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NASA NTRS2011

Illumination Conditions at the Asteroid 4 Vesta: Implications for the Presence of Water Ice

The mean illumination conditions and surface temperatures over one orbital period are calculated for the Asteroid 4 Vesta using a coarse digital elevation model produced from Hubble Space Telescope images. Even with the anticipated effects of finer-scale topography taken into account, it is unlikely that any significant permanently shadowed regions currently exist on Vesta due to its large axial tilt (approx. = 27deg). However, under present day conditions, it is predicted that about half of Vesta's surface has an average temperature of less than 145 K, which, based on previous thermal modeling of main belt asteroids, suggests that water ice could survive in the top few meters of the vestal regolith on billion-year timescales.

Stubbs, Timothy J.↗

NASA NTRS1972

Investigation of a possible solar-wind darkening of the lunar surface by photoelectron spectroscopy.

Detailed sequential study by photoelectron spectroscopy of the change in valence states of iron in Fe2O3, Fe3O4, FeO, and Fe foil samples, showing that chemical reduction does take place on the sample surface when argon ion bombardment occurs. These spectra give evidence that, after prolonged ion bombardment, the surface of all four samples consisted predominantly of iron in the metallic state. Argon ion sputtering of 15 silicate and oxide samples under similar experimental conditions produced surface darkening only in samples containing iron. Monitoring of the photoelectron peak of carbon during the experiment indicates that ion-bombardment darkening is not due to the buildup of hydrocarbon surface contaminants in the oil-free high-vacuum system used by the authors. On the basis of these studies, it is concluded that solar-wind bombardment should be included as one of the possible mechanisms for producing darkening of the lunar surface.

Yin, L. I.↗

NASA NTRS1972

Studies of oscillatory combustion and fuel vaporization

Research projects involving oscillatory combustion and fuel vaporization are reported. Comparisons of experimental and theoretical droplet vaporization histories under ambient conditions such that the droplet may approach its thermodynamic critical point are presented. Experimental data on instantaneous heat transfer from a gas to a solid surface under conditions of oscillatory pressure with comparisons to an unsteady one-dimensional model are analyzed. Droplet size and velocity distribution in a spray as obtained by use of a double flash fluorescent method were investigated.

Borman, G. L.↗

NASA NTRS2020

Quantification of the Land Surface and Brown Ocean Influence on Tropical Cyclone Intensification Over Land

An investigation of TC Kelvin in February 2018 over northeast Australia was conducted to understand the mechanisms of the Brown Ocean effect (BOE), and to develop a comprehensive analysis framework for land falling tropical cyclones (TCs) in the process. NASA’s Land Information System (LIS) coupled to the NASA Unified WRF (NU-WRF) system was employed as the numerical model framework for 12 land/soil moisture perturbation experiments. Impacts of soil moisture and surface enthalpy flux conditions on TC Kelvin were investigated by closely evaluating simulated track and intensity, midlevel atmospheric thermodynamic properties, vertical wind shear, total precipitable water (TPW), and surface moisture flux. The results suggest that there were recognized differentiations among the sensitivity simulations as a result of land surface (e.g., soil moisture and texture) conditions. However, the intensification of TC Kelvin over land was more strongly related to atmospheric moisture advection and the diurnal cycle of solar radiation (i.e., radiative cooling) than to overall soil moisture conditions or surface fluxes. The analysis framework employed here for TC Kelvin can serve as a foundation to specifically quantify the factors governing the BOE. It also demonstrates that the BOE is not a binary influence (i.e. all or nothing), but instead operates in a continuum from largely to minimally influential such that it could be utilized to help improve prediction of inland effects for all land falling TCs.

Jinwoong Yoo↗

NASA NTRS2020

Quantification of the Land Surface and Brown Ocean Influence on Tropical Cyclone Intensification Over Land

An investigation of TC Kelvin in February 2018 over northeast Australia was conducted to understand the mechanisms of the Brown Ocean effect (BOE), and to develop a comprehensive analysis framework for landfalling tropical cyclones (TCs) in the process. NASA’s Land Information System (LIS) coupled to the NASA Unified WRF (NU-WRF) system was employed as the numerical model framework for 12 land/soil moisture perturbation experiments. Impacts of soil moisture and surface enthalpy flux conditions on TC Kelvin were investigated by closely evaluating simulated track and intensity, midlevel atmospheric thermodynamic properties, vertical wind shear, total precipitable water (TPW), and surface moisture flux. The results suggest that there were recognized differentiations among the sensitivity simulations as a result of land surface (e.g., soil moisture and texture) conditions. However, the intensification of TC Kelvin over land was more strongly related to atmospheric moisture advection and the diurnal cycle of solar radiation (i.e., radiative cooling) than to overall soil moisture conditions or surface fluxes. The analysis framework employed here for TC Kelvin can serve as a foundation to specifically quantify the factors governing the BOE. It also demonstrates that the BOE is not a binary influence (i.e. all or nothing), but instead operates in a continuum from largely to minimally influential such that it could be utilized to help improve prediction of inland effects for all landfalling TCs.

Brown Ocean Effect↗

DOE OSTI2021

The role of environmental conditions on the carbonation of an alkali-activated cementitious waste form

Cast Stone is a cementitious waste form being considered for the solidification of low activity waste at the DOE Hanford Site. Under near-surface disposal conditions in an arid environment, Cast Stone is subject to drying and carbonation which may impact retention of waste constituents. Here this study investigates the effects of environmental CO 2 concentration and relative humidity (RH) on the carbonation of Cast Stone. The rate of carbonation front ingress and the extent of carbonation reaction were characterized for samples aged up to 48 weeks at three RH levels and two CO 2 concentrations. While the 68% RH environment allowed the greatest reaction extent, the 15% RH environment yielded the deepest carbonation front ingress. At 68% RH, there was a linear relationship between the ingress rate and CO 2 concentration. Carbonation reactions increased the drying rate of Cast Stone. Redistribution of sodium toward the wetting front was observed under drying and carbonation conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Surface processing and discharge-conditioning of high voltage electrodes for the Ra EDM experiment

The Ra EDM experiment uses a pair of high voltage electrodes to search for the atomic electric dipole moment of 225 Ra. We use identical, plane–parallel electrodes with a primary high gradient surface of 200 mm 2 to generate reversible DC electric fields. Our statistical sensitivity is linearly proportional to the electric field strength in the electrode gap. We adapted surface decontamination and processing techniques from accelerator physics literature to chemical polish and clean a suite of newly fabricated large-grain niobium and grade-2 titanium electrodes. Three pairs of niobium electrodes and one pair of titanium electrodes were discharge-conditioned with a custom high voltage test station at electric field strengths as high as +52.5 kV/mm and –51.5 kV/mm over electrode gap sizes ranging from 0.4 mm to 2.5 mm. One pair of large-grain niobium electrodes was discharge-conditioned and validated to operate at ±20 kV/mm with steady-state leakage current ≤ 25 pA (1σ) and a polarity-averaged 98 ± 19 discharges per hour. These electrodes were installed in the Ra EDM experimental apparatus, replacing a copper electrode pair, and were revalidated to ±20 kV/mm. Here, the niobium electrodes perform at an electric field strength 3.1 times larger than the legacy copper electrodes and are ultimately limited by the maximum output of our 30 kV bipolar power supply.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1983

The control of float zone interfaces by the use of selected boundary conditions

The main goal of the float zone crystal growth project of NASA's Materials Processing in Space Program is to thoroughly understand the molten zone/freezing crystal system and all the mechanisms that govern this system. The surface boundary conditions required to give flat float zone solid melt interfaces were studied and computed. The results provide float zone furnace designers with better methods for controlling solid melt interface shapes and for computing thermal profiles and gradients. Documentation and a user's guide were provided for the computer software.

Foster, L. M.↗

NASA NTRS1990

Camera Would Monitor Weld-Pool Contours

Weld pool illuminated and viewed coaxially along welding torch. Proposed monitoring subsystem for arc welder provides image in which horizontal portions of surface of weld pool highlighted. Monitoring and analyzing subsystems integrated into overall control system of robotic welder. Control system sets welding parameters to adapt to changing conditions, maintaining surface contour giving desired pattern of reflections.

Gordon, Stephen S.↗

NASA NTRS1991

The effect of surface radiation on flame spread in a quiescent, microgravity environment

In most theories of laminar flame spread over solid combustibles, radiation is neglected. However, when gas motion is completely absent, which may occur in the quiescent, microgravity environment of a spacecraft, the importance of radiation compared to convection is enhanced. Here, a theoretical model is developed of flame spread over a thin solid fuel into an opposing flow of oxidizer, the opposing flow being present in the quiescent environment in flame-fixed coordinates, including the effects of radiative heat transfer from the fuel surface. Numerical solutions to the conservation equations in the gas and the solid phase that describe the spreading flame are presented for a variety of ambient conditions and surface emittances. When surface radiation is significant, the solid surface acts as a heat sink, causing the flame to cool, shrink in size, and spread more slowly. Better agreement with experiment for net heat transfer to the surface is obtained when surface radiation is included. For low ambient oxygen levels, radiative effects lead to flame extinction. A radiation/conduction parameter is identified that adequately describes the importance of surface radiation.

Bhattacharjee, S.↗

NASA NTRS2014

Hypersonic Separated Flows About "Tick" Configurations With Sensitivity to Model Design

This paper presents computational results obtained by applying the direct simulation Monte Carlo (DSMC) method for hypersonic nonequilibrium flow about "tick-shaped" model configurations. These test models produces a complex flow where the nonequilibrium and rarefied aspects of the flow are initially enhanced as the flow passes over an expansion surface, and then the flow encounters a compression surface that can induce flow separation. The resulting flow is such that meaningful numerical simulations must have the capability to account for a significant range of rarefaction effects; hence the application of the DSMC method in the current study as the flow spans several flow regimes, including transitional, slip, and continuum. The current focus is to examine the sensitivity of both the model surface response (heating, friction and pressure) and flowfield structure to assumptions regarding surface boundary conditions and more extensively the impact of model design as influenced by leading edge configuration as well as the geometrical features of the expansion and compression surfaces. Numerical results indicate a strong sensitivity to both the extent of the leading edge sharpness and the magnitude of the leading edge bevel angle. Also, the length of the expansion surface for a fixed compression surface has a significant impact on the extent of separated flow.

Moss, J. N.↗

NASA NTRS2024

Short Exploration Extravehicular Mobility Unit Testing Setup: Evaluation Under Realistic Pressure and Thermal Conditions

The purpose of Short Exploration Extravehicular Mobility Unit (SxEMU) thermal vacuum testing was to verify the functionality of the Design Verification Testing (DVT) prototype xEMU (SxEMU for this test) at vacuum pressures and extreme space and lunar surface temperature conditions. The SxEMU Thermal Vacuum Test was the culmination of the DVT xEMU project. This paper’s focus is on the pre-Extravehicular Activity (EVA) test setup, and general performance of the SxEMU Portable Life Support Subsystem (xPLSS), with focus on the performance of the Primary Oxygen Assembly (POA) and Secondary Oxygen Assembly (SOA), including Secondary Oxygen Regulator (SOR) takeover and the POA and SOA low-setpoint change inhibit. The initial pre-EVA test preparation included recharging the batteries and replenishing consumables, including test-system water, oxygen assemblies (with gaseous nitrogen), and the integrated thermal loops, including the Feedwater Supply Assemblies. xPLSS functionality testing included carbon dioxide (CO2) removal via the Rapid Cycle Amine swingbed system, thermal loop temperature control, and monitoring of suit ventilation loop pressure, temperature, and CO2 percentages. Testing evaluated automatic takeover of suit pressure control by the SOR after the primary oxygen supply is depleted. The Primary Oxygen Regulator and SOR low-setpoint change inhibit function prevents the crewmember from inadvertently setting the primary regulator to a low pressure setpoint during an EVA.

xPLSS↗

NASA NTRS1965

A study of the blistering of metal surfaces by solar system ions Interim report

Conditions for aluminum surface blister formation from hydrogen introduced by proton irradiation

METAL SURFACE↗

NASA NTRS1990

Flow separation in shock wave boundary layer interactions at hypersonic speeds

An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed.

Hamed, A.↗

NASA NTRS1992

Hypersonic flow separation in shock wave boundary layer interactions

Hamed, A.↗

NASA NTRS2006

Desert Research and Technology Studies 2005 Report

During the first two weeks of September 2005, the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) Advanced Extravehicular Activity (AEVA) team led the field test portion of the 2005 Research and Technology Studies (RATS). The Desert RATS field test activity is the culmination of the various individual science and advanced engineering discipline areas year-long technology and operations development efforts into a coordinated field test demonstration under representative (analog) planetary surface terrain conditions. The purpose of the RATS is to drive out preliminary exploration concept of operations EVA system requirements by providing hands-on experience with simulated planetary surface exploration extravehicular activity (EVA) hardware and procedures. The RATS activities also are of significant importance in helping to develop the necessary levels of technical skills and experience for the next generation of engineers, scientists, technicians, and astronauts who will be responsible for realizing the goals of the Constellation Program. The 2005 Desert RATS was the eighth RATS field test and was the most systems-oriented, integrated field test to date with participants from NASA field centers, the United States Geologic Survey (USGS), industry partners, and research institutes. Each week of the test, the 2005 RATS addressed specific sets of objectives. The first week focused on the performance of surface science astro-biological sampling operations, including planetary protection considerations and procedures. The second week supported evaluation of the Science, Crew, Operations, and Utility Testbed (SCOUT) proto-type rover and its sub-systems. Throughout the duration of the field test, the Communications, Avionics, and Infomatics pack (CAI-pack) was tested. This year the CAI-pack served to provide information on surface navigation, science sample collection procedures, and EVA timeline awareness. Additionally, 2005 was the first year since the Apollo program that two pressurized suited test subjects have worked together simultaneously. Another first was the demonstration of recharge of cryogenic life support systems while in-use by the suited test subjects. The recharge capability allowed the simulated EVA test duration to be doubled, facilitating SCOUT proto-type rover testing. This paper summarizes Desert RATS 2005 test hardware, detailed test objectives, test operations and test results.

Ross, Amy J.↗

NASA NTRS2011

Deriving Soil Moisture with the Combined L-Band Radar and Radiometer Measurements

In this study, we develop a combined active/passive technique to estimate surface soil moisture with the focus on the short vegetated surfaces. We first simulated a database for both active and passive signals under SMAP s sensor configurations using the radiative transfer model with a wide range of conditions for surface soil moisture, roughness and vegetation properties that we considered as the random orientated disks and cylinders. Using this database, we developed 1) the techniques to estimate surface backscattering and emission components and 2) the technique to estimate soil moisture with the estimated surface backscattering and emission components. We will demonstrate these techniques with the model simulated data and its validation with the airborne PALS image data from the soil moisture SGP 99 and SMEX 02 experiments.

Shi, Jiancheng↗

NASA NTRS2016

Validation of AIRS V6 Surface Temperature over Greenland with GCN and NOAA Stations

This work compares the temporal and spatial characteristics of the AIRSAMSU (Atmospheric Infrared Sounder Advanced Microwave Sounding Unit A) Version 6 and MODIS (Moderate resolution Imaging Spectroradiometer) Collection 5 derived surface temperatures over Greenland. To estimate uncertainties in space-based surface temperature measurements, we re-projected the MODIS Ice Surface Temperature (IST) to 0.5 by 0.5 degree spatial resolution. We also re-gridded AIRS Skin Temperature (Ts) into the same grid but classified with different cloud conditions and surface types. These co-located data sets make intercomparison between the two instruments relatively straightforward. Using this approach, the spatial comparison between the monthly mean AIRS Ts and MODIS IST is in good agreement with RMS 2K for May 2012. This approach also allows the detection of any long-term calibration drift and the careful examination of calibration consistency in the MODIS and AIRS temperature data record. The temporal correlations between temperature data are also compared with those from in-situ measurements from GC-Net (GCN) and NOAA stations. The coherent time series of surface temperature evident in the correlation between AIRS Ts and GCN temperatures suggest that at monthly time scales both observations capture the same climate signal over Greenland. It is also suggested that AIRS surface air temperature (Ta) can be used to estimate the boundary layer inversion.

AIRS↗