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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Direct evidence for two-stage (bimodal) acceleration of ionospheric ions

Energetic ion composition spectrometer data gathered on hybrid conical ion distributions by the Dynamics Explorer 1 in the topside ionosphere are reported. The observed ion distributions were field-aligned and upward flowing, with energies up to 5 keV. Increases in ion energy were accompanied by a departure from field-alignment and a cone patterned upward flow, with the apex in the auroral field lines and the cone angle widening upward as the energy increased. Both transverse and parallel accelerations were imparted to the ions, with the transverse heating occurring in a 5000 km extent region centered at 18,000 km altitude. A bi-Maxwellian distribution, a temperature of 1.2 keV and a 260 eV parallel temperature were found at the top of the region.

Klumpar, D. M.↗
NASA NTRS1985

Development of Design Data for Propulsion PMR-15 Composites

The continuing development of PMR-15 composite materials and their associated design properties is pacing the implementation of this technology on commercial aircraft. The guidelines that the FAA has issued regarding the certification of advanced composite structures are very significant with respect to future PMR-15 research and development activities. The FAA has issued an advisory circular dated 1-5-83 concerning guidelines for composite aircraft structures. Of particular significance to PMR-15 technology development is the reliance on combined environmental exposure and component testing, coupled with the stipulation that reliance on previous experience be limited to where common structures and materials have been used for a similar function. Critical environmental exposures for commercial propulsion structures include 50,000 cycle service life, exposure to skydrol, moisture and other fluids, and nacelle fire conditions.

Postlewaite, J.↗
NASA NTRS1988

Properties of two composite materials made of toughened epoxy resin and high-strain graphite fiber

Results are presented from an experimental evaluation of IM7/8551-7 and IM6/18081, two new toughened epoxy resin, high strain graphite fiber composite materials. Data include ply-level strengths and moduli, notched tension and compression strengths and compression-after-impact assessments. The measured properties are compared with those of other graphite-epoxy materials.

Dow, Marvin B.↗
NASA NTRS1989

Space radiation effects on dimensional stability of composites

The long-term space environment at GEO, consisting of high doses (less than 10 to the 9th rads) of electron radiation and large cyclic (-157 C to +121 C) temperature changes, can significantly affect the dimensional stability of polymer matrix composites. Radiation alters the chemical structure of epoxies by both chain scission and cross-linking. In this paper, an attempt is made to summarize and examine the effects of electron radiation damage on dimensional stability of composites. Microcracking measurements were made for standard 177 C cure Gr/Ep, rubber toughened Gr/Ep, Gr/Polymide, and GR/Thermoplastic composites. Results show that radiation damage can significantly change matrix-dependent mechanical and physical properties of composites, with data explaining how these changes can affect their dimensional stability.

Tenney, Darrel R.↗
NASA NTRS1990

Satellite measurements of large-scale air pollution - Measurements of forest fire smoke

The transport, optical properties, total mass, and removal of smoke produced by forest fires in western Canada during late July and early August 1982 are studied using NOAA 7 AVHRR data. Color composite imagery is produced to track the movement of the smoke over Canada and the U.S. as the smoke traveled thousands of km from the source region. Smoke optical thickness, particle size, and single scattering albedo are computed using radiances measured by AVHRR bands 1 and 2. Results show that smoke optical thickness ranged from less that 0.1 to greater than 3.7 and the geometric mean mass radii ranged from 300 to 900 nm. The smoke single scattering albedo ranged from 0.9 to nearly 1.0. The total smoke mass over the eastern U.S. ranged from 0.1 to 0.5 Tg, which is close to the 0.5 Tg estimated from the forest fuel content. The smoke lifetime is estimated to be between 15 and 20 days.

Ferrare, Richard A.↗
NASA NTRS1991

Limits to the lunar atmosphere

Apollo UV spectrometer experiment set limits on the density of oxygen of less than 500/cu cm, and the Apollo Lunar Atmospheric Composition Experiment data imply a value less than 50/cu cm above the subsolar point. These limits are surprisingly small relative to the measured value for sodium. A simple consideration of sources and sinks predicts significantly greater densities of oxygen. It is possible but doubtful that the Apollo measurements occurred during an epoch in which source rates were small. A preferential loss process for oxygen on the darkside of the moon is considered in which ionization by electron capture in surface collisions leads to escape through acceleration in the local electric field. Cold trapping in permanently shadowed regions as a net sink is considered and discounted, but the episodic nature of cometary insertion may allow formation of ice layers which act as a stabilized source of OH. On the basis of an assumed meteoroid impact source, a possible emission brightness of 50 R in the OH(A - X)(0,0) band above the lunar bright limb is predicted.

Morgan, T. H.↗
NASA NTRS1990

Theoretical modelling and meteorological analysis for the AASE mission

Providing real time constituent data analysis and potential vorticity computations in support of the Airborne Arctic Stratospheric Experiment (AASE) is discussed. National Meteorological Center (NMC) meteorological data and potential vorticity computations derived from NMC data are projected onto aircraft coordinates and provided to the investigators in real time. Balloon and satellite constituent data are composited into modified Lagrangian mean coordinates. Various measurements are intercompared, trends deduced and reconstructions of constituent fields performed.

Schoeberl, Mark R.↗
NASA NTRS1992

Intercomparisons of Lidar Backscatter Measurements and In-situ Data from GLOBE

The Global Backscatter Experiment (GLOBE) took place during Nov. 1989 and May - Jun. 1990 and involved flight surveys of the Pacific region by the NASA DC-8 aircraft. The experimental instruments were lidars operating at wavelengths ranging from the visible to the thermal infrared and various optical particle counters for in-situ measurements. The primary motivation for GLOBE was the development of spaceborne wind sensing lidar. This paper will concern a comparison of direct backscatter measurements and backscatter calculated from particle counter data. Of special interest is that the particle measurements provided data on composition, and thus refractive index variation may be included in the analysis.

Chudamani, S.↗
NASA NTRS1992

Voyager energetic particle observations at interplanetary shocks and upstream of planetary bow shocks - 1977-1990

The Voyager 1 and 2 vehicles include instrumentation that makes comprehensive electron and ion measurements in several energy channels with good energy, temporal, and compositional resolution. Data gathered from 1977 to 1988, including observations downstream and upstream of four planetary bow shocks (earth, Saturn, Uranus, Jupiter) and numerous interplanetary shocks to about 30 AU, are analyzed in the context of the Fermi and shock drift acceleration models. Overall results indicate that electrons and ions observed upstream of planetary bow shocks have their source inside the parent magnetosphere, with first order Fermi acceleration playing a secondary role at best.

Krimigis, S. M.↗
NASA NTRS1992

Classification of mafic clasts from mesosiderites - Implications for endogenous igneous processes

Results are presented from an analysis of 13 igneous pebbles from the Vaca Muerta, EET87500, and Bondoc mesosiderites, using electron microprobe and instrumental neutron activation techniques. These data, combined with literature data on compositions of 43 mesosiderite clasts were used to compile a classification scheme for the various types of mafic silicate clasts that occur in mesosiderites. These clasts were classified into five principal groups: (1) polygenic and monogenic cumulates (30 percent); (2) polygenic basalts (30 percent); (3) quench-textured rocks, comprising two compositional subgroups (those which resemble basaltic eucrites (5 percent), and those which resemble cumulate eucrites (2 percent)); (4) monogenic basalts (11 percent); and (5) ultramafic rocks, consisting mainly of large crystals of orthopyroxene (9 percent) or olivine (4 percent). The conditions under which these clasts were formed are discussed.

Rubin, Alan E.↗
NASA NTRS1991

Design and analysis of low-loss linear analog phase modulator for deep space spacecraft X-band transponder (DST) application

This paper summarizes the design concepts, analyses, and the development of an X-band transponder low-loss linear phase modulator for deep space spacecraft applications. A single section breadboard circulator-coupled reflection phase modulator has been analyzed, fabricated, and evaluated. Two- and three-cascaded sections have been modeled and simulations performed to provide an X-band DST phase modulator with +/- 2.5 radians of peak phase deviation to accommodate down-link signal modulation with composite telemetry data and ranging with a deviation linearity tolerance +/- 8 percent and insertion loss of less than 10 +/- 0.5 dB. A two-section phase modulator using constant gamma hyperabrupt varactors and an efficient modulator driver circuit was breadboarded. The measured results satisfy the DST phase modulator requirements, and excellent agreement with the predicted results.

Mysoor, Narayan R.↗
NASA NTRS1993

Developing satellite-derived estimates of surface moisture status

An evaluation is made of the remotely sensed surface temperature (Ts)/normalized difference vegetation index (NDVI) relationship in studies of the influence of biome type on the slope of Ts/NDVI, and of the automation of the process of defining the relationship so that the surface moisture status can be compared with Ts/NDVI at continental scales. The analysis is conducted using the NOAA AVHRR over a 300 x 300 km area in western Montana, as well as biweekly composite AVHRR data. A strong negative relationship is established between NDVI and Ts over all biome types.

Nemani, Ramakhrishna↗
NASA NTRS1992

A cloud and radiation model-based algorithm for rainfall retrieval from SSM/I multispectral microwave measurements

A hybrid statistical-physical retrieval scheme is explored which combines a statistical approach with an approach based on the development of cloud-radiation models designed to simulate precipitating atmospheres. The algorithm employs the detailed microphysical information from a cloud model as input to a radiative transfer model which generates a cloud-radiation model database. Statistical procedures are then invoked to objectively generate an initial guess composite profile data set from the database. The retrieval algorithm has been tested for a tropical typhoon case using Special Sensor Microwave/Imager (SSM/I) data and has shown satisfactory results.

Xiang, Xuwu↗
NASA NTRS1991

Acoustic composition sensor for cryogenic gas mixtures

An acoustic sensor useful for the determination of the composition of a gaseous binary mixture in cryogenic liquid spills has been characterized. One version of the instrument traps a known mixture of helium and nitrogen at ambient temperature in a tube which is interrogated by sonic pulses to determine the speed of sound and hence the composition. Experimental data shows that this sensor is quite accurate. The second version uses two unconfined microphones which sense sound pulses. Experimental data acquired during mixing when liquid nitrogen is poured into a vessel of gaseous helium is presented. Data during transient cooling of the tubular sensor containing nitrogen when the sensor is dipped into liquid nitrogen and during transient warm-up when the sensor is withdrawn are also presented. This sensor is being developed for use in the mixing of liquid cryogens with gas evolution in the simulation of liquid hydrogen/liquid oxygen explosion hazards.

Shakkottai, P.↗
NASA NTRS1991

Design and analysis of a low-loss linear analog phase modulator for deep space spacecraft X-band transponder applications

This article summarizes the design concepts, analyses, and development of an X-band (8145 MHz) transponder low-loss linear phase modulator for deep space spacecraft applications. A single-section breadboard circulator-coupled reflection phase modulator has been analyzed, fabricated, and evaluated. A linear phase deviation of 92 deg with a linearity tolerance of +/- 8 percent was measured for this modulator from 8257 MHz to 8634 MHz over the temperature range -20 to 75 C. The measured insertion loss and the static delay variation with temperature were 2 +/- 0.3 dB and 0.16 psec/ C, respectively. Based on this design, cascaded sections have been modeled, and simulations were performed to provide an X-band deep space transponder (DST) phase modulator with +/- 2.5 radians (+/- 143 deg) of peak phase deviation to accommodate downlink signal modulation with composite telemetry data and ranging, with a deviation linearity tolerance of +/- 8 percent and insertion loss of less than 10 +/- 0.5 dB. A two-section phase modulator using constant gamma hyperabrupt varactors and an efficient modulator driver circuit was breadboarded. The measured results satisfy the DST phase-modulator requirements and show excellent agreement with the predicted results.

Mysoor, N. R.↗
NASA NTRS1998

The Sun and the Solar Wind Close to the Sun

The structure of the solar corona is directly reflected in the structure of the solar wind. But, the importance of this simple observation to coronal modeling has become much greater with the arrival of results from Ulysses and SOHO. High speed wind is relatively smooth and uniform (Ulysses) but the coronal holes from which it comes contain highly filamented flows that expand in area by factors of two to sevenfold between the solar surface and 10 solar radii (SOHO). Different models of the relationship between solar and interplanetary magnetic fields produce similar predictions and are still being reconciled. Slow wind seems to come from the boundaries of streamers (Ulysses) by a process which is even less well understood. Again, there are different ideas for the leakage of slow wind from streamers but these models are quickly becoming highly constrained by new data on composition in the core and boundaries of streamers (SOHO). Perhaps the most significant conclusion is that there is a changing paradigm for the processes governing solar wind acceleration and energy flow, one that requires the presence of filamented, energetic, transient flows in a low-beta plasma close to the Sun that become mixed to produce the evolving turbulent MHD plasma that Is observed in the interplanetary medium.

Suess, S. T.↗
NASA NTRS2000

Optical Characterization of Bulk ZnSeTe Solid Solutions

Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe and ZnSe (sub 1-x) Te (sub x) (0 less than x less than 0.4) grown by physical vapor transport technique. The energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. The best fit to the band gap vs. composition, x, data gives a bowing parameter of 1.336 which is between the value of 1.23 determined previously on ZnSeTe bulk crystals by reflectivity and the value of 1.621 reported on epilayers by photoconductivity. Low-temperature photoluminescence (PL) spectra were measured on 6 samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe (sub 1-x) Te (sub x) samples, 0.09 less than x less than 0.39. For x = 0.09, this emission energy is about 0.2eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x = 0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted to be associated with the exciton bound to Te clusters because of the high Te content in these samples.

Su, Ching-Hua↗