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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 847 records · Page 47
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NASA NTRS2022

Trajectory Generation for Flexible-Joint Space Manipulators

Space manipulator arms often exhibit significant joint flexibility and limited motor torque. Future space missions, including satellite servicing and large structure assembly, may involve the manipulation of massive objects, which will accentuate these limitations. Currently, astronauts use visual feedback on-orbit to mitigate oscillations and trajectory following issues. Large time delays between orbit and Earth make ground teleoperation difficult in these conditions, so more autonomous operations must be considered to remove the astronaut resource requirement and expand robotic capabilities in space. Trajectory planning for autonomous systems must therefore be considered to prevent poor trajectory tracking performance. We provide a model-based trajectory generation methodology that incorporates constraints on joint speed, motor torque, and base actuation for flexible-joint space manipulators while minimizing total trajectory time. Full spatial computer simulation results, as well as physical experiment results with a single-joint robot on an air bearing table, show the efficacy of our methodology.

Space robotics↗
NASA NTRS1983

Mass and Momentum Turbulent Transport Experiments

The downstream mixing of coaxial jets discharging in an expanded duct was studied to improve turbulent transport models which are used in computational procedures throughout the propulsion community for combustor flow modeling. Laser velocimeter (LV) and laser induced fluorescence (LIF) techniques were used to measure velocities and concentration and flow visualization techniques to determine the time dependent characteristics of the flow and the scale of the turbulent structure.

Johnson, B. V.↗
NASA NTRS1993

Silicon and carbon abundances in the Orion nebula

We assess the gas-phase abundances of Si and C from our recent measurements of Si(2+), C(2+), and C(+) in the Orion Nebula by expanding on our earlier 'blister' models. The C and Si abundances are derived from new IUE high-dispersion spectra of the C(2+) 1907, 1909 A and Si(2+) 1883, 1892 A lines and archival IUE data. Gas-phase Si/C = 0.016 in the Orion ionized volume and is particularly insensitive to uncertainties in extinction and temperature structure. The solar value is 0.098. Gas-phase C/H = 2.8 x 10 exp -4 and Si/H = 4.5 x 10 exp -6. Compared to solar, Si is depleted by a factor of about 8 in the ionized region, while C is much less depleted (factor of 1.3), if depleted at all. This suggests that most Si resides in dust grains even in the ionized volume. Thus, most of the observed forbidden Si II 34.8-micron emission in Orion does not arise in the H II region.

Rubin, Robert H.↗
NASA NTRS2002

The Arabidopsis SKU5 gene encodes an extracellular glycosyl phosphatidylinositol-anchored glycoprotein involved in directional root growth

To investigate how roots respond to directional cues, we characterized a T-DNA-tagged Arabidopsis mutant named sku5 in which the roots skewed and looped away from the normal downward direction of growth on inclined agar surfaces. sku5 roots and etiolated hypocotyls were slightly shorter than normal and exhibited a counterclockwise (left-handed) axial rotation bias. The surface-dependent skewing phenotype disappeared when the roots penetrated the agar surface, but the axial rotation defect persisted, revealing that these two directional growth processes are separable. The SKU5 gene belongs to a 19-member gene family designated SKS (SKU5 Similar) that is related structurally to the multiple-copper oxidases ascorbate oxidase and laccase. However, the SKS proteins lack several of the conserved copper binding motifs characteristic of copper oxidases, and no enzymatic function could be assigned to the SKU5 protein. Analysis of plants expressing SKU5 reporter constructs and protein gel blot analysis showed that SKU5 was expressed most strongly in expanding tissues. SKU5 was glycosylated and modified by glycosyl phosphatidylinositol and localized to both the plasma membrane and the cell wall. Our observations suggest that SKU5 affects two directional growth processes, possibly by participating in cell wall expansion.

NASA Discipline Plant Biology↗
NASA NTRS2012

Mission Sizing and Trade Studies for Low Ballistic Coefficient Entry Systems to Venus

The U.S and the U.S.S.R. have sent seventeen successful atmospheric entry missions to Venus. Past missions to Venus have utilized rigid aeroshell systems for entry. This rigid aeroshell paradigm sets performance limitations since the size of the entry vehicle is constrained by the fairing diameter of the launch vehicle. This has limited ballistic coefficients (beta) to well above 100 kg/m2 for the entry vehicles. In order to maximize the science payload and minimize the Thermal Protection System (TPS) mass, these missions have entered at very steep entry flight path angles (gamma). Due to Venus thick atmosphere and the steep-gamma, high- conditions, these entry vehicles have been exposed to very high heat flux, very high pressures and extreme decelerations (upwards of 100 g's). Deployable aeroshells avoid the launch vehicle fairing diameter constraint by expanding to a larger diameter after the launch. Due to the potentially larger wetted area, deployable aeroshells achieve lower ballistic coefficients (well below 100 kg/m2), and if they are flown at shallower flight path angles, the entry vehicle can access trajectories with far lower decelerations (~50-60 g's), peak heat fluxes (~400 W/cm2) and peak pressures. The structural and TPS mass of the shallow-gamma, low-beta deployables are lower than their steep-gamma, high-beta rigid aeroshell counterparts at larger diameters, contributing to lower areal densities and potentially higher payload mass fractions. For example, at large diameters, deployables may attain aeroshell areal densities of 10 kg/m2 as opposed to 50 kg/m2 for rigid aeroshells. However, the low-beta, shallow-gamma paradigm also raises issues, such as the possibility of skip-out during entry. The shallow-gamma could also increase the landing footprint of the vehicle. Furthermore, the deployable entry systems may be flexible, so there could be fluid-structure interaction, especially in the high altitude, low-density regimes. The need for precision in guidance, navigation and control during entry also has to be better understood. This paper investigates some of the challenges facing the design of a shallow-gamma, low-beta entry system.

Dutta, Soumyo↗
NASA NTRS1990

Evolution of a superbubble blastwave in a magnetized medium

Researchers investigate the effects of interstellar magnetic fields on the evolution and structure of interstellar superbubbles, using both analytic and numerical magnetohydrodynamic (MHD) calculations. These cavities of hot gas, surrounded by shells of cold dense material preceded by a shock wave result from the combined action of stellar winds and supernova explosions in OB associations. If the medium in which a superbubble goes off is homogeneous and unmagnetized, the blast wave expands isotropically. As the interstellar gas flows through the shock, it cools significantly and gets strongly compressed such that thermal pressure remains approximately equal to ram pressure. Hence, the swept up material is confined to a very thin shell. However, if the ambient medium is permeated by a uniform magnetic field B sub o approx. 3 mu G (typical value for the interstellar matter (ISM)), the configuration loses its spherical symmetry, and, due to magnetic pressure, the shell of swept up material does not remain thin. Researchers found the following qualitative differences: (1) Except in the immediate vicinity of the magnetic poles, the shell is supported by magnetic pressure. (2) The refraction of field lines at the shock and the thermal pressure gradient along the shell both contribute to accelerating the gas toward the equator. The resulting mass flux considerably decreases the column density at the magnetic poles. (3) Away from the poles, magnetic tension in the shell causes the field lines (particularly the inner boundary) to elongate in the direction of B sub o. In contrast, the shock wave radius increases with increasing theta. (4) The reduced inertia of a parcel in the polar neighborhood makes it easier to decelerate, and accounts for the dimple which appears at the poles in numerical simulations. This dimple also results from the necessity to call on intermediate shocks in order to insure a smooth transition between a purely thermal shock at the poles and a magnetic shock in the rest of the shell. (5) The shock wave propagates faster than in the absence of magnetic field, except near the poles where the reduced mass of the shell allows it to be more efficiently decelerated.

Ferriere, Katia M.↗
NASA NTRS2012

SN 1987A: A Unique Laboratory for Shock Physics

Supernova 1987 A is the brightest and nearest supernova observed since Kepler's SN1604, and is the only one close enough to resolve and directly observe the temporal growth of the ejecta. Over the past 25 years, intensive observations across the electromagnetic spectrum with observatories on the ground (Australia Telescope Compact Array, Gemini-S, Magellan, VLT) and in space (IUE, KAO, CGRO, Hubble, Chandra, Spitzer, Herschel) have given us an unprecedented view of the evolution of the debris of the supernova and of its shock interaction with circumstellar matter. The outer supernova debris, now expanding with velocities -8000 km/s, encountered the relatively dense circumstellar ring formed by presupernova mass loss starting in 1994. The resulting shock interaction has been manifested by: rapidly brightening UV-optical "hotspots", an expanding X-ray ring. an expanding ring of knotty non-thermal radio emission, and a ring of thermal IR emission from silicate dust. The recent evolution of these emissions reveal new details about the shock interaction, circumstellar material, and the star that exploded. Certain critical problems about SN 1987 A, such as the still undiscovered compact object formed in the explosion and the structure of the central debris, require the capabilities of JWST.

Sonneborn, George↗
NASA NTRS2017

The Global Precipitation Measurement (GPM) Mission for Science and Society

Precipitation is a key source of freshwater; therefore, observing global patterns of precipitation and its intensity is important for science, society, and understanding our planet in a changing climate. In 2014, the National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA) launched the Global Precipitation Measurement (GPM) Core Observatory (CO) spacecraft. The GPM CO carries the most advanced precipitation sensors currently in space including a dual-frequency precipitation radar provided by JAXA for measuring the three-dimensional structures of precipitation and a well-calibrated, multifrequency passive microwave radiometer that provides wide-swath precipitation data. The GPM CO was designed to measure rain rates from 0.2 to 110.0 mm h1 and to detect moderate to intense snow events. The GPM CO serves as a reference for unifying the data from a constellation of partner satellites to provide next-generation, merged precipitation estimates globally and with high spatial and temporal resolutions. Through improved measurements of rain and snow, precipitation data from GPM provides new information such as details on precipitation structure and intensity; observations of hurricanes and typhoons as they transition from the tropics to the midlatitudes; data to advance near-real-time hazard assessment for floods, landslides, and droughts; inputs to improve weather and climate models; and insights into agricultural productivity, famine, and public health. Since launch, GPM teams have calibrated satellite instruments, refined precipitation retrieval algorithms, expanded science investigations, and processed and disseminated precipitation data for a range of applications. The current status of GPM, its ongoing science, and its future plans are presented.

Gail Skofronick-Jackson↗
NASA NTRS1998

Centrosome structure and function is altered by chloral hydrate and diazepam during the first reproductive cell cycles in sea urchin eggs

This paper explores the mode of action of the tranquillizers chloral hydrate and diazepam during fertilization and mitosis of the first reproductive cell cycles in sea urchin eggs. Most striking effects of these drugs are the alteration of centrosomal material and the abnormal microtubule configurations during exposure and after recovery from the drugs. This finding is utilized to study the mechanisms of centrosome compaction and decompaction and the dynamic configurational changes of centrosomal material and its interactions with microtubules. When 0.1% chloral hydrate or 350-750 microM diazepam is applied at specific phases during the first cell cycle of sea urchin eggs, expanded centrosomal material compacts at distinct regions and super-compacts into dense spheres while microtubules disassemble. When eggs are treated before pronuclear fusion, centrosomal material aggregates around each of the two pronuclei while microtubules disappear. Upon recovery, atypical asters oftentimes with multiple foci are formed from centrosomal material surrounding the pronuclei which indicates that the drugs have affected centrosomal material and prevent it from functioning normally. Electron microscopy and immunofluorescence studies with antibodies that routinely stain centrosomes in sea urchin eggs (4D2; and Ah-6) depict centrosomal material that is altered when compared to control cells. This centrosomal material is not able to reform normal microtubule patterns upon recovery but will form multiple asters around the two pronuclei. When cells are treated with 0.1% chloral hydrate or 350-750 microM diazepam during mitosis, the bipolar centrosomal material becomes compacted and aggregates into multiple dense spheres while spindle and polar microtubules disassemble. With increased incubation time, the smaller dense centrosome particles aggregate into bigger and fewer spheres. Upon recovery, unusual irregular microtubule configurations are formed from centrosomes that have lost their ability to reform normal mitotic figures. These results indicate that chloral hydrate and diazepam affect centrosome structure which results in the inability to reform normal microtubule formations and causes abnormal fertilization and mitosis.

Non-NASA Center↗
NASA NTRS1986

X-29A advanced technology demonstrator program overview

The present discussion of the X-29A forward-swept wing experimental aircraft's functional flight program and concept evaluation program gives attention to the program management structure for a test team that encompasses NASA, the U.S. Air Force, and the prime contractor for the X-29A. The preflight, flight-functional, envelope-expansion and flight research test objectives of the program are also noted, together with the qualitative characterizations obtained to date for both a limited envelope flight control system and one for an expanded envelope.

Sefic, W. J.↗
NASA NTRS1986

Radio variability and structure of T Tauri stars

Observations of radio variability in V410 Tau and in HP Tau/G2 and /G3, and striking variations in the radio structure of DG Tau, are reported. The position of the radio peak of DG Tau has shown apparent motion between 1982 and 1985 along the flow axis from this star, while its morphology has varied from point-like to bipolar. These changes and the spectral index of 0.6 at high frequencies are interpreted as indicative of a variable, freely expanding radio jet in DG Tau.

Cohen, Martin↗
NASA NTRS1988

The evolution of the radio emission from Kepler's Supernova remnant

High-resolution radio maps of Kepler's Supernova remnant (SNR) using all four arrays of the VLA have been obtained at wavelengths of 20 and 6 cm. They show the complete structure of the remnant; all features are resolved with sizes greater than about 2 arcsec, and the relative brightness of the smooth component near the center is about 1/4 the brightness of the rim. The results have been compared with earlier more limited data to measure changes in the remnant over a four-year time span. The SNR is expanding with a mean rate of R proportional to t exp 0.50 with considerable variations around the shell. Values range from R proportional to t exp 0.35 on the bright northern rim to R proportional to t exp 0.65 on the eastern part of the shell. The measurements are consistent with expansion into a variable circumstellar medium.

Dickel, John R.↗
NASA NTRS1992

One Year of Rayleigh Lidar Measurements at Toronto

The Rayleigh lidar technique is being used at York University to study middle atmospheric thermal structure with particular emphasis on the properties and influence of internal gravity waves. These measurements are now carried out on a routine basis (every clear night) in order to determine seasonal variability and, eventually, long term trends. The transmitter consists of a doubled Nd:YAG laser with an output of 0.4 Joules per pulse at 20Hz (8 Watts) which is expanded to obtain a divergence of 0.4 milliradians. Backscattered photons are collected by a half meter cassegrain telescope, filtered to a bandwidth of 1nm, detected by a PMT, and counted with a multi-channel scaling averager. Strong backscatter from lower altitudes is blocked using a rotating chopper (25000rpm) which triggers the laser. The range gate and hardware averaging interval are variable but typically 300m and 5 minutes. Relative density profiles are obtained by simply normalizing to a model (eg. CIRA) at some altitude. Absolute temperature is derived using the hydrostatic equation, ideal gas law, and a model pressure value at the altitude where the photocount statistical uncertainty is about 15 percent - typically 90km for the entire night's average. The lower limit is currently about 30-35km due the presence aerosol from the volcanic eruption of Mt. Pinatubo.

Whiteway, James A.↗
NASA NTRS1999

Slate Islands, Lake Superior, Canada: A mid-size, Complex Impact Structure

The target rocks of the 30-32-km diameter Slate Islands impact structure in northern Lake Superior, Canada, are Archean supracrustal and igneous rocks and supracrustal Proterozoic rocks. Shatter cones, pseudotachylites, impact glasses, and microscopic shock metamorphic features were formed during the contact and compression phase of the impact process, followed, during excavation and central uplift, by polymict, clastic matrix breccias in the uplifted target, and by allogenic fall-back breccias (suevite and bunte breccia). Monomict, autoclastic breccias were mainly observed on Mortimer Island and the other outlying islands of the archipelago and were probably generated relatively late in the impact process (central uplift and/or crater modification). The frequency of low index planar shock metamorphic features in quartz was correlated with results from shock experiments to estimate shock pressures experienced by the target rocks. The resulting shock attenuation plan across the archipelago is irregular, probably because the shock wave did not expand from a point or spherical source, and because of the destruction of an originally more regular shock attenuation plan during the central uplift and crater modification stages of the impact process. No impact melt rock bodies have been positively identified on the islands. An impact melt may be present in the annular trough around the islands, though and-based on a weighted mixture of target rocks-may have an intermediate-mafic composition. No such impact melt was found on the archipelago. An Ar-40-Ar-39 release spectrum of a pseudotachylite provides an age of about 436 Ma for the impact structure, substantiating age constraints based on various stratigraphic considerations.

Dressler, B. O.↗
NASA NTRS2016

Mapping Past, Present, and Future Climatic Suitability for Invasive Aedes Aegypti and Aedes Albopictus in the United States: A Process-Based Modeling Approach Using CMIP5 Downscaled Climate Scenarios

The ongoing spread of the mosquitoes, Aedes aegypti and Aedes albopictus, in the continental United States leaves new areas at risk for local transmission of dengue, chikungunya, and Zika viruses. All three viruses have caused major disease outbreaks in the Americas with infected travelers returning regularly to the U.S. The expanding range of these mosquitoes raises questions about whether recent spread has been enabled by climate change or other anthropogenic influences. In this analysis, we used downscaled climate scenarios from the NASA Earth Exchange Global Daily Downscaled Projections (NEX GDDP) dataset to model Ae. aegypti and Ae. albopictus population growth rates across the United States. We used a stage-structured matrix population model to understand past and present climatic suitability for these vectors, and to project future suitability under CMIP5 climate change scenarios. Our results indicate that much of the southern U.S. is suitable for both Ae. aegypti and Ae. albopictus year-round. In addition, a large proportion of the U.S. is seasonally suitable for mosquito population growth, creating the potential for periodic incursions into new areas. Changes in climatic suitability in recent decades for Ae. aegypti and Ae. albopictus have occurred already in many regions of the U.S., and model projections of future climate suggest that climate change will continue to reshape the range of Ae. aegypti and Ae. albopictus in the U.S., and potentially the risk of the viruses they transmit.

process-based modeling↗
NASA NTRS1973

A lower limit to the altitude of coronal particle storage regions deduced from solar proton energy spectra

The spectrum of low energy protons observed at 1 AU following solar flares shows little or no evidence of energy degradation down to approximately 0.3 MeV. Such observations may be used to set a lower limit on the altitude of hypothetical coronal particle storage regions, ranging from 2 to 7 R sub s. It is pointed out that closed coronal magnetic loop structures are observed to extend to 2R sub s, so that long-term storage of low energy protons does not take place in the immediate vicinity of the sun. It is further suggested that in the few cases where the proton spectrum appears to be degraded at low energies, the energy loss may be due to adiabatic deceleration in the expanding solar wind. The alternative of continual acceleration is suggested as a plausible substitute for the particle storage hypothesis.

Krimigis, S. M.↗
NASA NTRS1985

High-speed photometry of Z Chamaeleontis covering the 1983 March normal outburst

High-speed photometry over a three-week period covering the Mar. 13, 1983 normal outburst of Z Cha is presented. Multicolor observations revealed significant reddening during eclipse in both the quiescent and outburst states. Quiescent primary eclipse timings remained consistent with an increasing orbital period. Hotspot eclipse timings revealed that the accretion disk had physically expanded in radius after the outburst. The duration of the eclipse during outburst, however, limited the optical emission to a region bounded by the radius of the preoutburst accretion disk. In the final stages of decline this emission region had shrunk in size by a factor of approximately 4. The postoutburst observations showed the hotspot eclipse to be less stable in structure compared to before the outburst.

Cook, M. C.↗
NASA NTRS1985

General theory of the transverse dielectric constant of III-V semiconducting compounds

A general model of the transverse dielectric constant of III-V compounds is developed using a hybrid method which combines the kp method with a nonlocal pseudopotential calculation. In this method the Brillouin zone is partitioned into three regions by expanding the energy bands and matrix elements about the F, X, and L symmetry points. The real and imaginary parts of the dielectric constant are calculated as a sum of the individual contributions of each region. By using this partition method, it is possible to get good insight into the dependence of the dielectric constant on the shape of the band structure.

Kahen, K. B.↗