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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.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Efficient dynamic simulation for multiple chain robotic mechanisms

An efficient O(mN) algorithm for dynamic simulation of simple closed-chain robotic mechanisms is presented, where m is the number of chains, and N is the number of degrees of freedom for each chain. It is based on computation of the operational space inertia matrix (6 x 6) for each chain as seen by the body, load, or object. Also, computation of the chain dynamics, when opened at one end, is required, and the most efficient algorithm is used for this purpose. Parallel implementation of the dynamics for each chain results in an O(N) + O(log sub 2 m+1) algorithm.

Lilly, Kathryn W.↗
NASA NTRS1991

Valles Marineris, Mars: Are pit chains formed by erosion and troughs by tectonism?

The origin of the Valles Marineris remains controversial. Erosional, tectonic, and hybrid processes have been proposed. To clarify these contradictions, the widths and depths of pit chains and troughs were compared and it was found that the features do not form a continuum. Rather, results are consistent with the hypothesis that pit chains formed by surficial collapse and troughs by deeper seated and coherent failure. All pit chains and linear depressions in the Valles Marineris region were classified by inspection into six morphologic categories: pit chains (linear arrays of small pits); floored chains (arrays of pit chains having flat or hummocky floors); scalloped troughs (wider linear depressions with scalloped wall segments); narrow troughs (depressions of intermediate width with straight wall segments); wide troughs (broad, linear depressions); and chaotic troughs (more irregular depressions displaying some channel morphologies). Topographic profiles were drawn across the classified depressions and the erosional width was determined between plateau margins along with the depth from the surrounding plateau level to the deepest part.

Lucchitta, Baerbel K.↗
NASA NTRS1999

Carbon chain abundance in the diffuse interstellar medium

Thanks to the mid-IR sensitivities of the ISO and IRTS orbiting spectrometers it is now possible to search the diffuse interstellar medium for heretofore inaccessible molecular emission. In view of the recent strong case for the presence of C(7-) (Kirkwood et al. 1998, Tulej et al. 1998),and the fact that carbon chains possess prominent infrared active modes in a very clean portion of the interstellar spectrum, we have analyzed the IRTS spectrum of the diffuse interstellar medium for the infrared signatures of these species. Theoretical and experimental infrared band frequencies and absolute intensities of many different carbon chain species are presented. These include cyanopolyynes, neutral and anionic linear carbon molecules, and neutral and ionized, even-numbered, hydrogenated carbon chains. We show that--as a family--these species have abundances in the diffuse ISM on the order of 10(-10) with respect to hydrogen, values consistent with their abundances in dense molecular clouds. Assuming an average length of 10 C atoms per C-chain implies that roughly a millionth of the cosmically available carbon is in the form of carbon chains and that carbon chains can account for a few percent of the visible to near-IR diffuse interstellar band (DIB) total equivalent width (not DIB number).

Carbon/analysis/chemistry↗
NASA NTRS2018

Chain Formation as a Mechanism for Mass-Independent Fractionation of Sulfur Isotopes in the Archean Atmosphere

The anomalous abundances of sulfur isotopes in ancient sediments provide the strongest evidence for an anoxic atmosphere prior to ∼2.45 Ga, but the mechanism for producing this 'mass-independent' fractionation pattern remains in question. The prevailing hypothesis has been that it is created by differences in the UV photolysis rates of different SO2 isotopologues. We investigate here a recently proposed additional source of fractionation during gas-phase formation of elemental sulfur (S4 and S8). Because two minor S isotopes rarely occur in the same chain, the longer S4 and S8 chains should be strongly, and roughly equally, depleted in all minor isotopes. This gives rise to negative ∆(sup 33) S values and positive ∆(sub 36) S values in elemental sulfur-just the opposite of (and much larger than) what is predicted from SO2 photolysis itself. Back-reactions during chain formation, specifically photolysis of S2 and S3, pass sulfur having the opposite fractionation back to atomic S, and thence to other sulfur species, causing H2S, SO2, sulfate, and short-chain elemental sulfur to have positive ∆(sup 33) S and negative ∆(sup 36) S. Positive ∆(sup 33) S values in elemental sulfur produced in laboratory SO2 photolysis experiments could be caused by the initial fractionation during photolysis, combined with rapid condensation of short-chain sulfur species on the walls of the reaction chamber, along with a scarcity of back-reactions. The simulated fractionations produced by the chain formation mechanism do not directly match fractionations from the rock record. The mismatch might be explained if the isotopic signals leaving the atmosphere were significantly modulated by life, by uncertainties in the rates of reactions of both major and minor isotopic sulfur species, or by the relatively large potential range of atmospheric parameters. Further work is needed to better constrain these uncertainties, but this novel mechanism suggests new avenues to explore in our search for a explanation for the S-MIF record.

Great Oxidation Event↗
NASA NTRS2018

Chain Formation as a Mechanism for Mass-Independent Fractionation of Sulfur Isotopes in the Archean Atmosphere

The anomalous abundances of sulfur isotopes in ancient sediments provide the strongest evidence for an anoxic atmosphere prior to ∼2.45 Ga, but the mechanism for producing this ‘mass-independent’ fractionation pattern remains in question. The prevailing hypothesis has been that it is created by differences in the UV photolysis rates of different SO2 isotopologues. We investigate here a recently proposed additional source of fractionation during gas-phase formation of elemental sulfur (S4 and S8). Because two minor S isotopes rarely occur in the same chain, the longer S4 and S8 chains should be strongly, and roughly equally, depleted in all minor isotopes. This gives rise to negative Δ(exp 33)S values and positive Δ(exp 33)S values in elemental sulfur—just the opposite of (and much larger than) what is predicted from SO2 photolysis itself. Back-reactions during chain formation, specifically photolysis of S2 and S3, pass sulfur having the opposite fractionation back to atomic S, and thence to other sulfur species, causing H2S, SO2, sulfate, and short-chain elemental sulfur to have positive Δ(exp 33)S and negative Δ(exp 33)S. Positive Δ(exp 33)S values in elemental sulfur produced in laboratory SO2 photolysis experiments could be caused by the initial fractionation during photolysis, combined with rapid condensation of short-chain sulfur species on the walls of the reaction chamber, along with a scarcity of back-reactions. The simulated fractionations produced by the chain formation mechanism do not directly match fractionations from the rock record. The mismatch might be explained if the isotopic signals leaving the atmosphere were significantly modulated by life, by uncertainties in the rates of reactions of both major and minor isotopic sulfur species, or by the relatively large potential range of atmospheric parameters. Further work is needed to better constrain these uncertainties, but this novel mechanism suggests new avenues to explore in our search for a explanation for the S-MIF record.

C. E. Harman↗
NASA NTRS2018

Supply Chain Research and Analysis for Space Systems

The implementation of NASA GSFC's portfolio of mission projects relies upon inter-connected, multi-tiered supply chains of organizations operating under direct and indirect contracts and other agreements throughout the U.S. and around the world. These supply chains are subject to an inter-related array of technical/production, business, market and security risks that are amplified by the ongoing globalization of industry and technology and which can disrupt or threaten the production and delivery of products and services when needed and in conformance with requirements. In recognition of such risks and associated challenges, GSFC's SMA directorate launched an innovative Supply Chain Research and Analysis capability three years ago to gain greater insight into the operating environment, performance, capabilities and viability of current and prospective suppliers for GSFC projects and proposals. The capability uses business intelligence techniques and primarily open source information resources as part of a cost-effective, non-intrusive methodology to produce several types of research and analysis reports. The reports are based on a holistic analytical framework encompassing key technical/production, business enterprise management, market and security factors, and feature in-depth information, summary information profiles, SWOT (Strengths, Weaknesses, Opportunities, Threats) analysis, and candidate risk concerns in order to pro-actively support SMA and project management needs. The SRA capability, which is designed to complement and support ongoing SMA/project management activities and practices, has produced over 105 reports since its start-up in early 2015.This presentation addresses the approach, methodology and performance of the Supply Chain Research and Analysiscapability and its value in assuring the success of NASA mission projects. In doing so, the presentation provides lessons-learned, best practices, case examples and address how it fits into the development of an enterprise-level Supply Chain Risk Management capability.

supply chain risk management↗
NASA NTRS1979

On geoid heights derived from GEOS 3 altimeter data along the Hawaiian-Emperor seamount chain

The geoid heights derived from preliminary GEOS 3 satellite radar altimeter data over the Hawaiian-Emperor seamount chain are examined. Two objectives are pursued: (1) to evaluate the contribution of the topography of the seamount chain and its compensation to the marine geoid; and (2) to determine whether geoid heights derived from GEOS 3 altimeter data can be used to provide information on isostasy at geological features such as the Hawaiian-Emperor seamount chain which formed as relatively young loads on the oceanic lithosphere. Short-wavelength geoid highs of 5-12 m over the crest of the seamount chain and geoid lows over flanking regions are observed. The geological undulations can be explained by a simple model in which the seamount-chain load is supported by a strong rigid lithospheric plate. The elastic thickness estimates agree with values based on surface ship gravity and bathymetry observations, and provide further support to the hypothesis that the elastic thickness acquired at a surface load depends on the temperature gradient of the lithosphere at the time of loading.

Watts, A. B.↗
NASA NTRS1985

Lagrangian observations of surface circulation at the Emperor Seamount chain

In a Kuroshio tracking experiment initiated in February 1977, two satellite-reporting buoys, drogued to 100-m depth, were released southeast of Kuyshu Island, Japan. These drifters crossed the Shatskiy Rise in the Kuroshio extension during May and October and then traversed the Emperor Seamount Chain. Although they reached the chain 117 days apart, their movements near the seamounts display remarkably similar patterns, demonstrating upstream meanders in the surface flow; cyclonic eddy activity immediately west of the chain; passage through the same gap associated with the Jingu and Nintoku seamounts; and a wavelike pattern present over the Hess Rise east of the chain. One drifter exhibited cyclonic eddy motion east of the chain in the lee of the Kinmei Seamount.

Vastano, A. C.↗
NASA NTRS1990

Molecular arrangements and conformations of liquid n-tridecane chains confined between two hard walls

Monte Carlo simulations based on united CH2 atoms linked with fixed bond lengths and angles, and continuously varying torsional angles subject to appropriate interaction energies, were used to study liquid n-tridecane chains confined between two parallel hard walls with 5 mm separation. The molecules located in the central region are noted to be in very close agreement with ideal unperturbed chains. Nearly all the chain units in the first segmental layer adjacent to the walls belong to two-dimensional chains, and exhibit considerable orientational correlations between neighboring segments of different chains.

Vacatello, Michele↗
NASA NTRS1991

Data-driven backward chaining

The C Language Integrated Production System (CLIPS) cannot effectively perform sound and complete logical inference in most real-world contexts. The problem facing CLIPS is its lack of goal generation. Without automatic goal generation and maintenance, forward chaining can only deduce all instances of a relationship. Backward chaining, which requires goal generation, allows deduction of only that subset of what is logically true which is also relevant to ongoing problem solving. Goal generation can be mimicked in simple cases using forward chaining. However, such mimicry requires manual coding of additional rules which can assert an inadequate goal representation for every condition in every rule that can have corresponding facts derived by backward chaining. In general, for N rules with an average of M conditions per rule the number of goal generation rules required is on the order of N*M. This is clearly intractable from a program maintenance perspective. We describe the support in Eclipse for backward chaining which it automatically asserts as it checks rule conditions. Important characteristics of this extension are that it does not assert goals which cannot match any rule conditions, that 2 equivalent goals are never asserted, and that goals persist as long as, but no longer than, they remain relevant.

Haley, Paul↗
NASA NTRS2003

Translocation of a Polymer Chain across a Nanopore: A Brownian Dynamics Simulation Study

We carried out Brownian dynamics simulation studies of the translocation of single polymer chains across a nanosized pore under the driving of an applied field (chemical potential gradient). The translocation process can be either dominated by the entropic barrier resulted from restricted motion of flexible polymer chains or by applied forces (or chemical gradient across the wall), we focused on the latter case in our studies. Calculation of radius of gyrations at the two opposite sides of the wall shows that the polymer chains are not in equilibrium during the translocation process. Despite this fact, our results show that the one-dimensional diffusion and the nucleation model provide an excellent description of the dependence of average translocation time on the chemical potential gradients, the polymer chain length and the solvent viscosity. In good agreement with experimental results and theoretical predictions, the translocation time distribution of our simple model shows strong non-Gaussian characteristics. It is observed that even for this simple tubelike pore geometry, more than one peak of translocation time distribution can be generated for proper pore diameter and applied field strengths. Both repulsive Weeks-Chandler-Anderson and attractive Lennard-Jones polymer-nanopore interaction were studied, attraction facilitates the translocation process by shortening the total translocation time and dramatically improve the capturing of polymer chain. The width of the translocation time distribution was found to decrease with increasing temperature, increasing field strength, and decreasing pore diameter.

Tian, Pu↗
NASA NTRS2010

Using SCOR as a Supply Chain Management Framework for Government Agency Contract Requirements

Enterprise Supply Chain Management consists of: Specifying suppliers to support inter-program and inter-agency efforts. Optimizing inventory levels and locations throughout the supply chain. Executing corrective actions to improve quality and lead time issues throughout the supply chain. Processing reported data to calculate and make visible supply chain performance (provide information for decisions and actions). Ensuring the right hardware and information is provided at the right time and in the right place. Monitoring the industrial base while developing, producing, operating and retiring a system. Seeing performance deep in the supply chain that could indicate issues affecting system availability and readiness.

Paxton, Joe↗
NASA NTRS2007

A Case Study Using Modeling and Simulation to Predict Logistics Supply Chain Issues

Optimization of critical supply chains to deliver thousands of parts, materials, sub-assemblies, and vehicle structures as needed is vital to the success of the Constellation Program. Thorough analysis needs to be performed on the integrated supply chain processes to plan, source, make, deliver, and return critical items efficiently. Process modeling provides simulation technology-based, predictive solutions for supply chain problems which enable decision makers to reduce costs, accelerate cycle time and improve business performance. For example, United Space Alliance, LLC utilized this approach in late 2006 to build simulation models that recreated shuttle orbiter thruster failures and predicted the potential impact of thruster removals on logistics spare assets. The main objective was the early identification of possible problems in providing thruster spares for the remainder of the Shuttle Flight Manifest. After extensive analysis the model results were used to quantify potential problems and led to improvement actions in the supply chain. Similarly the proper modeling and analysis of Constellation parts, materials, operations, and information flows will help ensure the efficiency of the critical logistics supply chains and the overall success of the program.

Tucker, David A.↗
NASA NTRSDate not supplied

Development of an End-to-End Demonstration Readout Chain for Athena-X-IFU

The X-IFU (X-ray Integral Field Unit) of the Athena (Advanced Telescope for High-ENergy Astrophysics) telescope, scheduled for launch in the early 2030's, will provide X-ray spectroscopy data with unprecedented spectral and spatial resolution. This will be achieved by a 3 kilo-pixel array of TES (transition-edge sensor) microcalorimeters. The complete detection chain is under development by a large international collaboration. The detector array will be provided by NASA Goddard Space Flight Center, the cold TDM (time domain multiplexing) electronics by NIST, the cold amplifier by VTT, the cold focal-plane assembly by SRON, the warm front-end electronics by APC, and the DRE (digital readout electronics) by IRAP. In order to perform an end-to-end demonstration of the X-IFU readout chain, a 50 mK test bench is being developed at IRAP in collaboration with CNES. The test bench is based on a two-stage ADR cryostat from Entropy GmbH and a 1024-pixel array from Goddard associated with its cold TDM readout from NIST. The setup will initially be validated using a warm electronic chain from NIST and Goddard. We will describe the complete system being installed in the cryostat and the first results obtained with these electronics. We will also review the status of the integration of the DRE prototype in the demonstration chain and the way forward in the integration and testing of the complete X-IFU readout chain.

S Beaumont↗
NASA NTRS2021

Computational Inference of Vibratory System with Incomplete Modal Information Using Parallel, Interactive and Adaptive Markov Chains

Inverse analysis of vibratory system is an important subject in fault identification, model updating, and robust design and control. It is challenging subject because 1) the problem is oftentimes underdetermined while the measurements are limited and/or incomplete; 2) many combinations of parameters may yield results that are similar with respect to actual response measurements; and 3) uncertainties inevitably exist. The aim of this research is to leverage upon computational intelligence through statistical inference to facilitate an enhanced, probabilistic framework using incomplete modal response measurement. This new framework is built upon efficient inverse identification through optimization, whereas Bayesian inference is employed to account for the effect of uncertainties. To overcome the computational cost barrier, we adopt Markov chain Monte Carlo (MCMC) to characterize the target function/distribution. Instead of using single Markov chain in conventional Bayesian approach, we develop a new sampling theory with multiple parallel, interactive and adaptive Markov chains and incorporate it into Bayesian inference. This can harness the collective power of these Markov chains to realize the concurrent search of multiple local optima. The number of required Markov chains and their respective initial model parameters are automatically determined via Monte Carlo simulation-based sample pre-screening followed by K-means clustering analysis. These enhancements can effectively address the aforementioned challenges in finite element inverse analysis. The validity of this framework is systematically demonstrated through case studies.

K Zhou↗
NASA NTRS2022

Development of an End-to-end Demonstration Readout Chain for Athena/X-IFU

The X-ray Integral Field Unit(X-IFU) of the Athena observatory, scheduled for launch in the mid2030's, will provide X-ray spectroscopy data with unprecedented spectral and spatial resolution. This will be achieved with a 2kilo-pixel array of transition-edge sensor (TES) microcalorimeters. The complete detection chain is under development by a large international collaboration. In order to perform an end-to-end demonstration of the X-IFU readout chain, a 50 mK test bench is being developed at IRAP in collaboration with CNES. The test bench uses a two-stage ADR cryostat from Entropy GmbH, a 1024-pixelarray, and will initially be operated using a warm electronics chain from NIST and NASA Goddard Space Flight Center. We describe the complete system being installed in the cryostat and the current results obtained with these electronics. We also review the status of the integration of the digital readout electronics (DRE)prototype into the demonstration chain and the plan for integrating and testing the complete X-IFU readout chain.

S Beaumont↗
NASA NTRS2007

The NASA Human Space Flight Supply Chain, Current and Future

The current NASA Human Space Flight transportation system, the Space Shuttle, is scheduled for final flight in 2010. The Exploration initiative will create a new capability with a combination of existing systems and new flight and ground elements. To fully understand and act on the implications of such change it is necessary to understand what, how, when and where such changes occur and more importantly, how all these interact. This paper presents Human Space Flight, with an emphasis on KSC Launch and Landing, as a Supply Chain of both information and materials. A supply chain methodology for understanding the flow of information and materials is presented. Further, modeling and simulation projects funded by the Exploration initiative to understand the NASA Exploration Supply Chain are explained. Key concepts and their purpose, including the Enterprise, Locations, Physical and Organizational Functional Units, Products, and Resources, are explained. It is shown that the art, science and perspective of Supply Chain Management is not only applicable to such a government & contractor operation, it is also an invaluable approach for understanding, focusing improvement and growth. It is shown that such commercial practice applies to Human Space Flight and is invaluable towards one day creating routine, affordable access to and from space.

supply chain managemen↗
NASA NTRS2019

Utilizing Supply Chain Assessments to Achieve Excellence, Reduce Risks and Improve Processes

Utilizing Supply Chain Assessments to Achieve Excellence, Reduce Risks and Improve Processes Supply Chain Management: Why it is important Strategic Challenge: Supply Chain RisksHistory of supply chain assessments at GoddardExamining case studies on successes and lessons learnedEnabling teams to develop tools to manage GSFC supply chainGaining supplier insight through IT tools that combines supplier data and provides supplier alerts

Risk Management↗