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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

TPSAS-NF1676L-32652-DND

Space weather is an important driver of the exposure of aircrew and passengers to cosmic rays at flight altitudes. The assessment of the corresponding radiation doses can be realized by measurements or model calculations that cover the whole range of the radiation field in terms of geomagnetic shielding, atmospheric shielding, and the effects of space weather. Since the radiation field at aviation altitudes is very complex in terms of particle composition and energy distribution, the accurate experimental determination of doses at aviation altitudes is still a challenging task. Accordingly, the amount of data with comparatively small uncertainties is scarce. The Community Coordinated Modeling Center invited the Federal Aviation Administration, the German Aerospace Center, and the National Aeronautics and Space Administration to make their radiation models for aviation CARI-7A, PANDOCA, and NAIRAS available for interested users via the Community Coordinated Modeling Center web site. A concomitant comparison of model calculations with measuring data provided information on the predicting capabilities and the uncertainties of the current versions of these models under quiet space weather conditions.

Matthias M Meier↗
NASA NTRS2021

Simulation of Landing and Take-Off Noise for Supersonic Transport Aircraft at a Conceptual Design Fidelity Level

The German Aerospace Center has launched an internal project to assess the noise impact associated with supersonic transport aircraft during approach and departure. A dedicated simulation process is established to cover all relevant disciplines, i.e., aircraft and engine design, engine installation effects, flight simulation, and system noise prediction. The core of the simulation process is comprised of methods at the complexity and fidelity level of conceptual aircraft design, i.e., typical overall aircraft design methods and a semi-empirical approach for the noise modeling. Dedicated interfaces allow to process data from high fidelity simulation that will support or even replace initial low fidelity results in the long run. All of the results shown and discussed in this study are limited to the fidelity level of conceptual design. The application of the simulation process to the NASA 55t Supersonic Technology Concept Aeroplane, i.e., based on non-proprietary data for this vehicle, yields similar noise level predictions when compared to the published NASA results. This is used as an initial feasibility check of the new process and confirms the underlying methods and models. Such an initial verification of the process is understood as an essential step due to the lack of available noise data for supersonic transport aircraft in general. The advantageous effect of engine noise shielding on the resulting system noise is demonstrated based on predicted level time histories and certification noise levels. After this initial verification, the process is applied to evaluate a conceptual supersonic transport design based on a PhD thesis with two engines mounted under the wing, which is referred to as aircraft TWO. Full access to this vehicle’s design and performance data allows to investigate the influence of flight procedures on the resulting noise impact along approach and departure. These noise results are then assembled according to proposed Federal Aviation Agency regulations in their Notice of Proposed Rulemaking, e.g., speed limitations, for Supersonic transport noise certification and the regulations from Noise Chapters of the Annex 16 from the International Civil Aviation Organization in order to evaluate the resulting levels as a function of the flight procedure.

noise↗
NASA NTRS1972

Radiofrequency-sputtered coatings for lubrication system components and other complex surfaces

Irregularly shaped surfaces, such as lubrication system components (ball bearings, seals, gears, etc.), can be coated on all surfaces, including irregular shapes, when radiofrequency sputtering is used. When the specimen is properly located with respect to the sputtering target, the sputtered material covers the entire surface of the object irrespective of its geometrical configuration. An adherent, dense film is formed. The film thickness varies from 20 to 50 percent on, for example, a hearing cage or race depending on its geometry. When sputtered solid film lubricants such as molybdenum disulfide are used, a film thickness only of the order of 10 to the minus 7th power m (thousands of angstroms) is required at the contacting areas. It is only essential to determine the required film thickness at the critical areas in need of lubrication. The sections outside the areas to be lubricated fall within the thickness deviation range of 20 to 50 percent, which still constitutes a negligible change respect to tolerance requirements.

Spalvins, T.↗
NASA NTRSDate not supplied

Generation of Continental Scale Percent Tree Cover Product Using Deep-learning and Multi-scale Remote Sensing Data

Spatially explicit percent tree cover (TC) estimation is critical for mapping forest aboveground biomass and its dynamics. While various TC products have been developed, there has not been a generalized framework that can be applied to diverse terrestrial ecosystems due to underlain extreme complexities. Deep learning algorithms can learn a spatial pattern and radiometric characteristics of tree canopy as a robust approximation of physical or empirical models, and thus have emerged as promising and efficient tools for large-scale TC mapping. In this study, we synergistically use very high-resolution aerial imageries (National Agriculture Imagery Program, NAIP) and medium resolution Landsat data to map continental-scale TC (CONUS and Mexico) through a hierarchical deep learning approach (Convolutional Neural Network), i.e., NAIP TC generated from a NAIP model is utilized to train a Landsat model. The produced TC product (hereafter, NEX-TC) is able to capture the spatial pattern of TC distribution and its changes driven by natural disturbance and human land management. We further explore and analyze the reliability and potential uncertainty of the NEX-TC by comparing it to lidar- (lidar-TC), National Land Cover Database (NLCD-TC), and MODIS Vegetation Continuous Field (MODIS-TC). This evaluation practice reveals that TC products based on passive optical sensors tend to underestimate TC across all land cover types while Landsat-based TCs (i.e., NEX-TC & NLCD-TC) perform better than the coarser MODIS TC estimate. Our results show that the NEX-TC is generally comparable to NLCD-TC but it particularly outperforms NLCD-TC and MODIS-TC over the dense forests where lidar-TC indicates >80% TC. These results indicate that our hierarchical deep learning approach and TC product will be effective and useful for characterizing large-scale tree cover and possibly associated carbon dynamics.

Landsat↗
NASA NTRS1989

Turbulence modeling for aerodynamic flows

The state of statistical turbulence modeling is reviewed with emphasis on compressible aerodynamic flows. A three-stage modeling process is suggested to act as a frame-work for improving turbulence models for complex flows. This process is then used to guide assessments of the comparative performance of various levels of turbulence models for several examples of flow fields of aerodynamic interest. The examples cover flows in two and three dimensions and with a broad range of Mach numbers. In addition to considerations of individual flow fields, some generalizations are drawn from the aggregate behavior of the comparisons.

Rubesin, Morris W.↗
NASA NTRS2003

The Stardust Mission

The primary goal of the Stardust Mission is to collect >1000 particles >15 micron in diameter from comet Wild2 and return them to Earth in January 2006. The main samples will be captured by 6.1 km/s impact into low density silica aerogel and additional particles will crater into approx. 150 sq cm of 100 micron thick pure aluminum foil that covers the aerogel holding grid. It is expected that the impacts into the aerogel will produce tracks that range from deep narrow cones for non-fragmenting particles to shallower more complex tracks for particles that fragment. The impacts into aluminum foil will produce craters but a significant amount of projectile residue is expected to line the crater walls.

Brownlee, D. E.↗
NASA NTRS2007

Characterization of Forested Landscapes From Remotely Sensed Data Using Fractals and Spatial Autocorrelation

The characterization of forested areas is frequently required in resource management practice. Passive remotely sensed data, which are much more accessible and cost effective than are active data, have rarely, if ever, been used to characterize forest structure directly, but rather they usually focus on the estimation of indirect measurement of biomass or canopy coverage. In this study, some spatial analysis techniques are presented that might be employed with Landsat TM data to analyze forest structure characteristics. A case study is presented wherein fractal dimensions, along with a simple spatial autocorrelation technique (Moran s I), were related to stand density parameters of the Oakmulgee National Forest located in the southeastern United States (Alabama). The results of the case study presented herein have shown that as the percentage of smaller diameter trees becomes greater, and particularly if it exceeds 50%, then the canopy image obtained from Landsat TM data becomes sufficiently homogeneous so that the spatial indices reach their lower limits and thus are no longer determinative. It also appears, at least for the Oakmulgee forest, that the relationships between the spatial indices and forest class percentages within the boundaries can reasonably be considered linear. The linear relationship is much more pronounced in the sawtimber and saplings cases than in samples dominated by medium sized trees (poletimber). In addition, it also appears that, at least for the Oakmulgee forest, the relationships between the spatial indices and forest species groups (Hardwood and Softwood) percentages can reasonably be considered linear. The linear relationship is more pronounced in the forest species groups cases than in the forest classes cases. These results appear to indicate that both fractal dimensions and spatial autocorrelation indices hold promise as means of estimating forest stand characteristics from remotely sensed images. However, additional work is needed to confirm that the boundaries identified for Oakmulgee forest and the linear nature of the relationship between image complexity indices and forest characteristics are generally evident in other forests. In addition, the effects of other parameters such ,as topographic relief and image distortion due to sun angle and cloud cover, for example, need to be examined.

Al-Hamdan, Mohammad Z.↗
NASA NTRS2015

Remote Sensing

Remote sensing is one of a suite of geospatial technologies that are having a growing impact in a wide variety of areas from commerce to science to public policy. The field of remote sensing evolved from the interpretation of aerial photographs to the analysis of satellite imagery, and from local area studies to global analyses, with advances in sensor system technologies and digital computing. Today remote sensor systems can provide data from energy emitted, reflected, and/or transmitted from all parts of the electromagnetic spectrum. Examples of applications of these data include population and demography studies, study of archaeological sites, energy studies using hydrological models, urban planning, environmental monitoring, environments, treaty enforcement, land use/land cover planning, weather forecasting, and agricultural production estimation, just to name a few. The material that follows provides a brief overview of the historical development of remote sensing, emphasizing the increasing complexity of platforms, systems, and tasks.

electromagnetic spectrum↗
NASA NTRS2010

Compact Ku-Band T/R Module for High-Resolution Radar Imaging of Cold Land Processes

Global measurement of terrestrial snow cover is critical to two of the NASA Earth Science focus areas: (1) climate variability and change and (2) water and energy cycle. For radar backscatter measurements, Ku-band frequencies, scattered mainly within the volume of the snowpack, are most suitable for the SWE (snow-water equivalent) measurements. To isolate the complex effects of different snowpack (density and snowgrain size), and underlying soil properties and to distinctly determine SWE, the space-based synthetic aperture radar (SAR) system will require a dual-frequency (13.4 and 17.2 GHz) and dual polarization approach. A transmit/receive (T/R) module was developed operating at Ku-band frequencies to enable the use of active electronic scanning phased-array antenna for wide-swath, high-resolution SAR imaging of terrestrial snow cover. The T/R module has an integrated calibrator, which compensates for all environmental- and time-related changes, and results in very stable power and amplitude characteristics. The module was designed to operate over the full frequency range of 13 to 18 GHz, although only the two frequencies, 13.4 GHz and 17.2 GHz, will be used in this SAR radar application. Each channel of the transmit module produces > 4 W (35 dbm) over the operating bandwidth of 20 MHz. The stability requirements of <0.1 dB receive gain accuracy and <0.1 dB transmit power accuracy over a wide temperature range are achieved using a self-correction scheme, which does real-time amplitude calibration so that the module characteristics are continually corrected. All the calibration circuits are within the T/R module. The timing and calibration sequence is stored in a control FPGA (field-programmable gate array) while an internal 128K 8bit high-speed RAM (random access memory) stores all the calibration values. The module was designed using advanced components and packaging techniques to achieve integration of the electronics in a 2 x6.5x1-in. (5x17x2.5-cm) package. The module size allows 4 T/R modules to feed the 16 16-element subarray on an antenna panel. The T/R module contains four transmit channels and eight receive channels (horizontal and vertical polarizations).

Andricos, Constantine↗
NASA NTRS1984

Large seasonal variations in Triton's atmosphere

Consideration is given to the consequences of Triton's surface covering of volatile substances in view of the circularity of Neptune's orbit, which implies that Triton would have virtually no seasonal variations in either surface temperature or atmospheric bulk despite the complex precessional effects of its orbit. It is hypothesized that Triton's most volatile surface substances are probably relegated to latitudes higher than 35 deg, probably forming polar caps whose temperatures would be nearly equal even during the midwinter/midsummer peak insolation of the summer pole. If the summer pole completely sublimates during one of the 'major' summers, Triton's atmosphere may begin to freeze out over the winter caps and yield large and complex seasonal variations.

Trafton, L.↗
NASA NTRS1989

Attenuation of soil microwave emissivity by corn and soybeans at 1.4 and 5 GHz

Theory and experiments have shown that passive microwave radiometers can be used to measure soil moisture. However, the presence of a vegetative cover alters the measurement that might be obtained under bare conditions. Deterministically accounting for the effect of vegetation and developing algorithms for extracting soil moisture from observations of a vegetable-soil complex present significant obstacles to the practical use of this approach. The presence of a vegetation canopy reduces the sensitivity of passive microwave instruments to soil moisture variations. The reduction in sensitivity, as compared to a bare-soil relationship, increases as microwave frequency increases, implying that the longest wavelength sensors should provide the most information. Sensitivity also decreases as the amount of vegetative wet biomass increases for a given type of vegetation.

Jackson, Thomas J.↗
NASA NTRS1995

Thermal Springs and the Search for Past Life on Mars

Ancient thermal spring sites have several features which make them significant targets in a search for past life. Chemical (including redox) reactions in hydrothermal systems possibly played a role in the origin of life on Earth and elsewhere. Spring waters frequently contain reduced species (sulfur compounds, Fe(sup +2), etc.) which can provide chemical energy for organic synthesis. Relatively cool hydrothermal systems can sustain abundant microbial life (on Earth, at temperatures greater than 110 C). A spring site on Mars perhaps might even have maintained liquid water for periods sufficiently long to sustain surface-dwelling biota had they existed. On Earth, a variety of microbial mat communities can be sampled along the wide range of temperatures surrounding the spring, thus offering an opportunity to sample a broad biological diversity. Thermal spring waters frequently deposit minerals (carbonates, silica, etc.) which can entomb and preserve both fluid inclusions and microbial communities. These deposits can be highly fossiliferous and preserve biological inclusions for geologically long periods of time. Such deposits can cover several square km on Earth, and their distinctive mineralogy (e.g., silica- and/or carbonate-rich) can contrast sharply with that of the surrounding region. As with Martian volcanoes, Martian thermal spring complexes and their deposits might typically be much larger than their counterparts on Earth. Thus Martian spring deposits are perhaps readily detectable and even accessible. Elysium Planitia is an example of a promising region where hydrothermal activity very likely remobilized ground ice and sustained springs.

DesMarais, D. J.↗
NASA NTRS2009

Infectious Considerations in Space Flight

Slightly more than 500 people have flown in space, most of them for short periods of time. The total number of person years in space is small. Given this fact, and given rigorous astronaut screening, it is not surprising that the accumulated infectious disease experience in space is also small, and mostly, theoretical. As the human space presence expands, we may expect mission length, total accumulated person years and the environmental complexity to increase. Add to the mix both changes in human immunity and microbial virulence, and it becomes realistic to consider infectious scenarios and the means to mitigate them. This lecture will cover the inhabited space environment from the perspective of host-microbe interactions, current relevant research, and the current countermeasures used. Future challenges will be discussed and there will be opportunity to ask questions about Space Operations. The audience is encouraged to think about what medical tools you would choose to have in different types of mission, what you would be willing to leave behind, and how you would compensate for the necessary trade offs in mission design.

Haddon, Robert↗
NASA NTRS2023

Launch Complex 39A, SWMU 008 and Launch Complex 39B, SWMU 009 Performance Monitoring Report Kennedy Space Center, Florida

This Performance Monitoring Report (PMR) presents the findings, observations, and results for Air Sparging (AS) operations and sitewide groundwater monitoring for Launch Complex 39A (LC39A), Solid Waste Management Unit (SWMU) 008, and Launch Complex 39B (LC39B), SWMU 009, at Kennedy Space Center (KSC), Florida. Results from direct push technology (DPT) sampling at LC39B are also included in this report. The reporting period for AS operations covered under this PMR is from January 1, 2022, to December 31, 2022.

groundwater↗
NASA NTRSDate not supplied

ISRU Pilot Excavator (IPEx) Technology Readiness Level 5 Design Overview

This paper details the mechanical and mechatronic design of the Technology Readiness Level (TRL)-5 In-Situ Resource Utilization (ISRU) Pilot Excavator (IPEx). IPEx is a robotic excavator designed for a technology demonstration of regolith mining in the lunar south -pole region. The novel design uses pairs of counter-acting excavation tools called bucket drums, that dig at the same time in opposing directions to reduce the reaction force needed, thereby enabling mining with a small, low-mass, robotic system. IPEx builds on the prior work of the Regolith Advanced Surface Systems Operations Robot (RASSOR), which is the TRL-4 implementation of this concept. The TRL-5 IPEx subsystems that are discussed in this paper include: Regolith Delivery Subsystem (RDS), Mobility Subsystem (MS), Cameras and Dust Mitigation Subsystem (CDMS), and Thermal Control Subsystem (TCS). Each subsystem is described in detail with rationale for design selections. Dust tolerance is a key feature for IPEx and this paper details a thermal control system with an actuated radiator cover and phase change material as well as camera modules with removable electrodynamic dust shields (EDS). Additional components such as actuators, wheels, and bucket drums are discussed in detail. Due to their complexity, the avionics and software subsystems will be discussed in a separate publication.

RASSOR↗
NASA NTRS2003

Case for Deploying Complex Systems Utilizing Commodity Components

This viewgraph representation presents a study of the transition of computer networks and software engineering at the Huntsville Operations Support Center (HOSC) from a client/server UNIX based system to a client/server system based on commodity priced and open system components. Topics covered include: an overview of HOSC ground support systems, an analysis for changes to the existing ground support system, an analysis of options considered for the transition to a new system, and a consideration of goals for a new system.

Bryant, Barry S.↗
NASA NTRS2009

Towards a Framework for Generating Tests to Satisfy Complex Code Coverage in Java Pathfinder

We present work on a prototype tool based on the JavaPathfinder (JPF) model checker for automatically generating tests satisfying the MC/DC code coverage criterion. Using the Eclipse IDE, developers and testers can quickly instrument Java source code with JPF annotations covering all MC/DC coverage obligations, and JPF can then be used to automatically generate tests that satisfy these obligations. The prototype extension to JPF enables various tasks useful in automatic test generation to be performed, such as test suite reduction and execution of generated tests.

Staats, Matt↗
NASA NTRSDate not supplied

Windform® XT 2.0 Use as 3U CubeSat Primary Structure

CubeSats provide a platform for small-scale space research and technology demonstration at reduced complexity, cost, and development time. These advantages drove the NASA Langley Research Center (LaRC) to develop and launch the GPX2 3U CubeSat to explore the viability of using Commercial Off-The-Shelf (COTS) differential GPS (dGPS) in low earth orbit. To reduce manufacturing costs and increase design flexibility, the project chose additive manufactured Windform® XT 2.0 as the primary bus material rather than traditional subtractive manufactured (milled) metal. The bus is a two-part, Selective Laser Sintered, 3D-print structure consisting of a single-piece, five-walled chassis and single-walled cover. The bus was specially designed to allow the project to accommodate the payload electronics stack as well as antennas, receivers, and deployable mechanisms. By using an additive manufactured solution, LaRC was able to design in features unrealizable through traditional milling, with a lead-time of roughly two weeks. In comparison, traditional subtractive manufacturing limits geometry options due to toolpath reach and bus construction would have required multiple components for each wall. This would have resulted in a more costly, longer lead-time article with more joints, fasteners, and complexity with a commensurate increase in overall mass. A number of lessons-learned were captured during the design, analysis, and testing of the GPX2 CubeSat covering thermal and structural analysis, vibration modeling, and geometric tolerancing. Additionally, a variety of material testing and verification were performed before and during spacecraft design and integration to assure the suitability of Windform® XT 2.0 for the launch and mission environments. This article provides the highlights of designing and testing the GPX2 bus.

CubeSat↗