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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 451 records · Page 25

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NASA NTRS1992

Estimation of the absolute position of mobile systems by an optoelectronic processor

A method that determine the absolute position of a mobile system with a hybrid optoelectronic processor has been developed. Position estimates are based on an analysis of circular landmarks that are detected by a TV camera attached to the mobile system. The difference between the known shape of the landmark and its image provides the information needed to determine the absolute position of the mobile system. For robust operation, the parameters of the landmark image are extracted at high speeds using an optical processor that performs an optical Hough transform. The coordinates of the mobile system are computed from these parameters in a digital co-processor using fast algorithms. Different sources of position estimation errors have also been analyzed, and consequent algorithms to improve the navigation performance of the mobile system have been developed and evaluated by both computer simulation and experiments.

Feng, Liqiang↗

NASA NTRS2000

Mars Umbilical Technology Demonstrator

The objective of this project is to develop a autonomous umbilical mating for the mars umbilical technology demonstrator. The Mars Umbilical Technology Demonstrator (MUTD) shall provide electrical power and fiber optic data cable connections between two simulated mars vehicles. The Omnibot is used to provide the mobile base for the system. The mate to umbilical plate is mounted on a three axis Cartesian table, which is installed on the Omnibot mobile base. The Omnibot is controlled in a teleoperated mode. The operator using the vision system will guide the Omnibot to get close to the mate to plate. The information received from four ultrasonic sensors is used to identify the position of mate to plate and mate the umbilical plates autonomously. A successful experimentation verifies the approach.

Houshangi, Nasser↗

NASA NTRS2007

Detailed Studies of Pixelated CZT Detectors Grown with the Modified Horizontal Bridgman Method

The detector material Cadmium Zinc Telluride (CZT) achieves excellent spatial resolution and good energy resolution over a broad energy range, several keV up to some MeV. Presently, there are two main methods to grow CZT crystals, the Modified High-Pressure Bridgman (MHB) and the High-Pressure Bridgman (HPB) process. The study presented in this paper is based on MHB CZT substrates from the company Orbotech Medical Solutions Ltd. [Orbotech Medical Solutions Ltd., 10 Plaut St., Park Rabin, P.O. Box 2489, Rehovot, Israel, 76124]. Former studies have shown that high-work-function materials on the cathode side reduce the leakage current and, therefore, improve the energy resolution at lower energies. None of the studies have emphasized on the anode contact material. Therefore, we present in this paper the result of a detailed study in which for the first time the cathode material was kept constant and the anode material was varied. We used four different anode materials: Indium, Titanium, Chromium and Gold, metals with work-functions between 4.1 eV and 5.1 eV. The detector size was 2.0 x 2.0 x 0.5 cu cm with 8 x 8 pixels and a pitch of 2.46 mm. The best performance was achieved with the low-work-function materials Indium and Titanium with energy resolutions of 2.0 keV (at 59 keV) and 1.9 keV (at 122 keV) for Titanium and 2.1 keV (at 59 keV) and 2.9 keV (at 122 keV) for Indium. Taking into account the large pixel pitch of 2.46 mm, these resolutions are very competitive in comparison to those achieved with detectors made of material produced with the more expensive conventional HPB method. We present a detailed comparison of our detector response with 3D simulations. The latter comparisons allow us to determine the mobility-lifetime-products (mu tau-products) for electrons and holes. Finally, we evaluated the temperature dependency of the detector performance and ls-products. For many applications temperature dependence is important, therefore, we extended the scope of our study to temperatures as low as -30 C. There are two important results. The breakdown voltage increases with decreasing temperature, and electron mobility-lifetime-product decreases by about 30% over a range from 20 C to -30 C. The latter effect causes the energy resolution to deteriorate, but the concomitantly increasing breakdown voltage makes it possible to increase the applied bias voltage and restore the full performance

Jung, I.↗

NASA NTRSDate not supplied

Optimal Sensor Mobility Design for Target Tracking with Distributed Sensing, Communication and Computing Infrastructure

The paper presents an airborne target tracking approach with data fusion from distributed stationary and mobile sensor network transmitted through a wireless/wired communication network and using a distributed computing infrastructure. To obtain high quality measurements, sensor flight platforms' positions and orientations are optimized with respect to the available target's position and velocity estimates, and a formation control strategy is applied to derive desired trajectories for the flight platforms. As sensors move, the communication network topology switching is determined using the worst-case approach to handle uncertainties in the target's and sensors' positions, which alters communication delays for sensors' data transmission to computing centers. An optimal data migration algorithm is periodically applied to determine these communication delays for each sensor and the optimal location with minimum end-to-end latency for the target tracking algorithm execution, which is based on adaptive information fusion from multi-modal mobile and stationary sensors inside an Extended Kalman Filter framework. The approach is validated in a desktop simulation environment using synthetic sensor data generated for a simulated target's flight.

Distributed sensing↗

NASA NTRS2007

Surface Operations: Two Case Studies of Simulated Lunar Operations

In September 2007, a team of scientists and engineers from several NASA centers participated in a field exercise at Meteor Crater, Arizona. The tests in this field exercise utilized recently developed robots of varying scales and capabilities and humans in pressurized space suits. Two examples of operations performed in the field are presented: a surface operations scenario involving suited crew supported by a number of mobile robots and setup operations for accessing a crater. The surface operations scenario simulated the end of a crew sortie and involved the following agents: 1) Suit subjects from Johnson Space Center s (JSC) advanced spacesuit laboratory 2) JSC's unpressurized crewed rover testbed, SCOUT 3) The Jet Propulsion Laboratory s (JPL) rough terrain, payload carrying robot, ATHLETE 4) JSC's Astronaut assist robot, Robonaut 5) Ames Research Center's (ARC) inspection robot, K-10. Operations began with ATHLETE positioning a pressurized rover compartment (PRC) as two crew members drove the SCOUT unpressurized rover from the field. The crew dismounted SCOUT, walked to the PRC for recharging. Robonaut then removed a sample box from the SCOUT equipment tray. K-10 then performed a drive around inspection of SCOUT, assembling a mosaic image. Lastly, the SCOUT vehicle was remotely driven to the next site. The setup operations for crater access scenario involved ATHLETE and Robonaut. This scenario began with Robonaut approaching ATHLETE and extracting a tether line. ATHLETE then extracted a drill and drilled an anchor into the surface. Robonaut then reconnected the tether to the anchor and backed away. ATHLETE is then ready to descend into the crater. This descending into the crater step is currently in the planning phase.

Bluethmann, William J.↗

DOE OSTI2025

Role of effective mass and long-range interactions in the band-gap renormalization of photoexcited semiconductors

Understanding how to control changes in the electronic structure and related dynamical renormalizations by external driving fields is the key for understanding ultrafast spectroscopy and applications in electronics. Here, we focus on the band gap's modulation by external electric fields and uncover the effect of band dispersion on the gap renormalization. We employ the Green's function formalism using the real-time Dyson expansion to account for dynamical correlations induced by photodoping. The many-body formalism captures the dynamics of systems with long-range interactions, carrier mobility, and variable electron and hole effective mass. We also demonstrate that mean-field simulations based on the Hartree-Fock Hamiltonian, which lacks dynamical correlations, yields a qualitatively incorrect picture of band-gap renormalization. We find the trend that increasing effective mass, thus decreasing mobility, leads to as much as a 6% enhancement in band-gap renormalization. Further, the renormalization is strongly dependent on the degree of photodoping. As the screening induced by free electrons and holes effectively reduces any long-range and interband interactions for highly excited systems, we show that there is a specific turnover point with a minimal band gap. Here, we further demonstrate that the optical gap renormalization follows the same trend though its magnitude is altered by the Moss-Burstein effect.

Approximation methods for many-body systems↗

NASA NTRS2024

Measurements of Silicosis Factors in Lunar and Martian Simulants

Simulants are geologically complex materials that are developed to represent the physical and/or compositional characteristics of a planetary surface (e.g., a naturally occurring soil or regolith). There are dozens of commercially available simulants that have been developed over the years; each simulant exhibits unique physical, chemical, and mineralogical characteristics. Simulants are derived from either natural or synthetic sources (i.e., “feedstocks”) of glass, minerals, and rocks. These feedstock components are processed by crushing, pulverizing, melting, etc., and then combined in the appropriate proportions to represent a particular site, surface, or region (e.g., Lunar Highlands Regolith). The process of creating simulants therefore requires the mechanical breakdown and reincorporation of feedstock components which may contain crystalline silica minerals such as quartz, cristobalite, and tridymite. Certain crystalline silica particles of the respirable fraction (<10 μm in diameter) are of great concern; chronic and acute exposure to these respirable crystalline silica (RCS) can lead to permanent damage and scarring of lung tissue, incurable lung diseases (i.e., silicosis), lung cancer, COPD (chronic obstructive pulmonary disease), and kidney disease. Planetary simulants are used extensively as test materials in the in scientific and engineering communities (e.g., testing of dust mitigation technologies, in-situ resource utilization, rover mobility, hardware, soft goods etc.). As such, this assessment was developed to serve as a guide for simulant users, local Safety and Occupational Health professionals, and Industrial Hygienists to evaluate the risk of silicosis across a wide variety of Lunar and Martian simulants. The goal of these works is to ensure that those working with simulant can do so safely and with an informed understanding of potential health risks.

Lunar↗

NASA NTRSDate not supplied

Measurements of Silicosis Factors in Lunar and Martian Simulants

Lunar↗

NASA NTRSDate not supplied

Designing a Distributed Web-based Simulation Environment for Enabling Autonomous Systems Research

In the continued pursuit of creating a future with robust Urban Air Mobility (UAM) operations defined as safe and efficient air traffic operations in metropolitan environments for both piloted and autonomous systems, development of the concepts, technologies, and procedures to establish this UAM ecosystem remains an active area of research. In particular, as autonomous systems continue to grow in both complexity and use throughout UAM concepts the need for simulation environments to both test individual components and systems and to study the complex interactions between them is paramount. In this paper we address design considerations, technologies, and challenges of adapting native simulation environment application concepts to an interactive and distributed web-based framework. The proposed web-based design allows for easier and wider access for developing, testing, integrating, and studying emergent behaviors of complex autonomous systems interaction. We demonstrate the utility of the proposed approach by showing multi-agent interaction and emergent behavior in two scenarios: (1) autonomous urban air mobility vehicles flying in a convoy and (2) interaction of a convoy with a search and rescue operation.

Benjamin N Kelley↗

NASA NTRS2002

Impact-Mobilized Dust in the Martian Atmosphere

We consider dust production and entrainment into the atmosphere of Mars by impacts. Numerical simulations based on the multidimensional multimaterial hydrocode were conducted for impactors 1 to 100 m in size and velocities 11 and 20 kilometers per second. The size distribution of particles was based on experimentrr wing TNT explosions. Dust can be mobilized even when the impactor does not reach the ground through the release of energy in the atmosphere, We found that the blast produced winds entrained dust by a mechanism similar to boundary layer winds as determined from the wind-tunnel tests. For a l-m radius stony asteroid releasing its energy in the atmosphere the lifted mass of dust is larger than that in a typical dust devil and could trigger local dust storms, For a 100-m-radius meteoroid the amount of injected dust is comparable with the tota! mass of a global dust storm.

Nemtchinov, I. V.↗

NASA NTRS1991

Energy Models for One-Carrier Transport in Semiconductor Devices

Moment models of carrier transport, derived from the Boltzmann equation, made possible the simulation of certain key effects through such realistic assumptions as energy dependent mobility functions. This type of global dependence permits the observation of velocity overshoot in the vicinity of device junctions, not discerned via classical drift-diffusion models, which are primarily local in nature. It was found that a critical role is played in the hydrodynamic model by the heat conduction term. When ignored, the overshoot is inappropriately damped. When the standard choice of the Wiedemann-Franz law is made for the conductivity, spurious overshoot is observed. Agreement with Monte-Carlo simulation in this regime required empirical modification of this law, or nonstandard choices. Simulations of the hydrodynamic model in one and two dimensions, as well as simulations of a newly developed energy model, the RT model, are presented. The RT model, intermediate between the hydrodynamic and drift-diffusion model, was developed to eliminate the parabolic energy band and Maxwellian distribution assumptions, and to reduce the spurious overshoot with physically consistent assumptions. The algorithms employed for both models are the essentially non-oscillatory shock capturing algorithms. Some mathematical results are presented and contrasted with the highly developed state of the drift-diffusion model.

Jerome, Joseph W.↗

NASA NTRS1993

Development of a multilayer interference simulation program for MSS systems

This paper discusses the development of a multilayer interference analysis and simulation program which is used to evaluate interference between non-geostationary and geostationary satellites. In addition to evaluating interference, this program can be used in the development of sharing criteria and coordination among various Mobile Satellite Services (MSS) systems. A C++/Windows implementation of this program, called Globalstar Interference Simulation Program (GISP), has been developed.

Izadian, Jamal S.↗

DOE OSTI2026

NLR Core Modeling & Decision Support Capabilities: FASTSim, RouteE, T3CO & OpenPATH

This project is part of the program area to develop and improve core capabilities for the Energy-Efficient Mobility Systems (EEMS) program that enable research, development and deployment of advanced mobility solutions and enhance the EEMS Program's ability to address system-level transportation challenges. Advancements to the Future Automotive Systems Technology Simulator (FASTSim), Route Energy Prediction Model (RouteE), Transportation Technology Total Cost of Ownership (T3CO) and Open Platform for Agile Trip Heuristics (OpenPATH) core capabilities under this project supports the overall EEMS Program goals to effectively evaluate energy and mobility impacts of future transportation technologies and services, and to identify the most promising pathways to reduce transportation costs and environmental harms, and to improve mobility access. This presentation was prepared for the 2026 Annual Merit Review of this project.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2023

Simulations of self- and Xe diffusivity in uranium mononitride including chemistry and irradiation effects

A combination of density functional theory and empirical potential atomic scale simulations have been used to determine a model for defect stability and mobility in uranium mononitride (UN), as a function of temperature (T) and N 2 partial pressure (p N 2 ). Using the model, predictions of hypo-stoichiometry under U-rich conditions compare favorably to CALPHAD calculations using the TAF-ID database. Furthermore, our predictions of U and N self-diffusivity are in good agreement with experiments carried out as a function of T at specific partial pressures under thermal equilibrium. The validated atomic scale data have then been implemented within a cluster dynamics method to simulate irradiation-enhanced defect concentrations. All defects and clusters studied have significantly enhanced concentrations, with respect to thermal equilibrium, as T is lowered. The irradiation-enhanced Xe diffusivity is compared to post-irradiation annealing and in-pile experiments. In conclusion, the contributions of various defects and clusters to non-stoichiometry, self-diffusivity, and Xe diffusivity are discussed.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

NASA NTRS2011

Assessment of Proficiency During Simulated Rover Operations Following Long-Duration Spaceflight

Following long-duration space travel, pressurized rovers will enhance crew mobility to explore Mars and other planetary surfaces. Adaptive changes in sensorimotor function may limit the crew s proficiency when performing some rover operations shortly after transition to the new gravitoinertial environment. The primary goal of this investigation is to quantify postflight decrements in operational proficiency in a motion-based rover simulation after International Space Station (ISS) expeditions. Given that postflight performance will also be influenced by the level of preflight proficiency attained, a ground-based normative study was conducted to characterize the acquisition of skills over multiple sessions.

Wood, S. J.↗

NASA NTRS2014

Assessment of Proficiency During Simulated Rover Operations Following Long-Duration Spaceflight

Beltran, E. J.↗

DOE OSTI2026

Experimental Characterization and Modeling of High Hole Mobility GeSn Quantum Wells: The Role of Alloy Disorder Scattering

Understanding mechanisms influencing electrical transport in material systems not only provides a scientific explanation for observed behavior but also offers insight into ways to enhance transport in devices. This study reports experimental hole mobility of 8 x 10 4 cm 2 V -1 s -1 in a Ge 0.92 Sn 0.08 , the highest recorded mobility for the GeSn system. A study of the material's quality is presented using structural and electrical characterization techniques, with transport data being supported by simulations using an extensive modeling framework. Quantum Hall measurements further indicate the material's high quality and potential spintronic applications, with extracted values of 0.0689$m$ 0 and 13.6 for the effective mass and effective g‐factor, respectively. It is observed that transport is limited by alloy disorder scattering at cryogenic temperatures. A comparative study between the presented structure and similar quantum well heterostructures revealed that the difference in hole mobilities is captured by a disparity in the reduced nominal alloy disorder scattering potential (Δ U alloy = 0.8 eV), that is lower than the value of a fully random alloy (Δ U alloy = 1.4–1.7 eV) potential. The difference in Δ U alloy suggests that heterostructures with similar geometries and alloy compositions can have different alloy disorder scattering, implying that an underlying mechanism, such as short‐range order, may be responsible and warrants further investigation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2021

Discrete stochastic model of point defect-dislocation interaction for simulating dislocation climb

Dislocation climb is an important high temperature process in metals plasticity, responsible for the phenomena such as creep, swelling, or hardening. Climb is defined by the ability of dislocations to leave their original glide plane by interacting with point defects. As such, dislocation climb is controlled by point defect diffusion/absorption/emission, all of which involve thermal activation. The existing thermodynamically consistent models for climb are generally formulated in a continuum framework, through the definition of effective defect fluxes and climb propensities in response to thermodynamic driving forces. However, the point-wise discrete nature of vacancies (and/or self-interstitials) confers a highly discrete nature to the climb dynamics, which is also strongly affected by elastic forces. The combination of discreteness, thermal activation, and elasticity makes this process too challenging for direct atomistic methods such as molecular dynamics. Here we develop a kinetic Monte Carlo model that captures vacancy generation and transport kinetics acting in conjuction with the evolving elastic fields provided by discrete dislocation dynamics simulations. The two models are coupled via the applied stresses and stress gradients generated by dislocation structures at vacancy locations. Our simulations reveal two surprising results. First that climb is dominated by vacancy emission even when the background vacancy concentration is much higher than the equilibrium one. And, second, that climb velocities might be much faster than otherwise believed when one uses the classical theories of climb. These effects are due to the locality of vacancy-dislocation processes, which are not captured in classical treatments that assume smooth vacancy fluxes and homogeneous concentrations. We apply the method to study elementary climb processes in body-centered cubic iron and furnish climb mobility functions to be used in parametric dislocation dynamics and/or crystal plasticity simulations. Here, we apply the technique to study non-conservative plastic bypass of spherical precipitates by edge dislocations and point out the differences between our discrete approach and existing continuum formulations.

36 MATERIALS SCIENCE↗