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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Grazing incidence technique to obtain spatially resolved spectra from laser heated plasmas

An experimental method is described in which a grazing incidence spectrograph is used to obtain spatially resolved spectra of laser heated plasmas in the 6-370-A region. In the experiment, small target spheres were irradiated by tightly focused laser beams. A tilted grazing incidence elliptical mirror placed 1.3 m from the target focuses the plasma radiation on the spectrograph slit at a distance of 0.7 m producing a useful degree of spatial resolution in the recorded spectral lines. The spectrum from a copper target is presented together with an X-ray pinhole camera image of the plasma.

Behring, W. E.↗
NASA NTRS1988

Supernova 1987A - A radiosphere resolved with VLBI five days after the neutrino burst

The results of VLBI observations of SN1987A are reported. No emission from the supernova above a level of about 20 percent of the supernova's total flux density was detected, although signals were detected from two calibrator sources with amplitudes roughly equal to those determined in earlier VLBI observations. It is inferred that the supernova's radiosphere was resolved, and a lower bound on the radiosphere's radius of 2.2 mas is estimated from an epoch 5.2 days after the neutrino burst. Given the photometric data from the supernova, a distance to the LMC of 50 + or - 5 kpc, and an apparent expansion velocity that varied systematically with time from 18,000-16,000 km/s, as estimated from the blue-shifted H-alpha absorption lines on the days preceding the observations, it is concluded that 5.2 days after the neutrino burst the supernova's radiosphere was at least 2.5 times larger than the inferred blackbody photosphere, and at least as large as the H-alpha line-forming region.

Jauncey, D. L.↗
NASA NTRS1987

An optimal resolved rate law for kindematically redundant manipulators

The resolved rate law for a manipulator provides the instantaneous joint rates required to satisfy a given instantaneous hand motion. When the joint space has more degrees of freedom than the task space, the manipulator is kinematically redundant and the kinematic rate equations are underdetermined. These equations can be locally optimized, but the resulting pseudo-inverse solution was found to cause large joint rates in some case. A weighting matrix in the locally optimized (pseudo-inverse) solution is dynamically adjusted to control the joint motion as desired. Joint reach limit avoidance is demonstrated in a kinematically redundant planar arm model. The treatment is applicable to redundant manipulators with any number of revolute joints and to nonplanar manipulators.

Bourgeois, B. J.↗
NASA NTRS1988

Spatially resolved quantitative spectroscopy of comets

Because of their temporal and spatial variations, modern ground-based studies of comets within approximately 4 A.U. of the sun are observationally demanding tasks. Over the years, researchers have attempted resolved spectroscopy of comets covering a wide range of intrinsic luminosity. Recently this group has developed spectral and direct-imaging procedures to detect weak ion tails submerged into the comae of even fairly faint comets. Although the last year was devoid of any really bright comet, re-analysis of older dust and gas production data of the 1986 P/Halley apparition has been almost completed. The main changes are that the nucleus does make a significant contribution to continuum light, and that the gravity effect in the dust escape velocity is somewhat larger than previously assumed. On the direct observational side, spectral studies of the 1987's Comet Bradfield show it to be qualitatively carbon-rich, at least in the outer coma ratio of CO(+) and CO2(+), compared the H2O(+) with respect to Halley at similar heliocentric distances.

Spinrad, Hyron↗
NASA NTRS1989

Time-resolved simplified chemical kinetics modelling using computational singular perturbation

A CO-CH4-air reaction system is used to demonstrate the computational singular perturbation (CSP) method for deriving time-resolved simplified chemical kinetics models. CSP provides a programmable algorithm to group the given collection of elementary reactions into reaction groups which are ordered according to their speed. The concept of Importance Index k(m)exp s is introduced: k(m)exp s is defined to be a number between 0 and 1 which measures the importance of the m-th reaction group to the s-th reactant and can readily be computed from data generated by CSP. It is suggested that the robustness of the solutions of the reaction system can be qualitatively assessed by inspecting the Importance Index data.

Lam, S. H.↗
NASA NTRS1989

Method of resolving radio phase ambiguity in satellite orbit determination

For satellite orbit determination, the most accurate observable available today is microwave radio phase, which can be differenced between observing stations and between satellites to cancel both transmitter- and receiver-related errors. For maximum accuracy, the integer cycle ambiguities of the doubly differenced observations must be resolved. To perform this ambiguity resolution, a bootstrapping strategy is proposed. This strategy requires the tracking stations to have a wide ranging progression of spacings. By conventional 'integrated Doppler' processing of the observations from the most widely spaced stations, the orbits are determined well enough to permit resolution of the ambiguities for the most closely spaced stations. The resolution of these ambiguities reduces the uncertainty of the orbit determination enough to enable ambiguity resolution for more widely spaced stations, which further reduces the orbital uncertainty. In a test of this strategy with six tracking stations, both the formal and the true errors of determining Global Positioning System satellite orbits were reduced by a factor of 2.

Councelman, Charles C., III↗
NASA NTRS1989

Optimized resolved rate control of seven-degree-of-freedom Laboratory Telerobotic Manipulator (LTM) with application to three-dimensional graphics simulation

The Laboratory Telerobotic Manipulator (LTM) is a seven-degree-of-freedom robot arm. Two of the arms were delivered to Langley Research Center for ground-based research to assess the use of redundant degree-of-freedom robot arms in space operations. Resolved-rate control equations for the LTM are derived. The equations are based on a scheme developed at the Oak Ridge National Laboratory for computing optimized joint angle rates in real time. The optimized joint angle rates actually represent a trade-off, as the hand moves, between small rates (least-squares solution) and those rates which work toward satisfying a specified performance criterion of joint angles. In singularities where the optimization scheme cannot be applied, alternate control equations are devised. The equations developed were evaluated using a real-time computer simulation to control a 3-D graphics model of the LTM.

Barker, L. Keith↗
NASA NTRS1989

Jet-resolved vibronic structure in the higher excited states of N2O - Ultraviolet three-photon absorption spectroscopy from 80,000 to 90,000/cm

Ionization-detected UV multiphoton absorption spectroscopy of the excited states of N2O is presented, showing Rydberg structure within 20,000/cm of the first ionization threshold. Despite evidence for strong Rydberg-continuum coupling in the form of broadened bands and Fano line-shapes, the Rydberg structure persists, with atomic-like quantum defects and vibration structure well-matched with that of the ion. In the most clearly resolved spectrum, corresponding to the 3p(delta)1Pi state, Renner-Teller and Herzberg-Teller coupling of electronic and vibrational angular momentum are revealed. It is suggested that these mixings are properties of the N2O(+)Pi ion core.

Patsilinakou, E.↗
NASA NTRS1989

Time-resolved spectroscopy and photometry of the eclipsing AM Herculis binary EXO 033319 - 2554.2

Time-resolved optical observations of the eclipsing AM Herculis binary EXO 033319 - 2554.2 are presented. High-speed photometry of an eclipse is presented and used to derive a new ephemeris for the system and to estimate the size of the region responsible for the cyclotron emission. Optical spectra that span the orbital cycle are presented, the cyclotron emission in these spectra is discussed, and the flux and radial velocity variations of H-beta, H-gamma, and He II 4686 A are examined. Models of the flux and radial velocity variations of the emission lines indicate that about half the line emission comes from low-velocity material that is about 1.4 x 10 to the 10th cm from the white dwarf. The rest comes from high-velocity material that is about 10 to the 10th cm from the white dwarf and is moving toward it at about 600 km/s.

Allen, Richard G.↗
NASA NTRS1989

A sensitive time-resolved radiation pyrometer for shock-temperature measurements above 1500 K

The general design, calibration, and performance of a new high-sensitivity radiation pyrometer are described. The pyrometer can determine time-resolved temperatures (as low as 1500 K) in shocked materials by measuring the spectral radiance of light emitted from shocked solid samples in the visible and near-infrared wavelength range (0.5-1.0 micron). The high sensitivity of the radiation pyrometer is attributed to the large angular aperture (0.06 sr), the large bandwidth per channel (up to 0.1 micron), the large photodiode detection areas (1.0 sq cm), and the small number of calibrated channels (4) among which light is divided.

Boslough, Mark B.↗
NASA NTRS1990

Continuous assimilation of simulated Geosat altimetric sea level into an eddy-resolving numerical ocean model. I - Sea level differences. II - Referenced sea level differences

The optimal interpolation method of Lorenc (1981) was used to conduct continuous assimilation of altimetric sea level differences from the simulated Geosat exact repeat mission (ERM) into a three-layer quasi-geostrophic eddy-resolving numerical ocean box model that simulates the statistics of mesoscale eddy activity in the western North Pacific. Assimilation was conducted continuously as the Geosat tracks appeared in simulated real time/space, with each track repeating every 17 days, but occurring at different times and locations within the 17-day period, as would have occurred in a realistic nowcast situation. This interpolation method was also used to conduct the assimilation of referenced altimetric sea level differences into the same model, performing the referencing of altimetric sea sevel differences by using the simulated sea level. The results of this dynamical interpolation procedure are compared with those of a statistical (i.e., optimum) interpolation procedure.

White, Warren B.↗
NASA NTRS1990

CCD time-resolved photometry of faint cataclysmic variables. III

CCD time-resolved photometry in V, B, and near-IR for 17 faint cataclysmic variables (CVs) is presented and analyzed. The data are obtained at Kitt Peak National Observatory, the Perkins reflector, Lowell Observatory, and the Observatorio del Roque de los Muchachos from April-June 1989. The degree of variability and periodicities for the CVs are examined. It is observed that the variability of most of the stars is consistent with CV class behavior. Orbital periods for five CVs are determined, and three potential eclipsing systems are detected.

Howell, Steve B.↗
NASA NTRS1991

Resolving Phase Ambiguities In OQPSK

Improved design for modulator and demodulator in offset-quaternary-phase-key-shifting (OQPSK) communication system enables receiver to resolve ambiguity in estimated phase of received signal. Features include unique-code-word modulation and detection and digital implementation of Costas loop in carrier-recovery subsystem. Enchances performance of carrier-recovery subsystem, reduces complexity of receiver by removing redundant circuits from previous design, and eliminates dependence of timing in receiver upon parallel-to-serial-conversion clock.

Nguyen, Tien M.↗
NASA NTRS1991

CCD time-resolved photometry of faint cataclysmic variables. IV

Time-resolved CCD photometry in V, B, and the near-IR has been obtained, with average time-series length of 3 hours, for 15 certified or candidate cataclysmic-variable faint stars. Orbital periods are found in three of the stars, and nine others are noted to exhibit evidence leading toward confirmation of cataclysmic-variable status. The characteristics of PG 0917+342 and PG 2240+193 are as yet unclear.

Howell, Steve B.↗
NASA NTRS1991

Descriptions of the neutral gas outflow in Comets P/Halley and Wilson (1987 VII) from analyses of velocity-resolved H2O line profiles

The spatial distribution and expansion velocity of the Comets Wilson (1987 VII) and pre- and postperihelion P/Halley are derived on the bases of velocity-resolved H2O spectral line profiles, using a kinematic model which synthesizes line profiles for comparison with observed line shapes. The results thus obtained demonstrate that the spherically symmetric outflow at constant velocity is a poor characterization of cometary neutral-gas outflow. While the radial dependence of the H2O expansion velocity is noted to be consistent with theoretically envisioned trends, the high H2O outflow velocity observed in Comet Wilson resists reconciliation with any existing kinematic model.

Larson, Harold P.↗
NASA NTRS1992

Time resolved simulation of lightning by LIP

Results of time-resolved spectra of lightning simulation in air by laser-induced plasma (LIP) are reported. The measured electron temperatures varied from 17,000 +/-1000 K at 600 ns to 12,000 +/-1000 K at 4 microsec after the ignition of the plasma. Electron densities in the plasma varied from (7.0 +/-1.4) x 10 exp 17/cu cm to (9.0 +/-1.8) x 10 exp 16/cu cm for the above times. A comparison of state variables for LIP and natural lightning is presented. Immediately following the ignition, both natural lightning and LIP are found to reach temperatures in excess of 16,000 K and relax to ambient pressure with different rates. They are expected to approach the 2000-4000-K temperature range, which is important to chemical synthesis, in an asymptotically similar fashion.

Jebens, D. S.↗
NASA NTRS1992

Microstructure characterization by angle-resolved scatter and comparison to measurements made by other techniques

The theory and measurement of angle-resolved scatter are described. Values of rms roughness that were obtained by using this technique to characterize four different materials are compared with values that were obtained by using a total integrated scatter measuring instrument, an optical profiler, and a mechanical profiler. The spatial frequency bandwidths and modulation transfer functions of the four instruments are different, and results are described in light of these differences.

Jacobson, R. D.↗