Results for “surface operations analysis” — Page 74

NASA NTRS2001

Validation of MODIS Aerosol Optical Depth Retrieval Over Land

Aerosol optical depths are derived operationally for the first time over land in the visible wavelengths by MODIS (Moderate Resolution Imaging Spectroradiometer) onboard the EOSTerra spacecraft. More than 300 Sun photometer data points from more than 30 AERONET (Aerosol Robotic Network) sites globally were used in validating the aerosol optical depths obtained during July - September 2000. Excellent agreement is found with retrieval errors within (Delta)tau=+/- 0.05 +/- 0.20 tau, as predicted, over (partially) vegetated surfaces, consistent with pre-launch theoretical analysis and aircraft field experiments. In coastal and semi-arid regions larger errors are caused predominantly by the uncertainty in evaluating the surface reflectance. The excellent fit was achieved despite the ongoing improvements in instrument characterization and calibration. This results show that MODIS-derived aerosol optical depths can be used quantitatively in many applications with cautions for residual clouds, snow/ice, and water contamination.

Chu, D. A.↗

NASA NTRS2008

Analysis of Thermal and Reaction Times for Hydrogen Reduction of Lunar Regolith

System analysis of oxygen production by hydrogen reduction of lunar regolith has shown the importance of the relative time scales for regolith heating and chemical reaction to overall performance. These values determine the sizing and power requirements of the system and also impact the number and operational phasing of reaction chambers. In this paper, a Nusselt number correlation analysis is performed to determine the heat transfer rates and regolith heat up times in a fluidized bed reactor heated by a central heating element (e.g., a resistively heated rod, or a solar concentrator heat pipe). A coupled chemical and transport model has also been developed for the chemical reduction of regolith by a continuous flow of hydrogen. The regolith conversion occurs on the surfaces of and within the regolith particles. Several important quantities are identified as a result of the above analyses. Reactor scale parameters include the void fraction (i.e., the fraction of the reactor volume not occupied by the regolith particles) and the residence time of hydrogen in the reactor. Particle scale quantities include the particle Reynolds number, the Archimedes number, and the time needed for hydrogen to diffuse into the pores of the regolith particles. The analysis is used to determine the heat up and reaction times and its application to NASA s oxygen production system modeling tool is noted.

Hegde, U.↗

NASA NTRS2009

Analysis of Thermal and Reaction Times for Hydrogen Reduction of Lunar Regolith

System analysis of oxygen production by hydrogen reduction of lunar regolith has shown the importance of the relative time scales for regolith heating and chemical reaction to overall performance. These values determine the sizing and power requirements of the system and also impact the number and operational phasing of reaction chambers. In this paper, a Nusselt number correlation analysis is performed to determine the heat transfer rates and regolith heat up times in a fluidized bed reactor heated by a central heating element (e.g., a resistively heated rod, or a solar concentrator heat pipe). A coupled chemical and transport model has also been developed for the chemical reduction of regolith by a continuous flow of hydrogen. The regolith conversion occurs on the surfaces of and within the regolith particles. Several important quantities are identified as a result of the above analyses. Reactor scale parameters include the void fraction (i.e., the fraction of the reactor volume not occupied by the regolith particles) and the residence time of hydrogen in the reactor. Particle scale quantities include the particle Reynolds number, the Archimedes number, and the time needed for hydrogen to diffuse into the pores of the regolith particles. The analysis is used to determine the heat up and reaction times and its application to NASA s oxygen production system modeling tool is noted.

Hegde, U.↗

NASA NTRS2016

Innovative Flow Control Concepts for Drag Reduction

This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs. The ERA systems analysis studies performed by NASA indicated that AFC-enhanced vertical tail could produce approximately 0.9% drag reduction for a large twin aisle aircraft and IAM coatings could enable approximately 1.2% drag reduction recovery for a potential total drag reduction of approximately 3.3% for a single aisle aircraft with a natural laminar flow (NLF) wing design.

Lin, John C.↗

NASA NTRSDate not supplied

Gateway Program Safety And Mission Assurance Integration - The Future Of Safe Deep Space Human Exploration

This next wave of lunar exploration will be fundamentally different than the past. The goal today is long term human presence in Earth orbit, exploration around the Moon, exploration anywhere on the Moon, and challenging exploration missions beyond the Moon. Sustainability is the key to enabling human expansion across the solar system and bringing back to Earth new knowledge and opportunities, and requires the early engagement of scientific, international, and U.S. commercial interests, innovations, and new approaches. The Gateway’s agile acquisition strategy will shape the entire system life cycle, from design and analysis through production, verification, launch, logistics and operations. This strategy will encourage new ways of doing business to accommodate new techniques, technologies and approaches; improving affordability and maximizing Gateway utility. The full range of acquisition authorities and contracting mechanisms available to NASA will be considered and appropriately tailored in response to the unique demands of each procurement activity. Gateway will provide scientific and research benefits, in addition to providing a sustainable staging location for crewed lunar surface landings and technology demonstrations that help NASA develop the knowledge and technology needed for Mars missions. These payloads are expected to provide operational and scientific benefit for the duration of their stay on Gateway, as the hardware will provide data during the transit to the Gateway and while in lunar orbit as changes in solar activity occur over time. Gateway is designed to support a variety of utilization activities during both crewed and uncrewed periods and is planned for continuous operations throughout its lifetime. These operations include demonstrating key exploration capabilities in a relevant deep space environment, conducting science beyond the influence of Earth, and providing opportunities for Gateway partners and customers for deep space exploration. Located in cislunar orbit, the Gateway capabilities can be further leveraged to enhance lunar and Mars exploration. With the Gateway and other elements of the Artemis Program, NASA is encouraging new ways of doing business to accommodate new techniques, technologies and approaches, consider affordability, and encourage innovation from U.S. industry.

Helen Vaccaro↗

NASA NTRSDate not supplied

Gateway Program Safety and Mission Assurance IAASS Conference Keynote Presentation

This next wave of lunar exploration will be fundamentally different than the past. The goal today is long term human presence in Earth orbit, exploration around the Moon, exploration anywhere on the Moon, and challenging exploration missions beyond the Moon. Sustainability is the key to enabling human expansion across the solar system and bringing back to Earth new knowledge and opportunities, and requires the early engagement of scientific, international, and U.S. commercial interests, innovations, and new approaches. The Gateway’s agile acquisition strategy will shape the entire system life cycle, from design and analysis through production, verification, launch, logistics and operations. This strategy will encourage new ways of doing business to accommodate new techniques, technologies and approaches; improving affordability and maximizing Gateway utility. The full range of acquisition authorities and contracting mechanisms available to NASA will be considered and appropriately tailored in response to the unique demands of each procurement activity. Gateway will provide scientific and research benefits, in addition to providing a sustainable staging location for crewed lunar surface landings and technology demonstrations that help NASA develop the knowledge and technology needed for Mars missions. These payloads are expected to provide operational and scientific benefit for the duration of their stay on Gateway, as the hardware will provide data during the transit to the Gateway and while in lunar orbit as changes in solar activity occur over time. Gateway is designed to support a variety of utilization activities during both crewed and uncrewed periods and is planned for continuous operations throughout its lifetime. These operations include demonstrating key exploration capabilities in a relevant deep space environment, conducting science beyond the influence of Earth, and providing opportunities for Gateway partners and customers for deep space exploration. Located in cislunar orbit, the Gateway capabilities can be further leveraged to enhance lunar and Mars exploration. With the Gateway and other elements of the Artemis Program, NASA is encouraging new ways of doing business to accommodate new techniques, technologies and approaches, consider affordability, and encourage innovation from U.S. industry.

Terri Castillo↗

NASA NTRS2000

Acousto-Optic Imaging Spectrometers for Mars Surface Science

NASA's long term plan for Mars sample collection and return requires a highly streamlined approach for spectrally characterizing a landing site, documenting the mineralogical make-up of the site and guiding the collections of samples which represent the diversity of the site. Ideally, image data should be acquired at hundreds of VIS and IR wavelengths, in order to separately distinguish numerous anticipated species, using principal component analysis and linear unmixing. Cameras with bore-sighted point spectrometers can acquire spectra of isolated scene elements, but it requires 10(exp 2) to 10(exp 2) successive motions and precise relative pointing knowledge in order to create a single data cube which qualifies as a spectral map. These and other competing science objectives have to be accomplished within very short lander/rover operational lifetime (a few sols). True, 2-D imaging spectroscopy greatly speeds up the data acquisition process, since the spectra of all pixels in the scene are collected at once. This task can be accomplished with cameras that use electronically tunable acousto-optic tunable filters (AOTFs) as the optical tuning element. AOTFs made from TeO2 are now a mature technology, and operate at wavelengths from near-UV to about 5 microns. Because of incremental improvements in the last few years, present generation devices are rugged, radiation-hard and operate at temperatures down to at least 150K so they can be safely integrated into the ambient temperature optics of in-situ instruments such as planetary or small-body landers. They have been used for ground-based astronomy, and were also baselined for the ST-4 Champollion IR comet lander experiment (CIRCLE), prior to cancellation of the ST-4 mission last year. AIMS (for Acousto-optic Imaging spectrometer), is a prototype lander instrument which is being built at GSFC with support by the NASA OSS Advanced Technologies and Mission Studies, Mars Instrument Definition and Development Program (MIDP). AIMS is capable of tunable spectroscopic imaging of surface mineralogy, ices and dust between 0.5 and 2.4 microns, at a resolving power (lambda/delta lambda) which is typically several hundred. The design spatial resolution, similar to IMP and SSI, will allow mapping at scales down to about 1 cm.

Glenar, D. A.↗

DOE OSTI2022

Nanotomographic observation and statistical analysis of overcharging induced cracks in LiCoO 2 single crystalline particles

Particle fracture represents an important mode of battery electrode degradation. Extensive cracking occurs in the layered oxide cathodes of lithium-ion rechargeable batteries when they are charged beyond safe operational voltages. In this paper, we analyze the morphology and distribution of cracks in over 100 overcharged LiCoO 2 (LCO) single-crystalline particles imaged via X-ray nanotomography. Herein, we observe a strong particle size dependence in both nucleation and growth of cracks, with percentage of cracked particles, crack size, and crack surface area per unit volume all increasing significantly with particle volume. Increasing the cutoff voltage above 4.6V is found to trigger much more pronounced crack growth, which we attribute to the large misfit stress caused by the H1-3 to O1 phase transition. This study offers valuable statistical insights into the fracture behavior of layered oxide cathodes and reveals the importance of particle size control on electromechanical degradation of battery electrodes.

25 ENERGY STORAGE↗

NASA NTRS2017

Daily Kilometer-Scale MODIS Satellite Maps of PM2.5 Describe Wintertime Episodes

The San Joaquin Valley (SJV) suffers from severe health-endangering episodes of PM2.5 aerosol loadings in wintertime; episodes last approximately 5 days and differ in geographical distribution and composition. PM2.5 stations are scattered; consequently the use of remote sensing to map variable regional patterns of these varying respirable aerosol concentrations is desirable. High-precision AOT retrievals can capture column particulate loading. However,PM2.5 mapping is challenging due to several reasons: particularly thin mixed layers (ML) and thus relatively low aerosol optical thickness (AOT) close to current measurement limits, variable and a typical composition of the aerosols, and complex surface bidirectional reflectance. However, the West does present some advantages in analysis. Air basins are isolated from long-distance transport, and experience predominant strong meteorological subsidence. Thus these Western basin regions have fewer problematic cases of overriding aerosol layers detached from the surface. To counter such local overriding, Chu et al. have described an approach for the Eastern US, and He et al have described a synoptic classification approach useful in Shanghai. The Bay Area Air Quality Management District (BAAQMD) expands our experience with the use of AOT, with lower PM2.5 and several isolated sub-basins. We have prepared daily maps of episodes in each region. We present also a sequence of increasingly detailed statistical models, AOT initially appears to contribute little information; however, inclusion of weather information reveals its utility. Lyapustin and Wang's MultiAngle Implementation of Atmospheric Correction (MAIAC) retrieval for AOT provided the most useful operational remote sensing information for these regions. It provides high (1-km) spatial resolution maps and a high percentage of availability. Empirical regression methods have found that random effects regression models (aka mixed effects models, ME) employing AOT provide good estimates of ground PM2.5 concentrations.Here, we attempt to extend these methods and evaluate the usefulness of AOT with greater physical analysis, based on DISCOVER-AQ4 experience.

Chatfield, Robert B.↗

NASA NTRS1999

The Mars Pathfinder Mission and Science Results

Mars Pathfinder, the first low-cost, quick Discovery class mission to be completed, successfully landed on the surface of Mars on July 4, 1997, deployed and navigated a small rover, and collected data from 3 science instruments and 10 technology experiments. The mission operated on Mars for 3 months and returned 2.3 Gbits of new data, including over 16,500 lander and 550 rover images, 16 chemical analyses of rocks and soil, and 8.5 million individual temperature, pressure and wind measurements. The rover traversed 100 m clockwise around the lander, exploring about 200 square meters of the surface. The mission captured the imagination of the public, and garnered front page headlines during the first week. A total of about 566 million internet "hits" were registered during the first month of the mission, with 47 million "hits" on July 8th alone, making the Pathfinder landing by far the largest internet event in history at the time. Pathfinder was the first mission to deploy a rover on Mars. It carried a chemical analysis instrument, to characterize the rocks and soils in a landing area over hundreds of square meters on Mars, which provided a calibration point or "ground truth" for orbital remote sensing observations. The combination of spectral imaging of the landing area by the lander camera, chemical analyses aboard the rover, and close-up imaging of colors, textures and fabrics with the rover cameras offered the potential of identifying rocks (petrology and mineralogy). With this payload, a landing site in Ares Vallis was selected because it appeared acceptably safe and offered the prospect of analyzing a variety of rock types expected to be deposited by catastrophic floods, which enabled addressing first-order scientific questions such as differentiation of the crust, the development of weathering products, and the nature of the early Martian environment and its subsequent evolution. The 3 instruments and rover allowed seven areas of scientific investigation: the geology and geomorphology of the surface, mineralogy and geochemistry of rocks and soils, physical properties of surface materials, magnetic properties of airborne dust, atmospheric science including aerosols, and rotational and orbital dynamics of Mars. Scientists were assembled into 7 Science Operations Groups that were responsible for requesting measurements by the 3 instruments, rover and engineering subsystems for carrying out their scientific investigations and for analyzing the data and reporting on their findings. The spacecraft was launched on December 4, 1996 and had a 7 month cruise to Mars, with four trajectory correction maneuvers. The vehicle entered the atmosphere directly following cruise stage separation. Parachute deployment, heatshield and lander separation, radar ground acquisition, airbag inflation and rocket ignition all occurred before landing at 2:58 AM true local solar time (9:56:55 AM PDT). The lander bounced at least 15 times up to 12 in high without airbag rupture, demonstrating the robustness of this landing system. Reconstruction of the final landing sequence indicates that the parachute/backshel1/1ander was tilted due to a northwest directed wind and wind shear, which resulted in the lander bouncing about I km to the northwest and initially downhill about 20 m from where the solid rockets fired. Two anomalously bright spots located in the lander scene are likely the heatshield, which continued in a ballistic trajectory about 2 km downrange (west southwest), and the backshell/parachute, which stayed nearer to where the rockets fired. Unconnected disturbed soil patches in the scene indicate that the final few bounces of the lander were from the east-southeast and were followed by a gentle roll to the west before coming to rest on the base petal. The location of the lander away from where the solid rockets fired and considerations of the exhaust products used to inflate the airbags and their fate, indicate that the Pathfinder landing system is one of the cleanest designed leaving the local area essentially contaminant free. The radio signal from the low-=gain antenna was received at 11:34 AM PDT indicating a successful landing.

Golombek, M. P.↗

DOE OSTI2021

Effect of the Addition of a Low Equivalent Stress Mechanism to the Analysis of Geomechanical Behavior of the SPR West Hackberry Site

Sandia National Laboratories has long used the Munson-Dawson (M-D) model to predict the geomechanical behavior of salt caverns used to store oil at the Strategic Petroleum Reserve (SPR). Salt creep causes storage caverns to deform inward, thus losing volume. This loss of volume affects the salt above and around the caverns, puts stresses and strains on borehole casings, and creates surface subsidence which affects surface infrastructure. Therefore, accurate evaluation of salt creep behavior drives decisions about cavern operations. Parameters for the M-D model are typically fit against laboratory creep tests, but nearly all historic creep tests have been performed at equivalent stresses of 8 MPa or higher. Creep rates at lower equivalent stresses are very slow, such that tests take months or years to run, and the tests are sensitive to small temperature perturbations (<0.1°C). A recent collaboration between US and German researchers, recently characterized the creep behavior at low equivalent (deviatoric) stresses (<8 MPa) of salt from the Waste Isolation Pilot Plant. In addition, the M-D model was recently extended to include a low stress creep “mechanism”. This paper details new simulations of SPR caverns that use this extended M-D model, called the M-D Viscoplastic model. The results show that the inclusion of low stress creep significantly alters the prediction of steady-state cavern closure behavior and indicate that low stress creep is the dominant displacement mechanism at the dome scale. The implications for evaluating cavern and well integrity are demonstrated by investigating three phenomena: the extent of stress changes around the cavern; the predicted vertical strains applied to wellbore casings; and the evaluation of oscillating stress changes around the cavern due to oil sale cycles and their potential effect on salt fatigue.

58 GEOSCIENCES↗

NASA NTRSDate not supplied

Development of the Suited Injury Modes and Effects Analysis for Identification of Top Injury Risks in Lunar Missions and Training

A new Exploration Extravehicular Activity Suit (xEVAS) is being designed to replace the current Extravehicular Mobility Unit (EMU) for the National Aeronautics and Space Administration’s (NASA’s) Artemis program to return astronauts to the lunar surface. This new suit will allow for increased range of motion compared the current EMU and Apollo era suits and will have additional features that will enhance the health and safety of exploration. With the design of lunar missions and the xEVAS progressing, it is important to consider possible injuries and injury mechanisms that could occur in the suit. To address these concerns, the suited Injury Modes and Effects Analysis (IMEA) was developed to outline suited injury scenarios and rank them based on risk score. The IMEA documents possible scenarios and underlying mechanisms of injury while wearing an extravehicular activity (EVA) suit. Tasks during lunar surface EVA as well as training events to prepare for lunar missions were considered as history has shown that more suit injuries occur during training than in flight. Each scenario is ranked with a consequence and likelihood scoring based on our current understanding of the suit and Artemis design reference missions to identify high-risk cases that will drive further work in suited injury. Injuries, mechanisms of injury, and mitigation strategies are evaluated within each scenario. The Suited Injury Summit was held on January 5, 2022, to vet the IMEA with external experts. This was an all-day virtual meeting with the suited injury team, ergonomists, suit engineers, safety engineers, the flight operations directorate, flight doctors, astronauts, astronaut strength, conditioning, and rehabilitation specialists (ASCRS), and external subject matter experts (SMEs). External SMEs consisted of surgeons with varying specialties. The intent of this meeting was to walk through the top injury risks identified in the analysis, identify any gaps that were not captured, and discuss mitigations. With participation from all groups, countless lessons-learned came from the Summit meeting. Using the lessons-learned and discussion from the Summit, the top 10 risks have been identified: neutral buoyancy laboratory training, hand/glove injuries, poor suit fit, field training, specific EVA tasks/design of task, boots/ankle injuries, falls from heights, background radiation, repetitive contact, and ambulation/long-distance ambulation. Mitigation steps have also been determined for each of the top risks. The IMEA and documentation of top risks is a living document. Yearly meetings are planned to update the analysis and reevaluate top risks and mitigations. The IMEA is being used to drive work in suited injury, and this work will continue to evolve with IMEA and lunar mission updates.

Teresa Reiber↗

NASA NTRSDate not supplied

Development of the Suited Injury Modes and Effects Analysis for Identification of Top Injury Risks in Lunar Missions and Training

A new Exploration Extravehicular Activity Suit (xEVAS) is being designed to replace the current Extravehicular Mobility Unit (EMU) for the National Aeronautics and Space Administration’s (NASA’s) Artemis program to return astronauts to the lunar surface. This new suit will allow for increased range of motion compared the current EMU and Apollo era suits and will have additional features that will enhance the health and safety of exploration. With the design of lunar missions and the xEVAS progressing, it is important to consider possible injuries and injury mechanisms that could occur in the suit. To address these concerns, the suited Injury Modes and Effects Analysis (IMEA) was developed to outline suited injury scenarios and rank them based on risk score. The IMEA documents possible scenarios and underlying mechanisms of injury while wearing an extravehicular activity (EVA) suit. Tasks during lunar surface EVA as well as training events to prepare for lunar missions were considered as history has shown that more suit injuries occur during training than in flight. Each scenario is ranked with a consequence and likelihood scoring based on our current understanding of the suit and Artemis design reference missions to identify high-risk cases that will drive further work in suited injury. Injuries, mechanisms of injury, and mitigation strategies are evaluated within each scenario. The Suited Injury Summit was held on January 5, 2022, to vet the IMEA with external experts. This was an all-day virtual meeting with the suited injury team, ergonomists, suit engineers, safety engineers, the flight operations directorate, flight doctors, astronauts, astronaut strength, conditioning, and rehabilitation specialists (ASCRS), and external subject matter experts (SMEs). External SMEs consisted of surgeons with varying specialties. The intent of this meeting was to walk through the top injury risks identified in the analysis, identify any gaps that were not captured, and discuss mitigations. With participation from all groups, countless lessons-learned came from the Summit meeting. Using the lessons-learned and discussion from the Summit, the top 10 risks have been identified: neutral buoyancy laboratory training, hand/glove injuries, poor suit fit, field training, specific EVA tasks/design of task, boots/ankle injuries, falls from heights, background radiation, repetitive contact, and ambulation/long-distance ambulation. Mitigation steps have also been determined for each of the top risks. The IMEA and documentation of top risks is a living document. Yearly meetings are planned to update the analysis and reevaluate top risks and mitigations. The IMEA is being used to drive work in suited injury, and this work will continue to evolve with IMEA and lunar mission updates.

Tessa Reiber↗

DOE OSTI2024

Methodological guidelines on concrete degradation based on predictive models and the release of MOSAIC for industry use

In light-water reactors (LWRs), the concrete biological shield (CBS) designates the concrete structure directly facing the reactor pressure vessel (RPV). The primary function of the CBS is to protect equipment and personnel from the neutron and gamma radiation exiting the RPV. Most CBSs in operation in the United States also provide structural support to the RPV. Based on a long-term structural analysis, the structural integrity of the CBS to transfer the in-service passive load to the foundation, dynamic loading during an earthquake, and thermal loading during a loss-of-coolant accident (LOCA) must be maintained. Based on test reactor data for accelerated conditions, the mechanical properties of irradiated concrete are affected when exposed to neutron fluence higher than ≈ 10 19 n.cm -2 (E > 0.1 MeV). At 80 years of operation, the fluence estimates at the surface of the CBS range between 1×10 19 and 7×10 19 n.cm -2 (E > 0.1 MeV): the fluence value depends mostly on the design. Although fluence attenuates through the CBS by virtue of the shielding properties of concrete, about 5% to 10% of the CBS wall depth is affected by high fluence. The main degradation mechanism is the so-called radiation-induced volumetric expansion (RIVE) caused by the amorphization of aggregate-forming minerals. RIVE causes large deformation of up to 18% in pure quartz, and it also reduces the structural properties of concrete. The structural effects of long-term exposure to fast neutron irradiation in LWRs was studied in the report entitled “Assessment of the Effect of the Irradiation-Induced Degradation on the In-Service Structural Performance of the Concrete Biological Shields” (M3LW-23OR0403013). This report illustrates that (1) irradiation-induced damage expands further than the region subject to a cumulative fluence of 10 19 n.cm -2 (E > 0.1 MeV) to reach the steel reinforcement location, and (2) the irradiation-induced damage region shows no substantial residual bearing capacity and should not be accounted for in the integrity assessment of the CBS.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS1987

Modeling the interactions between the ocean and the environment for microwave radar sensing

An extensive set of X-band microwave backscatter measurements has been analyzed to determine its dependence on winds near the surface, atmospheric stability, and long-wave slopes. These radar measurements, made from a tower in the Gulf of Mexico, were performed in conjunction with an extensive set of simultaneous environmental measurements. The CW microwave system operated at an incidence angle of 45 deg, with antennas directed into winds and waves. Model functions for the radar cross section (RCS) and the modulation transfer function (MTF) are developed that depend on the geophysical variables, including wind stress. Statistical analysis shows that these models functions yield a significant smaller error when fit to the RCS data than a simple wind-speed function displays. A Taylor-series expansion of the returned power from a small area provides a unified function that demonstrates the complementary roles of wave slope and atmospheric fluctuations on both the RCS, the MTF, and the coherence. The issue of linearity of the MTF is addressed with this data set, yielding evidence that this is a valid assumption. These results have direct application to the remote sensing of the mean and fluctuating winds, and the wave spectrum with coherent and incoherent active radars.

Weissman, David E.↗

NASA NTRS1991

Thermal control surfaces experiment: Initial flight data analysis

The behavior of materials in the space environment continues to be a limiting technology for spacecraft and experiments. The thermal control surfaces experiment (TCSE) aboard the Long Duration Exposure Facility (LDEF) is the most comprehensive experiment flown to study the effects of the space environment on thermal control surfaces. Selected thermal control surfaces were exposed to the LDEF orbital environment and the effects of this exposure were measured. The TCSE combined in-space orbital measurements with pre and post-flight analyses of flight materials to determine the effects of long term space exposure. The TCSE experiment objective, method, and measurements are described along with the results of the initial materials analysis. The TCSE flight system and its excellent performance on the LDEF mission is described. A few operational anomalies were encountered and are discussed.

Wilkes, Donald R.↗

NASA NTRS1991

Microanalysis of extended-test xenon hollow cathodes

Four hollow cathode electron sources were analyzed via boroscopy, scanning electron microscopy, energy dispersive x ray analysis, and x ray diffraction analysis. These techniques were used to develop a preliminary understanding of the chemistry of the devices that arise from contamination due to inadequate feed-system integrity and improper insert activation. Two hollow cathodes were operated in an ion thruster simulator at an emission current of 23.0 A for approximately 500 hrs. The two tests differed in propellant-feed systems, discharge power supplies, and activation procedures. Tungsten deposition and barium tungstate formation on the internal cathode surfaces occurred during the first test, which were believed to result from oxygen contamination of the propellant feed-system. Consequently, the test facility was upgraded to reduce contamination, and the test was repeated. The second hollow cathode was found to have experienced significantly less tungsten deposition. A second pair of cathodes examined were the discharge and the neutralizer hollow cathodes used in a life-test of a 30-cm ring-cusp ion thruster at a 5.5 kW power level. The cathodes' test history was documented and the post-test microanalyses are described. The most significant change resulting from the life-test was substantial tungsten deposition on the internal cathode surfaces, as well as removal of material from the insert surface. In addition, barium tungstate and molybdate were found on insert surfaces. As a result of the cathode examinations, procedures and approaches were proposed for improved discharge ignition and cathode longevity.

Verhey, Timothy R.↗

NASA NTRS1992

Space Station Freedom Environmental Health Care Program

The paper discusses the environmental planning and monitoring aspects of the Space Station Freedom (SSF) Environmental Health Care Program, which encompasses all phases of the SSF assembly and operation from the first element entry at MB-6 through the Permanent Manned Capability and beyond. Environmental planning involves the definition of acceptability limits and monitoring requirements for the radiation dose barothermal parameters and potential contaminants in the SSF air and water and on internal surfaces. Inflight monitoring will be implemented through the Environmental Health System, which consists of five subsystems: Microbiology, Toxicology, Water Quality, Radiation, and Barothermal Physiology. In addition to the environmental data interpretation and analysis conducted after each mission, the new data will be compared to archived data for statistical and long-term trend analysis and determination of risk exposures. Results of these analyses will be used to modify the acceptability limits and monitoring requirements for the future.

Richard, Elizabeth E.↗