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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Development of a laser-induced heat flux technique for measurement of convective heat transfer coefficients in a supersonic flowfield

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the load surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimental results agreed reasonably well with theoretical predictions of convective heat transfer of flat plate laminar boundary layers. The results indicate that this non-intrusive optical measurement technique has the potential to obtain high quality surface convective heat transfer measurements in high speed flowfields.

Porro, A. Robert↗
NASA NTRS1991

Significant reduction in arc frequency biased solar cells: Observations, diagnostics, and mitigation technique(s)

A variety of experiments were performed which identify key factors contributing to the arcing of negatively biased high voltage solar cells. These efforts have led to reduction of greater than a factor of 100 in the arc frequency of a single cell following proper remediation procedures. Experiments naturally lead to and focussed on the adhesive/encapsulant that is used to bond the protective cover slip to the solar cell. An image-intensified charge coupled device (CCD) camera system recorded UV emission from arc events which occurred exclusively along the interfacial edge between the cover slip and the solar cell. Microscopic inspection of this interfacial region showed a bead of encapsulant along this entire edge. Elimination of this encapsulant bead reduced the arc frequency by two orders of magnitude. Water contamination was also identified as a key contributor which enhances arcing of the encapsulant bead along the solar cell edge. Spectrally resolved measurements of the observable UV light shows a feature assignable to OH(A-X) electronic emission, which is common for water contaminated discharges. Experiments in which the solar cell temperature was raised to 85 C showed a reduced arcing frequency, suggesting desorption of H2O. Exposing the solar cell to water vapor was shown to increase the arcing frequency. Clean dry gases such as O2, N2, and Ar show no enhancement of the arcing rate. Elimination of the exposed encapsulant eliminates any measurable sensitivity to H2O vapor.

Upschulte, B. L.↗
NASA NTRS1991

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields.

Porro, A. R.↗
NASA NTRS1991

Characteristics of return stroke electric fields produced by lightning flashes at distances of 1 to 15 kilometers

Electric field derivative signals from single and multiple lightning strokes are presented. For about 25 pct. of all acquired waveforms, produced by return strokes, stepped leaders or intracloud discharges, type and distance of the signal source are known from the observations by an all sky video camera system. The analysis of the electric field derivative waveforms in the time domain shows a significant difference in the impulse width between return stroke signals and those of stepped leaders and intracloud discharges. In addition, the computed amplitude density spectrum of return stroke waveforms lies by a factor of 10 above that of stepped leaders and intracloud discharges in the frequency range from 50 to 500 kHz.

Hopf, CH.↗
NASA NTRS1991

Polarimetric imaging of the Galactic center at 12.4 microns - The detailed magnetic field structure in the northern arm and the east-west bar

Recent closely sampled imaging polarimetry of the central 0.5 pc of the Galaxy at 12.4 microns with a 58 x 62 array camera system is presented. The results clearly show that the magnetic field is a property of the diffuse material of the large-scale structures in Sgr A (the northern arm and east-west bar) rather than the embedded sources. The magnetic field is independent of the changes of density and temperature in the compact source environments. The magnetic field direction in much of the east-west bar is complex, and its polarization is probably the result of the superposition of differently oriented filaments. The abrupt decrease of polarization southwest of IRS 1 observed previously is confirmed and shown to reverse sign. This is due either to a rapid change of magnetic field direction close to the dynamical center, or to the superposition of nearly orthogonal fields. The field direction changes smoothly across IRS 1, and no discontinuity of motion here is found.

Aitken, David K.↗
NASA NTRS1989

Holographic diagnostics of breakup phenomena of impinging jets for liquid rocket motor applications

The use of pulsed laser holography in analyzing the atomization of impinging jets is evaluated using a holographic camera system capable of recording a 3D image of the atomization process in 3 x 10 exp -8 seconds. The holocamera and the experimental configuration and procedure are described in detail. Two nozzles were fabricated to produce 1-mm diameter liquid water jets that impinged at 60 and 90 deg. Holograms were obtained for each nozzle at liquid velocities of 20 and 40 m/s. Analysis of the holograms revealed the evolution of the jets from the plane of emergence through the region of droplet formation. Features of interest included the growth of disturbances prior to the breakup region and the effect of these disturbances on the formation of ligaments and liquid globules. Preliminary analyses show that waves of atomized liquid formed after impingement are closely correlated to waves measured on the jets, leading to the possibility of controlling the atomization process at the nozzle.

Hess, C. F.↗
NASA NTRS1992

Arcing of negatively biased solar cells in a plasma environment. I - Experimental observations

A variety of experiments have been performed which identify key factors contributing to the arcing of negatively biased high voltage solar cells operating in a low earth orbit plasma environment. These efforts have led to a reduction of greater than a factor of 100 in the arc frequency of a single cells following proper remeditation procedures. Experiments naturally led to and focused on the adhesive/encapsulating that is used to bond the protective cover slip to the solar cell. An image-intensified CCD camera system recorded UV emission from arc events which occurred exclusively along the interfacial edge between the cover slip and the solar cell. Microscopic inspection of this interfacial region showed a bead of encapsulant along this entire edge. Elimination of this encapsulant bead reduced the arc frequency by two orders of magnitude.

Upschulte, B. L.↗
NASA NTRS1991

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high-speed flowfields.

Porro, A. R.↗
NASA NTRS1993

Video-Level Monitor

Video-level monitor developed to provide full-scene monitoring of video and indicates level of brightest portion. Circuit designed nonspecific and can be inserted in any closed-circuit camera system utilizing RS170 or RS330 synchronization and standard CCTV video levels. System made of readily available, off-the-shelf components. Several units are in service.

Gregory, Ray W.↗
NASA NTRS1992

Earth observation photography: Looking back 20 years after Skylab

A committee of trained classroom teachers, backed by a volunteer team of technical experts and academic advisors has developed a program for earth science based on photographs obtained from low earth orbit. In selecting targeting objectives, immediate note was made of the fact nearly one generation (20 years) has passed since the United States' ambitious SKYLAB program was conducted. A critical part of those missions was the acquisition of earth photography using a six camera, multi-spectral camera system. This objective was systematically furthered through the term of three separate crew visits to the Space Station. Not merely an exercise in randomly photographing the Earth below, the purpose of the Earth Resource Experiment Package (EREP) was to determine what kind, and how much, photographic data could be acquired of the broad variety of Earth features witnessed on the mission's ground track. The collection of 35,000 photos produced by EREP represents the most complete coverage of Earth. However, it remains under used. GAS 324 intends to revisit, and to add a tier of relevancy to this inventory. The photography of GAS 324 should allow a direct examination and comparison of the changes in the globe in the last 20 years. format in both coverage and quality. The photogra phy acquired by CAN DO should allow a direct examination and comparison of the changes that have occured to the Globe in the last twenty years.

Nicholson, James H.↗
NASA NTRS1992

Recent developments in space shuttle remote sensing, using hand-held film cameras

The authors report on the advantages and disadvantages of a number of camera systems which are currently employed for space shuttle remote sensing operations. Systems discussed include the modified Hasselbad, the Rolleiflex 6008, the Linkof 5-inch format system, and the Nikon F3/F4 systems. Film/filter combinations (color positive films, color infrared films, color negative films and polarization filters) are presented.

Amsbury, David L.↗
NASA NTRS1993

Amphibian fertilization and development in microgravity

During the year before launch, female frogs will be tested every 3 months for the quantity and quality of eggs produced. Two weeks or more prior to launch, male and female frogs will be transported to the John F. Kennedy Space Center (KSC). During the few weeks before launch, groups will be periodically tested for egg quality to assure that the frogs have adapted to the KSC laboratory environment. About 27 hours before launch, four females will be placed in a damp foam-lined box, called the Adult Frog Box (AFB), through which 100 cc/min of air wil be circulated. The AFB will be lowered into the Spacelab and loaded into the Frog Environmental Unit (FEU) during the final pre-launch preparations. A sperm suspension, for use in flight to fertilize the eggs, will also be prepared and loaded during the pre-launch period. The sperm suspension, together with a kit of syringes containing Human Chorionic Gonadotropin (HCG), will be stored in a refrigerator aboard the shuttle until needed in flight. On the first day of flight, the AFB will be transferred from the FEU to the General Purpose Work Station (GPWS), which is a type of glove box specially designed to allow the crew to use chemicals and biological materials during the flight without contaminating the shuttle/Spacelab environment. Inside the GPWS the four adult frogs will be injected with the HCG hormone and returned to the FEU. Approximately 16 hours after injection, ovulation should have taken place and 15 to 20 eggs from each frog will be placed on each of two egg baskets and covered with sperm for 10 minutes. The egg baskets are inserted into acrylic egg chambers and 50 ml of 'pond water' (20 percent strength Modified Ringers solution (is added. One of the chambers from each frog will be placed on a centrifuge within the FEU and rotated to simulate normal terrestrial gravity (1 g). The remaining chambers are incubated under microgravity conditions within the FEU. Forty minutes after fertilization, the four chambers exposed to 1 g will be removed and observed within the GPWS using a dissecting microscope and camera system. On the basis of egg rotation and egg appearance, the 'best' and 'second best' frogs will be selected to contribute additional eggs. Using the two best frogs, 22 egg chambers will be loaded with eggs and fertilized. Eleven chambers wil be incubated at microgravity and eleven will be incubated on the centrifuge. At various times during the flight, chambers will be removed from the FEU and transferred to the GPWS where a formaldehyde-based fixative will be injected in order to preserve important developmental stages for in depth study following the flight. Five of the 22 chambers plus the eight fertilization test chambers will be returned to Earth with live tadpoles. The swimming behavior of these free swimming tadpoles will be examined within several hours of landing and some will be fixed for a detailed analysis of their inner ear, the otolity, the animals 'balance system.' Lychakov and Vinikov reported an increase in otolith size in tadpoles that developed (but were not fertilized) in space. Live tadpoles from the SL-J flight will be raised through metamorphsis for studies of maturation including an analysis of the effects of space flight on their ability to produce normal progency. Following the flight, the fixed embryos will be serially sectioned and stained using procedures that were developed for this experiment. The embroys fixed at the 2-4 cell stage will be examined for the distribution of cytoplasmic contents, including the various classes of yolk platelets, and the location and shape of the cleavage furrows. The gastrulae will be assessed for the normality of the complex cellular rearrangements that constitute blastopore formation and involution, i.e., the differentiation of the embryo into its specialized body parts. Using a new procedure, the gastrulae will be bleached which will enable the initial sperm entry point (SEP) to be located. The correlation between the SEP and the dorsal lip of the blastopore will be determined. Under normal terrestrial conditions it was shown that the SEP typically is located on the side of the egg opposite the future dorsal side of the embryo. The neurulae will be examined for the normality and completeness of the neural plate and archenteron expansion. The tadpole stages will be used to study the allometry and morphology of the various organ systems.

Souza, Kenneth A.↗
NASA NTRS1993

Earth imaging results from Galileo's second encounter

The recent flyby of the Galileo spacecraft en route to Jupiter contributes a unique perspective to our view of our home planet. Imaging activities conducted during the second Earth encounter provide an important opportunity to assess new methods and approaches on familiar territory. These include unique multispectral observations, low light-level imaging (searches for aurorae, lightning and artificial lights on the nightside) and experiments with multiple exposure times to extend the effective radiometric resolution and dynamic range of the camera system. Galileo imaging data has the potential to make important contributions to terrestrial remote sensing. This is because the particular set of filters included in the Solid State Imaging system are not presently incorporated in any currently operating Earth-orbiting sensor system. The visible/near-infrared bandpasses of the SSI filters are well suited to remote sensing of geological, glaciological, botanical, and meteorological phenomena. Data from this and the previous Earth encounter may provide an extremely valuable reference point in time for comparison with similar data expected from EOS or other systems in the future, contributing directly to our knowledge of global change. The highest resolution imaging (0.2 km/pixel) during the December, 1992 encounter occurred over the central Andes; a five filter mosaic of visible and near infrared bands displays the remarkable spectral heterogeneity of this geologically diverse region. As Galileo departed the Earth, cooperative imaging with the Near Infrared Mapping Spectrometer (NIMS) instrument targeted Antarctica, Australia, and Indonesia at 1.0 to 2.5 km/pixel resolutions in the early morning local times near the terminator. The Antarctic data are of particular interest, potentially allowing ice grain size mapping using the 889 and 968 nm filters and providing an important means of calibrating the technique for application to the Galilean satellites. As the spacecraft receded further, regional scale imaging provided data which, along with data from the previous encounter, will enable the production of global multispectral mosaics of Earth in each of the SSI filters.

Greenberg, R.↗
NASA NTRS1994

High-resolution imaging with a tip-tilt Cassegrain secondary

A prototype adaptive secondary mirror has been developed on a 2.3-m telescope to stabilize rapid motion caused by atmospheric turbulence. The instantaneous position of an image's centroid, or brightest speckle, is measured by a near-infrared camera system which enables the tip-tilt mirror to recenter the image. Correction is accomplished at closed-loop frequencies of less than or = 100 Hz on guide stars with K (2.2 micrometers) magnitudes less than or = 8. Image motion is reduced to less than 0.1 sec rms, removing over 90% of low-frequency (f less than or = 5 Hz) tilt power, leaving less than or = 1 rad exp 2 mean square wave front tilt phase error. In seeing conditions where D/r sub o approximately = 4, long exposures in the H band (1.6 micrometers) exhibit a nearly diffraction-limited resolution of 0.19 sec full width at half maximum (FWHM) (Strehl ratio aprroximately = 0.14)-a factor of 4 improvement over uncorrected images. Reduction of the present static optical errors will improve the Strehl ratio another factor of 2, leading to approximately 70% of the maximum possible Strehl ratio.

Close, L. M.↗
NASA NTRS1994

Propagation velocities of laser-produced plasmas from copper wire targets and water droplets

Experiments were performed to determine the plasma propagation velocities resulting from KrF laser irradiation of copper wire target (75 microns diameter) and water droplets (75 microns diameter) at irradiance levels ranging from 25 to 150 GW/sq cm. Plasma propagation velocities were measured using a streak camera system oriented orthogonally to the high-energy laser propagation axis. Plasma velocities were studied as a function of position in the focused beam. Results show that both the shape of the plasma formation and material removal from the copper wire are different and depend on whether the targets are focused or slightly defocused (approximately = 0.5 mm movement in the beam axis). Plasma formation and its position relative to the target is an important factor in determining the practical focal point during high-energy laser interaction with materials. At irradiance of 100 GW/sq cm, the air plasma has two weak-velocity components which propagate toward and away from the incident laser while a strong-velocity component propagates away from the laser beam as a detonation wave. Comparison of the measured breakdown velocities (in the range of 2.22-2.27 x 10(exp 5) m/s) for air and the value calculated by the nonlinear breakdown wave theory at irradiance of 100 GW/sq cm showed a quantitative agreement within approximately 50% while the linear theory and Gaussian pulse theory failed. The detonation wave velocities of plasma generated from water droplets and copper wire targets for different focused cases were measured and analyzed theoretically. The propagation velocities of laser-induced plasma liquid droplets obtained by previous research are compared with current work.

Song, Kyo-Dong↗
NASA NTRS1995

The envelopes around young stellar objects: What can far-infared observations tell us?

High resolution, far-infrared spatial observations offer a way to probe the density structure of the envelopes around young stellar objects, and thus provide a test of star formation theories. As part of a long term program, we are using the Kuiper Airborne Observatory with the Yerkes Far-Infrared Camera system to study the far-infrared emission (60, 100, 160, and 200 microns) from a number of low mass embedded objects in Taurus. By comparing the observations with the results of radiative transfer models, we are able to estimate the envelope density distribution around these systems. We present our initial results for 4 embedded objects (L1551-IRS 5, L1489-IR, L1551-NE, and L1527-IR).

Butner, H. M.↗