Elemental carbons have also been identified by their characteristic K-edge features in electron energy loss spectra (EELS). However, the spectroscopic data do not necessarily coincide with those obtained by selected area electron diffraction (SAED). In order to interpret these data in terms of rational crystalline structures, it may be useful to consider the principles underlying electron diffraction and spectroscopic analyses. Electron diffraction depends on electron scattering, on the type of atom and the distance between atoms in a crystal lattice. Spectroscopic data are a function of the type of atom and the energy of bonds between atoms. Also, SAED is a bulk sampling technique when compared to techniques such as Raman spectroscopy or EELS. Thus, it appears that combined analyses provide contradictory results and that amorphous, or short-range ordered, carbon identified by conventional TEM imaging and SAED may show evidence for sp(3) bonds in EELS spectra. It is suggested that complex, nanometer-scale, mineralogical interrelations are common to all elemental carbons irrespective of their origin. The subsequent thermal history, or energy balance, will determine the ultimate microstructure.

Rietmeijer, Frans J. M.↗
NASA NTRS1992

An approach to constrained aerodynamic design with application to airfoils

An approach was developed for incorporating flow and geometric constraints into the Direct Iterative Surface Curvature (DISC) design method. In this approach, an initial target pressure distribution is developed using a set of control points. The chordwise locations and pressure levels of these points are initially estimated either from empirical relationships and observed characteristics of pressure distributions for a given class of airfoils or by fitting the points to an existing pressure distribution. These values are then automatically adjusted during the design process to satisfy the flow and geometric constraints. The flow constraints currently available are lift, wave drag, pitching moment, pressure gradient, and local pressure levels. The geometric constraint options include maximum thickness, local thickness, leading-edge radius, and a 'glove' constraint involving inner and outer bounding surfaces. This design method was also extended to include the successive constraint release (SCR) approach to constrained minimization.

Campbell, Richard L.↗
NASA NTRS2002

Pulsed Electromagnetic Acceleration of Plasmas

A major shift in paradigm in driving pulsed plasma thruster is necessary if the original goal of accelerating a plasma sheet efficiently to high velocities as a plasma "slug" is to be realized. Firstly, the plasma interior needs to be highly collisional so that it can be dammed by the plasma edge layer not (upstream) adjacent to the driving 'vacuum' magnetic field. Secondly, the plasma edge layer needs to be strongly magnetized so that its Hall parameter is of the order of unity in this region to ensure excellent coupling of the Lorentz force to the plasma. Thirdly, to prevent and/or suppress the occurrence of secondary arcs or restrike behind the plasma, the region behind the plasma needs to be collisionless and extremely magnetized with sufficiently large Hall parameter. This places a vacuum requirement on the bore conditions prior to the shot. These requirements are quantified in the paper and lead to the introduction of three new design parameters corresponding to these three plasma requirements. The first parameter, labeled in the paper as gamma (sub 1), pertains to the permissible ratio of the diffusive excursion of the plasma during the course of the acceleration to the plasma longitudinal dimension. The second parameter is the required Hall parameter of the edge plasma region, and the third parameter the required Hall parameter of the region behind the plasma. Experimental research is required to quantify the values of these design parameters. Based upon fundamental theory of the transport processes in plasma, some theoretical guidance on the choice of these parameters are provided to help designing the necessary experiments to acquire these data.

Thio, Y. C. Francis↗
NASA NTRS2005

Machine Vision for High Precision Volume Measurement Applied to Levitated Containerless Materials Processing

By combining the best practices in optical dilatometry with new numerical methods, a high-speed and high precision technique has been developed to measure volume of levitated, containerlessly processed samples with sub- pixel resolution. Containerless processing provides the ability to study highly reactive materials without the possibility of contamination affecting thermo-physical properties. Levitation is a common technique used to isolate a sample as it is being processed. Noncontact optical measurement of thermo-ophysical properties is very important as traditional measuring methods cannot be used. Modern, digitally recorded images require advanced numerical routines to recover the sub-pixel locations of sample edges and, in turn produce high precision measurements.

Bradshaw, R. C.↗
NASA NTRS2015

Numerical and Theoretical Considerations for the Design of the AVT-183 Diamond-Wing Experimental Investigations

A diamond-wing configuration has been developed to isolate and study blunt-leading edge vortex separation with both computations and experiments. The wing has been designed so that the results are relevant to a more complex Uninhabited Combat Air Vehicle concept known as SACCON. The numerical and theoretical development process for this diamond wing is presented, including a view toward planned wind tunnel experiments. This work was conducted under the NATO Science and Technology Organization, Applied Vehicle Technology panel. All information is in the public domain.

Boelens, Okko J.↗
NASA NTRS2010

Finned Carbon-Carbon Heat Pipe with Potassium Working Fluid

This elemental space radiator heat pipe is designed to operate in the 700 to 875 K temperature range. It consists of a C-C (carbon-carbon) shell made from poly-acrylonitride fibers that are woven in an angle interlock pattern and densified with pitch at high process temperature with integrally woven fins. The fins are 2.5 cm long and 1 mm thick, and provide an extended radiating surface at the colder condenser section of the heat pipe. The weave pattern features a continuous fiber bath from the inner tube surface to the outside edges of the fins to maximize the thermal conductance, and to thus minimize the temperature drop at the condenser end. The heat pipe and radiator element together are less than one-third the mass of conventional heat pipes of the same heat rejection surface area. To prevent the molten potassium working fluid from eroding the C C heat pipe wall, the shell is lined with a thin-walled, metallic tube liner (Nb-1 wt.% Zr), which is an integral part of a hermetic metal subassembly which is furnace-brazed to the inner surface of the C-C tube. The hermetic metal liner subassembly includes end caps and fill tubes fabricated from the same Nb-1Zr alloy. A combination of laser and electron beam methods is used to weld the end caps and fill tubes. A tungsten/inert gas weld seals the fill tubes after cleaning and charging the heat pipes with potassium. The external section of this liner, which was formed by a "Uniscan" rolling process, transitions to a larger wall thickness. This section, which protrudes beyond the C-C shell, constitutes the "evaporator" part of the heat pipe, while the section inside the shell constitutes the condenser of the heat pipe (see figure).

Juhasz, Albert J.↗
NASA NTRS1998

Mechanistic Models of Friction Stir Welding

Friction stir welding is a welding process developed at The Welding Institute (TWI) in England. The method uses very large strain plastic deformation of the material to join two pieces of metal together. The material is deformed using a tool which is forced between the two pieces which rotates causing a bond. Beyond this, very little is actually known although many people working in the field are willing to speculate on the detailed mechanisms involved. Some measurements made using sacrificial thermocouples at the weld joint indicate that the maximum temperature during the weld process is on the order of 370C - well below the melting temperature of the material. However, at this temperature, the material properties are highly temperature dependent, and the yield stress is approximately an order of magnitude less at this temperature than it is at room temperature. As expected, there are many interpretations of the physical mechanisms occurring during the weld process. Although there is very little published concerned with FSW, some of the anecdotal theories will be described. One describes the primary mechanism as frictional heating at the front of the tool caused by slip between the tool and the material. At elevated temperatures, the weld material becomes soft and deforms around the tool but not essentially altered by the tool rotation, similar to an extrusion. As the material meets again at the rear of the tool, the temperatures and pressures are sufficient to cause the material to bond. All other structures seen are secondary and unimportant. Another theory examined last summer at NASA's Marshall Space Flight Center (MSFC) was that there was no slip between the tool and the material resulting in a rotating mass of plastic weld material traveling at a variety of angular velocities - the greatest at the tool surface diminishing to zero at the outer edge of the plastic mass surrounding the tool. This conceptual model was followed by simplified calculations which showed that the balance of moments through the weld plug was not possible under steady state conditions and realistic temperature profiles. This led to some consideration of a quasi-steady oscillating process. Later when force measurements became available some models were modified and new ones were proposed.

Stewart, Michael B.↗
NASA NTRS1982

On the structure of the Io Torus

Since the plasma flow near Io is reduced, neutrals originating in charge exchange are not energetic enough to leave the Jovian system and are therefore distributed over an extensive region, as indicated by the sodium cloud. New ions subsequently created in the distributed neutral atomic cloud as a result of charge exchange or electron impact ionization are picked up by the corotating magnetic field, and the radial current driven by the pickup process cannot close in the Io torus, so that it must instead be connected to the planetary ionosphere by field-aligned currents. These field-aligned currents will flow away from the equator at the outer edge of the neutral cloud, and towards it at the inner edge. It is found that the Jovian ionospheric photoelectrons also cannot supply the current flowing away from the equator, so that torus ions accelerated by a parallel electric field could be involved. The parallel potential drop is large enough to push the torus into the Jovian atmosphere, explaining both the sharp, discontinuous change of flux tube content and ion temperature at L equals 5.6, as well as the generation of Auroral-type hiss at that point.

Goertz, C. K.↗
NASA NTRS1984

Particle erosion mechanisms and mass redistribution in Saturn's rings

A variety of physical processes can erode the surfaces of planetary ring particles. According to current estimates, the most efficient of these over the bulk of Saturn's rings is hypervelocity impact by 100 microns to one centimeter radius meteoroids. The atoms, molecules, and fragments ejected from ring particles by erosion arc across the rings along elliptical orbits to produce a tenuous halo of solid ejecta and an extensive gaseous atmosphere. Continuous exchange of ejecta between different ring regions can lead to net radial transport of mass and angular momentum. The equations governing this ballistic transport process are presented and discussed. Both numerical and analytic studies of idealized ring systems illustrate that ballistic transport can cause significant mass redistribution in the rings, especially near regions of high density contrast, such as the inner edges of the A and B rings. Ejecta exchanges can also alter local particle sizes and compositions and may produce pulverized regoliths at least several centimeters deep. The meteoroid erosion rate is so high that significant global torques and mass loss are possible on times shorter than a solar system life time.

Durisen, R. H.↗
NASA NTRS1986

Surface pressure measurement during low speed two-dimensional blade-vortex interaction

Unsteady blade surface pressures were measured during two-dimensional blade-vortex interaction. A periodically generated vortex filament interacted with a blade model instrumented over the first 20 percent of the blade surface. Analysis of data confirm the leading edge nature of BVI and show the amplitude of the interaction to be a strong function of blade-to-vortex spacing. Lift perturbation time histories were computed and are used to examine details of the encounter process.

Booth, E. R., Jr.↗
NASA NTRS1991

The origin of the systematic component of planetary rotation. I - Planet on a circular orbit

A computation is undertaken of the rotation rate of a planet that has accreted from small solid planetesimals, as a function of the eccentricities of the planetesimals' orbits at or near the plane of the planet's orbit. The spin angular momentum generated by a given collision can be either positive or negative; due to the tendency to approximately cancel out, this perturbation process must be pursued to the second order in the ratio of the planetary radius to the planetesimal radial excursions' amplitude. It is found that material accreted from the area of the planet feeding zone's outer edges furnishes the planet positive spin angular momentum.

Lissauer, Jack J.↗
NASA NTRS1993

Ridge belt-related scarps and troughs: Compressional crustal bending on Venus

Cytherean ridge arcs resulted in crustal shortening in places with either the strongest compression or weakest surface layers. Arcuate scarps on or close to the edge of the ridge arcs were compressional fronts formed by overthrust over or subduction of adjacent lowland. These ridge arcs became wider due to the propagation of new ridge formation close to previous one(s). As this process repeated itself with time, the crust became thicker and the foreland was bent either due to the excess load, overthrust or subduction event. The Salme Dorsa arc measures 100 km in width and 600 km in length. It consists of a horseshoe-like set of ridges and grooves on a gently sloping lowland. The westward arcuate ridge belt indicates lateral compressional stresses and crustal deformation from SE against the southern Ishtar Terra foreland plain. The trough on the western side of the ridge belt and tensional grabens close to the crest of the bulge to the west of the trough are due to the crustal bending and indicate effects of the load and thrust. Compression and relative movement from southeast against and over the foreland planitia have resulted in ridge belt, trough and bulge formation. The load- and/or stress-induced bending of the uppermost crust allows some estimations of the uppermost elastic lithosphere thickness. Repeated folding and thrust faulting of surface layers due to compression are indicated by four more ridge belts located close to Salme Dorsa. The northeasternmost one has short ridges located in troughs. The west-opening arcuate ridge belt interlocks with the Salme Dorsa horseshoe.

Raitala, J.↗
NASA NTRS1993

Patterns of deformation and volcanic flows associated with lithospheric loading by large volcanoes on Venus

Magellan radar imaging and topography data are now available for a number of volcanoes on Venus greater than 100 km in radius. These data can be examined to reveal evidence of the flexural response of the lithosphere to the volcanic load. On Venus, erosion and sediment deposition are negligible, so tectonic evidence of deformation around large volcanoes should be evident except where buried by very young flows. Radar images reveal that most tectonic features and flow units on the flanks of these volcanoes have predominantly radial orientations. However, both Tepev Mons in Bell Regio and Sapas Mons in Atla Regio exhibit circumferential graben on their flanks. In addition, images reveal several flow units with an annular character around the north and west flanks of Tepev Mons. This pattern most likely results from ponding of flows in an annular flexural moat. Maat Mons in Atla Regio and Sif Mons in Eistla Regio are examples of volcanoes that lack circumferential graben and annular flows; discernible flow units and fractures on these constructs appear to be predominantly radial. Altimetry data can also provide evidence of flexural response. Tepev Mons is partially encircled by depressions that may be sections of a flexural moat that has not been completely filled. The locations of these depressions generally coincide with the annular flows described above. There is weaker evidence for such depressions around Maat Mons as well. The lack of circumferential tectonic features around most volcanoes on Venus might be explained by gradual moat filling and coverage by radial flows. The depressions around Tepev (and possible Maat) may indicate that this process is currently continuing. We use analytic models of plate flexure in an axisymmetric geometry to constrain the elastic plate thickness supporting Tepev Mons. If we consider the outer radius of the ponded flows to be the edge of a moat, we find that models with elastic plate thickness of 10-20 km fit best. Finite element models of a volcanic load detached from the underlying lithosphere predict overthrusting and radial normal faulting at the volcano's edge. Such a mechanism for the formation of radial rift zones on Venus volcanoes would make such features analogous to structures on the flanks of volcanoes on Earth.

Mcgovern, Patrick J.↗
NASA NTRS1994

Direct numerical simulations of leading-edge receptivity for freestream sound

The objective of this paper is to review our efforts in spatial direct numerical simulations for modeling leading-edge receptivity to freestream sound and vorticity. These results begin to provide the link between the freestream and the initial boundary-layer response and can provide the upstream conditions for further simulations marching through the transition process toward turbulence.

Fuciarelli, David A.↗
NASA NTRS1998

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the en- tire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8) eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Khazanov, G. V.↗