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At least 379 records · Page 21

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NASA NTRS1991

Venus impact craters: Implications for atmospheric and resurfacing processes from Magellan observations

Observations of impact craters on Venus by Magellan yield important insights into: (1) atmospheric effects on the formation of impact craters and their attendant ejecta deposits and (2) the resurfacing history of the planet. Most craters smaller than 15 km are classified as irregular; they possess irregularly shaped rims, and multiple hummocky floors. The irregular nature of these craters is interpreted to be the consequence of breakup and dispersion of incoming meteoroids by the dense atmosphere. Two major ejecta facies of venusian impact craters are hummocky ejecta and outer ejecta. A number of craters documented in the Magellan images possess often non-radial, flow-like ejecta indicative of a low viscosity materials. Approximately half of the impact craters observed with the Magellan radar are partially or wholly surrounded by areas with low radar backscatter cross sections.

Phillips, Roger J.↗

NASA NTRS1993

Electron distributions in the inner Jovian magnetosphere: Voyager 1 observations

Using several improvements in the analysis of the observations of the Low Energy Charged Particle (LECP) experiment on Voyager 1, electron phase space densities in the inner Jovian magnetosphere (5 - 10 R(sub J) were first calculated at constant first and second invariants (represented by mu and K, respectively), based on the LECP measurements. The calculated electron phase space density profiles show that in the inner Jovian magnetosphere there exist evident time and longitude variations, energetic electron injections, and present radial transport and distributed losses. To study the radial and pitch angle diffusions of Jovian electrons, we have calculated the phase space densities in the K-L space. It is found that the electron population in the inner Jovian magnetosphere seems to consist of two components: electrons radially diffusing from a main external source and electrons generated from local sources. The radially diffusing electrons have a relatively time stationary and isotropic distribution, while the locally created electrons mainly concentrate around the equatorial plane and have relatively lower energies, in comparison with the inward diffusing electrons. Consequently, the sources of precipitation losses to the ionosphere must be primarily electrons transported from outer sources, and the major precipitations occur in the inner magnetosphere (L less than 7.5 R(sub J). In the inner Jovian magnetosphere (L = 5 to approximately 10 R(sub J)) it is estimated that for electrons with magnetic moment mu = 300 MeV/G, the diffusion coefficient D is roughly 10(exp -8) to approximately 10(exp -6) R(exp 2)(sub J)/s, and the lifetime against the diffusion losses is of the order of 10(exp 4) to approximately 10(exp 6) s.

Ye, G.↗

NASA NTRS2003

Aerodynamic Design Study of an Advanced Active Twist Rotor

An Advanced Active Twist Rotor (AATR) is currently being developed by the U.S. Army Vehicle Technology Directorate at NASA Langley Research Center. As a part of this effort, an analytical study was conducted to determine the impact of blade geometry on active-twist performance and, based on those findings, propose a candidate aerodynamic design for the AATR. The process began by creating a baseline design which combined the dynamic design of the original Active Twist Rotor and the aerodynamic design of a high lift rotor concept. The baseline model was used to conduct a series of parametric studies to examine the effect of linear blade twist and blade tip sweep, droop, and taper on active-twist performance. Rotor power requirements and hub vibration were also examined at flight conditions ranging from hover to advance ratio = 0.40. A total of 108 candidate designs were analyzed using the second-generation version of the Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD II) code. The study concluded that the vibration reduction capabilities of a rotor utilizing controlled, strain-induced twisting are enhanced through the incorporation of blade tip sweep, droop, and taper into the blade design, while they are degraded by increasing the nose-down linear blade twist. Based on the analysis of rotor power, hub vibration, and active-twist response, a candidate aerodynamic design for the AATR consisting of a blade with approximately 10 degrees of linear blade twist and a blade tip design with 30 degree sweep, 10 degree droop, and 2.5:1 taper ratio over the outer five percent of the blade is proposed.

Sekula, Martin K.↗

NASA NTRS2018

Payload Utilization in NASA's Space Launch System

A revitalized National Space Council has directed NASA to return to the moon, with a series of preparatory missions paving the way for eventual human exploration. NASA's new deep space exploration system -- the heavy-lift Space Launch System (SLS), the Orion crew spacecraft and revitalized launch facilities at Kennedy Space Center -- will enable NASA and its commercial and international partners to meet these goals for human deep space exploration. SLS will be the most capable launch vehicle for these efforts, with an initial Block 1 capability of at least 26 metric tons (t) to trans-lunar injection (TLI). A more powerful Block 1B, available in crew and cargo configurations, with have the power to loft more than 37 t to TLI; the ultimate Block 2 variant will lift more than 45 t to TLI. For payload utilization, the Block 1 vehicle will carry 13 6U CubeSats as secondary payloads while the Block 1B crew vehicle will provide as much volume as the space shuttle payload bay in a Universal Stage Adapter (USA). Block 1B cargo vehicles will offer 8.4 m fairings in 19.1 m and 27.4 m lengths, with enough volume to accommodate habitat modules and landers. For missions beyond the Earth-moon system, SLS offers greater characteristic energy (C3), enabling faster transit or heavier payloads to the outer planets. The first mission of SLS and Orion, launching no earlier than December 2019, will send Orion into lunar distant retrograde orbit (DRO) on an approximately 25-day shakedown cruise known as Exploration Mission-1 (EM-1), enabling NASA to verify and validate new systems before sending astronauts to deep space on the next exploration mission. The SLS program and its prime contractors have made significant progress toward first launch, with several major components of the vehicle completed and delivered to the Exploration Ground Systems (EGS) Program at Kennedy Space Center. Major forward work includes integrating tanks, engines and other major sections into the EM-1 core stage at Michoud Assembly Facility and then shipping the entire core stage assembly to Stennis Space Center. There, it will be installed in the refurbished B-2 test stand for a series of integrated stage tests culminating in a green run hotfire test. The Program's Spacecraft Payload Integration and Evolution (SPIE) Office, responsible for the in-space stage, adapters and payload interfaces, has largely completed its effort on the Block 1 vehicle and is supporting manufacture of the first Block 1B vehicle. This paper will provide an overview of the Block 1 vehicle, its expected capabilities, secondary payload accommodations and manufacturing status, including structural testing and the challenges of developing a new launch vehicle. A lookahead to the Block 1B vehicle and the payload utilization opportunities it will provide in the 2020s will also be discussed, including the unique capabilities of the vehicle.

Creech, Stephen D.↗

NASA NTRSDate not supplied

Fundamental Regolith Properties, Handling and Water Capture (FLEET) Project Update

The FLEET project, begun in FY21, was designed to research several concepts for components and subsystems needed for extracting water from planetary ice deposits. This is one of two approaches for providing water off-Earth for direct use and also for feedstock to manufacture spacecraft propellants. The other approach is to extract lattice-bound water and hydroxyl from the minerals that make up the solid grains of rock and regolith. The ultimate intent is to integrate the findings with other efforts, such as, in the creation of complete water-from-ice production systems for various down-stream uses. The project consists of several elements, now in various stages of completion. They are presented here in the approximate order they would generally be applied to a water-extraction system: Digging icy regolith, transporting it, capturing water vapor, and sealing chambers from the outer environment.

L Gertsch↗

NASA NTRSDate not supplied

Fundamental Regolith Properties, Handling and Water Capture (FLEET) Update

regolith excavation↗

NASA NTRS1999

GHRS Observations of Cool, Low-Gravity Stars: The Outer Atmosphere and Wind of the Nearby K Supergiant Lambda Velorum - 5

UV spectra of lambda Velorum taken with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope are used to probe the structure of the outer atmospheric layers and wind and to estimate the mass-loss rate from this K5 lb-II supergiant. VLA radio observations at lambda = 3.6 cm are used to obtain an independent check on the wind velocity and mass-loss rate inferred from the UV observations, Parameters of the chromospheric structure are estimated from measurements of UV line widths, positions, and fluxes and from the UV continuum flux distribution. The ratios of optically thin C II] emission lines indicate a mean chromospheric electron density of log N(sub e) approximately equal 8.9 +/- 0.2 /cc. The profiles of these lines indicate a chromospheric turbulence (v(sub 0) approximately equal 25-36 km/s), which greatly exceeds that seen in either the photosphere or wind. The centroids of optically thin emission lines of Fe II and of the emission wings of self-reversed Fe II lines indicate that they are formed in plasma approximately at rest with respect to the photosphere of the star. This suggests that the acceleration of the wind occurs above the chromospheric regions in which these emission line photons are created. The UV continuum detected by the GHRS clearly traces the mean flux-formation temperature as it increases with height in the chromosphere from a well-defined temperature minimum of 3200 K up to about 4600 K. Emission seen in lines of C III] and Si III] provides evidence of material at higher than chromospheric temperatures in the outer atmosphere of this noncoronal star. The photon-scattering wind produces self-reversals in the strong chromospheric emission lines, which allow us to probe the velocity field of the wind. The velocities to which these self-absorptions extend increase with intrinsic line strength, and thus height in the wind, and therefore directly map the wind acceleration. The width and shape of these self-absorptions reflect a wind turbulence of approximately equal 9-21 km/s. We further characterize the wind by comparing the observations with synthetic profiles generated with the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code, assuming simple models of the outer atmospheric structure. These comparisons indicate that the wind in 1994 can be described by a model with a wind acceleration parameter beta approximately 0.9, a terminal velocity of 29-33 km/s, and a mass-loss rate approximately 3 x 10(exp -9) solar M/yr. Modeling of the 3.6 cm radio flux observed in 1997 suggests a more slowly accelerating wind (higher beta) and/or a higher mass-loss rate than inferred from the UV line profiles. These differences may be due to temporal variations in the wind or from limitations in one or both of the models. The discrepancy is currently under investigation.

Carpenter, Kenneth G.↗

DOE OSTI2018

High Temperature Corrosion of a Pt-30 wt.% Rh Alloy in a Phosphorizing Gas

High temperature corrosion of a Pt-30 wt.% Rh alloy in a phosphorizing gas was isothermally investigated at 1285 K using a gas switching technique. Diffusion of P into the alloy created an outer layer of Pt-rich liquid and blocky (Pt, Rh) 2 P precipitates along with an inner layer of fcc and (Pt, Rh) 2 P plates in a cellular microstructure. Concentration profiles measured by SEM-WDS and EPMA across the layers at room temperature showed that there were three fcc phases: first was a 12 at.% Rh phase in the outer layer; second was a 37 at.% Rh phase in the cellular microstructure; and third was the initial 43 at.% Rh alloy. Also, the EPMA data registered approximately 0.1 at.% P in fcc of these layers. Based on the surrounding binary phase diagrams and the experimental data obtained in this study, a partial Pt-Rh-P phase diagram was constructed. A diffusion path for the corrosion microstructure was drawn on the partial phase diagram to help develop a step by step model for how the microstructure evolved. In conclusion, growth kinetics of the inner layer were used to calculate a P diffusivity of about 10 –12 m 2 /s in the Pt-Rh alloy at 1285 K, suggesting rapid diffusion by either an interstitial or interstitialcy mechanism.

36 MATERIALS SCIENCE↗

NASA NTRS1989

Vapor condensation on liquid surface due to laminar jet-induced mixing: The effects of system parameters

The effects of system parameters on the interface condensation rate in a laminar jet induced mixing tank are numerically studied. The physical system consists of a partially filled cylindrical tank with a slightly subcooled jet discharged from the center of the tank bottom toward the liquid-vapor interface which is at a saturation temperature corresponding to the constant tank pressure. Liquid is also withdrawn from the outer part of the tank bottom to maintain the constant liquid level. The jet velocity is selected to be low enough such that the free surface is approximately flat. The effect of vapor superheat is assumed to be negligible. Therefore, the interface condensation rate can be determined from the resulting temperature field in the liquid region alone. The nondimensional form of the steady state conservation equations are solved by a finite difference method for various system parameters including liquid height to tank diameter ratio, tank to jet diameter ratio, liquid inflow to outflow area ratio, and a heat leak parameter which characterizes the uniform wall heat flux. Detailed analyses based on the numerical solutions are performed and simplified equations are suggested for the prediction of condensation rate.

Lin, Chin-Shun↗

NASA NTRS1990

Vapor condensation on liquid surface due to laminar jet-induced mixing - The effects of system parameters

Lin, Chin-Shun↗

NASA NTRS2004

Bubble Eliminator Based on Centrifugal Flow

The fluid bubble eliminator (FBE) is a device that removes gas bubbles from a flowing liquid. The FBE contains no moving parts and does not require any power input beyond that needed to pump the liquid. In the FBE, the buoyant force for separating the gas from the liquid is provided by a radial pressure gradient associated with a centrifugal flow of the liquid and any entrained bubbles. A device based on a similar principle is described in Centrifugal Adsorption Cartridge System (MSC- 22863), which appears on page 48 of this issue. The FBE was originally intended for use in filtering bubbles out of a liquid flowing relatively slowly in a bioreactor system in microgravity. Versions that operate in normal Earth gravitation at greater flow speeds may also be feasible. The FBE (see figure) is constructed as a cartridge that includes two concentric cylinders with flanges at the ends. The outer cylinder is an impermeable housing; the inner cylinder comprises a gas-permeable, liquid-impermeable membrane covering a perforated inner tube. Multiple spiral disks that collectively constitute a spiral ramp are mounted in the space between the inner and outer cylinders. The liquid enters the FBE through an end flange, flows in the annular space between the cylinders, and leaves through the opposite end flange. The spiral disks channel the liquid into a spiral flow, the circumferential component of which gives rise to the desired centrifugal effect. The resulting radial pressure gradient forces the bubbles radially inward; that is, toward the inner cylinder. At the inner cylinder, the gas-permeable, liquid-impermeable membrane allows the bubbles to enter the perforated inner tube while keeping the liquid in the space between the inner and outer cylinders. The gas thus collected can be vented via an endflange connection to the inner tube. The centripetal acceleration (and thus the radial pressure gradient) is approximately proportional to the square of the flow speed and approximately inversely proportional to an effective radius of the annular space. For a given FBE geometry, one could increase the maximum rate at which gas could be removed by increasing the rate of flow to obtain more centripetal acceleration. In experiments and calculations oriented toward the original microgravitational application, centripetal accelerations between 0.001 and 0.012 g [where g normal Earth gravitation (.9.8 m/s2)] were considered. For operation in normal Earth gravitation, it would likely be necessary to choose the FBE geometry and the rate of flow to obtain centripetal acceleration comparable to or greater than g.

Gonda, Steve R.↗

NASA NTRS2003

Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure

A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10 deg to 20 deg) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft -- an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.

Spilker, Thomas↗

NASA NTRS2017

Thermal Inspection of a Composite Fuselage Section Using a Fixed Eigenvector Principal Component Analysis Method

A composite fuselage aircraft forward section was inspected with flash thermography. The fuselage section is 24 feet long and approximately 8 feet in diameter. The structure is primarily configured with a composite sandwich structure of carbon fiber face sheets with a Nomex(Trademark) honeycomb core. The outer surface area was inspected. The thermal data consisted of 477 data sets totaling in size of over 227 Gigabytes. Principal component analysis (PCA) was used to process the data sets for substructure and defect detection. A fixed eigenvector approach using a global covariance matrix was used and compared to a varying eigenvector approach. The fixed eigenvector approach was demonstrated to be a practical analysis method for the detection and interpretation of various defects such as paint thickness variation, possible water intrusion damage, and delamination damage. In addition, inspection considerations are discussed including coordinate system layout, manipulation of the fuselage section, and the manual scanning technique used for full coverage.

Zalameda, Joseph N.↗

NASA NTRS1977

The radial variation of corotating energetic particle streams in the inner and outer solar system

The radial gradient of long-lived, corotating energetic particle streams was measured using observations of .9-2.2 MeV protons from Helios 1 and 2, IMP 7, Pioneer 10 and Pioneer 11. A positive gradient of approximately 350% per AU is found between .3 AU and 1 AU. Between 1 AU and some 3-5 AU, the gradient is variable with an average value of 100% per AU which is consistent with earlier statistical results. A comparison between measurements at 9 AU and approximately 4 AU shows a negative gradient which is variable from -40 to -100% per AU. Possible solar latitudinal effects on these gradient studies are also discussed. Using solar wind and magnetic field data from Helios 1 between 1 AU and .3 AU, the relation between corotating energetic particle events in the inner solar system and the interplanetary medium is examined. It is found that the energetic particles are contained inside the high speed solar wind stream in a region adjacent to the interaction region between low speed and high speed streams.

Vanhollebeke, M. A. I.↗

NASA NTRS1989

Distribution function of continuously created newborn and pickup ions in outer cometary exospheres

The time evolution of the distribution function of newborn ions in the solar wind is investigated using a quasi-linear-type diffusion equation. The initial distribution is taken to be a ring beam, which is approximated by delta function in pitch angle and velocity, and it is assumed that the ions are created at a constant rate with a similar distribution. A long-time asymptotic form of ion distribution is obtained, which is a mixture of newborn ions and ions generated throughout the entire process. It is shown that the time asymptotic distribution function exists even in the presence of a continuous ionization process. The stability of the long-time asymptotic distribution was examined for the case of parallel propagation, and the results show that the distribution function can be unstable to low-frequency hydromagnetic waves. The results of the analysis were found to agree with recent satellite observations.

Gaffey, J. D., Jr.↗

DOE OSTI2017

A Measure Approximation for Distributionally Robust PDE-Constrained Optimization Problems

In numerous applications, scientists and engineers acquire varied forms of data that partially characterize the inputs to an underlying physical system. This data is then used to inform decisions such as controls and designs. Consequently, it is critical that the resulting control or design is robust to the inherent uncertainties associated with the unknown probabilistic characterization of the model inputs. Here in this work, we consider optimal control and design problems constrained by partial differential equations with uncertain inputs. We do not assume a known probabilistic model for the inputs, but rather we formulate the problem as a distributionally robust optimization problem where the outer minimization problem determines the control or design, while the inner maximization problem determines the worst-case probability measure that matches desired characteristics of the data. We analyze the inner maximization problem in the space of measures and introduce a novel measure approximation technique, based on the approximation of continuous functions, to discretize the unknown probability measure. Finally, we prove consistency of our approximated min-max problem and conclude with numerical results.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1973

The nature of dark-etching rims in meteoritic taenite.

Taenite fields when etched develop a cloudy brown rim with approximate compositional limits of 25 and 40% Ni. In iron meteorites this cloudy zone is only a few microns wide, with a sharp, high-Ni edge about 1 micron from the kamacite interface and a diffuse edge several microns from the central plessite. It is always present in irons unless the meteorite has been cosmically or terrestrially reheated. X-ray and electron diffraction of grains scratched from exceptionally larger areas of cloudy taenite in the mesosiderite Estherville show that this etching zone contains a fine exsolution of kamacite. Detailed electron-probe investigations of taenite in Estherville show that there is a step in the M-shaped Ni profile at the sharp, high-Ni edge of the cloudy region, the Ni dropping suddenly from approximately 45 to 42%. It is proposed that exsolution in the cloudy region effectively froze in the Ni profile at that temperature. On subsequent cooling only the clear outer taenite continued to equilibrate with the kamacite matrix, producing the kink in the M profile. Cloudy taenite is therefore a variety of plessite differing from the usual varieties in that it forms at lower temperatures in areas much richer in Ni, and the morphology is not crystallographically oriented. Its absence can provide a sensitive indication of reheating.

Scott, E. R. D.↗

NASA NTRS1991

Nonadiabatic and three-dimensional effects in compressible turbulent boundary layers

A defect stream function formulation for nonadiabatic flow with small crossflow is developed. The first-integral property of this formulation provides for two removal of the streamline curvature term in the governing equation so that the form of the reduced equation for small crossflow is the same as that for two dimensional flow. The combined law of the wall and wake is used in place of the no-slip boundary condition. The tangential velocity equation for law-of-the-wall flow is shown to be the same for three-dimensions as for two when the Boussinesq approximation applies, and a closed form solution for the crossflow angle in the inner region is obtained. Analytic solutions for nonadiabatic, compressible, equilibrium flow with a Clauser outer-region eddy-viscosity model are obtained, and excellent agreement with experimental skin friction and velocity profile data for nonadiabatic, compressible flat-plate flow is achieved. An analytic solution for a linear inner-region eddy-viscosity model is also obtained; the wake function part of this solution is found to be inconsistent with the empirically established law of the wake.

Barnwell, Richard W.↗