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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Absorbed dose measurements and predictions on LDEF

The overall radiation environment of the Long Duration Exposure Facility (LDEF) was determined in part through the use of thermoluminescent detectors (TLD's) which were included in several experiments. The results given are from four experiments (A0015 Biostack, M0004 Fiber Optics Data Link, P0004 Seeds in Space, and P0006 Linear Energy Transfer Spectrum Measurement) and represent a large fraction of existing absorbed dose data. The TLD's were located on the leading and the trailing edges and the Earth end of the spacecraft under various shielding depths (0.48 to 15.4 g/sq cm). The measured absorbed doses were found to reflect both directional dependence of incident trapped protons and shielding. At the leading edge, doses ranged from 2.10 to 2.58 Gy under shielding of 2.90 to 1.37 g/sq cm Al equivalent (M0004). At the trailing edge, doses varied from 3.04 to 4.49 Gy under shielding of 11.7 to 3.85 g/sq cm (A0015), doses varied from 2.91 to 6.64 Gy under shielding of 11.1 to 0.48 g/sq cm (P0004), and a dose range of 2.66 to 6.48 Gy was measured under shielding of 15.4 to 0.48 g/sq cm (P0006). At the Earth end of the spacecraft, doses from 2.41 to 3.93 Gy were found under shielding of 10.0 to 1.66 g/sq cm (A0015). The effect of the trapped proton anisotropy was such that the western side of LDEF received more than 2 times the dose of the eastern side at shielding depths of approximately 1 g/sq cm. Calculations utilizing a directional model of trapped proton spectra predict smaller doses than those measured, being about 50 percent of measured values at the trailing edge and Earth end, and about 80 percent near the leading edge.

Frank, A. L.↗
NASA NTRS1993

Semiempirical fragmentation models on galactic cosmic ray transport calculations with hydrogen target

Nuclear fragmentation cross sections of Silberberg and Tsao that are more accurate for a hydrogen target were implemented in the data base to replace those of Rudstam for a galactic cosmic ray transport code (HZETRN). Sample calculations were made for the transported galactic cosmic ray flux through a liquid hydrogen shield at solar minimum condition to determine the effect of such a change. The transported flux based on the Silberberg-Tsao semiempirical formalism contains fewer high-LET (linear energy transfer) components but more low-LET components than the results based on Rudstam's formalism: and this disparity deepens as the shield thickness increases. A comparison of the results obtained from using both energy-dependent and energy-independent cross sections of Silberberg and Tsao indicates that the energy-independent assumption results in an underestimation of high-LET flux above 100 keV/micron by approximately 40 percent for a 15-g/cm(sup 2) thickness of liquid hydrogen. Similar results were obtained in a previous study when both energy-dependent and energy-independent cross sections of Rudstam were considered. Nonetheless, the present study found that an energy-independent calculation would be best accomplished by using Rudstam's cross sections as done in the past for various engineering applications.

Shinn, Judy L.↗
NASA NTRS1992

Effects of fragmentation parameter variations on estimates of galactic cosmic ray exposure: Dose sensitivity studies for aluminum shields

Initial studies of the sensitivities of estimates of particle fluence, absorbed dose, and dose equivalent to fragmentation parameter variations are undertaken by using the LaRC galactic cosmic ray transport code (HZETRN). The new results, presented as a function of aluminum shield thickness, include upper and lower bounds on dose/dose equivalent corresponding to the physically realistic extremes of the fragmentation process and the percentage of variation of the dose/dose equivalent as a function of fragmentation parameter variation.

Townsend, Lawrence W.↗
NASA NTRS2012

Effect of Solar Exposure on the Atomic Oxygen Erosion of Hubble Space Telescope Aluminized-Teflon Thermal Shields

When exposed to low Earth orbital (LEO) environment, external spacecraft materials degrade due to radiation, thermal cycling, micrometeoroid and debris impacts, and atomic oxygen (AO) interaction. Collisions between AO and spacecraft can result in oxidation of external spacecraft surface materials, which can lead to erosion and severe structural and/or optical property deterioration. It is therefore essential to understand the AO erosion yield (Ey), the volume loss per incident oxygen atom (cu cm/atom), of polymers to assure durability of spacecraft materials. The objective of this study was to determine whether solar radiation exposure can increase the rate of AO erosion of polymers in LEO. The material studied was a section of aluminized-Teflon (DuPont) fluorinated ethylene propylene (Al-FEP) thermal shield exposed to space on the Hubble Space Telescope (HST) for 8.25 years. Retrieved samples were sectioned from the circular thermal shield and exposed to ground laboratory thermal energy AO. The results indicate that the average Ey of the solar facing HST Al-FEP was 1.9 10(exp -24)cu cm/atom, while the average Ey of the anti-solar HST Al-FEP was 1.5 10(exp -24)cu cm/atom. The Ey of the pristine samples was 1.6- 1.7 10(exp -24)cu cm/atom. These results indicate that solar exposure affects the post-flight erosion rate of FEP in a plasma asher. Therefore, it likely affects the erosion rate while in LEO.

Guo, Aobo↗
NASA NTRS1982

Analysis of the effect of heated jet flow on the far field radiation from a noise source

The influence on jet noise radiation of the interaction with the heated moving flow of a parallel twin jet is investigated. An analytical model of jet shielding is developed which consists of the sound field emitted from a stationary, discrete frequency point source impinging on a cylinder of locally parallel flow. The zones in which the various shielding mechanisms dominate are analyzed using the model. The effects of parameters such as jet temperature and flow speed are examined. It is found that the results obtained using the model are comparable to the experimental results for a point noise source impinging on a subsonic isothermal air jet.

Gerhold, C.↗
NASA NTRS2000

Radiation Transport Modeling and Assessment to Better Predict Radiation Exposure, Dose, and Toxicological Effects to Human Organs on Long Duration Space Flights

NASA's long-range plans include possible human exploratory missions to the moon and Mars within the next quarter century. Such missions beyond low Earth orbit will expose crews to transient radiation from solar particle events which include high-energy galactic cosmic rays and high-energy protons. Because the radiation levels in space are high and the missions long, adequate shielding is needed to minimize the deleterious health effects of exposure to radiation. The focus of this study is radiation exposure to the blood-forming organs of the NASA astronauts. NASA/JSC developed the Phantom Torso Experiment for Organ Dose Measurements which housed active and passive dosimeters that would monitor and record absorbed radiation levels at vital organ locations. This experiment was conducted during the STS-9 I mission in May '98 and provided the necessary space radiation data for correlation to results obtained from the current analytical models used to predict exposure to the blood-forming organs. Numerous models (i.e., BRYNTRN and HZETRN) have been developed and used to predict radiation exposure. However, new models are continually being developed and evaluated. The Space Environment Information Systems (SPENVIS) modeling program, developed by the Belgian Institute for Space Aeronomy, is to be used and evaluated as a part of the research activity. It is the intent of this research effort to compare the modeled data to the findings from the STS-9 I mission; assess the accuracy and efficiency of this model; and to determine its usefulness for predicting radiation exposure and developing better guidelines for shielding requirements for long duration manned missions.

Denkins, Pamela↗
NASA NTRS1994

Space proton transport in one dimension

An approximate evaluation procedure is derived for a second-order theory of coupled nucleon transport in one dimension. An analytical solution with a simplified interaction model is used to determine quadrature parameters to minimize truncation error. Effects of the improved method on transport solutions with the BRYNTRN data base are evaluated. Comparisons with Monte Carlo benchmarks are given. Using different shield materials, the computational procedure is used to study the physics of space protons. A transition effect occurs in tissue near the shield interface and is most important in shields of high atomic number.

NASA Discipline Number 45-10↗
NASA NTRS1999

Aircraft Radiation Shield Experiments--Preflight Laboratory Testing

In the past, measurements onboard a research Boeing 57F (RB57-F) aircraft have demonstrated that the neutron environment within the aircraft structure is greater than that in the local external environment. Recent studies onboard Boeing 737 commercial flights have demonstrated cabin variations in radiation exposure up to 30 percent. These prior results were the basis of the present study to quantify the potential effects of aircraft construction materials on the internal exposures of the crew and passengers. The present study constitutes preflight measurements using an unmoderated Cf-252 fission neutron source to quantify the effects of three current and potential aircraft materials (aluminum, titanium, and graphite-epoxy composite) on the fast neutron flux. Conclusions about the effectiveness of the three selected materials for radiation shielding must wait until testing in the atmosphere is complete; however, it is clear that for shielding low-energy neutrons, the composite material is an improved shielding material over aluminum or titanium.

Singleterry, Robert C., Jr.↗
NASA NTRS1971

Long term cryogenic storage system integration

Investigations have revealed significant increases in performance when a reliquefier and solar shield in conjunction with a zero-gravity vapor vent system are utilized. Application of a reliquefier and solar shield in long term deep space missions may effect a 60% reduction in propellant loss, compared to that associated with the vapor vent system only. Significant improvements in storage system performance are possible for low earth orbit applicatons; for the typical system that was evaluated, system performance gains were realized for mission durations exceeding 7 days. Spherical solar shields are generally not competitive for low earth orbit applications.

Stonemetz, R. E.↗
NASA NTRS2001

Radiation transport modeling and assessment to better predict radiation exposure, dose, and toxicological effects to human organs on long duration space flights

NASA is very interested in improving its ability to monitor and forecast the radiation levels that pose a health risk to space-walking astronauts as they construct the International Space Station and astronauts that will participate in long-term and deep-space missions. Human exploratory missions to the moon and Mars within the next quarter century, will expose crews to transient radiation from solar particle events which include high-energy galactic cosmic rays and high-energy protons. Because the radiation levels in space are high and solar activity is presently unpredictable, adequate shielding is needed to minimize the deleterious health effects of exposure to radiation. Today, numerous models have been developed and used to predict radiation exposure. Such a model is the Space Environment Information Systems (SPENVIS) modeling program, developed by the Belgian Institute for Space Aeronautics. SPENVIS, which has been assessed to be an excellent tool in characterizing the radiation environment for microelectronics and investigating orbital debris, is being evaluated for its usefulness with determining the dose and dose-equivalent for human exposure. Thus far. the calculations for dose-depth relations under varying shielding conditions have been in agreement with calculations done using HZETRN and PDOSE, which are well-known and widely used models for characterizing the environments for human exploratory missions. There is disagreement when assessing the impact of secondary radiation particles since SPENVIS does a crude estimation of the secondary radiation particles when calculating LET versus Flux. SPENVIS was used to model dose-depth relations for the blood-forming organs. Radiation sickness and cancer are life-threatening consequences resulting from radiation exposure. In space. exposure to radiation generally includes all of the critical organs. Biological and toxicological impacts have been included for discussion along with alternative risk mitigation methods--shielding and anti-carcinogens. c 2001. Elsevier Science Ltd. All rights reserved.

STS-91 Shuttle Project↗
NASA NTRS1992

Composite materials microstructure for radiation shielding

Shielding against radiation is a concern for applications on earth, in space, and on extraterrestrial surfaces. On earth EMI is an important factor, while in space and on extraterrestrial surfaces particle (high charge-Z and high energy-E) radiation is a critical issue. Conventional metallic materials currently used for EMI shielding incur large weight penalties. To overcome this weight penalty, ultra-lightweight composite materials utilizing fillers ranging from carbon microballoons to silver coated ceramic microballoons are proposed. The crucial shielding requirement is conductivity of the constituent materials, while the hollow microballoon geometry is utilized to yield low weight. Methods of processing and composition effects are examined and these results are compared to the effectiveness of varying the conductive microballoon material. The resulting ultralightweight materials, developed for EMI shielding, can be tailored through the application of the understanding of the relative effects of variables such as those tested. Initial experimental results reveal that these tailored ultralightweight composite materials are superior to traditional aluminum shielding at only a small fraction of the weight.

Radford, Donald W.↗
DOE OSTI2020

Comparison of Magnetic Field Emission from Unipolar and Bipolar Coil-Based Wireless Charging Systems

In this study, the leakage magnetic field (LMF) from the unipolar (circular, rectangular, etc.) and bipolar (double-D) coil-based wireless charging systems (WCSs) are investigated and compared. The unipolar and bipolar pads, which are the two most widely adopted charging-pads, have significantly different magnetic field emission characteristics. In this paper, the spatial-distribution and vector-pattern of the leakage magnetic field are studied and compared for similar 11 kW unipolar and bipolar coil-based WCSs. The field emissions are simulated using finite element analysis (FEA) and tested experimentally with an 11 kW bipolar coil-based WCS prototype. The results show that the leakage magnetic field of the unipolar and bipolar pads have widely different vector-orientation and spatial distributions of the leakage magnetic field. The results show that the unipolar coil based WCS has a dominant vertical and the bipolar pads coil-based WCS has dominant horizontally aligned leakage magnetic field. Considering the shielding, the aluminum plate is found highly effective for the unipolar pad and almost ineffective for bipolar pads.

Mohammad, Mostak↗
NASA NTRS1972

Impact of radiation dose on nuclear shuttle configuration

The impact of nuclear radiation (from the NERVA propulsion system) on the selection of a reference configuration for each of two classes of the reusable nuclear shuttle is considered. One class was characterized by a single propellant tank, the shape of whose bottom was found to have a pronounced effect on crew radiation levels and associated shield weight requirements. A trade study of shield weight versus structural weight indicated that the minimum-weight configuration for this class had a tank bottom in the shape of a frustum of a 10 deg-half-angle cone. A hybrid version of this configuration was found to affect crew radiation levels in substantially the same manner. The other class of RNS consisted of a propulsion module and eight propellant modules. Radiation analyses of various module arrangements led to a design configuration with no external shield requirements.

Goetz, C. A.↗
NASA NTRS1972

Preliminary noise tests of the engine-over-the-wing concept. i: 30 deg - 60 deg flap position

The results of preliminary acoustic tests of the engine over the wing concept are summarized. The tests were conducted with a small wing section model (32 cm chord) having two flaps set at the landing position, which is 30 and 60 deg respectively. The engine exhaust was simulated by an air jet from a convergent nozzle having a nominal diameter of 5.1 centimeters. Factors investigated for their effect on noise include nozzle location, wing shielding, flap leakage, nozzle shape, exhaust deflectors, and internally generated exhaust noise.

Reshotko, M.↗
NASA NTRS1972

Silica reinforcement and char reactions in the Apollo heat shield.

Reactions of the silica reinforcement fiber and ablation char of the Apollo heat shield have been investigated by laboratory tests in an arc image furnace (at temperature levels up to 5000 R, pressures up to 0.7 atm, and heat flux similar to reentry) and by an actual reentry test. Microchemical analyses and X-ray diffraction studies have been made to determine the presence of SiC formation in the char. Experimental data and analytical predictions of thermal and density profiles have been compared for the ablation of virgin heat shield and precharred materials to determine the effects of SiC formation on ablation performance. In all analyses, general agreement was found between chemical composition and the thermal predictions for laboratory tests and reentry materials. In all ablated materials, SiC was formed in the front surface of the char. The highest SiC content found was 58% by weight and found in a high-pressure environment. The SiC formed was found to act as a heat sink in the ablation process and can lower the front surface temperature by 300 R.

Cagliostro, D. E.↗
NASA NTRS1974

Development of a high Reynolds number quiet tunnel for transition research

High noise levels in conventional supersonic and hypersonic wind tunnels prevent further advances in transition research. Recent data confirm previous results that transition is dominated by tunnel noise when the rms pressure intensities exceed about 1%. High facility noise levels also dominate fluctuating pressure loads under fully turbulent boundary layers. Recent data on the power spectra of surface pressures indicate that the basic structure of turbulent boundary layers may be modified by high facility noise levels. Experimental data for current techniques to control and reduce noise levels in supersonic and hypersonic wind tunnels by laminarization of nozzle wall boundary layers and by noise radiation shields are presented. These results and possible effects of Taylor-Gortler vortices observed in a nozzle wall boundary layer are used to predict the limits of quiet performance for a proposed 20-in. quiet tunnel.

Beckwith, I. E.↗