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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 397 records · Page 22
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NASA NTRS1986

The excitation of the iron K-alpha feature in solar flares

The relationship between the hard X-ray photon spectrum and the flux of iron K-alpha emission in a thick-target electron bombardment model is evaluated. Results are presented for various power-law hard X-ray spectra. These results are applied to two events observed with the Hard X-Ray Burst Spectrometer and the K-alpha channel of the X-Ray Polychromator Bent Crystal Spectrometer on the Solar Maximum Mission satellite. For one of the events, on March 29, 1980, at 09:18 UT, the K-alpha flux predicted for a thick-target nonthermal process is significant compared to the background fluorescent component, and the data are indeed consistent with an enhancement of the predicted amount. For the other event, on October 14, 1980 at 0.6:09 UT, the hard X-ray spectrum is so steep that no significant K-alpha flux is predicted for this process, and no enhancement is seen. It is concluded that the agreement between the predicted K-alpha flux and the observed magnitude of the K-alpha enhancement above the fluorescent background at the time of the large hard X-ray bursts lends support to a thick-target nonthermal interpretation of impulsive hard X-ray emission in solar flares.

Emslie, A. G.↗
NASA NTRS1986

A search for Earth-approaching asteroids

New automated methods were developed for the detection and discrimination of Earth-approaching asteriods. Specifically, utilizing state-of-the-art, electron-bombarded, silicon diode, beam scanned, low light level television cameras and the most advanced video processing equipment available. The improvement of the limiting magnitude for a 50% probability of detection, increase the areal search rate, and minimize the burden on humans of the search effort. To this end, three increasingly automated and sophisticated versions of the data acquisition, storage, and processing systems, were designed and implemented. The celestial sphere were searched for Earth-approaching minor planets. An example of this effort is the recent cataloging of 1982 HS=3343 VNEDZEL. This particular high eccentricity, high inclination object is of a type even more rare than are Earth-approaching asteriods. Several of these were found.

Taff, L. G.↗
NASA NTRS1987

Photon counting image sensor development for astronomical applications

Specially built intensified CCD (ICCD) detector tubes were purchased and the performance of the electron bombardment process was investigated. In addition to studying the signal characteristics of the photoevents, there was interest in demonstrating that back-illuminated chips were not susceptible to radiation damage to their clocking electrodes. How to perform a centroid analysis for a 2-dimensional Gaussian distribution of charge is described. Measurement of the projection (along columns or rows) of the average charge spread profile is discussed. The development and flight of the Interstellar Medium Absorption Profile Spectrograph (IMAPS) is discussed.

Jenkins, Edward B.↗
NASA NTRS1988

Auger electron spectroscopy of contrast-forming layers on metals

As shown by Auger electron spectroscopy, the layers formed during contrasting metallographic polished Cu and Ni with an apparatus using intense electron bombardment consist of metal sputtered from the Au, Fe, or Pb cathode. This layer takes up oxygen from the residual atmosphere. The mechanism of contrast enhancement is the same as that of vapor-deposited interference layers.

Hoffmann, Siegfried↗
NASA NTRS1987

A study of the infrared emission from the O I (3d 3D0) and (4s 5S0) states produced by electron impact excitation of O2

The absolute emission cross section values for the O I(3p 3P-3d 3D0, lambda = 11,287 A) and the (3p 5P-4s 5S0, lambda = 11,299 A) multiplets excited by electron impact on O2 have been measured. These infrared oxygen emission features appear prominently in auroral spectra and were observed in electron bombardment of O2. The former cross section has a value of 3.05 x 10 to the -19th + or - 15 percent at 100 eV, while the latter's value is 4.14 x 10 to the -19th sq cm + or - 15 percent. The quintet emission at lambda = 11,299 A is the only deexcitation channel for the 4s 5S0 state and thus represents the total excitation cross section for that state. However, the lambda = 11,287 A branch from the O I (3d 3D0) state only constitutes about 25 percent of the total 3d 3D0 cross section, with the major branch from this state being the transition to the ground state observed at lambda = 1027 A. The branching ratio is in good agreement with the theoretical calculation of Padhan and Saraph (1977).

Erdman, P. W.↗
NASA NTRS1988

A self-consistent interpretation of the solar flare extreme-ultraviolet to hard X-ray ratio in large events

This paper shows quantitatively that when a limiting X-ray yield is considered, a universal area of 10 to the 17th sq cm used in the thick-target electron bombardment model of McClymont and Canfield (1986) cannot explain the observed hard X-ray flux in large solar flare events without recourse to extreme values of the physical parameters of the flaring corona. The return current ohmic heating produced by a beam of flux 10 to the 13th ergs/sq cm/s results in a coronal temperature in excess of 100 million K. In this case, the thermal hard X-ray emission dominates the nonthermal emission and the EUV-to-hard X-ray ratio would not decrease with increasing hard X-ray flux, as observed. Hence, any model that requires a beam flux of 10 to the 13th ergs/sq cm/s is untenable. It is proposed that these apparently contradictory results can be reconciled if the X-ray emitting area is substantially larger than the area of the chromospheric precipitation site.

Larosa, T. N.↗
NASA NTRS1989

Observations of ionosphere/magnetosphere interactions from the Dynamics Explorer satellites

The Dynamics Explorer program was a dual spacecraft mission designed to study the interactions between the upper atmosphere, ionosphere and magnetosphere. The global auroral images acquired from the high altitude spacecraft have provided a revolutionary new time-dependent frame of reference for the interpretation of data acquired in situ. Using data especially from the low altitude spacecraft, interrelationships are developed between the various electrodynamic parameters measured. Ionospheric irregularities are found to be especially intense in regions of electric field convection shears, which are closely related to the dusk hemisphere field-aligned currents. These region 1 currents are spatially connected to the boundary plasma sheet electron precipitation. At all local times, there appears to be a universal relationship between regions where div E is less than 0 and electron precipitation structures. Depending upon the characteristics of the electrons bombarding the atmosphere, the atmosphere will radiate various spectral optical emissions, which can be imaged from high above the polar caps, with temporal resolution sufficient to follow the time-dependent evolution of a substorm. It is concluded that with further detailed analyses of the electrodynamic parameters obtained from in situ measurements, analyses of auroral images will yield specific information on many of the important ionospheric parameters over an entire auroral oval and polar cap, including regions of intense ionospheric irregularities.

Hoffman, R. A.↗
NASA NTRS1990

Xenon ion propulsion for orbit transfer

The status of critical ion propulsion system elements is reviewed. Electron bombardment ion thrusters for primary propulsion have evolved to operate on xenon in the 5-10 kW power range. Thruster efficiencies of 0.7 and specific impulse values of 4000 s have been documented. The baseline thruster currently under development by NASA LeRC includes ring-cusp magnetic field plasma containment and dished two-grid ion optics. Based on past experience and demonstrated simplifications, power processors for these thrusters should have approximately 500 parts, a mass of 40 kg, and an efficiency near 0.94. Thrust vector control, via individual thruster gimbals, is a mature technology. High pressure, gaseous xenon propellant storage and control schemes, using flight qualified hardware, result in propellant tankage fractions between 0.1 and 0.2. In-space and ground integration testing has demonstrated that ion propulsion systems can be successfully integrated with their host spacecraft.

Rawlin, V. K.↗
NASA NTRS1990

Xenon ion propulsion for orbit transfer

For more than 30 years, NASA has conducted an ion propulsion program which has resulted in several experimental space flight demonstrations and the development of many supporting technologies. Technologies appropriate for geosynchronous stationkeeping, earth-orbit transfer missions, and interplanetary missions are defined and evaluated. The status of critical ion propulsion system elements is reviewed. Electron bombardment ion thrusters for primary propulsion have evolved to operate on xenon in the 5 to 10 kW power range. Thruster efficiencies of 0.7 and specific impulse values of 4000 s were documented. The baseline thruster currently under development by NASA LeRC includes ring-cusp magnetic field plasma containment and dished two-grid ion optics. Based on past experience and demonstrated simplifications, power processors for these thrusters should have approximately 500 parts, a mass of 40 kg, and an efficiency near 0.94. Thrust vector control, via individual thruster gimbals, is a mature technology. High pressure, gaseous xenon propellant storage and control schemes, using flight qualified hardware, result in propellant tankage fractions between 0.1 and 0.2. In-space and ground integration testing has demonstrated that ion propulsion systems can be successfully integrated with their host spacecraft. Ion propulsion system technologies are mature and can significantly enhance and/or enable a variety of missions in the nation's space propulsion program.

Rawlin, V. K.↗
NASA NTRS1990

X-ray photoelectron and mass spectroscopic study of electron irradiation and thermal stability of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was subjected to 3 keV electron bombardment and then heated in vacuum to 300 C. The behavior of the material as a function of radiation dose and temperature was studied by X-ray photoelectron spectroscopy (XPS) of the surface and mass spectroscopy of the species evolved. A quantitative comparison of the radiation dose rate with that in other reported studies showed that, for a given total dose, the damage observed by XPS is greater for higher dose rates. Lightly damaged material heated to 300 C evolved saturated fluorocarbon species, whereas unsaturated fluorocarbon species evolved from heavily damaged material. After heating the heavily damaged material, those features in the XPS that were associated with damage diminished, giving the appearance that the radiation damage annealed. The apparent annealing of the radiation damage was found to be due to the covering of the network by saturated fragments that easily diffused through the decomposed material to the surface region upon heating.

Wheeler, Donald R.↗
NASA NTRS1990

Large-format electrographic and array detectors for a space Schmidt imaging telescope

Possible optical designs of imaging detectors for the spaceborne Schmidt telescope proposed by Carruthers et al. (1990) are discussed, surveying the currently or potentially available technology. Consideration is given to FUV electrographic detectors of large format (e.g., 120 mm with 10-micron resolution) using CsI photocathodes, the possible extension of the same technology to the mid-UV using Cs2Te instead of CsI, large CCD arrays for the visible and NIR, electron-bombarded CCDs for the FUV and mid-UV, and the data handling and processing requirements of these detectors.

Carruthers, George R.↗
NASA NTRS1990

Thermal stability of electron-irradiated poly(tetrafluoroethylene) - X-ray photoelectron and mass spectroscopic study

Polytetrafluoroethylene (PTFE) was subjected to 3 keV electron bombardment and then heated in vacuum to 300 C. The behavior of the material as a function of radiation dose and temperature was studied by X-ray photoelectron spectroscopy (XPS) of the surface and mass spectroscopy of the species evolved. Lightly damaged material heated to 300 C evolved saturated fluorocarbon species, whereas unsaturated fluorocarbon species were evolved from heavily damaged material. After heating the heavily damaged material, those features in the XPS spectrum that were associated with damage diminished, giving the appearance that the radiation damage had annealed. The observations were interpreted by incorporating mass transport of severed chain fragments and thermal decomposition of severely damaged material into the branched and cross-linked network model of irradiated PTFE. The apparent annealing of the radiation damage was due to covering of the network by saturated fragments that easily diffused through the decomposed material to the surface region upon heating.

Wheeler, Donald R.↗
NASA NTRS1992

Enhanced fatigue and retention in ferroelectric thin film memory capacitors by post-top electrode anneal treatment

Thin film ferroelectric capacitors comprising a ferroelectric film sandwiched between electrodes for nonvolatile memory operations are rendered more stable by subjecting the capacitors to an anneal following deposition of the top electrode. The anneal is done so as to form the interface between the ferroelectric film and the top electrode. Heating in an air oven, laser annealing, or electron bombardment may be used to form the interface. Heating in an air oven is done at a temperature at least equal to the crystallization temperature of the ferroelectric film. Where the ferroelectric film comprises lead zirconate titanate, annealing is done at about 550 to 600 C for about 10 to 15 minutes. The formation treatment reduces the magnitude of charge associated with the nonswitching pulse in the thin film ferroelectric capacitors. Reduction of this charge leads to significantly more stable nonvolatile memory operations in both digital and analog memory devices. The formation treatment also reduces the ratio of change of the charge associated with the nonswitching pulse as a function of retention time. These improved memory devices exhibit greater performance in retention and reduced fatigue in memory arrays.

Thakoor, Sarita↗
NASA NTRS1992

Correcting x ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters correcting for the reflectivity of the mirror and convolving with the detector response.

Chartas, G.↗
NASA NTRS1993

Correcting X-ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters, correcting for the reflectivity of the mirror and convolving with the detector response.

Chartas, G.↗
NASA NTRS1993

Measurement of the transition probability of the C III 190.9 nanometer intersystem line

A radio-frequency ion trap has been used to store C(2+) ions created by electron bombardment of CO. The transition probability for the 2s2p 3Po1-2s2 1S0 intersystem line of C m has been measured by recording the radiative decay at 190.9 nm. The measured A-value is 121 +/- 7/s and agrees, within mutual uncertainty limits, with that of Laughlin et al. (1978), but is 20 percent larger than that of Nussbaumer and Storey (1978). The effective collision mixing rate coefficient among the fine structure levels of 3Po and the combined quenching and charge transfer rate coefficients out of the 3Po1 level with the CO source gas have also been measured.

Kwong, Victor H. S.↗
NASA NTRS1993

Property changes induced by the space environment in composite materials on LDEF: Solar array materials passive LDEF experiment A0171 (SAMPLE)

Surface modifications to composite materials induced by long term exposure in low earth orbit (LEO) were dominated by atomic oxygen erosion and micrometeoroid and space debris impacts. As expected, calculated erosion rates were peculiar to material type and within the predicted order of magnitude. Generally, about one ply of the carbon fiber composites was eroded during the 70 month LDEF experiment. Matrix erosion was greater than fiber erosion and was more evident for a polysulfone matrix than for epoxy matrices. Micrometeoroid and space debris impacts resulted in small (less than 1mm) craters and splattered contaminants on all samples. Surfaces became more diffuse and darker with small increases in emissivity and absorption. Tensile strength decreased roughly with thickness loss, and epoxy matrices apparently became slightly embrittled, probably as a result of continued curing under UV and/or electron bombardment. However, changes in the ultimate yield stress of the carbon reinforced epoxy composites correlate neither with weave direction nor fiber type. Unexpected developments were the discovery of new synergistic effects of the space environment in the interaction of atomic oxygen and copious amounts of contamination and in the induced luminescence of many materials.

Source record↗
NASA NTRS1994

Predissociation in N2(C'4, 1 Sigma u +) and other N2 states and its importance in the atmospheres of Titan and Triton

The objectives of this program are to further the understanding of the upper atmospheres of Titan, Triton, and the Earth in terms of the observed emissions of the 13-14 eV states of N2. These states are generated at quite high rates, yet very little emission is observed from them. The reasons are complex, involving resonance trapping and predissociation, and it is desired to quantify the effects of predissociation, particularly on the c(sub 4)' 1 Sigma(sub u),(sup +) state of N2. Earlier experiments had indicated that predissociation of the c(sub 4)' state was of little importance, yet over the last two years a growing body of evidence has shown that for levels above v = 2, predissociation is in fact a major process. It is the v = 0 level for which production by electron bombardment and photoexcitation is highest, and so it has been most important to evaluate the effects of predissociation on this particular level. The goal has been to target c(sub 4)' (v = 0) for a thorough analysis, in which both the extent of predissociation as a function of rotational level and the atomic product branching ratio, where the only possible products are N(4S) + N(4S) and N(2D) + N(4S), are determined. For the first year of funding, the intention was to demonstrate two-photon excitation of the intermediate N2(a(sup 1) Pi(sub g)) state, so that the gap to the 13 eV energy region could be bridged, and then use a second laser to reach the c(sub 4)' state itself.

Slanger, Tom G.↗