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NASA NTRS1972

Mean elements of GEOS-1 and GEOS-2

A combined analytical-numerical procedure for determining precise mean orbital elements is presented and applied to the orbits of GEOS-1 and GEOS-2. The precision of the mean semi-major axes of these orbits is a few tens of centimeters when optical flash data is used to determine two-day orbital arcs. Four-day Minitrack orbits give mean semi-major axes of a few meters precision. The mean orientation parameters are obtained to a precision of about 0.1 sec (about 3m) or better from the optical orbits. This precision is adequate for determinations of tidal parameters, particularly in the case of GEOS-2, where the tidal perturbation of the inclination is 10 sec.

Douglas, B. C.↗

NASA NTRS1979

Pressure and temperature dependence kinetics study of the NO + BrO yielding NO2 + Br reaction - Implications for stratospheric bromine photochemistry

The reactivity of NO with BrO radicals over a wide range of pressure (100-700 torr) and temperature (224-398 K) is investigated using the flash photolysis-ultraviolet absorption technique. The flash photolysis system consists of a high-pressure xenon arc light source, a reaction cell/gas filter/flash lamp combination, and a 216.5 half-meter monochromator/polychromator/spectrography for wavelength selectivity. The details of the reaction and its corresponding Arrhenius expression are identified. The results are compared with previous measurements, and atmospheric implications of the reaction are discussed. The NO + BrO yielding NO2 + Br reaction is shown to be important in controlling the concentration ratios of BrO/Br and BrO/HBr in the stratosphere, but this reaction does not affect the catalytic efficiency of BrOx in ozone destruction.

Watson, R. T.↗

NASA NTRS1991

Welding in space and the construction of space vehicles by welding; Proceedings of the Conference, New Carrollton, MD, Sept. 24-26, 1991

The present conference discusses such topics in spacecraft welding as the NASA Long Duration Exposure Facility's evidence on material properties degradation, EVA/telerobotic construction techniques, welding of the superfluid helium on-orbit transfer flight demonstration tanks and hardware, electron-beam welding of aerospace vehicles, variable-polarity plasma arc keyhole welding of Al, aircraft experiments of low-gravity fusion welding, flash-butt welding of Al alloys, and a computer-aided handbook for space welding fabrication. Also discussed are the welded nozzle extension for Ariane launch vehicles, the existence of on-orbit cold-welding, structural materials performance in long-term space service, high-strength lightweight alloys, steels, and heat-resistant alloys for aerospace welded structures, the NASA-Goddard satellite repair program, and the uses of explosion welding and cutting in aerospace engineering.

Source record↗

NASA NTRS1977

Direct effects protection

Protection of an aircraft and each of its various systems against the direct effects of lightning were analyzed. Components located in different sections of the aircraft were individually examined since they are likely to experience different degrees of susceptibility to lightning, and may be vulnerable to different components of the lightning flash. The basic steps to be followed in establishing lightning protection were presented by discussing the varieties of arc entry and current flow-through damage. The lightning-strike zones and lightning current environments are established, since environmental conditions in the zones are those under which specific protective measures must perform. Airworthiness regulations which apply to lightning protection are cited.

Franklin A Fisher↗

DOE OSTI2022

Non-Destructive In-Process Assessment of Thermal Spray Repairs

This exploratory project, entitled “Non-Destructive In-process Assessment of Thermal Spray Repairs,” evaluated the capabilities and limitations of four non-destructive testing (NDE) technologies for detection of defects in as-sprayed thermal spray coatings: acousto-ultrasonics, vibro-thermography, thermal wave infrared (IR) imaging, and flash IR thermography. The project goal was to identify a single technology suitable for use as an in-process inspection for two common classes of defects in thermal spray coatings, porosity and disbonds. Two rounds of test coupons were fabricated with intentionally seeded defects in AISI 420 stainless steel coatings deposited by twin wire arc (TWA) spray onto gray cast iron substrates. These standardized test coupons allowed the sensitivity of the four NDE methods to be directly compared. The results indicated that the acousto-ultrasonic method will not meet requirements for accuracy, inspection time, and reproducibility, while the vibrothermography method will not meet requirements for integration within remanufacturing cells and process flows. The IR methods, thermal wave imaging and flash thermography, both exhibited acceptable accuracy and reproducibility; however, the former method does not meet the requirement for inspection time. Flash IR thermography met all requirements in the initial round of testing, and that result was confirmed in a second round of testing on samples with a larger, more complex geometry. A final recommendation for further development of flash IR thermography was therefore made based upon i) detection performance, and ii) feasibility of deployment into the target application of resurfacing CAT engine blocks and headers.

36 MATERIALS SCIENCE↗

NASA NTRS1972

Tracking-station coordinates from Geos 1 and Geos 2 optical flash data.

Center-of-mass coordinates for 28 NASA MOTS and SAO Baker-Nunn camera sites have been obtained from optical flash data from Geos 1 (1965 89A) and Geos 2 (1968 002A). More than 25,000 observations in about 100 two-day arcs were used in dynamical solutions (SAO 1969 AGU gravity model). Comparison of results with local survey solutions and with solutions from deep-space vehicle tracking suggests accuracy of about 2 meters in longitude and height and 5 meters in latitude. The relatively larger error in latitude arose from propagation of gravity-model error largely along the track of these high-inclination satellites. The results have also been compared with the solutions of the SAO 1969 standard earth for station coordinates on the North American datum. The solution obtained in the present work is much closer to the survey results in chord length between stations.

Marsh, J. G.↗

NASA NTRS1988

Interiors of the giant planets

This theoretical/observational project constrains interior structure of Jovian planets through observational data. Researchers continue to concentrate on Neptune in support of the 1989 Voyager encounter. Occultations of stars by Neptune are observed from the Tucson area and from Chile to obtain information about Neptune's atmosphere and to continue to search for Neptune arcs. Occultations by other solar system objects are also observed as part of collaborative efforts from time to time. New results on the structure of scintillations in the central flash occultation by Neptune on 20 August 1985 were derived. Analysis shows that scintillations are present throughout the lightcurve, both near the half-intensity points (at a pressure of 1 microbar) and near the central flash (at 0.4 mbar). Near the planetary limb, the scintillations are extended parallel to the limb; near the shadow center, they are extended parallel to the limb; near the shadow center, they are extended in a radial direction. Researchers collaborated with Ramesh Narayan to derive a theory relating the scintillations to density fluctuations in Neptune's atmosphere. The theory will ultimately enable researchers to test whether the scintillations are caused by internal gravity waves in Neptune's upper atmosphere.

Hubbard, W. B.↗

NASA NTRS1988

Final results of the NASA storm hazards program

Lightning swept-flash attachment patterns and the associated flight conditions were recorded from 1980-1986 during 1496 thunderstorm penetrations and 714 direct strikes with a NASA F-1068 research airplane. These data were studied with an emphasis on lightning avoidance by aircraft and on aircraft protection design. The individual lightning attachment spots, along with crew comments and on-board photographic data were used to identify lightning swept-flash attachment patterns and the orientations of the lightning channels with respect to the airplane. The full-scale in-flight data were compared to results from scale-model arc-attachment tests. The airborne and scale-model data showed that any exterior surface of this airplane may be susceptible to direct lightning attachment. In addition, the altitudes, ambient temperatures, and the relative turbulence and precipitation levels at which the strikes occurred in thunderstorms are summarized and discussed. It was found that the peak strike rate occurred at pressure altitudes betwen 38,000 ft and 40,000 ft, corresponding to ambient temperatures colder than -40 C.

Fisher, Bruce D.↗

NASA NTRS1986

Interiors of the giant planets

The Neptune central flash data obtained from the August 20, 1985 occultation was analyzed. The three main objectives of the analysis, which combined the study of the CTIO data with the ESO data obtained by the Meudon groups were: deduce the oblateness, equatorial radius, and pole positon angle of Neptune from a combined analysis of the limb-occultation and central-flash data; determine the temperature/absorption profile in Neptune's atmosphere in the region probed by the occultation data (from 1 microbar to about 0.2 mbar), as well as atmospheric distortions produced by waves or turbulence; and search for additional Neptune ring arcs. Results were discussed in terms of the three main objectives.

Hubbard, W. B.↗

DOE OSTI2021

Enhancing thermal conductivity of UO 2 with the addition of UB 2 via conventional sintering techniques

We report that uranium dioxide has been the primary fuel type used in light water reactors for more than 40 years and proven to be reliable and robust. However, the Fukushima-Daiichi nuclear accident has motivated new work evaluating fuels with characteristics promoting accident tolerance, including enhanced thermal conductivity. Recently, additives have been investigated to increase thermal conductivity, but research has been largely focused on non-fissile additions. This study investigated the use of fissile additives to not only increase the thermal conductivity but also increase the uranium loading. Uranium diboride was chosen as the additive for this study due to its promising corrosion behavior as well as its significantly higher thermal conductivity at 573 K (25 Wm -1 K -1 ) when compared to UO 2 (7 Wm -1 K -1 ). Uranium diboride powder was fabricated via the arc melting technique and a ball milling process prior to mixing with UO 2 in a 90/10 wt% UO 2 /UB 2 ratio. Green bodies were made using a uniaxial die and subjected to a traditional pressureless sintering technique at 2073 K in argon. Sintered samples were analyzed via laser flash analysis for thermal diffusivity and differential scanning calorimetry for specific heat capacity in order to calculate thermal conductivity. The samples displayed an increase of 36-55% in thermal conductivity between 323 K and 1273 K when compared to the benchmark samples (pure UO 2 ) as reported in open literature.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRS1989

Flash-photoionized nebulae

Under conditions of high radiation intensity and low gas density, recombination may be neglected in determining the ionization state of a photoionized gas. Calculations of the ionization structure of nebulae in this 'flash-photoionized' regime are reported. Very hard spectra of ionizing ultraviolet radiation may be produced by filtration of the ionizing flux through a neutral hydrogen layer which preferentially absorbs photons just above the hydrogen photoionization threshold. Fluxes with these hard spectra produce gas layer in which helium is largely doubly ionized while hydrogen is largely neutral. Such a layer leads to anomalously high ratios of He II to H I recombination line strengths. These results are applied to the problem of the spectrum of the arc in the cluster of galaxies A370. It is found that the spectrum may possibly be reconciled with the light echo model.

Katz, J. I.↗

NASA NTRS2005

A multiparameter wearable physiologic monitoring system for space and terrestrial applications

A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.

NASA Center ARC↗

NASA NTRS2015

Space Environment Testing of Photovoltaic Array Systems at NASA's Marshall Space Flight Center

To successfully operate a photovoltaic (PV) array system in space requires planning and testing to account for the effects of the space environment. It is critical to understand space environment interactions not only on the PV components, but also the array substrate materials, wiring harnesses, connectors, and protection circuitry (e.g. blocking diodes). Key elements of the space environment which must be accounted for in a PV system design include: Solar Photon Radiation, Charged Particle Radiation, Plasma, and Thermal Cycling. While solar photon radiation is central to generating power in PV systems, the complete spectrum includes short wavelength ultraviolet components, which photo-ionize materials, as well as long wavelength infrared which heat materials. High energy electron radiation has been demonstrated to significantly reduce the output power of III-V type PV cells; and proton radiation damages material surfaces - often impacting coverglasses and antireflective coatings. Plasma environments influence electrostatic charging of PV array materials, and must be understood to ensure that long duration arcs do not form and potentially destroy PV cells. Thermal cycling impacts all components on a PV array by inducing stresses due to thermal expansion and contraction. Given such demanding environments, and the complexity of structures and materials that form a PV array system, mission success can only be ensured through realistic testing in the laboratory. NASA's Marshall Space Flight Center has developed a broad space environment test capability to allow PV array designers and manufacturers to verify their system's integrity and avoid costly on-orbit failures. The Marshall Space Flight Center test capabilities are available to government, commercial, and university customers. Test solutions are tailored to meet the customer's needs, and can include performance assessments, such as flash testing in the case of PV cells.

Phillips, Brandon S.↗

NASA NTRS2012

Gas Shielding Technology for Welding and Brazing

Welding is a common method that allows two metallic materials to be joined together with high structural integrity. When joints need to be leak-tight, light-weight, or free of contaminant-trapping seams or surface asperities, welding tends to be specified. There are many welding techniques, each with its own advantages and disadvantages. Some of these techniques include Forge Welding, Gas Tungsten Arc Welding, Friction Stir Welding, and Laser Beam Welding to name a few. Whichever technique is used, the objective is a structural joint that meets the requirements of a particular component or assembly. A key practice in producing quality welds is the use of shielding gas. This article discusses various weld techniques, quality of the welds, and importance of shielding gas in each of those techniques. Metallic bonds, or joints, are produced when metals are put into intimate contact. In the solid-state "blacksmith welding" process, now called Forge Welding (FOW), the site to be joined is pounded into intimate contact. The surfaces to be joined usually need to be heated to make it easier to deform the metal. The surfaces are sprinkled with a flux to melt surface oxides and given a concave shape so that surface contamination can be squeezed out of the joint as the surfaces are pounded together; otherwise the surface contamination would be trapped in the joint and would weaken the weld. In solid-state welding processes surface oxides or other contamination are typically squeezed out of the joint in "flash."

Nunes, Arthur J.↗

DOE OSTI2025

Results of a Geant4 benchmarking study for bio‐medical applications, performed with the G4‐Med system

Geant4, a Monte Carlo Simulation Toolkit extensively used in bio-medical physics, is in continuous evolution to include newest research findings to improve its accuracy and to respond to the evolving needs of a very diverse user community. In 2014, the G4-Med benchmarking system was born from the effort of the Geant4 Medical Simulation Benchmarking Group, to benchmark and monitor the evolution of Geant4 for medical physics applications. The G4-Med system was first described in our Medical Physics Special Report published in 2021. Results of the tests were reported for Geant4 10.5. Purpose In this work, we describe the evolution of the G4-Med benchmarking system. Methods The G4-Med benchmarking suite currently includes 23 tests, which benchmark Geant4 from the calculation of basic physical quantities to the simulation of more clinically relevant set-ups. New tests concern the benchmarking of Geant4-DNA physics and chemistry components for regression testing purposes, dosimetry for brachytherapy with a 125 I source, dosimetry for external x-ray and electron FLASH radiotherapy, experimental microdosimetry for proton therapy, and in vivo PET for carbon and oxygen beams. Regression testing has been performed between Geant4 10.5 and 11.1. Finally, a simple Geant4 simulation has been developed and used to compare Geant4 EM physics constructors and physics lists in terms of execution times. Results In summary, our EM tests show that the parameters of the multiple scattering in the Geant4 EM constructor G4EmStandardPhysics_option3 in Geant4 11.1, while improving the modeling of the electron backscattering in high atomic number targets, are not adequate for dosimetry for clinical x-ray and electron beams. Therefore, these parameters have been reverted back to those of Geant4 10.5 in Geant4 11.2.1. The x-ray radiotherapy test shows significant differences in the modeling of the bremsstrahlung process, especially between G4EmPenelopePhysics and the other constructors under study (G4EmLivermorePhysics, G4EmStandardPhysics_option3, and G4EmStandardPhysics_option4). These differences will be studied in an in-depth investigation within our Group. Improvement in Geant4 11.1 has been observed for the modeling of the proton and carbon ion Bragg peak with energies of clinical interest, thanks to the adoption of ICRU90 to calculate the low energy proton stopping powers in water and of the Linhard–Sorensen ion model, available in Geant4 since version 11.0. Nuclear fragmentation tests of interest for carbon ion therapy show differences between Geant4 10.5 and 11.1 in terms of fragment yields. In particular, a higher production of boron fragments is observed with Geant4 11.1, leading to a better agreement with reference data for this fragment. Conclusions Based on the overall results of our tests, we recommend to use G4EmStandardPhysics_option4 as EM constructor and QGSP_BIC_HP with G4EmStandardPhysics_option4, for hadrontherapy applications. The Geant4-DNA physics lists report differences in modeling electron interactions in water, however, the tests have a pure regression testing purpose so no recommendation can be formulated.

62 RADIOLOGY AND NUCLEAR MEDICINE↗