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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 109 records · Page 6

A ray tracing model for leaf bidirectional scattering studies

A leaf is modeled as a deterministic two-dimensional structure consisting of a network of circular arcs designed to represent the internal morphology of major species. The path of an individual ray through the leaf is computed using geometric optics. At each intersection of the ray with an arc, the specular reflected and transmitted rays are calculated according to the Snell and Fresnel equations. Diffuse scattering is treated according to Lambert's law. Absorption is also permitted but requires a detailed knowledge of the spectral attenuation coefficients. An ensemble of initial rays are chosen for each incident direction with the initial intersection points on the leaf surface selected randomly. The final equilibrium state after all interactions then yields the leaf bidirectional reflectance and transmittance distributions. The model also yields the internal two dimensional light gradient profile of the leaf.

Brakke, T. W.↗

Contamination of grazing incidence EUV mirrors - An assessment

Contamination assessment for space optical systems requires an understanding of the sensitivity of component performance, e.g. mirror reflectance, to materials deposited on the mirror surface. In a previous study, the sensitivity of typical normal incidence mirror coatings to surface deposits of generic hydrocarbons was reported. Recent activity in the development of grazing incidence telescopes for extreme ultraviolet space astronomy has stimulated the need for a similar assessment in the spectral region extending from approximately 100 A to 1000 A. The model used for analysis treats the contamination layer as a continuous thin film deposited on the mirror surface. The mirror surfaces selected for this study are opaque vacuum deposited gold and the uncoated and polished Zerodur. Scatter caused by film irregularities or particulates are not included in this assessment. Parametric evaluations at 100, 500, and 1000 A determine the sensitivity of mirror reflectance to a range of optical constants selected for the generic contaminants. This sensitivity analysis combined with the limited amount of optical data in the EUV for hydrocarbons, is used to select representative optical constants for the three wavelength regions. Reflectance versus contamination layer thickness curves are then calculated and used to determine critical thickness limits based on allowable reflectance change. Initial observations indicate that thickness limits will be highly dependent on the real part of the complex index of refraction of the contaminant film being less than 1.0. Preliminary laboratory measurements of samples contaminated with some commonly encountered hydrocarbons confirm trends indicated in the analytical studies.

Osantowski, John F.↗

Mars rover sample return missions

An important intermediate step in the path to human exploration of Mars is the accomplishment of a mission which lands an unmanned rover on the Martian surface, selects and collects various samples of the terrain and atmosphere, and returns them to earth for analysis. Such a mission is being developed under the management of NASA's JPL and the Johnson Space Center. The concepts for a wide range of rover capabilities are studied and an assessment of the driving technological developments required to implement these capabilities is made.

Cunningham, Glenn E.↗

Designs for the ATDRSS tri-band reflector antenna

Two approaches to design a tri-band reflector antenna for the Advanced TDRSS are examined. Two reflector antenna configurations utilizing frequency selective surfaces for operation in three frequency bands, S, Ku, and Ka, are proposed. Far-field patterns and the antenna feed losses were computed for each configuration. An offset-fed single reflector antenna configuration was adapted for conceptual spacecraft design. CADAM drawings were completed and a 1/13th scale model of the spacecraft was constructed.

Lee, Shung-Wu↗

Single-screen triband FSS with double-square-loop elements

A single-screen double-square-loop (DSL) frequency selective surface (FSS) has been developed to multiplex the three frequency (S, X, and Ku) bands for NASA's CRAF/CASSINI mission. This triband DSL FSS reflects the X-band (7.2 and 8.4 GHz) waves and transmits the S-band (2.3 GHz) and the Ku-band (13.8 GHz) waves. A good agreement between predicted and measured transmission performance is found on a 0.001-in.-thick Kapton with/without a flat Kevlar honeycomb sandwich panel. It is found that the single-screen DSL FSS with/without the Kevlar honeycomb has a resonant frequency of 8.4 GHz for incident angle steered from normal to 45 deg and for both TE and TM polarizations.

Wu, T. K.↗

Environmental interactions and the SP-100 power system

Interactions of the SP-100 power system with its expected ambient environments are defined. SP-100 payloads will float 100 V negative of the low Earth orbit (LEO) plasma. Choice of proper geometries and materials will prevent arcing at conductor-insulator junctions in LEO. Care in selecting surface coatings will prevent dielectric breakdown. Sputtering is a concern for long-duration LEO missions. Atomic oxygen durability of SP-100 materials will be tested in ground and flight tests. Evaluation of SP-100 in lunar and planetary environments has begun. The report of a recent workshop on Chemical and Electrical Interactions on Mars identified many of the primary interactions.

Ferguson, Dale C.↗

Theoretical and experimental investigation of a rectenna element for microwave power transmission

A microstrip measurement system has been designed to analyze packaged GaAs Schottky barrier diodes under small and large signal conditions. The nonlinear equivalent circuit parameters of the diode are determined using a small signal test method that analyzes the diode's scattering parameters at various bias levels. The experimental results of a 2.45 GHz diode are verified using a nonlinear circuit simulation program based on a multireflection algorithm. A 35 GHz rectenna has been built using a microstrip patch antenna and Ka-band mixer diode. The measured efficiency was 29 percent at 120 mW input power. A frequency selective surface is designed using an equivalent circuit model to reduce the second harmonic radiations for a 2.45 GHz rectenna. Theoretical results are found to be in fairly good agreement with experiments.

Mcspadden, James O.↗

Evaluation of frequency-selective reflector antenna systems

The performance of a four-frequency (S/X/Ku/Ku bands) frequency-selective surface (FSS) with double-ring elements (the type of geometry particularly well suited for the circular polarization requirement of the NASA's Cassini project) is evaluated for a planar and a curved FSS subreflector in a dual reflector antenna system. Good agreement is obtained between the calculated and measured data for the planar FSS model. The FSS effects in a four-frequency Cassegrain reflector antenna were accurately evaluated by taking into account the surface curvature and the FSS subreflector's transmitted/reflected field variation as functions of the polarization and the incident angles with respect to the local coordinates.

Wu, T. K.↗

Diffraction analysis of frequency selective reflector antennas

In this paper, a unified computational technique is presented which allows the incorporation of the curved frequency-selective surface (FSS) geometry in the computation of the reflector antenna radiation pattern. The scattered fields from an illuminated FSS reflector are formalized using Huygens' principle in such a way that the 'reflecting' and the 'transparent' FSS subreflector cases are treated identically and the thickness of the FSS subreflector remains arbitrary. The analysis utilizes local surface coordinates to describe the reflection/transmission matrices of the FSS subreflector where it is assumed that these matrices are available. In most cases one may use the local tangent plane for approximating the plane of the FSS in the local coordinate surface of the reflector. The paper demonstrates how the local curved coordinate system can be introduced in the diffraction modeling of FSS reflectors and its importance in accurately predicting the side-lobe and crosspolarization levels. Results of numerical simulations are presented for several FSS subreflector configurations.

Rahmat-Samii, Yahya↗

Antennas and Propagation; Proceedings of the International Conference, 8th, Heriot-Watt Univeristy, Edinburgh, UK, Mar. 30 - Apr. 2, 1993. Vols. 1 & 2

Conference papers from sessions on the following topics are presented: satellite antennas; modal analysis of transmission line structures; fading and scintillation; microcellular; numerical analysis; Olympus; indoor mobile; mechanical aspects of satellite antennas; flat plate and printed antennas; fade counter measures; electromagnetic theory; feeds for satellites; antennas for personal communications; frequency selected surfaces; remote sensing; active patch antennas; antenna measurements; clear air/trans horizon; high frequency system and noise; rain attenuation and rain scatter; and high frequency direction finding.

Source record↗

Efficient finite element simulation of slot spirals, slot radomes and microwave structures

This progress report contains the following two documents: (1) 'Efficient Finite Element Simulation of Slot Antennas using Prismatic Elements' - A hybrid finite element-boundary integral (FE-BI) simulation technique is discussed to treat narrow slot antennas etched on a planar platform. Specifically, the prismatic elements are used to reduce the redundant sampling rates and ease the mesh generation process. Numerical results for an antenna slot and frequency selective surfaces are presented to demonstrate the validity and capability of the technique; and (2) 'Application and Design Guidelines of the PML Absorber for Finite Element Simulations of Microwave Packages' - The recently introduced perfectly matched layer (PML) uniaxial absorber for frequency domain finite element simulations has several advantages. In this paper we present the application of PML for microwave circuit simulations along with design guidelines to obtain a desired level of absorption. Different feeding techniques are also investigated for improved accuracy.

Gong, J.↗

Computer Game

Using NASA studies of advanced lunar exploration and colonization, KDT Industries, Inc. and Wesson International have developed MOONBASE, a computer game. The player, or team commander, must build and operate a lunar base using NASA technology. He has 10 years to explore the surface, select a site and assemble structures brought from Earth into an efficient base. The game was introduced in 1991 by Texas Space Grant Consortium.

Source record↗

Hummingbird Comet Nucleus Analysis Mission

Hummingbird is a highly focused scientific mission, proposed to NASA s Discovery Program, designed to address the highest priority questions in cometary science-that of the chemical composition of the cometary nucleus. After rendezvous with the comet, Hummingbird would first methodically image and map the comet, then collect and analyze dust, ice and gases from the cometary atmosphere to enrich characterization of the comet and support landing site selection. Then, like its namesake, Hummingbird would carefully descend to a pre-selected surface site obtaining a high-resolution image, gather a surface material sample, acquire surface temperature and then immediately return to orbit for detailed chemical and elemental analyses followed by a high resolution post-sampling image of the site. Hummingbird s analytical laboratory contains instrumentation for a comprehensive molecular and elemental analysis of the cometary nucleus as well as an innovative surface sample acquisition device.

Kojiro, Daniel↗

Dichroic Design for the Orbiting VLBI Earth Station Antenna

In this paper the design and performance of a single screen frequency selective surface with gridded square loop patch elements are described for diplexing the X-and Ku-band signals in an Orbiting Very Long Baseline Interferometer (OVLBI) earth station reflector antenna system.

gridded square element resonant frequency drift Or↗

Entry, Descent, and Landing Mission Design for the Crew Exploration Vehicle Thermal Protection System Qualification Flight Test

The TORCH team was challenged to generate the lowest cost mission design solution that meets the CEV aerothermal test objectives on a sub-scale flight article. The test objectives resulted from producing representative lunar return missions and observing the aerothermal envelopes of select surface locations on the CEV. From these aerothermal envelopes, two test boxes were established: one for high shear and one for high radiation. The unique and challenging trajectory design objective for the flight test was to fly through these aerothermal boxes in shear, pressure, heat flux, and radiation while also not over testing. These test boxes, and the max aerothermal limits, became the driving requirements for defining the mission design.

Ivanov, Mark↗

Effects of Space Flight on Neutrophil Functions in Astronauts

Neutrophil phagocytosis, oxidative burst, degranulation, and the expression of selected surface markers were studied in 25 astronauts following 4 space shuttle missions. Space flight duration ranged from 5 to 11 days. Blood specimens were obtained 10 days before launch, immediately after landing, and again at 3 days after landing. The number of neutrophils increased at landing by 85%. Phagocytosis of Escherichia coli (E. coli) and oxidative burst following the medium length (9 to 11 days) missions were lower than the control mean values. Whereas, following the short-duration (5 days) mission, these functions were unchanged from control values. No consistent changes in degranulation were observed following either short or medium length space missions. The expression of CD16, CD32, CD11a, CD11b, CD11c, L-selectin and CD36 were measured and found to be variable. Specifically, CD16 and CD32 did not correlate with the changes in oxidative burst. Mission duration appears to be a factor in phagocytic and oxidative functions.

Kaur, Indreshpal↗

GeoLab in NASA's Pressurized Excursion Module: First Results from the 2010 Field Trials

Before humans explore other planets, NASA must develop advanced techniques for collection, preservation and return of unique extraterrestrial samples. To help evaluate hardware requirements and operational concepts for future sample-return missions, we designed and built GeoLab our first generation lab for geological samples into NASA s Habitat Demonstration Unit in the Pressurized Excursion Module (HDU1-PEM). The center of GeoLab is a glovebox for the examination of samples in a shirt-sleeve environment. As part of a deployable habitat, GeoLab can participate in NASA s analog missions that simulate planetary exploration activities and support the testing of relevant technologies for collecting and handling geological samples. Over time, these tests will evaluate sample handling environments (field and lab), sampling tools and analytical instruments, and different scenarios involving both robotic and human procedures. The GeoLab design supports evolving tests and configurations. The glovebox is mounted on the habitat bulkhead, with three sample pass-though chambers that allow for direct sample transfer into the glovebox from the outside. The glovebox design and construction (low-particle shedding, minimally off-gassing materials) provides a clean environment to reduce sample contamination; in the future, we will integrate a positive pressure, enriched nitrogen atmosphere. The glovebox is equipped with configurable instrument ports. The 2010 test included a mass balance, a stereomicroscope with a HD camera for detailed imaging of samples, and a handheld XRF analyzer for preliminary geochemical characterization of samples. Network cameras provided context imagery and sample handling activities. We present early results from the initial field trial of GeoLab during the 2010 Desert Research and Technology Studies (D-RATS) planetary analog test near Flagstaff AZ. The 2010 D-RATS mission involved two rovers, the habitat with GeoLab, four crew members, and a team of scientists and flight controllers. The crewed rovers conducted geological traverses and collected samples on the planetary surface. Selected samples were transferred into GeoLab for detailed examination and initial analysis, providing critical data to the science team for evaluation and prioritization of samples.

Evans, Cynthia A.↗

Non-Uniform Bias Enhancement of a Varactor-Tuned FSS used with a Low Profile 2.4 GHz Dipole Antenna

In this paper a low profile antenna using a nonuniformly biased varactor-tuned frequency selective surface (FSS) is presented. The tunable FSS avoids the use of vias and has a simplified DC bias network. The voltages to the DC bias ports can be varied independently allowing adjustment in the frequency response and enhanced radiation properties. The measured data demonstrate tunability from 2.15 GHz to 2.63 GHz with peak efficiencies that range from 50% to 90% and instantaneous bandwidths of 50 MHz to 280 MHz within the tuning range. The total antenna thickness is approximately lambda/45.

Cure, David↗