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At least 1,063 records · Page 59
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NASA NTRS2003

Oversight and Development of a Community Monte Carlo Radiative Transfer Model

Under this grant we have developed a Monte Carlo radiative transfer code that will act as the nucleus for the 13RC Community Monte Carlo Model. All code is written in ANSI-compliant Fortran-95. Many modules define public type and procedures to manipulate them, but do not allow access to the type's internal components. This allows each module to do its own exhaustive error checking up-front, then proceed in a streamlined way. Many modules can read and write the state of their objects to persistent files. The code has been tested on a Macintosh running OS 10.2.4 and the Absoft Fortran compiler, and on Sun UltraSparcs running Solaris 5.8 and Forte V8 compilers. The code exposed bugs in the Intel Fortran Compiler (ifc) on the 13RC Linux host, and we are waiting for a resolution of these bugs before finished the port. the code base is under CVS versions control. The code base consists of the core code (nine modules providing the infrastructure), example integrators, and a suite of utilities and examples.

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NASA NTRS2002

Isothermal Calorimetric Observations of the Affect of Welding on Compatibility of Stainless Steels with High-Test Hydrogen Peroxide Propellant

Compatibility is determined by the surface area, the chemical constituency and the surface finish of a material. In this investigation exposed area is obviously not a factor as the welded samples had a slightly smaller surface than the unwelded, but were more reactive. The chemical makeup of welded CRES 316L and welded CRES 304L have been observed in the literature to change from the parent material as chromium and iron are segregated in zones. In particular, the ratio of chromium to iron in CRES 316L increased from 0.260 to 0.79 in the heat affected zone (HAZ) of the weld and to 1.52 in the weld bead itself. In CRES 304L the ratio of chromium to iron increased from 0.280 to 0.44 in the HAZ and to 0.33 in the weld bead. It is possible that the increased reactivity of the welded samples and of those welded without purge gas is due to this segregation phenomenon. Likewise the reactivity increased in keeping with the greater roughness of the welded and welded without purge gas samples. Therefore enhanced roughness may also be responsible for the increased reactivity.

Gostowski, Rudy C.↗
NASA NTRS2003

Design Through Manufacturing: The Solid Model - Finite Element Analysis Interface

State-of-the-art computer aided design (CAD) presently affords engineers the opportunity to create solid models of machine parts which reflect every detail of the finished product. Ideally, these models should fulfill two very important functions: (1) they must provide numerical control information for automated manufacturing of precision parts, and (2) they must enable analysts to easily evaluate the stress levels (using finite element analysis - FEA) for all structurally significant parts used in space missions. Today's state-of-the-art CAD programs perform function (1) very well, providing an excellent model for precision manufacturing. But they do not provide a straightforward and simple means of automating the translation from CAD to FEA models, especially for aircraft-type structures. The research performed during the fellowship period investigated the transition process from the solid CAD model to the FEA stress analysis model with the final goal of creating an automatic interface between the two. During the period of the fellowship a detailed multi-year program for the development of such an interface was created. The ultimate goal of this program will be the development of a fully parameterized automatic ProE/FEA translator for parts and assemblies, with the incorporation of data base management into the solution, and ultimately including computational fluid dynamics and thermal modeling in the interface.

Rubin, Carol↗
NASA NTRS2003

Helium Cryo Testing of a SLMS(TM) (Silicon Lightweight Mirrors) Athermal Optical Assembly

SLMS (TM) a thermal technology has been demonstrated in the small 4-foot helium cryogenic test chamber located at the NASA/MSFC X-Ray Calibration Facility (XRCF). A SLMS (TM) Ultraviolet Demonstrator Mirror (UVDM) produced by Schafer under a NASA/MSFC Phase I SBIR was helium cryo tested both free standing and bonded to a Schafer designed prototype carbon fiber reinforced silicon carbide (Cesic) mount. Surface figure data was obtained with a test measurement system that featured an Instantaneous Phase Interferometer (IPI) by ADE Phase Shift. The test measurement system s minimum resolvable differential figure deformation and possible contributions from test chamber ambient to cryo window deformation are under investigation. The free standing results showed differential figure deformation of 10.4 nm rms from 295K to 27K and 3.9 nm rms after one cryo cycle. The surface figure of the UVDM degraded by lambda/70 rms HeNe once it was bonded to the prototype Cesic mount. The change was due to a small astigmatic aberration in the rototype Cesic mount due to lack of finish machining and not the bonding technique. This effect was seen in SLMST (TM) optical assembly results, which showed differential figure deformation of 46.5 nm rms from 294K to 27K, 42.9 nm rms from 294K to 77K, 28.0 nm rms from 294K to 193K and 6.2 nm rms after one cryo cycle.

Jacoby, Marc T.↗
NASA NTRS2003

AM03-AM121-115 Hard X-Ray Optics Development at MSFC

We have developed the electroformed-nickel replication process to enable us to fabricate light-weight hard-x-ray region. Two projects currently utilizing this technology are the production of over 250 r from 5 to 10 cm, for our HERO balloon payload, and 15- and 23-cm-diameter shells for a prototype module. The challenge for the former is to fabricate, mount, align and fly a large number of high-r constraints of a modest budget. For the latter, the challenge is to maintain high angular resolution shell thicknesses (100 micron) which make the shells extremely sensitive to electroforming stresses process does not degrade the ultra-smooth surface finish (approx. 3 A required for eventual multilayer c on these two programs.

Ramsey, Brian↗
NASA NTRS2003

Development of a 1K x 1K GaAs QWIP Far IR Imaging Array

In the on-going evolution of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have developed a 1,024 x 1,024 (1K x1K), 8.4-9 microns infrared focal plane array (FPA). This 1 megapixel detector array is a hybrid using the Rockwell TCM 8050 silicon readout integrated circuit (ROIC) bump bonded to a GaAs QWIP array fabricated jointly by engineers at the Goddard Space Flight Center (GSFC) and the Army Research Laboratory (ARL). The finished hybrid is thinned at the Jet Propulsion Lab. Prior to this development the largest format array was a 512 x 640 FPA. We have integrated the 1K x 1K array into an imaging camera system and performed tests over the 40K-90K temperature range achieving BLIP performance at an operating temperature of 76K (f/2 camera system). The GaAs array is relatively easy to fabricate once the superlattice structure of the quantum wells has been defined and grown. The overall arrays costs are currently dominated by the costs associated with the silicon readout since the GaAs array fabrication is based on high yield, well-established GaAs processing capabilities. In this paper we will present the first results of our 1K x 1K QWIP array development including fabrication methodology, test data and our imaging results.

Jhabvala, M.↗
NASA NTRS2003

Home Insulation With the Stroke of a Brush

Hy-Tech Thermal Solutions, LLC, of Melbourne, Florida, is producing a very complex blend of ceramic vacuum-filled refractory products designed to minimize the path of hot air transfer through ceilings, walls, and roofs. The insulating ceramic technology blocks the transfer of heat outward when applied to paint on interior walls and ceilings, and prevents the transfer of heat inward when used to paint exterior walls and roofs, effectively providing year-round comfort in the home. As a manufacturer and marketer of thermal solutions for residential, commercial, and industrial applications, Hy-Tech Thermal Solutions attributes its success to the high performance insulating ceramic microsphere originally developed from NASA thermal research at Ames Research Center. Shaped like a hollow ball so small that it looks as if it is a single grain of flour to the naked eye (slightly thicker than a human hair), the microsphere is noncombustible and fairly chemical-resistant, and has a wall thickness about 1/10 of the sphere diameter, a compressive strength of about 4,000 pounds per square inch, and a softening point of about 1,800 C. Hy-Tech Thermal Solutions improved upon these properties by removing all of the gas inside and creating a vacuum. In effect, a 'mini thermos bottle' is produced, acting as a barrier to heat by reflecting it away from the protected surface. When these microspheres are combined with other materials, they enhance the thermal resistance of those materials. In bulk, the tiny ceramic 'beads' have the appearance of a fine talcum powder. Their inert, nontoxic properties allow them to mix easily into any type of paint, coating, adhesive, masonry, or drywall finish. Additionally, their roundness causes them to behave like ball bearings, rolling upon each other, and letting the coatings flow smoothly. When applied like paint to a wall or roof, the microsphere coating shrinks down tight and creates a dense film of the vacuum cells. The resulting ceramic layer improves fire resistance, protects from ultraviolet rays, repels insects such as termites, and shields from the destructive forces of nature.

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NASA NTRS2003

Soft X-Ray Observations of the Galactic Halo

In this project, my co-I (K.D. Kuntz) and I plan to extract the soft X-ray spectrum emitted by the hot gas along a high latitude line of sight. We plan to subtract off the local component (garnered from other observations) in order to isolate the halo component. We then plan to combine this spectral information with the ultraviolet resonance line emission produced by slightly cooler gas along the line of sight and use the two observations as a constraint on models. My co-I, K.D., Kuntz has been working on the determination of the instrumental background. I have not yet drawn any of the funds for this project. I have just moved from J h s Hopkins University to the University of Georgia and anticipate finishing the project while at the University of Georgia.

Shelton, Robin↗
NASA NTRS2003

Ceramic Strain Gages for Use at Temperatures up to 1500 Celsius

Indium-tin-oxide (ITO) thin film strain gages were successfully demonstrated at temperatures beyond 1500 C. High temperature static strain tests revealed that the piezoresistive response and electrical stability of the ceramic sensors depended on the thickness of the ITO films comprising the active strain elements. When 2.5 microns-thick ITO films were employed as the active strain elements, the piezoresistive response became unstable at temperatures above 1225 C. In contrast to this, ceramic sensors prepared with 5 microns-thick ITO were stable beyond 1430 C and sensors prepared with 8 microns-thick ITO survived more than 20 hr of operation at 1481 C. Very thick (10 microns) ITo strain gages were extremely stable and responsive at 1528 C. ESCA depth profiles confirmed that an interfacial reaction between the ITO strain gage and alumina substrate was responsible for the high temperature electrical stability observed. Similar improvements in high temperature stability were achieved by doping the active ITO strain elements with aluminum. Several Sic-Sic CMC constant strain beams were instrumented with ITO strain gages and delivered to NASA for testing. Due to the extreme surface roughness of the CMC substrates, new lithography techniques and surface preparation methods were developed. These techniques relied heavily on a combination of Sic and A12O3 cement layers to provide the necessary surface finish for efficient pattern transfer. Micro-contact printing using soft lithography and PDMS stamps was also used to successfully transfer the thin film strain gage patterns to the resist coated CMC substrates. This latter approach has considerable potential for transferring the thin film strain gage patterns to the extremely rough surfaces associated with the CMC's.

Gregory, Otto↗
NASA NTRS2003

Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films

A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.

Roberts, F. E.↗
NASA NTRS2003

ASK Talks with Dennis Grounds

Dennis Grounds recently finished a one-year assignment at NASA Headquarters in the Office of Bioastronautics as the Acting Flight Program Manager He has returned to Johnson Space Center (JSC), where he is Director of the International Space Station Bioastronautics Research Program Office with the NASA Life Sciences Projects Division. Under his management, the Human Research Facility (HRF) was developed to support a broad range of scientific investigations pertaining to human adaptation to the spaceflight environment and issues of human space exploration. The HRF rack was developed to international standards in order to be compatible with payloads developed anywhere in the world, thereby streamlining the process of getting payloads on the Space Station. Grounds has worked with NASA for more than 15 years. Prior to joining ISS, he worked with General Electric as a manager of payloads and analysis in support of the NASA Life Science Projects Division at JSC. ASK spoke with Grounds in Washington, D.C., during his Headquarters assignment.

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NASA NTRS2003

SLMS(Trademark) Athermal Technology for UV and Cryogenic Applications

SLMS (Trademark) Technology with an areal density of 5-10 kg/square meter has demonstrated exceptional figure accuracy (as low as 0.005 waves rms HeNe) and surface finish (less than 3 Angstroms rms) for Ultraviolet and Extreme Ultraviolet Imaging Applications, with dimensional stability of approx. 6 nm rms from 300 K to 27 K for Cryogenic Tests performed at NASA MSFC XRCF. This talk describes results of Phase I and Phase II SBIR work for both NASA and the Air Force.

Goodman, William A.↗
NASA NTRS2003

Ultra-Lightweight Borosilicate Gas-Fusion Mirror for Cryogenic Testing

Hextek Corporation fabricated a 250 mm diameter ultra-lightweight borosilicate mirror substrate for cryogenic testing at NASA MSFC XRCF facility in Huntsville AL under contract# H-34475D. The objectives of the program were to demonstrate that the Hextek Gas-Fusion technology is capable of meeting the 15kg/sq m areal density target required for future space missions, and to provide a demonstration substrate for NASA MSFC to finish and test at cryogenic temperature. This presentation reviews company background and capabilities, features and benefits of the Gas-Fusion technology, historical data on cryogenic performance of borosilicate glass showing near zero cte at 30-35 degrees Kelvin, design and fabrication results of the 250 mm 15kg/sq m areal density substrate, and finally, projected scaling, lightweighing and fabrication lead-times for meter class segments.

Voevodsky, Michael↗
NASA NTRS2004

[Calibration, Analysis, and Interpretation of SERTS and EUNIS Observation]

We have made satisfactory and expected progress in the first year of this project. The spectrophotometric data for the S asteroids of interest have been reduced, and lightcurve effects accounted for. We have begun mixing models for spectra of 6 Hebe, and expect to have a publication late in 2004 or early in 2005 on that part of the project. Preliminary models suggest that Hebe requires hydrated minerals to explain its spectrum in the 3-pm region. We will also perform mixing models with additional data which has been recently obtained. We have been able to constrain thermal properties on near-Earth asteroids (NEAs) as a result of thermal modeling done as part of this project. This work provides a means of obtaining albedo data from common visible-near IR data. This portion of the project has been presented at the DPS meeting in Monterey, and is being presented in expanded form at the Yarkovsky workshop at Arecibo Observatory in February. A manuscript is in preparation. In the coming year we expect to finish the thermal corrections for the spectrophotometric data, and complete the mixing models. The results will be prepared for publication, and the data offered to the PDS. It will also be available on the SMASS website (smass.mit.edu), for which the PI is webmaster.

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NASA NTRS2003

Stochastic Mixing Model with Power Law Decay of Variance

Here we present a simple stochastic mixing model based on the law of large numbers (LLN). The reason why the LLN is involved in our formulation of the mixing problem is that the random conserved scalar c = c(t,x(t)) appears to behave as a sample mean. It converges to the mean value mu, while the variance sigma(sup 2)(sub c) (t) decays approximately as t(exp -1). Since the variance of the scalar decays faster than a sample mean (typically is greater than unity), we will introduce some non-linear modifications into the corresponding pdf-equation. The main idea is to develop a robust model which is independent from restrictive assumptions about the shape of the pdf. The remainder of this paper is organized as follows. In Section 2 we derive the integral equation from a stochastic difference equation describing the evolution of the pdf of a passive scalar in time. The stochastic difference equation introduces an exchange rate gamma(sub n) which we model in a first step as a deterministic function. In a second step, we generalize gamma(sub n) as a stochastic variable taking fluctuations in the inhomogeneous environment into account. In Section 3 we solve the non-linear integral equation numerically and analyze the influence of the different parameters on the decay rate. The paper finishes with a conclusion.

Fedotov, S.↗
NASA NTRS2004

The Star Formation History of Orion and its Environs

During this period of performance, we have obtained the following observations and carried out the analysis of the Orion associations itemized below. 1. Quest Optical Photometry: The photometric survey carries out with the Quest camera is finished. The strips at declinations +1 degree and -1 degree have already been processed. Photometry for a total of around 400,000 stars was obtained in these two strips with the Quest camera pipeline. Around 24,000 variables were picked out of this total by our variability software. Of these, around 2,500 stars fall above the main sequence and so were picked as candidates for spectroscopic follow-up. 2. Slit spectroscopy of bright candidates: Spectra for some 800 candidate PMS stars were obtained with the FAST spectrograph at the SAO 1.5m telescope in Mt. Hopkins. The spectra are being analyzed; 300 stars have been confirmed as young. 3. Multifiber spectroscopy: The first test of the multifiber spectrograph Hectoechelle were carried out in December 2003. One field of the Orion Nebula Cluster was observed with Hectochelle at three wavelength settings. A total of 157 spectra were obtained. Of these, 63 stars have been confirmed as Classical T Tauri stars, and 36 additional stars need further follow up. A paper is in preparation. 4. UBVRI photometry: We were granted time with the 4-shooter CCD Mosaic Camera at the SAO 1.2m telescope, to obtain UBVRI photometry of a subset of 53 newly identified T Tauri stars in the strips centered at DEC=-1 and +l. This sample is composed of strong Halpha emitting PMS stars (Classical T Tauri stars) located mostly in the Orion OB l b association, around the Orion Belt area. We have estimated mass accretion rates for 22 for these stars using the U photometry and the calibration of Gullbring et al. (1998), and found it to be similar to that of young stars in associations of similar age. 5. Near and mid-IR photometry: During the winter of 2003, we used the IR Camera on the SAO 1.2m telescope, to obtain L- band photometry of a set of the newly identified Orion OB l a and l b stars, in order to look for IR excess emission coming from the hotter inner parts of circumstellar disks. These data is being combined with the GEMINI/OSCIR 10 micron photometry obtained during 2002 and the mass accretion rates to determine the properties of disks in Ori lb. A paper is presently on preparation.

Calvet, Nuria↗
NASA NTRS2003

New ISTP Solar Max: A Multi-Spacecraft Study of the Flow of Ionospheric Plasma

The unique instrumentation on the Polar satellite combined with the simultaneous measurement of different parts of the magnetosphere with multiple satellites make possible the study of magnetospheric processes in a special way. In particular, the study of the ionospheric supply of plasma to the magnetosphere can by accomplished to give important results on the plasmas which drive the dynamics of the magnetosphere. This study concentrated on the period of September to December, 2001 in which the Polar orbit had precessed to the point that the line of apsides was near the equatorial plane. This unique orbital configuration enabled the TIDE instrument to measure outflowing ions across the polar cap and then transit the magnetotail lobes and observe the dramatic change in plasma characteristics as the satellite entered the plasma sheet. Contact was made with investigators on the Cluster and Geotail satellite missions and corresponding time frames were studied in the data. There were two approximate conjunctions between Polar and Geotail and data were compared to look for features which might be related. The higher energy concentration of the Geotail instrument made direct comparisons with TIDE difficult, and the Cluster measurements did not surface any cases that corresponded closely in space and time. There were, however, many interesting aspects of the Polar orbits which permitted the observation of the changing ionospheric outflowing plasma characteristics. As in earlier measurements, the ionospheric plasma could be seen flowing up the magnetic field lines out of the northern and southern polar caps. Its energy suggested a polar wind origin energized by the centrifugal acceleration of flow through the polar cusp. The roughly 10eV ions then moved out into the lobes of the magnetotail where they could be seen flowing toward the plasma sheet in both the northern and southern magnetotail lobes. There was also a double field-aligned region of warm ions observed just outside the plasmasphere, stretching toward the auroral zone and inner plasma sheet boundary. Upon entering the plasma sheet, the plasma energy jumped from 10 s of eV to greater than 1 keV. The single field aligned flows transitioned to highly variable spatially choppy energized ion distributions with a variety of pitch angle configurations. This pattern was quite repeatable in all of the Polar orbits that were examined and are compatible with the source of ions being the polar wind which is then energized to 10 s of eV by the centrifugal acceleration. These modestly energized polar wind ions are then carried to the magnetotail where they are substantially energized by the curvature drift-induced movement across the cross-tail potential of the magnetotail. This latter drift energizes the ions to the energies typically found in the plasma sheet. Subsequent drift and energization can cause the ions to become part of the ring current. The results of this study were presented at the Spring AGU meeting in 2002 and the GEM meeting in June 2003. They are the foundation for a paper that has been submitted by Matthew Huddleston to the Journal of Geophysical Research in December 2003. This work was part of the thesis that Matthew completed in finishing his Ph.D. in Physics at Vanderbilt University.

Chappell, Charles R.↗
NASA NTRS2004

Schedule Risk Assessment

Schedule Risk Assessment (SRA) determines the probability of finishing on or before a given point in time. This viewgraph presentation introduces the prerequisites, probability distribution curves, special conditions, calculations, and results analysis for SRA.

Smith, Grego↗