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At least 865 records · Page 48

High Sensitive and Low Power Nanosensors for Space and Terrestrial Applications

Nanotechnology offers the ability to work at the molecular level, atom by atom, to create large structures with fundamentally new molecular organization. It is essentially concerned with materials, devices, and systems whose structures and components exhibit novel and significantly improved physical, chemical and biological properties, phenomena, and process control due to their nanoscale size. A nanosensor technology has been developed at NASA Ames using nanostructure, single walled carbon nanotubes (SWNTs). The nanosensors have achieved low detection limit of chemicals in the concentration range of ppm to ppb. Due to large surface area, low surface energy barrier and high thermal and mechanical stability, nanostructured chemical sensors offer higher sensitivity, lower power consumption and a more robust solution than most state-of-the-art systems making them attractive for space and terrestrial applications. An example of a sensor module, the first space flown nano device, will be introduced in this presentation. Such sensors have drawn attention from space community for global weather monitoring, space exploration, life search in the universe, and launch pad fuel leak detection and in-flight cabin air and life support system monitoring, and engine operation monitoring. Additionally, the wireless capability of such sensors can be leveraged to network mobile and fixed-base detection and warning systems for civilian population centers, military bases and battlefields, as well as other high-value or high-risk assets and areas in industry.

Jing Li↗

Hydrogen Plasma Reduction

Hydrogen plasma increases efficiency by strategically using energy to break bonds within the regolith to liberate oxygen instead of heating the entire bed of regolith. The energy used by the plasma system would be imparted into the H2 gas, forming highly energetic ions, electrons, and neutrals that would interact with the regolith surface. The energized atomic and ionic H2 provide the energy needed to make reduction of SiO2 (Silicon Dioxide) and other regolith mineral oxides favorable. What’s more, the high-energy plasma interaction occurs in a small, localized volume, and thus requires relatively little energy. The lunar regolith is well-suited for the process as the fine particles naturally available provide a high surface area for the plasma to interact with. The process would require a system to collect the regolith composed of metal oxides (MxOy) and load it into a reactor. An H2 plasma would pass over the surface (potentially at a low pressure, reducing complexity of the system as it would not require large increases in pressure from the lunar vacuum), then the gases from the plasma reaction would be collected and processed, and the spent regolith would be carried away. The gross reaction temperature would be near ambient (due to the localized nature of the plasma), eliminating the necessity of a regolith heating mechanism or handling of molten regolith. Also, the H2 used in the plasma could be subsequently recovered from the water produced by the plasma reaction. Thus, this approach would not require significant amounts of added commodities.

Elspeth Petersen↗

Evaluation of selected thermal control coatings for long-life space structures

Graphite-reinforced resin matrix composites are being considered for spacecraft structural applications because of their light weight, high stiffness, and lower thermal expansion. Thin protective coatings with stable optical properties and the proper ratio of solar absorption (alpha sub s) to thermal emittance (epsilon) minimize orbital thermal extremes and protect these materials against space environment degradation. Sputtered coatings applied directly to graphite/epoxy composite surfaces and anodized coatings applied to thin aluminum foil were studied for use both as an atomic oxygen barrier and as thermal control coatings. Additional effort was made to develop nickel-based coatings which could be applied directly to composites. These coating systems were selected because their inherent tenacity made them potentially more reliable than commercial white paints for long-life space missions. Results indicate that anodized aluminum foil coatings are suitable for tubular and flat composite structures on large platforms in low Earth orbit. Anodized foil provides protection against some elements of the natural space environment (atomic oxygen, ultraviolet, and particulate radiation) and offers a broad range of tailored alpha sub s/epsilon. The foil is readily available and can be produced in large quantities, while the anodizing process is a routine commercial technique.

Teichman, Louis A.↗

Polyvinyl Alcohol and Medium Density Polyethylene Composite Materials for Neutron Radiation Shielding

Manned spacecraft venturing beyond the Earth’s Van Allen Belts will be subjected to high levels of radiation from both energetic particles emanating from the sun and from galactic atomic events, such as supernovae. The metal shell of a spacecraft offers some protection from gamma radiation and high energy particles originating from both the sun and cosmic sources. The interaction of these high energy particles and radiation with the spacecraft hull create secondary radiation and neutrons, additional hazards for astronauts and electronic systems. Shielding of neutrons is the most challenging of the high energy radiation, since neutrons have zero charge and are least affected by electrical fields, magnetic fields, and atomic forces. Previous studies showed that polyethylene is an effective neutron shielding material, due to its high hydrogen content. High energy neutrons are slowed to thermal neutrons through multiple collisions with the hydrogen atoms, increasing the effectiveness of neutron capture by boron-10 atoms. This study discusses the fabrication and testing of polyvinyl alcohol (PVOH) samples as a neutron shielding material, with comparison to medium density polyethylene (MDPE) composite samples to be used for neutron shielding for spacecraft. PVOH, an aqueous polymer, was chosen for hydrogen content and for enabling the use of organic reinforcement such as cellulose for secondary structural composites. OLTARIS (On-Line Tool for the Assessment of Radiation in Space) was used for radiation shielding simulation and compared with experimental data. Modeling indicates that the most effective shielding from radiation was in an aluminum layer backed by a polymer layer, either MDPE or PVOH. Cross-linked PVOH was also included in the OLTARIS modeling. All 3 polymer cases showed shielding improvement over aluminum alone, with similar dose equivalent reduction for galactic cosmic radiation(GCR)and for radiation from a solar particle event (SPE). Fourier Transform Infrared (FTIR) Spectroscopy was used to confirm the cross-linking in the PVOH sample and to determine the uniformity through the thickness. PVOH, cross-linked PVOH, and MDPE samples were tested for neutron shielding effectiveness using a 1 curie Americium-Beryllium neutron source. Test results indicated the most shielding in the cross-linked PVOH, followed by the pristine PVOH, and MDPE. Neutron testing suggests that polyvinyl alcohol is a good alternative to polyethylene for neutron shielding. The neutron shielding materials, PVOH and cross-linked PVOH developed under this research will enable the safe operation of spacecraft beyond the Earth’s protective Van Allen Radiation Belts. It will be crucial for NASA’s manned missions to the Moon or Mars to protect the health of astronauts and equipment from the harmful effects of excessive radiation.

neutron, shielding, radiation, polyvinyl alcohol, ↗

REACTER: A Heuristic Method for Reactive Molecular Dynamics

REACTER (www.reacter.org) is a heuristic protocol that enables the simulation of complex reactions using atomistic molecular dynamics (MD) with a fixed-valence force field. Incorporating reactions into classical MD with this approach allows modeling of reactive systems over greatly-increased time scales, enabling systems to be modeled with MD that would not otherwise be feasible. One or more competing multi-step reactions or series of reactions can be invoked simultaneously. Special treatment can be applied to neighboring atoms to relax high energy configurations while the simulation progresses. The original version of REACTER, which was implemented in the open-source LAMMPS simulation package as fix bond/react, was only available for serial simulations. This work describes the expansion of fix bond/react for use in parallel simulations, as well as the addition of various new options, including deletion of reaction by-products, reversible reactions, and custom reaction constraints. These new capabilities are demonstrated through large-scale simulations (200,000+ atoms) of the polymerization of polystyrene and nylon 6,6. The morphologies of both polymers are analyzed after reaching >99% extent of polymerization. Finally, the newly-added reversible reactions feature is demonstrated by rupturing these highly-entangled systems under uniaxial strain by defining a chain scission reaction.

polymer simulations, molecular dynamics↗

Response of Ablative Thermal Protection Materials to Degradation in Low Earth Orbit – Characterization of Specimens from MISSE-13

The environment of low Earth orbit presents unique material interactions due to the presence of atomic oxygen and solar spectrum UV. A variety of degradation mechanisms can occur depending, in large part, on the specific material system involved. This talk will review the characterization of two ablative materials, PICA-D and HEEET, as well as relevant adhesive joints and coatings. PICA-D is a variant of the phenolic impregnated carbon ablator (PICA) and is the baseline thermal protection system (TPS) on Dragonfly and the lander for Mars Sample Return (MSR). HEEET is a 3D woven system from which MSR’s Earth entry TPS is derived. The samples for these materials were flown in orbit during the Materials International Space Station Experiment-13 (MISSE-13) which launched on March 6, 2020 and returned to Earth on January 13, 2021. Changes to surface microstructure and reflectivity will be presented along with tomographic analysis. The effect of differential erosion rates on the composites and the impacts of the orbit environment on coating performances will be discussed in the context of TPS performance and mission design aspects.

MISSE↗

Iodine - Its possible role in tropospheric photochemistry

A detailed study of the photochemistry of iodine and its oxides indicates that iodine species may play an important role in the tropospheric photochemical system. Methyl iodide, often observed in the marine troposphere with an average concentration of 5-10 ppt, is photolyzed and thereby produces I atoms. Chemical interactions with O3, HxOy, and NOx cause I to be converted to other inorganic compounds such as IO, HOI, IONO2, and I2. The production of these species and their subsequent recycling back to I can lead to the catalytic removal of tropospheric O3, the enhancement of the NO2/NO ratio, the destruction of HxOy free radicals, and the conversion of HO2 to OH. Ultimately, tropospheric inorganic iodine is removed by heterogeneous processes. Calculations using a numerical model to simulate tropospheric photochemistry indicate that iodine may have a strong impact upon the atmospheric O3-NOx-HxOy system. The magnitude of these effects is dependent upon the value of several uncertain rate constants and the primary source distributions of CH3I and other organic and inorganic iodine compounds.

Chameides, W. L.↗

Chemical colloids versus biological colloids: a comparative study for the elucidation of the mechanism of protein fiber formation

Fiber formation from murine serum amyloid A1 (SAA) was compared to the linear aggregation and fiber formation of colloidal gold particles. Here we report the similarities of these processes. Upon incubation with acetic acid, SAA misfolds and adopts a new conformation, which we termed saa. saa apparently is less soluble than SAA in aqueous solution; it aggregates and forms nucleation units and then fibers. The fibers appear as a string of the nucleation units. Additionally, an external electric field promotes saa fiber formation. These properties of saa are reminiscent of colloidal gold formation from gold ions and one-dimensional aggregation of the gold colloids. Colloidal gold particles were also found to be capable of aggregating one-dimensionally under an electric field or in the presence of polylysine. These gold fibers resembled in structure that of saa fibers. In summary, protein aggregation and formation of fibers appear to follow the generalized principles derived in colloidal science for the aggregation of atoms and molecules, including polymers such as polypeptides. The analysis of colloidal gold formation and of one-dimensional aggregation provides a simple model system for the elucidation of some aspects of protein fiber formation.

Colloids↗

Continuum Absorption Coefficient of Atoms and Ions

The rate of heat transfer to the heat shield of a Jupiter probe has been estimated to be one order of magnitude higher than any previously experienced in an outer space exploration program. More than one-third of this heat load is due to an emission of continuum radiation from atoms and ions. The existing computer code for calculating the continuum contribution to the total load utilizes a modified version of Biberman's approximate method. The continuum radiation absorption cross sections of a C - H - O - N ablation system were examined in detail. The present computer code was evaluated and updated by being compared with available exact and approximate calculations and correlations of experimental data. A detailed calculation procedure, which can be applied to other atomic species, is presented. The approximate correlations can be made to agree with the available exact and experimental data.

Armaly, B. F.↗

New results from FRECOPA analysis

New results from the ongoing analysis of the FRECOPA's (FREnch COoperative PAssive payload) system hardware are discussed. FRECOPA (AO138) was one of the 57 experiments flown on the LDEF satellite. The experiment was located on the trailing edge (Tray B3) and was exposed to UV radiation (11,100 equivalent sun hours), approximately equal to 34,000 thermal cycles, higher vacuum levels than the leading edge, a low atomic oxygen flux, and minor doses of protons and electrons. Due to LDEF's extended mission (5.8 years), CNES decided to set up a team to analyze the FRECOPA system. Initial results were presented at the First Post-Retrieval Conference, June, 1991. The results obtained since then are summarized.

Durin, Christian↗

Monte Carlo simulations of precise timekeeping in the Milstar communication satellite system

The Milstar communications satellite system will provide secure antijam communication capabilities for DOD operations into the next century. In order to accomplish this task, the Milstar system will employ precise timekeeping on its satellites and at its ground control stations. The constellation will consist of four satellites in geosynchronous orbit, each carrying a set of four rubidium (Rb) atomic clocks. Several times a day, during normal operation, the Mission Control Element (MCE) will collect timing information from the constellation, and after several days use this information to update the time and frequency of the satellite clocks. The MCE will maintain precise time with a cesium (Cs) atomic clock, synchronized to UTC(USNO) via a GPS receiver. We have developed a Monte Carlo simulation of Milstar's space segment timekeeping. The simulation includes the effects of: uplink/downlink time transfer noise; satellite crosslink time transfer noise; satellite diurnal temperature variations; satellite and ground station atomic clock noise; and also quantization limits regarding satellite time and frequency corrections. The Monte Carlo simulation capability has proven to be an invaluable tool in assessing the performance characteristics of various timekeeping algorithms proposed for Milstar, and also in highlighting the timekeeping capabilities of the system. Here, we provide a brief overview of the basic Milstar timekeeping architecture as it is presently envisioned. We then describe the Monte Carlo simulation of space segment timekeeping, and provide examples of the simulation's efficacy in resolving timekeeping issues.

Camparo, James C.↗

Observation of Lyman-alpha emission in interplanetary space

The extraterrestrial Lyman-alpha emission was mapped by the OGO 5 satellite, when it was outside the geocorona. Three maps, obtained at different periods of the year, are presented and analyzed. The results suggest that at least half of the emission takes place in the solar system, and give strong support to the theory that in its motion toward the apex, the sun crosses neutral atomic hydrogen of interstellar origin, giving rise to an apparent interstellar wind.

Bertaux, J. L.↗

Quasars as very-accurate clock synchronizers

Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks.

Hurd, W. J.↗

The 1981 NASA ASEE Summer Faculty Fellowship Program, volume 2

A collection of papers on miscellaneous subjects in aerospace research is presented. Topics discussed are: (1) Langmuir probe theory and the problem of anisotropic collection; (2) anthropometric program analysis of reach and body movement; (3) analysis of IV characteristics of negatively biased panels in a magnetoplasma; (4) analytic solution to classical two body drag problem; (5) fast variable step size integration algorithm for computer simulations of physiological systems; (6) spectroscopic experimental computer assisted empirical model for the production of energetics of excited oxygen molecules formed by atom recombination shuttle tile surfaces; and (7) capillary priming characteristics of dual passage heat pipe in zero-g.

Robertson, N. G.↗

The Jovian ammonia abundance from interferometric observations of limb darkening at 3.4 mm

The relative abundances of the various atomic and molecular constituents in the Jovian atmosphere are important data for studies of the origin of the solar system. The determination of the ammonia abundance presents a number of difficulties. However, difficulties related to a use of the microwave sensing technique can be largely overcome by measuring the brightness distribution across the disk. In particular, information about the atmosphere can be obtained from the degree of limb darkening, which requires only a relative brightness measurement as opposed to an absolute measurement. Valdes and Welch (1978) have used the considered approach in a study of Jupiter at 1.3 cm. In the present investigation a more general relation between the amount of limb darkening in the broad 1.25-cm inversion band of ammonia and the ammonia abundance is derived. The model is applied to new measurements of Jupiter's limb darkening at 3.4 mm.

Valdes, F.↗

High-voltage spark atomic emission detector for gas chromatography

A dc-powered, double-gap, miniature nanosecond spark source for emission spectrochemical analysis of gas chromatographic effluents is described. The spark is formed between two thoriated tungsten electrodes by the discharge of a coaxial capacitor. The spark detector is coupled to the gas chromatograph by a heated transfer line. The gas chromatographic effluent is introduced into the heated spark chamber where atomization and excitation of the effluent occurs upon breakdown of the analytical gap. A microcomputer-controlled data acquisition system allows the implementation of time-resolution techniques to distinguish between the analyte emission and the background continuum produced by the spark discharge. Multiple sparks are computer averaged to improve the signal-to-noise ratio. The application of the spark detector for element-selective detection of metals and nonmetals is reported.

Calkin, C. L.↗

Effect of an oxygen plasma on uncoated thin aluminum reflecting films

Thin aluminum films were considered for use as a reflective surface for solar collectors on orbiting solar dynamic power systems. A matter of concern is the durability of such reflective coatings against oxidative attack by highly reactive neutral atomic oxygen, which is the predominate chemical specie in low Earth orbit. Research to date was aimed at evaluating the protective merit of thin dielectric coatings over the aluminum or other reflective metals. However, an uncoated aluminum reflector may self-protect by virtue of the oxide formed from its exposed surface, which constitutes a physical barrier to further oxidation. This possibility was investigated, and an attempt was made to characterize the effects of atomic oxygen on thin Al films using photomicrographs, scanning electron microscopy, spectrophotometry, Auger analysis, and mass measurements. Data collected in a parallel effort is discussed for its comparative value. The results of the investigation of uncoated aluminum supported the self-protection hypothesis, and importantly, it was found that long term specular reflectance for uncoated aluminum exceeded that of Al and Ag reflectors with dielectric coatings.

Parsons, Roger L.↗

Comparison of vibration dissociation coupling and radiative heat transfer models for AOTV/AFE flowfields

A series of detailed studies comparing various vibration dissociation coupling models, reaction systems and rates, and radiative heating models has been conducted for the nonequilibrium stagnation region of an AFE/AOTV vehicle. Atomic and molecular nonequilibrium radiation correction factors have been developed and applied to various absorption coefficient step models, and a modified vibration dissociation coupling model has been shown to yield good vibration/electronic temperature and concentration profiles. While results indicate sensitivity to the choice of vibration dissociation coupling model and to the nitrogen electron impact ionization rate, by proper combinations accurate flowfield and radiative heating results can be obtained. These results indicate that nonequilibrium effects significantly affect the flowfield and the radiative heat transfer. However, additional work is needed in ionization chemistry and absorption coefficient modeling.

Carlson, Leland A.↗