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NASA NTRS2017

Concepts for Mars On-Orbit Robotic Sample Capture and Transfer

A potential Mars Sample Return (MSR) mission could require robotic autonomous capture and manipulation of an Orbital Sample (OS) before returning the samples to Earth. In one scenario, an orbiter would capture the OS, manipulate to a preferential orientation, transition it through the steps required to break-the-chain with Mars, stowing it in a containment vessel or an Earth Entry Vehicle (EEV) and providing redundant containment to the OS (for example by closing and sealing the lid of the EEV). In this paper, we discuss the trade-space of concepts generated for both the individual aspects of capture and manipulation of the OS, as well as concepts for the end-to-end system. Notably, we discuss concepts for OS capture, manipulation of the OS to orient it to a preferred configuration, and steps for transitioning the OS between different stages of manipulation, ultimately securing it in a containment vessel or Earth Entry Vehicle.

Chamberlian-Simon, Brendan↗

NASA NTRS2017

Concepts for Mars On-Orbit Robotic Sample Capture and Transfer

Ohta, Preston↗

NASA NTRS1992

Algorithmic improvements for simulator motion drive

Contemporary simulator motion drive algorithms typically are designed in an analog (continuous) environment, but are implemented in a digital (discrete) environment. The intended continuous system, specified as frequency domain (Laplace transform) transfer functions, may not be represented properly by the algorithms used for digital implementation. The motion drive software in use with the Vertical Motion Simulator at Ames Research Center was investigated recently; the original algorithms (Euler) were changed to a state transition method. Comparison of the frequency responses of the original and new implementations showed that the state transition method more closely approximates the desired analog responses. In addition, test pilots who evaluated both implementations preferred the motions generated with the state transition method over those generated with the Euler integration method.

Laforce, Soren↗

NASA NTRS1994

Overcharge and overdischarge protection of ambient temperature secondary lithium cells

A cathode additive is provided for protecting an ambient temperature secondary lithium cell from overcharging or overdischarging. The cathode additive is chosen to create an upper voltage plateau which is slightly higher than a characteristic charge cutoff voltage of the cathode of the cell. The cathode additive additionally creates a lower voltage plateau which is slightly lower than the characteristic discharge cutoff voltage of the cell. Preferably, the cathode additive is a transition metal oxide or a sulfide and may, for example, include a mixture of Li2Mn2O4 and Li(0.1)MoO2.

Huang, Chen-Kuo↗

NASA NTRS2006

Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in Aluminum

A traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation

Yamakov, Vesselin I.↗

NASA NTRS2006

Central East Pacific Flight Routing

With the introduction of the Federal Aviation Administration s Advanced Technology and Oceanic Procedures system at the Oakland Oceanic Center, a level of automation now exists in the oceanic environment to potentially begin accommodating increased user preferred routing requests. This paper presents the results of an initial feasibility assessment which examines the potential benefits of transitioning from the fixed Central East Pacific routes to user preferred routes. As a surrogate for the actual user-provided routing requests, a minimum-travel-time, wind-optimal dynamic programming algorithm was developed and utilized in this paper. After first describing the characteristics (e.g., origin airport, destination airport, vertical distribution and temporal distribution) of the westbound flights utilizing the Central East Pacific routes on Dec. 14-16 and 19-20, the results of both a flight-plan-based simulation and a wind-optimal-based simulation are presented. Whereas the lateral and longitudinal distribution of the aircraft trajectories in these two simulations varied dramatically, the number of simulated first-loss-of-separation events remained relatively constant. One area of concern that was uncovered in this initial analysis was a potential workload issue associated with the redistribution of traffic in the oceanic sectors due to thc prevailing wind patterns.

Grabbe, Shon↗

NASA NTRS1990

Process for crosslinking methylene-containing aromatic polymers with ionizing radiation

A process for crosslinking aromatic polymers containing radiation-sensitive methylene groups (-CH2-) by exposing the polymers to ionizing radiation thereby causing crosslinking of the polymers through the methylene groups is described. Crosslinked polymers are resistant to most organic solvents such as acetone, alcohols, hydrocarbons, methylene, chloride, chloroform, and other halogenated hydrocarbons, to common fuels and to hydraulic fluids in contrast to readily soluble uncrosslinked polymers. In addition, the degree of crosslinking of the polymers depends upon the percentage of the connecting groups which are methylene which ranges from 5 to 50 pct and preferably from 25 to 50 pct of the connecting groups, and is also controlled by the level of irradiation which ranges from 25 to 1000 Mrads and preferably from 25 to 250 Mrads. The temperature of the reaction conditions ranges from 25 to 200 C and preferably at or slightly above the glass transition temperature of the polymer. The crosslinked polymers are generally more resistant to degradation at elevated temperatures such as greater than 150 C, have a reduced tendency to creep under load, and show no significant embrittlement of parts fabricated from the polymers.

Bell, Vernon L.↗

NASA NTRS1973

Ultrasonic investigation of the nematic-isotropic phase transition in MBBA.

Relaxation processes associated with the nematic-isotropic phase transition are investigated in liquid crystals of p-methoxybenzylidine-p-n-butylaniline. Sound velocity and absorption are measured at frequencies from 0.3 to 23 MHz at temperatures from 23 to 77 C in samples without preferred orientations. Particular attention is given to the region of transition at about 44 C. Sound absorption and velocity dispersion far from the phase transition region can be well described by a single relaxation process, while in the vicinity of the phase transition the acoustic properties are characteristic of a multiply relaxing fluid.

Eden, D.↗

NASA NTRS1985

Aspects of the stratospheric circulation as derived from SSU data

Five years of global data are available for the stratosphere up to 1 mb from Stratospheric Sounding Units (SSUs) on board NOAA satellites. These data form the basis for a climatological study which concentrates on the seasonal and inter-annual variability of the stratosphere and the connection between the stratospheric circulation and that of the troposphere. Particular emphasis is on the structure of the Southern Hemisphere and how it compares with that of the Northern Hemisphere. The characteristic difference in the vertical structure and propagation of disturbances in the two hemispheres is related to differences in the tropospheric flow and the long-term variation of the basic state of the stratosphere. Disturbances in both hemispheres occur in preferred geographical locations. The final warming, marking the transition from westerly to easterly winds, is an example. These occur asymmetrically with respect to the pole as warm air moves over the pole, usually from the same region.

Michaelis, V.↗

NASA NTRS1990

Transitions from Hadley to Rossby flows in internally forced rotating spherical systems

The possibility of global-scale transitions between the Hadley and Rossby atmospheric regimes is investiated using a simple three-dimensional rotating spherical model without a boundary layer structure, bottom topography, or cumulus friction, and the expected occurrence of the Hadley to Rossby transition is demonstrated. It is shown that a transition from Hadley flow to wavenumber-5 Rossby flow is preferred, in agreement with standard baroclinic instability results. This result gives a reasonable Rossby wave bifurcation from the Hadley solution. For the cases examined, it was found that the upper symmetric Hadley regime does not exist and that the Hadley to Rossby transition depends on the values of the eddy viscosities.

Higgins, Wayne R.↗

NASA NTRS1987

On the noncoplanarity of the magnetic field within a fast collisionless shock

Within the magnetic ramp of fast collisionless plasma shocks observed with spacecraft instruments and simulated numerically, the magnetic field undergoes an excursion out of the plane of coplanarity. This rotation is consistently in the direction such that the electrostatic potential jump across the shock, as measured in the de Hoffman-Teller frame of the reference (HTF), is about 2-6 times smaller than the electrostatic potential jump measured in the normal incidence frame. The preferred direction is consistent with a basic whistler mode transition between the upstream and downstream orientations. The potential jump in the HTF is considerably smaller than the change in bulk flow energy across the shock, confirming the recent suggestion that magnetic forces contribute importantly to the slowing of the plasma in that frame. A further consequence is that suprathermal particles leaking back into the upstream region across the shock do not gain much energy from the cross-shock electric field.

Thomsen, M. F.↗

NASA NTRS2010

Slicing AADL Specifications for Model Checking

To combat the state-space explosion problem in model checking larger systems, abstraction techniques can be employed. Here, methods that operate on the system specification before constructing its state space are preferable to those that try to minimize the resulting transition system as they generally reduce peak memory requirements. We sketch a slicing algorithm for system specifications written in (a variant of) the Architecture Analysis and Design Language (AADL). Given a specification and a property to be verified, it automatically removes those parts of the specification that are irrelevant for model checking the property, thus reducing the size of the corresponding transition system. The applicability and effectiveness of our approach is demonstrated by analyzing the state-space reduction for an example, employing a translator from AADL to Promela, the input language of the SPIN model checker.

Odenbrett, Maximilian↗

NASA NTRS1991

Elliptical flux vortices in YBa2Cu3O7

The most energetically favorable vortex in YBa2Cu3O7 forms perpendicular to an anisotropic plane. This vortex is elliptical in shape and is distinguished by an effective interchange of London penetration depths from one axis of the ellipse to another. By generalizing qualitatively from the isotropic to the anisotropic case, we suggest that the flux flow resistivity for the vortex that forms perpendicular to an anistropic plane should have a preferred direction. Similar reasoning indicates that the Kosterlitz-Thouless transition temperature for a vortex mediated transition should be lower if the vortex is elliptical in shape.

Hickman, H.↗

NASA NTRS2018

Do Close-in Giant Planets Orbiting Evolved Stars Prefer Eccentric Orbits?

The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity (RV) measurements of three of these systems, revealing signiﬁcantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moderately eccentric phase where they shrink faster than they circularize due to tides raised on evolved host stars. Additional RV measurements of currently known systems, along with new systems discovered by the recently launched NASA Transiting Exoplanet Survey Satellite (TESS) mission, may constrain the timescale and mass dependence of this process.

Thomas Barclay↗

NASA NTRSDate not supplied

CFD Predictions of Boiling Regime Transitions during Line Chilldown validated against a 1G LN2 Experiment

Introduction Before filling a propellant tank on the ground or in Space, the transfer line between the donor and receiver tanks must be cooled down preferably by sacrificing a minimum amount of the cryogenic fluid. The cryogenic line chill-down process involves a transition between different flow boiling regimes, namely, film boiling, transition film boiling, and nucleate boiling which are complex and may be quite gravity-dependent. Capturing these boiling phenomena and predicting the transition between them in a CFD framework is new and challenging both for 1g and microgravity applications. Materials & Methods The present work addresses this challenge by employing a two-phase Eulerian approach in the context of a homogeneous fluid mixture together with the Lee phase change model to capture the film boiling regime of the chill-down process using ANSYS Fluent®. The nucleate boiling regime is predicted by incorporating an in-house developed sub-grid model that accounts for bubble nucleation, bubble growth, bubble departure diameter, and their shedding frequency. The sub-grid model is encoded and implemented into Fluent via a user-defined function for the wall-fluid heat flux calculations. The mathematical formulation and numerical implementation of the CFD model are described in detail. The coupled CFD-Subgrid model is validated against published experimental data for liquid nitrogen chill-down of a heated stainless-steel pipe in 1g. Results Numerical simulation results show good agreements between the CFD predictions of the wall temperature evolution, rewetting temperature, and transition between film and nucleate boiling, with the experimental measurements published by Darr et al [2] for several different LN2 flowrates in the vertical pipe orientation. The CFD predictions for the wall temperature distribution indicate a rapid quenching of the wall at two upstream and downstream temperature sensing locations as compared to the experimental measurement. The only tuning parameter in the CFD model is the Lee mass transfer coefficient. The CFD Model predicts the Liedenfrost rewetting temperature in close agreement with the experiment. This marks a transition between stable and transitionary flow boiling regimes. The CFD-predicted boiling curve for the downstream sensor location is also compared against its experimental counterpart and indicates that the model is able to predict all the key temperature and heat flux parameters during the transitions from stable to transitionary film boiling to nucleate boiling in close agreement with the experiment. A sequence of predicted volume fraction, and temperature contours depicting these transitions will be presented.

Evaporation Condensation↗

NASA NTRSDate not supplied

The Impact of Transition-Edge Sensor Design on Internal Thermal Fluctuation Noise and Thermal Conductance

The measured noise in transition-edge sensor (TES) microcalorimeters with a Mo/Au bilayer has been shown to have a significant contribution from internal thermal fluctuation noise (ITFN) between the absorber and the TES. Previous measurements showed the relevant thermal link leading to the noise was the thermal conductance of the TES bilayer, and ITFN has been shown to correlate with the sheet resistance of the TES. As a result, ITFN is particularly significant in devices with a large bilayer sheet resistance. However, because of more favorable transition shapes, such high resistance devices have recently been shown to be preferable under alternating current bias, which is required for the frequency division multiplexed readout baselined for the X-ray Integral Field Unit (X-IFU) instrument on the ATHENA satellite. Therefore, it is important to investigate how else to minimize the ITFN beyond changes to the sheet resistance. In this presentation, we will discuss our investigation of how changes to the TES design can affect ITFN for a fixed sheet resistance. We will present how ITFN is altered by changes to the aspect ratio of the TES, the addition of normal metal banks parallel to the TES current direction, and the size and position of the connections between the absorber and the TES. We will also discuss how these design changes impact the superconducting transition shape, and the thermal conductance from the TES to the thermal bath. These results may provide routes for further improvements of TES performance, and a deeper understanding of the physics of the thermal network in a TES microcalorimeter.

Nicholas A Wakeham↗

NASA NTRS1979

Phase transitions in Group III-V and II-VI semiconductors at high pressure

The structures and transition pressures of Group III-V and II-VI semiconductors and of a pseudobinary system (Ga/x/In/1-x/Sb) have been investigated. Results indicate that GaP, InSb, GaSb, GaAs and possible AlP assume Metallic structures at high pressures; a tetragonal, beta-Sn-like structure is adopted by only InSb and GaSb. The rocksalt phase is preferred in InP, InAs, AlSb, ZnO and ZnS. The model of Van Vechten (1973) gives transition pressures which are in good agreement with measured values, but must be refined to account for the occurrence of the ionic rocksalt structure in some compounds. In addition, discrepancies between the theoretical scaling values for volume changes at the semiconductor-to-metal transitions are observed.

Yu, S. C.↗

NASA NTRS2004

Low conductivity and sintering-resistant thermal barrier coatings

A thermal barrier coating composition comprising a base oxide, a primary stabilizer oxide, and at least one dopant oxide is disclosed. Preferably, a pair of group A and group B defect cluster-promoting oxides is used in conjunction with the base and primary stabilizer oxides. The new thermal barrier coating is found to have significantly lower thermal conductivity and better sintering resistance. The base oxide is selected from the group consisting of zirconia and hafnia and combinations thereof. The primary stabilizing oxide is selected from the group consisting of yttria, dysprosia, erbia and combinations thereof. The dopant or group A and group B cluster-promoting oxide dopants are selected from the group consisting of rare earth metal oxides, transitional metal oxides, alkaline earth metal oxides and combinations thereof. The dopant or dopants preferably have ionic radii different from those of the primary stabilizer and/or the base oxides.

Zhu, Dongming↗