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NASA NTRS2013

Very Large Eddy Simulations of a Jet-A Spray Reacting Flow in a Single Element LDI Injector With and Without Invoking an Eulerian Scalar DWFDF Method

This paper presents the very large eddy simulations (VLES) of a Jet-A spray reacting flow in a single element lean direct injection (LDI) injector by using the National Combustion Code (NCC) with and without invoking the Eulerian scalar DWFDF method, in which DWFDF is defined as the density weighted time filtered fine grained probability density function. The flow field is calculated by using the time filtered compressible Navier-Stokes equations (TFNS) with nonlinear subscale turbulence models, and when the Eulerian scalar DWFDF method is invoked, the energy and species mass fractions are calculated by solving the equation of DWFDF. A nonlinear subscale model for closing the convection term of the Eulerian scalar DWFDF equation is used and will be briefly described in this paper. Detailed comparisons between the results and available experimental data are carried out. Some positive findings of invoking the Eulerian scalar DWFDF method in both improving the simulation quality and maintaining economic computing cost are observed.

Shih, Tsan-Hsing↗

NASA NTRS2014

Avionics Architectures for Exploration: Ongoing Efforts in Human Spaceflight

The field of Avionics is advancing far more rapidly in terrestrial applications than in spaceflight applications. Spaceflight Avionics are not keeping pace with expectations set by terrestrial experience, nor are they keeping pace with the need for increasingly complex automation and crew interfaces as we move beyond Low Earth Orbit. NASA must take advantage of the strides being made by both space-related and terrestrial industries to drive our development and sustaining costs down. This paper describes ongoing efforts by the Avionics Architectures for Exploration (AAE) project chartered by NASA's Advanced Exploration Systems (AES) Program to evaluate new avionic architectures and technologies, provide objective comparisons of them, and mature selected technologies for flight and for use by other AES projects. The AAE project team includes members from most NASA centers, and from industry. It is our intent to develop a common core avionic system that has standard capabilities and interfaces, and contains the basic elements and functionality needed for any spacecraft. This common core will be scalable and tailored to specific missions. It will incorporate hardware and software from multiple vendors, and be upgradeable in order to infuse incremental capabilities and new technologies. It will maximize the use of reconfigurable open source software (e.g., Goddard Space Flight Center's (GSFC's) Core Flight Software (CFS)). Our long-term focus is on improving functionality, reliability, and autonomy, while reducing size, weight, and power. Where possible, we will leverage terrestrial commercial capabilities to drive down development and sustaining costs. We will select promising technologies for evaluation, compare them in an objective manner, and mature them to be available for future programs. The remainder of this paper describes our approach, technical areas of emphasis, integrated test experience and results as of mid-2014, and future plans. As a part of the AES Program, we are encouraged to set aggressive goals and fall short if necessary, rather than to set our sights too low. We are also asked to emphasize providing our personnel with hands-on experience in development, integration, and testing. That we have embraced both of these philosophies will be evident in the descriptions below.

Goforth, Montgomery B.↗

NASA NTRS2015

Analysis of JPSS J1 VIIRS Polarization Sensitivity Using the NIST T-SIRCUS

The polarization sensitivity of the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) measured pre-launch using a broadband source was observed to be larger than expected for many reflective bands. Ray trace modeling predicted that the observed polarization sensitivity was the result of larger diattenuation at the edges of the focal plane filter spectral bandpass. Additional ground measurements were performed using a monochromatic source (the NIST T-SIRCUS) to input linearly polarized light at a number of wavelengths across the bandpass of two VIIRS spectral bands and two scan angles. This work describes the data processing, analysis, and results derived from the T-SIRCUS measurements, comparing them with broadband measurements. Results have shown that the observed degree of linear polarization, when weighted by the sensor's spectral response function, is generally larger on the edges and smaller in the center of the spectral bandpass, as predicted. However, phase angle changes in the center of the bandpass differ between model and measurement. Integration of the monochromatic polarization sensitivity over wavelength produced results consistent with the broadband source measurements, for all cases considered.

reflective bands↗

NASA NTRS2018

Aqueous, QUick-Charging Battery Integration For Electric Flight Research

AQUIFER establishes technical feasibility of an early-stage technology, a high-energy density, aqueous-based, flow battery, resulting in a near-term increase of 1.7 times range over an all-electric battery, while retiring fire and explosion hazards associated with lithium-based chemistries. The Nano-electrofuel (NEF) flow battery will be integrated with a rim-driven motor (RDM) as a multi-functional design to eliminate conductive EMI and weight from long cable runs, and provide liquid cooling from the aqueous fuel. When successful, the technology provides an improved safety energy storage solution for emission-free electric propulsion in commercial aviation.

power systems↗

NASA NTRS2020

Neural Network Repair of Lossy Compression Artifacts in the Sept 2015 – March 2016 Duration of the MMS/FPI Dataset

During the Sept 2015 –March 2016 duration (sometimes referred to as Phase 1A) of the Magnetospheric Multiscale Mission (MMS), the Dual Electron Spectrometers (DES) were configured to generously utilize lossy compression. While this maximized the number of velocity distribution functions downlinked, it cameat the expense of lost information content for a fractionof the frames. Following this period of lossy compression, the DES was re-configured in a way that allowed for 95% of the framesto arrive to the ground without loss. Using this high-quality set offrameson-orbit observations, we compressed and decompressed the frameson the ground to create a side-by-side record of the compression effect. This record was used to drive an optimization method that (a) derived basis functions capable of approximating the lossless sample space and with non-negative coefficients and (b) fitted a function which maps the lossy framesto basis weights that recreate the framewithout compression artifacts. This methodis introduced and evaluated in this paper.Data users should expect a higher level of confidence in the absolute scale of density/temperature measurements andnotice less sinusoidal bias in the velocity X and Y components(GSE).

Magnetosphere, Neural Networks, Image Processing, ↗

NASA NTRSDate not supplied

A Multivibrational Mode Relaxation Scheme for Two-Temperature Thermochemical State Models

An approach to estimate the effective vibrational relaxation time for polyatomic molecules under the context of two-temperature thermochecmial state model is proposed. Landau-Teller vibrational relaxation equation is used as a basis, and vibrational energies are estimated with partition energy functions assuming harmonic oscillator model. A special weighting procedure is presented, and effective vibrational relaxation time is derived. A series of numerical experiments with CO2 and NH3 mixtures is performed, and the aeroheating results are presented. The results of CO2 environment simulations are compared with the vibrational relaxation model of Park et al. [JTHT, 8(1994), pp. 9–23]. The simulations are also conducted with a modified Landau-Teller expression.

Vibrational relaxation time↗

NASA NTRSDate not supplied

Geopolymer Lunar Concrete under Reduced-Pressure Curing and Vacuum Exposure

Geopolymer concrete has emerged as a promising material for constructing habitats, roads, landing pads, and other necessary infrastructure on the lunar surface. Proper in-situ resource utilization (ISRU) is an important aspect of any candidate lunar construction material. Geopolymer concrete is effective at ISRU, as the lunar regolith can be used in the “as found” condition and mixed with an alkaline solution, such as sodium silicate and sodium hydroxide, which could also be mostly produced in-situ. It is envisioned that any concrete material on the lunar surface would be deposited with additive manufacturing techniques and would require a temporary environmental enclosure to mitigate the harsh lunar environment during construction and curing, such as pressure and temperature. Data are needed to set a benchmark for the conditions to be achieved within the deployable environmental enclosure during printing, as well as the resultant material properties after the enclosure is removed. This novel study investigated the influence of reduced atmospheric pressures during the initial curing period on the compressive strength of geopolymer lunar concrete created with two types of lunar regolith simulant. The simulants used in the study represent the regolith for the lunar mare (OPRL2N) and lunar highlands (OPRH2N) regions. Results show a noticeable decline in strength with a reduction in pressure and visible degradation. After the deployable environmental enclosure is removed from the printed segment of infrastructure on the lunar surface, it would then be exposed to the harsh vacuum environment. To understand the importance of curing time required within the deployable enclosure before it is removed, samples were cast and cured for different lengths of time and then exposed to a vacuum chamber capable of achieving 100 mTorr. Control samples were also cast at the same time but left in a standard laboratory environment after curing. The weight change and compressive strength as a function of time in the vacuum chamber were monitored for up to 56 days. The results showed that exposure to the vacuum limits further reaction and strength gain in comparison to control samples left in the laboratory environment. This research is in strong alignment with the 2020 NASA Technology Taxonomy materials area (12.1) and the in-situ resource utilization area (7.1), as it provides necessary data on the geopolymer lunar concrete material to support safe and sustainable options for maintaining a human presence on the Moon.

Moon to Mars Planetary Autonomous Construction Tec↗

NASA NTRSDate not supplied

NASA GPM Status and Future Activities

Global Precipitation Measuremen↗

NASA NTRSDate not supplied

NASA GPM Status and Future Activities

The joint U.S.-Japan Global Precipitation Measurement (GPM) mission is approaching a decade of operations, and continues to pursue research, dataset production, and outreach related to precipitation. Key activities over the last year were the release of an improved “Version 07” of all GPM precipitation and latent heating products, boosting the orbit of the GPM Core Observatory (GPM CO) to 435 km, and improving quality control on precipitation retrievals from the GPM constellation of passive microwave satellites. This presentation summarizes key improvements to the GPM products and provides some examples of the changes between Versions 06 and 07 in algorithm performance. One important operational change that affected Version 07 is that the scanning strategy for the Ka-band radar channel changed in May 2018; all products that depend on Ka were revised to accommodate this change. For example, in Version 07 the Goddard Profiling (GPROF) algorithm has implemented improvements in regions where orographic enhancement and suppression take place and where the surface is snowy/icy, and again covers radiometers reaching back to 1987. The Combined Radar Radiometer Algorithm (CORRA) now incorporates modified drop-size distribution constraints that substantially reduce bias. Revisions to the Convective-Stratiform Heating (CSH) algorithm employ new radiative transfer retrievals as well as accounting for terrain in the vertical coordinates. Each algorithm was adjusted to ensure continuity for each product across the boundary in 2014 between the predecessor Tropical Rainfall Measuring Mission (TRMM) and the GPM CO. The U.S. Science Team’s Integrated Multi-satellitE Retrievals for GPM (IMERG) was upgraded to account for distortions in the probability density function of regional precipitation rates due to weighted averaging in the Kalman filter used for “morphing” the passive microwave data. Maintaining the GPM CO orbital altitude in the the current very active solar cycle has been forcing the use of more fuel than planned and consequently shortening the forecasted life of the mission from the early 2030's to the late 2020's. It was considered vital to regain some of this lifetime to ensure overlap with the upcoming Atmosphere Observing System mission to provide crosscalibration of instruments. To accomplish this, the orbital altitude was raised from 400 to 435 km on 7-8 November 2023. Thereafter, the primary GPM CO algorithms had to be revised to account for the change in observing parameters. By meeting time this action should be complete. Recently, a screening algorithm based on auto-encoding was developed that uncovered 162 orbits (out of the many thousands of orbits across all years and all satellites) of passive microwave retrievals that had highly anomalous values. Removing these defective retrievals has improved the integrity of both the GPROF and IMERG records. However, the nature of the IMERG processing interacted sufficiently badly with the now-discovered anomalous orbits that it was necessary to completely reprocess the IMERG Final Run record, now labeled Version 07B. The presentation also considers major issues that require continued attention, including the use of machine learning algorithms and the operational challenge of swarms of “small”, perhaps short-lived satellites.

GPM↗

NASA NTRSDate not supplied

Improvements in VLBI Data Analysis for Advanced in Geodesy

I will provide an overview of advances in VLBI data analysis implemented at NASA GSFC. That include the use of B-splines for modeling non-linear station position evolution, the use of all non-tidal mass loadings in data reduction, the use of slant a priori path delays from the output of numerical weather models, the use of B-splines for evaluation of the Earth orientation parameters as a continuous function, the use of elevation-dependent weighting, processing both 24 hr and 1 hr experiments in a single least square solutions and other innovations. I will show how this changes in data analysis affect space geodesy results, such as estimation of station positions, Earth orientation parameters, and source coordinates.

Leonid Petrov↗

DOE OSTI2021

Insights into the Physical-Chemical Properties of a CO2-Responsive Fracturing Fluid

Here we determine the phase behavior of StimuFrac, a CO2 responsive fracturing fluid, under geothermal wellbore conditions. StimuFrac is an aqueous poly(allylamine) fluid that crosslinks in the presence of CO2. StimuFrac significantly reduces the net pressure required to induce fractures, relative to other fracture fluids, and has potential to reduce water use. However, the phase behavior and equations of state to describe StimuFrac’s phase behavior remain unavailable. Here we determine the density and molar volume of the fluid as a function of geothermal relevant temperatures, pressures, and weight fractions of StimuFrac added. In general, experiments find that StimuFrac’s density decreases as temperature and pressure increase. Using these results, equations of saturated state and phase diagrams for different polymer concentrations are reported. These results are critical inputs for planned numerical simulation efforts.

Pease, Leonard F.↗

DOE OSTI2021

On the Stochastic Stability of Deep Markov Models

Deep Markov models (DMM) are generative models which are scalable and expressive generalization of Markov models for representation, learning, and inference problems. However, the fundamental stochastic stability guarantees of such models have not been thoroughly investigated. In this paper, we present a novel stability analysis method and provide sufficient conditions of DMM's stochastic stability. The proposed stability analysis is based on the contraction of probabilistic maps modeled by deep neural networks. We make connections between the spectral properties of neural network's weights and different types of used activation function on the stability and overall dynamic behavior of DMMs with Gaussian distributions. Based on the theory, we propose a few practical methods for designing constrained DMMs with guaranteed stability. We empirically substantiate our theoretical results via intuitive numerical experiments using the proposed stability constraints.

Drgona, Jan↗

DOE OSTI2024

Polymers depolymerizable by metathesis of a cleavable unit

Novel polymers are depolymerizable by metathesis of a cleavable unit. As an example, a series of linear and crosslinked polyurethanes were prepared that can be selectively depolymerized under mild conditions. Two unique polyols were synthesized bearing unsaturated units in a configuration designed to favor ring-closing metathesis to five- and six-membered cycloalkenes. These polyols were co-polymerized with toluene diisocyanate to generate linear polyurethanes and trifunctional hexamethylene- and diphenylmethane-based isocyanates to generate crosslinked polyurethanes. The polyol design is such that the ring-closing metathesis reaction cleaves the backbone of the polymer chain. Upon exposure to dilute solutions of Grubbs' catalyst under ambient conditions, the polyurethanes were rapidly depolymerized to low molecular weight, soluble products bearing vinyl and cycloalkene functionalities. These functionalities enabled further re-polymerization by traditional strategies for polymerization of double bonds. This general approach can be expanded to develop a range of chemically recyclable condensation polymers that are readily depolymerized by orthogonal metathesis chemistry.

Jones, Brad Howard↗

NASA NTRS1972

Performance of correlation receivers in the presence of impulse noise.

An impulse noise model, which assumes that each noise burst contains a randomly weighted version of a basic waveform, is used to derive the performance equations for a correlation receiver. The expected number of bit errors per noise burst is expressed as a function of the average signal energy, signal-set correlation coefficient, bit time, noise-weighting-factor variance and probability density function, and a time range function which depends on the crosscorrelation of the signal-set basis functions and the noise waveform. Unlike the performance results for additive white Gaussian noise, it is shown that the error performance for impulse noise is affected by the choice of signal-set basis function, and that Orthogonal signaling is not equivalent to On-Off signaling with the same average energy. Furthermore, it is demonstrated that the correlation-receiver error performance can be improved by inserting a properly specified nonlinear device prior to the receiver input.

Moore, J. D.↗

NASA NTRS1971

Characterization of impulse noise and analysis of its effect upon correlation receivers

A noise model is formulated to describe the impulse noise in many digital systems. A simplified model, which assumes that each noise burst contains a randomly weighted version of the same basic waveform, is used to derive the performance equations for a correlation receiver. The expected number of bit errors per noise burst is expressed as a function of the average signal energy, signal-set correlation coefficient, bit time, noise-weighting-factor variance and probability density function, and a time range function which depends on the crosscorrelation of the signal-set basis functions and the noise waveform. A procedure is established for extending the results for the simplified noise model to the general model. Unlike the performance results for Gaussian noise, it is shown that for impulse noise the error performance is affected by the choice of signal-set basis functions and that Orthogonal signaling is not equivalent to On-Off signaling with the same average energy.

Houts, R. C.↗

NASA NTRS1993

Control of Complex Dynamic Systems by Neural Networks

This paper considers the use of neural networks (NN's) in controlling a nonlinear, stochastic system with unknown process equations. The NN is used to model the resulting unknown control law. The approach here is based on using the output error of the system to train the NN controller without the need to construct a separate model (NN or other type) for the unknown process dynamics. To implement such a direct adaptive control approach, it is required that connection weights in the NN be estimated while the system is being controlled. As a result of the feedback of the unknown process dynamics, however, it is not possible to determine the gradient of the loss function for use in standard (back-propagation-type) weight estimation algorithms. Therefore, this paper considers the use of a new stochastic approximation algorithm for this weight estimation, which is based on a 'simultaneous perturbation' gradient approximation that only requires the system output error. It is shown that this algorithm can greatly enhance the efficiency over more standard stochastic approximation algorithms based on finite-difference gradient approximations.

Spall, James C.↗

NASA NTRS2005

Thermal, Radiation and Impact Protective Shields (TRIPS) for Robotic and Human Space Exploration Missions

New concepts for protective shields for NASA s Crew Exploration Vehicles (CEVs) and planetary probes offer improved mission safety and affordability. Hazards include radiation from cosmic rays and solar particle events, hypervelocity impacts from orbital debris/ micrometeorites, and the extreme heating environment experienced during entry into planetary atmospheres. The traditional approach for the design of protection systems for these hazards has been to create single-function shields, i.e. ablative and blanket-based heat shields for thermal protection systems (TPS), polymer or other low-molecular-weight materials for radiation shields, and multilayer, Whipple-type shields for protection from hypervelocity impacts. This paper introduces an approach for the development of a single, multifunctional protective shield, employing nanotechnology- based materials, to serve simultaneously as a TPS, an impact shield and as the first line of defense against radiation. The approach is first to choose low molecular weight ablative TPS materials, (existing and planned for development) and add functionalized carbon nanotubes. Together they provide both thermal and radiation (TR) shielding. Next, impact protection (IP) is furnished through a tough skin, consisting of hard, ceramic outer layers (to fracture the impactor) and sublayers of tough, nanostructured fabrics to contain the debris cloud from the impactor before it can penetrate the spacecraft s interior.

Loomis, M. P.↗

DOE OSTI2025

Sustainable upcycling of polyethylene waste to compatibilizers and valuable chemicals

Controllable functionalization of polyethylene (PE) waste could generate new polymeric materials that are generally difficult to manufacture sustainably while also addressing the growing plastics waste problem. However, these modifications remain challenging due to the inherent stability of the PE backbone. Non-thermal atmospheric plasma enables molecular activation under mild conditions while utilizing renewable energy but is primarily employed for surface modification, as plasmas do not penetrate the bulk of materials. Herein, controllable bulk oxidative functionalization of PE wax (PEW) and low-density PE (LDPE) of varying molecular weights was achieved, with up to 6 mol% oxygen incorporation, by manipulating melt viscosity. This functionalization was accomplished either through temperature adjustment or by introducing a melt viscosity modifier, removable via simple extraction methods, to reduce LDPE viscosity, enhance diffusion and chain mobility, and enable bulk oxidation. The oxidized LDPE induces compatibilization in blends of poly(lactic acid) (PLA) and LDPE with improved interfacial adhesion and mechanical properties, such as a 70% increase in elongation-at-break values vs. the control. These findings pave the way for catalyst-free upcycling of direct plastics waste and plastics waste-derived products, enabling the creation of high-value products across various markets.

Plastic upcycling↗