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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 145 records · Page 8

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NASA NTRS1985

Analysis of adaptive algorithms for an integrated communication network

Techniques were examined that trade communication bandwidth for decreased transmission delays. When the network is lightly used, these schemes attempt to use additional network resources to decrease communication delays. As the network utilization rises, the schemes degrade gracefully, still providing service but with minimal use of the network. Because the schemes use a combination of circuit and packet switching, they should respond to variations in the types and amounts of network traffic. Also, a combination of circuit and packet switching to support the widely varying traffic demands imposed on an integrated network was investigated. The packet switched component is best suited to bursty traffic where some delays in delivery are acceptable. The circuit switched component is reserved for traffic that must meet real time constraints. Selected packet routing algorithms that might be used in an integrated network were simulated. An integrated traffic places widely varying workload demands on a network. Adaptive algorithms were identified, ones that respond to both the transient and evolutionary changes that arise in integrated networks. A new algorithm was developed, hybrid weighted routing, that adapts to workload changes.

Reed, Daniel A.↗

NASA NTRS1982

An NNSS satellite timing receiver

The U.S. Navy Navigation Satellite System, NNSS, offers a unique worldwide facility for precise time synchronization. Space Applications Centre (SAC) developed a simple timing receiver. Using this timing receiver first the internal time consistency of NNSS was studied and then its performance to synchronize time was compared with that of National Time Standard. The methodology of data analysis, results, and various sources of error which affect the time transfer accuracy were studied and described. The main source of error was found to be the receiver delay which varies with signal strength. It is possible to apply that this delay correction empirically provided signal strength is recorded.

Jain, C. L.↗

NASA NTRS2001

Flight Deck Data Link Displays: An Evaluation of Textual and Graphical Implementations

In Experiment 1, 16 pilots participated in a part-task simulation study that evaluated pilot data link communication for short and long message types and for two textual formats. No differences were found between the two textual formats when evaluating data link transaction times and pilot performance on a secondary task. Pilots initiated flight changes more quickly with the T-Scan format, where location of clearance information roughly corresponded to the cockpit instrument layout. Longer messages were less problematic than two short messages sent in close succession as pilots required more verbal clarification for closely spaced messages. 24 pilots participated in a second experiment that evaluated pilot communication performance for textual data link, two implementations of graphical data link, and a combined graphical and textual information modality. The two modalities incorporating text resulted in significantly faster transaction times and better performance on the secondary task than the two graphical-only implementations. The interval between messages was also more systematically varied in Experiment 2, and a short interval between messages significantly increased the access time for the second message. This delay in access was long enough to increase significantly the total transaction time of the second message, and this effect was exaggerated for the graphical-only implementations. Time to view the message before acknowledgement and time to initiate flight changes were not affected by the interval manipulation, This suggests that pilots adopt a sequential message handling strategy, and presenting messages closely in succession may present operational problems in a data link Air Traffic Control (ATC) environment. The results of this study also indicate that the perceived importance of message content is currently a crucial element in pilot data link communication.

McGann, Alison↗

NASA NTRSDate not supplied

Communication Delays, Disruptions, and Blackouts for Crewed Mars Missions

As NASA continues to develop the Moon2Mars campaign, there are a number of challenges that must be addressed to execute a successful crewed mission to Mars. One of those challenges is delays, disruptions, and blackouts that crew will experience during their mission to Mars, and that is the challenge evaluated in this paper. Our analysis showed that communication delays will vary from 0 to 22 minutes over the course of a mission, peaking while the crew is at or just departed from Mars. The disruptions occur in a similar time frame and can last for several days up to several months, depending on the solar disturbance sensitivity of the communication band being used. The delays and disruptions will have an impact on crewed Mars missions, and determining mitigations is future work to be informed by this analysis.

Katherine T McBrayer↗

NASA NTRSDate not supplied

Advances in Modeling Solar System Internet Structures and their Data Flows

With an ever-increasing presence in space, there is also an increasing burden on existing communications infrastructure. We are heading towards an inflection point where the traditional approach of scheduled, single-path communications for space will no longer be viable. One answer is Delay Tolerant Networking (DTN), which takes the once disparate system of point-to-point links and unifies them in a networked architecture, thereby making communications more scalable. However, much work remains for discovering and harnessing the underlying theory of DTN. For example, in the terrestrial setting the interplay between routing domains is well-understood, however this is not the case in DTNs. In this paper, we build up the fundamental foundations of DTN, with an emphasis on modeling time varying networks and data flows across them, with examples of cross-domain routing in a DTN. A lofty goal of DTN is to enable the so-called Solar System Internet (SSI), which implies a standardized and robust suite of protocols. These protocols include routing across disconnected networks using store, carry, and forward mechanisms, which is necessary due to the disconnections, delays, and mobility intrinsic to space networks. Due to these factors, each of which generalize traditional networking, there is a deep and rich theory of DTNs. Here we build off of past successes to broaden this theory while striving to keep actionable results a goal for future implementations and operations. The approach includes modeling the unicast, broadcast, and multicast communications using the language of hypergraphs, which capture the geometric properties of such networked communications algebraically. Also inherent to these networks is their time-varying nature, particularly given mobility, and hence we also cultivate modeling techniques that respect this time dependence. This leads us to develop models using tools from category theory and algebraic geometry, which provide a language well-suited to describing synchronization and optimization over such networks. We also introduce and study a novel generalization of curvature applicable to time-evolving networks, which provides quantitative controls on diffusion processes on the network. Because an interplanetary network would feature links with propagation delays the preclude discovery (feedback) mechanisms, they will always feature a scheduled component. However, it is beneficial to support discovery where possible. While DTNs do not yet have strong definitions for their analogues of autonomous systems or network areas, we show how to join dynamic and schedule-based routing domains, using the language of sheaves, which marks progress towards such definitions. We conclude with a discussion of the progress made, as well as suggestions for future work.

Delay Tolerant Networking↗

DOE OSTI2024

Kinetic relaxation and nucleation of Bose stars in self-interacting wave dark matter

We revisit kinetic relaxation and soliton/boson star nucleation in fuzzy scalar dark matter featuring short-ranged self-interactions H int = − λ | ψ | 4 / 2 m 2 , alongside gravitational self-interactions. We map out the full curve of nucleation timescale for both repulsive ( λ < 0 ) and attractive ( λ > 0 ) short-ranged self-interaction strength and in doing so reveal two new points. Firstly, besides the two usual terms, ∝ G 2 and ∝ λ 2 , in the total relaxation rate Γ relax , there is an additional cross term ∝ G λ arising due to interference between gravitational and short-ranged self-interaction scattering amplitudes. This yields a critical repulsive interaction strength λ cr ≃ − 2 π G m 2 / v 0 2 , at which the relaxation rate is smallest and serves as the transition point between typical net attractive self-interaction ( λ ≳ λ cr ) and net repulsive self-interaction ( − λ ≳ − λ cr ). Secondly, while in the net attractive regime, nucleation timescale is similar to inverse relaxation timescale τ nuc ∼ Γ relax − 1 ; in the net repulsive regime, nucleation occurs at a delayed time τ nuc ∼ ( λ / λ cr ) Γ relax − 1 . We confirm our analytical understanding by performing 3D field simulations with varying average mass density ρ ¯ , box size L and grid size N . Published by the American Physical Society 2024

Astronomy & Astrophysics↗

NASA NTRS2011

High-Precision Pulse Generator

A document discusses a pulse generator with subnanosecond resolution implemented with a low-cost field-programmable gate array (FPGA) at low power levels. The method used exploits the fast carry chains of certain FPGAs. Prototypes have been built and tested in both Actel AX and Xilinx Virtex 4 technologies. In-flight calibration or control can be performed by using a similar and related technique as a time interval measurement circuit by measuring a period of the stable oscillator, as the delays through the fast carry chains will vary as a result of manufacturing variances as well as the result of environmental conditions (voltage, aging, temperature, and radiation).

Katz, Richard↗

DOE OSTI2026

Data driven drift correction for complex optical systems

To exploit the thousand-fold increase in spectral brightness of modern light sources, increasingly intricate experiments are being conducted that demand extremely precise beam trajectory. Maintaining the optimal trajectory over several hours of an experiment with the needed precision necessitates active drift control. Here, we outline time varying Bayesian optimization (TVBO) as a data driven approach for robust drift correction, and illustrate its application for a split and delay optical system composed of six crystals and twelve input dimensions. Using numerical simulations, we exhibit the application of TVBO for linear drift, non-smooth temporal drift as well as constrained TVBO for multi-objective control settings, representing real-life operating conditions. This approach can be easily adapted to other X-ray beam conditioning and guidance systems, including multi-crystal monochromators and grazing-incidence mirrors, to maintain sub-micrometer and nanoradian beam stability over the course of an experiment spanning several hours.

Bayesian optimization↗

DOE OSTI2023

Safety Benefits Assessment for Accident Tolerant Fuels in Consideration of Steam Generator Tube Degradation Using Dynamic Event Tree Analysis

Accident tolerant fuel (ATF) is expected to delay or prevent core damage by providing additional coping time under accidents involving loss of core cooling. The effect of extended coping time may vary depending on the plant response to accidents. Age-related component degradation that deteriorates plant performance over time could have an impact on the actual advantages of ATF. The potential safety benefits of two near-term ATF candidates, including Cr-coated Zr cladding and FeCrAl cladding, are assessed for a 2-in. loss-of-coolant accident with failed high-pressure safety injection using the dynamic event tree (DET) approach considering possible stress corrosion cracking of steam generator (SG) tubing under aging. The DET approach allows likelihood quantification of accident sequences leading to core damage, including stochastic variation of system response and human actions during accident mitigation. The safety benefits of the selected ATF claddings in terms of additional coping time and the core damage frequency reduction rate under specified accident situations were quantitatively estimated. The results show that the deployment of the two selected ATF claddings is expected to lead to longer coping times and lower core damage frequency due to the wider safety margin to peak cladding temperature they provide. The safety advantages would be greater as SG tube degradation proceeds. Thus, the two ATF candidates would lead to less severe consequences in terms of likelihood of core damage and susceptibility to the SG tube degradation than UO 2 -Zr fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS2009

Aerothermodynamic Design of the Mars Science Laboratory Heatshield

Aerothermodynamic design environments are presented for the Mars Science Laboratory entry capsule heatshield. The design conditions are based on Navier-Stokes flowfield simulations on shallow (maximum total heat load) and steep (maximum heat flux, shear stress, and pressure) entry trajectories from a 2009 launch. Boundary layer transition is expected prior to peak heat flux, a first for Mars entry, and the heatshield environments were defined for a fully-turbulent heat pulse. The effects of distributed surface roughness on turbulent heat flux and shear stress peaks are included using empirical correlations. Additional biases and uncertainties are based on computational model comparisons with experimental data and sensitivity studies. The peak design conditions are 197 W/sq cm for heat flux, 471 Pa for shear stress, 0.371 Earth atm for pressure, and 5477 J/sq cm for total heat load. Time-varying conditions at fixed heatshield locations were generated for thermal protection system analysis and flight instrumentation development. Finally, the aerothermodynamic effects of delaying launch until 2011 are previewed.

Edquist, Karl T.↗

NASA NTRS1979

Azimuth correlator for real-time synthetic aperture radar image processing

An azimuth correlator architecture is defined wherein a number of serial range-line buffer memories are cascaded such that the output stages of all buffer memories together form a complete and unique range bin in the azimuthal dimension at any given time. A range bin is automatically read out of the last stages of the registers in parallel on a range line sample-by-sample basis for subsequent range migration correction and correlation. Range migration correction is performed on the range bins by effectively varying the length of a delay register at the output of each range-line buffer memory. The corrected range bin output from the delay registers is then correlated with a Doppler reference function to form an image element on a real-time basis.

Arens, W. E.↗

DOE OSTI2026

Basin-scale analysis of Mokelumne River Formation for multi-well CO 2 injection

Large-scale carbon sequestration will likely require multiple projects injecting CO 2 into the same subsurface formation, raising concerns about safe operation and efficient use of storage capacity. This study evaluates the long-term response of the Mokelumne River Formation in California’s Sacramento Basin to multi-megaton CO 2 injection using three geologic models of the formation and the open-source simulator GEOS. The analysis focuses on three aspects of reservoir performance: (1) average pressure increase and dissolved CO 2 mass after 30 years for varying well counts and injection rates, (2) pressure interference in a multi-well configuration, and (3) dynamic storage capacity with identification of overpressure-prone regions. The results show that average formation pressure increases linearly with injected mass, while CO 2 dissolution exhibits mixed scaling: approximately linear with the number of wells but sublinear with injection rate, indicating that distributing injection across more wells enhances dissolution more effectively than increasing per-well rates. Pressure-interference effects are significant, with lower-permeability conditions delaying their onset but amplifying their magnitude at later times. Dynamic capacity, defined by the first occurrence of pressure exceeding the local overburden-based limit anywhere in the formation, varies across geologic models and assumed overburden pressure gradients. A lower fidelity geologic model predicts nearly twice the storage capacity of the two higher fidelity models, which consistently estimate approximately 1 Gt under the upper-bound overburden pressure gradient considered for the Sacramento Basin. In all model scenarios, overpressure develops away from injection wells, particularly in higher-elevation regions, highlighting the importance of basin-scale modelling for identifying risks beyond the immediate well vicinity.

Basin-scale↗

DOE OSTI2021

Controlling the Aspect Ratios of Au Nanocrystals with Ag+ Addition Time in Seed-Mediated Synthesis: Implications for Surface-Enhanced Raman Scattering

Among various factors playing pivotal roles in the typical seed-mediated growth of Au nanocrystals (NCs), the role of Ag (AgNO3) has remained debatable over time and seminal research efforts have helped us in reaching a consensus, albeit from the standpoint of [Ag+] concentration. This study aims to provide an understanding of the role of Ag+ from the perspective of time. Here, we show that different Au NCs with tunable aspect ratios (ARs) can be generated in one system in high yield simply by varying the time of addition of Ag+ in the growth solution. The generality of the method has been demonstrated in tuning the ARs of anisotropic Au NCs like concave cuboid (CCB, AR = 2) and elongated tetrahexahedra (AR = 2.5), where the delayed addition of Ag+ leads to the formation of their isotropic counterpart concave cube (CC, AR = 1) and tetrahexahedra (AR = 1), respectively. This work, apart from establishing timed addition of Ag+ as a crucial parameter in controlling the AR, may also help in the realization of a universal growth mechanism of Au NCs. The Au NCs with varying ARs (CCB, AR = 2 and CC, AR = 1) have been further explored as potential substrates for surface-enhanced Raman scattering (SERS) due to the presence of their high-index facets and sharp tips.

KEYWORDS:Au nanoparticles seed-mediated growth hig↗

DOE OSTI2021

Fundamental investigation of unipolar and RF corona in atmospheric air

Here, unipolar (DC) and radio frequency (RF) corona at 3.3 MHz is studied at centimeter-sized gaps in a needle-plane geometry in atmospheric air at room temperature. Positive and negative corona using pure tungsten electrodes with varying tip angles revealed a lower onset voltage for the needle with the smaller included angle. The RF corona onset voltage and corresponding time delay were measured for a series of needles composed of pure tungsten or 2% lanthanated tungsten. The corona onset, established when the first instance of UV photon emission is detected via photomultiplier tube, occurred primarily during the negative half cycle of the applied RF voltage for pure tungsten needles. In contrast, with lanthanated tungsten needles, such preference was not observed. No distinguishable difference in onset voltage between pure tungsten and lanthanated tungsten was found, indicating that adding a small amount of lanthanum to tungsten has a negligible impact on the onset voltage at 3.3 MHz frequencies for electrodes at room temperature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Supernova Hydrodynamics: A Lab-scale Study of the Blast-driven Instability Using High-speed Diagnostics

A novel experimental approach to study the blast-driven instability at a nondiffuse, gaseous interface with a density gradient is presented. Under Euler similarity, this approach enables study of dissipative-scale hydrodynamics relevant to many astrophysical and laboratory high energy density phenomena in a well-resolved manner. The instability is initiated by passing a Taylor–Sedov blast wave originating from a controlled detonation through a perturbed and stably stratified interface between two gases. The facility and driving blast wave are characterized to obtain repeatable conditions and capture large ensembles of time-resolved Mie scattering imaging that show consistent hydrodynamic development. We analyze the instability evolution between different gas pairs to demonstrate the wide range of development and turbulent behavior that may occur between different supernova layers. The mean evolution of the hydrodynamic instability is compared to a buoyancy–drag model that is frequently used to estimate perturbation growth in supernova mixing research. We propose a time delay to this model in order to reproduce the measured instability behavior and demonstrate model robustness in handling flows driven by a time-varying acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1991

Analysis of delay reducing and fuel saving sequencing and spacing algorithms for arrival traffic

The air traffic control subsystem that performs sequencing and spacing is discussed. The function of the sequencing and spacing algorithms is to automatically plan the most efficient landing order and to assign optimally spaced landing times to all arrivals. Several algorithms are described and their statistical performance is examined. Sequencing brings order to an arrival sequence for aircraft. First-come-first-served sequencing (FCFS) establishes a fair order, based on estimated times of arrival, and determines proper separations. Because of the randomness of the arriving traffic, gaps will remain in the sequence of aircraft. Delays are reduced by time-advancing the leading aircraft of each group while still preserving the FCFS order. Tightly spaced groups of aircraft remain with a mix of heavy and large aircraft. Spacing requirements differ for different types of aircraft trailing each other. Traffic is reordered slightly to take advantage of this spacing criterion, thus shortening the groups and reducing average delays. For heavy traffic, delays for different traffic samples vary widely, even when the same set of statistical parameters is used to produce each sample. This report supersedes NASA TM-102795 on the same subject. It includes a new method of time-advance as well as an efficient method of sequencing and spacing for two dependent runways.

Neuman, Frank↗

NASA NTRS2013

GRAIL Refinements to Lunar Seismic Structure

Joint interpretation of disparate geophysical datasets helps to reduce drawbacks that can result from analyzing them individually. The Apollo seismic network was situated on the lunar nearside surface in a roughly equilateral triangle having sides approximately 1000 km long, with stations 12/14 nearly co‐located at one corner. Due to this limited geographical extent, near‐surface ray coverage from moonquakes is low, but increases with depth. In comparison, gravity surveys and their resulting gravity anomaly maps have traditionally offered optimal resolution at crustal depths. Gravimetric maps and seismic data sets are therefore well suited to joint inversion, since the complementary information reduces inherent model ambiguity. Previous joint inversions of the Apollo seismic data (seismic phase arrival times) and Clementine‐ or Lunar Prospector‐derived gravity data (mass and moment of inertia) attempted to recover the subsurface structure of the Moon by focusing on hypothetical lunar compositions that explore the density/velocity relationship. These efforts typically search for the best fitting thermodynamically calculated velocity/density model, allowing variables like core size, velocity, and/or composition to vary freely. Seismic velocity profiles previously derived from the Apollo seismic data through inversion of travel times vary both in the depth of the crust and mantle layers, and the seismic velocities and densities assigned to those layers. The lunar mass and moment of inertia likewise only constrain gross variations in the density profile beyond that of a uniform density sphere. As a result, composition and structure models previously obtained by jointly inverting these data retain the original uncertainties inherent in the input data sets. We will perform a joint inversion of Apollo seismic delay times and gravity data collected by the GRAIL lunar gravity mission, in order to recover seismic velocities and density as a function of latitude, longitude, and depth within the Moon. We will relate density to seismic velocity using a linear relationship that is allowed to be depth‐dependent. The corresponding coefficient (B) can reflect a variety of material properties that vary with depth, including temperature and composition. The inversion seeks to recover the set of density, velocity, and B‐coefficient perturbations that minimize (in a least‐squares sense) the difference between the observed and calculated data.

Weber, Renee C.↗

DOE OSTI2021

Effect of nitric oxide and exhaust gases on gasoline surrogate autoignition: iso-octane experiments and modeling

Exhaust gas recirculation (EGR) is widely used in advanced internal combustion engines to reduce engine emissions as well as control combustion phasing. Among various species present in EGR gases, CO 2 and H 2 O are two major components that can thermally and chemically affect fuel autoignition. It is of fundamental interest to isolate the thermal and chemical effects of CO 2 and H 2 O on fuel autoignition, especially as such an effort has not been reported in the literature. Moreover, nitric oxide (NO) is known to exhibit strong chemical effects on fuel autoignition, which in turn affects engine combustion phasing. The effects of ultra-low NO addition (< 100 ppm) on fuel autoignition at low temperatures are also not well understood. Recognizing these problems, autoignition experiments of iso-octane (a major gasoline surrogate component) in air are performed in this study using a rapid compression machine at varying compressed pressures, equivalence ratios, dilution levels with an EGR gas analogue (consisting of CO 2 , H 2 O, O 2 , and N 2 ) and N 2 only, and varying amounts of NO addition. Furthermore, the thermal and chemical effects of the EGR gas analogue are isolated and evaluated by comparing the ignition delay time datasets of EGR and N2-only diluted cases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗