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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 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Soft X-ray structure of the Coma cluster of galaxies

Results are reported for an observation of the Coma cluster with an imaging X-ray telescope system aboard a sounding rocket. A two-dimensional X-ray map of the cluster in the energy range from 0.15 to 2.0 keV is presented. The radial distribution, granularity, and ellipticity of the X-ray surface brightness are investigated, and the spectrum and flux within the field of view are analyzed. These properties are then examined quantitatively by comparing the observations with models through the use of a chi-squared test. It is found that: (1) no single galaxy contributes more than a few percent of the total X-ray flux of the Coma cluster; (2) the X-ray source is diffuse but granular on a scale of several arcmin, particularly in the central region; (3) the centroid of the X-ray source is at a local intensity minimum; and (4) the data are most consistent with an isothermal hydrostatic model.

Gorentstein, P.↗
NASA NTRS1979

Observations of Alpha Orionis, R Aquilae, and R Aquarii at 14.9 GHz

The 14.9-GHz continuum flux densities of the M-type stars Alpha Ori, R Aql, and R Aqr have been measured. For Alpha Ori and R Aql it is suggested that the emission at this frequency is primarily due to ionized gas associated with stellar chromospheres or coronae. For R Aqr a model consistent with available data is proposed in which the variable intensity of the radio emission depends on a variable mass-loss rate for the Mira.

Bowers, P. F.↗
NASA NTRS1978

A digital audio/video interleaving system

A method of interleaving an audio signal with its associated video signal for simultaneous transmission or recording, and the subsequent separation of the two signals, is described. Comparisons are made between the new audio signal interleaving system and the Skylab Pam audio/video interleaving system, pointing out improvements gained by using the digital audio/video interleaving system. It was found that the digital technique is the simplest, most effective and most reliable method for interleaving audio and/or other types of data into the video signal for the Shuttle Orbiter application. Details of the design of a multiplexer capable of accommodating two basic data channels, each consisting of a single 31.5-kb/s digital bit stream are given. An adaptive slope delta modulation system is introduced to digitize audio signals, producing a high immunity of work intelligibility to channel errors, primarily due to the robust nature of the delta-modulation algorithm.

Richards, R. W.↗
NASA NTRS1979

The observation and interpretation of the profile of C IV lambda-1548 emitted from a quiet region of the sun

The average properties of the quiet chromospheric network as seen in the transition region line of C IV at 1548 A have been investigated. Line profile data for the study were taken with the OSO 8 High Resolution Ultraviolet Spectrometer, which has moderate angular resolution, high spectral resolution, and good relative photometric accuracy. The profiles, when classified and averaged according to their intensities, were found to be symmetric and Gaussian in shape at all intensity levels. A marginally significant increase in line width with line intensity was detected but the average relative redshift in the network that has been a feature of other OSO 8 studies was not found. The network-to-cell contrast ratio was of the order of 13:1 with the extreme extending to 50.1. The measured average width of 0.22 A (FWHM) is in good agreement with earlier work. Finally, a theoretical interpretation is presented, based on both the line width measurement and consideration of the profile symmetry properties. It is concluded that acoustic waves alone cannot supply enough energy to balance the radiative and conductive losses from the corona. The data are, however, consistent with heating by Alfven waves.

Bruner, E. C., Jr.↗
NASA NTRS1979

A search for geographic control on the occurrence of magnetospheric ELF emissions

Search coil magnetometer data obtained in the magnetosphere on Ogo 5 and Ogo 6 were studied for evidence of man-induced stimulation of the two dominant electromagnetic emissions, chorus and plasmaspheric hiss. Variability of chorus with geographic longitude and enhancements, onsets, and quantum jumps in chorus emissions at frequencies related to harmonics of the earth's transmission lines are discussed. The enhancement of weak emissions in the 340-360 deg dipole longitude region during quiet geomagnetic conditions is present only when ELF hiss is weak, and will not contribute to the non-adiabatic dynamics of radiation belt electrons. It is concluded that the data analyzed is consistent with a predominantly natural origin for chorus and plasmaspheric hiss, and that triggered waves do not play a major role in the non-adiabatic dynamics of geomagnetically trapped electrons.

Tsurutani, B. T.↗
NASA NTRS1979

An upper limit on ultraviolet shot noise from Cygnus X-1

Rapid photometry of Cygnus X-1 through an ultraviolet filter centered on 0.35 micron has been obtained at 100-ms sampling intervals. The autocorrelation function of these data has been examined for shot noise analogous to the behavior of the X-ray light curve. The ultraviolet data are entirely consistent with white noise. Considering randomly occurring ultraviolet shots with the same duration (0.5 s) and average rate (1 per sec) as the X-ray shots, a 3-sigma upper limit on the ratio of optical to X-ray energies per shot is estimated to be 0.13, before the ultraviolet light is attenuated by interstellar dust. This limit is then generalized for shots of arbitrary duration and rate.

Duthie, J. G.↗
NASA NTRS1979

Advanced oxygen-hydrocarbon rocket engine study

A consistent engine system data base was generated for defining advantages and disadvantages, system performance and operating limits, engine parametric data, and technology requirements for candidate high pressure LO2/HC engine systems. Optimum LO2/HC engine power cycles were synthetized and representative conceptual engine design generated for a specified advanced surface to orbit transportation system.

Obrien, C. J.↗
NASA NTRS1980

Advanced oxygen-hydrocarbon rocket engine study

Preliminary identification and evaluation of promising liquid oxygen/ hydrocarbon (LO2/HC) rocket engine cycles is reported. A consistent and reliable data base for vehicle optimization and design studies, to demonstrate the significance of propulsion system improvements, and to select the critical technology areas necessary to realize such advances is presented.

Obrien, C. J.↗
NASA NTRS1980

Voyager detection of nonthermal radio emission from Saturn

The detection of bursts of nonthermal radio noise from Saturn by the planetary radio astonomy experiment onboard the Voyager spacecraft is discussed. The emissions occur near 200 kHz with a peak flux density comparable to higher frequency Jovian emissions. The radiation is right-hand polarized and is most likely emitted in the extraordinary magnetoionic mode from Saturn's northern hemisphere. Modulation is apparent in the data which is consistent with a planetary rotation period of 10 hr 39.9 min.

Kaiser, M. L.↗
NASA NTRS1980

HCMM: Soil moisture in relation to geologic structure and lithology, northern California

The author has identified the following significant results. Empirical observations on the ground and examination of aerial color IR photographs indicate that in grassland terrain, the vegetation overlying sandstone tends to become less vigorous sooner in the late spring season than does the area overlain by an adjacent shale unit. The reverse relationship obtains in the fall. These relationships are thought to be a reflection of the relative porosity of each of the units and hence of their ability to retain or lose soil moisture. A comparison of the optically enlarged day and nite IR imagery of the Late Mesozoic interbedded sandstone and shale units along the western margin of the Sacramento Valley, California, taken at seasonally critical times of the year (late spring/early summer and late fall/early winter) reveals subtle seasonal variations of graytone which tend to support the empirical observations after consideration of Sun angle and azimuth, and the internal consistency of the data on each set of satellite imagery.

Rich, E. I.↗
NASA NTRS1980

Electromagnetic scattering lifetimes for dust in Jupiter's ring

The lifetime of the charged, micron-sized dust particles found to lie in a ring at 1.8 Jupiter radii from Jupiter against electromagnetic scattering is estimated. Interactions of the particles with the Jovian magnetic field dipole are found to spread particle orbits out to a much greater extent than observed for particle charges greater than -10 V, and to result in slightly eccentric, open orbits for the dust particles, with eccentricities dependent on particle size. In addition, fluctuations within the magnetic field are found to lead to significant changes in the eccentricity and inclination of the ring particle orbits. It is concluded that Jovian ring particles, if charged to -10 V as is consistent with Voyager data, will be strongly perturbed and scattered on a short time scale (100 yr), so the ring must be constantly replenished or it is a temporary phenomenon. Finally, the dust cloud observed to extend above, below, and beyond the Jupiter ring is attributed to the electromagnetic scattering of particles smaller than the ring particles.

Consolmagno, G. J.↗
NASA NTRS1980

Results of a demonstration of the use of Differential Very Long Baseline Interferometry data for precise navigation of interplanetary spacecraft

A set of experiments in the use of Differential Very Long Baseline Interferometry for spacecraft navigation have been completed. Data using both Voyager spacecraft and a single quasar were acquired during the Jupiter encounter time period. The data were processed and analyzed in order to assess the navigation accuracy of Differential Very Long Baseline Interferometry. The paper focuses on the data reduction and techniques for assessing data quality and consistency.

Christensen, C. S.↗
NASA NTRS1980

Differential Very Long Baseline Interferometry (delta VLBI) spacecraft tracking system demonstration. Part 2: Data acquisition and processing

A set of experiments in the use of Differential Very Long Baseline Interferometry (delta VLBI) for spacecraft navigation were completed. Data using both Voyager spacecraft and a single quasar were acquired during the Jupiter encounter time period. The data were processed and analyzed to assess the navigation accuracy of delta VLBI. The data reduction and techniques for assessing data quality and consistency are discussed.

Christensen, C. S.↗
NASA NTRS1980

Advanced oxygen-hydrocarbon rocket engine study

The program consists of parametric analysis and design to provide a consistent engine system data base for defining advantages and disadvantages, system performance and operating limits, engine parametric data, and technology requirements for candidate high pressure LO2/Hydrocarbon engine systems. The parametric chamber and nozzle cooling analysis was completed for the four potential coolants: RP-1, LCH4, LO2, and LH2. A summary of the cooling capability of each propellant is presented.

Obrien, J. O.↗
NASA NTRS1981

Advanced oxygen-hydrocarbon rocket engine study

This study identifies and evaluates promising LO2/HC rocket engine cycles, produces a consistent and reliable data base for vehicle optimization and design studies, demonstrates the significance of propulsion system improvements, and selects the critical technology areas necessary to realize an improved surface to orbit transportation system. Parametric LO2/HC engine data were generated over a range of thrust levels from 890 to 6672 kN (200K to 1.5M 1bF) and chamber pressures from 6890 to 34500 kN (1000 to 5000 psia). Engine coolants included RP-1, refined RP-1, LCH4, LC3H8, LO2, and LH2. LO2/RP-1 G.G. cycles were found to be not acceptable for advanced engines. The highest performing LO2/RP-1 staged combustion engine cycle utilizes LO2 as the coolant and incorporates an oxidizer rich preburner. The highest performing cycle for LO2/LCH4 and LO2/LC3H8 utilizes fuel cooling and incorporates both fuel and oxidizer rich preburners. LO2/HC engine cycles permitting the use of a third fluid LH2 coolant and an LH2 rich gas generator provide higher performance at significantly lower pump discharge pressures. The LO2/HC dual throat engine, because of its high altitude performance, delivers the highest payload for the vehicle configuration that was investigated.

Obrien, C. J.↗
NASA NTRS1980

Advanced oxygen-hydrocarbon rocket engine study

Preliminary identification and evaluation of promising LO2/Hydrocarbon rocket engine cycles were used to produce a consistent and reliable data base for vehicle optimization and design studies. cycles G and C were chosen for design analysis. Preliminary design analysis of the heat transfer subsystem was performed to establish major technology requirements.

Obrien, C. J.↗
NASA NTRS1980

A 5.57 hr modulation in the optical counterpart of 2S 1822-371

A periodic 5.57 hr modulation has been observed in the optical counterpart of the X-ray source 2S 1822-371. Two alternative periods are consistent with the data: P = 0.232114d and P = 0.232191d, with statistical uncertainties of 0.000015d in each case. Minimum light occurred at JD 2,444,105.668 + or - 0.005. The amplitude of the modulation is about 1 mag, independent of UBV color, and no variability exceeding the 2% level other than the 5.57 hr effect is found on time scales down to a few seconds. The light curve of the star can be understood in terms of a highly inclined close binary system which contains a relatively large, luminous accretion disk that is periodically occulted by a companion star and an associated gas stream. On the assumption that the companion is a main-sequence star, the distance of the system is found to be more than 600 pc, based on the absence of color variations commensurate with the 5.57 hr intensity cycle.

Mason, K. O.↗
NASA NTRS1980

Orbit accuracy assessment for Seasat

Laser range measurements are used to determine the orbit of Seasat during the period from July 28, 1978, to Aug. 14, 1978, and the influence of the gravity field, atmospheric drag, and solar radiation pressure on the orbit accuracy is investigated. It is noted that for the orbits of three-day duration, little distinction can be made between the influence of different atmospheric models. It is found that the special Seasat gravity field PGS-S3 is most consistent with the data for three-day orbits, but an unmodeled systematic effect in radiation pressure is noted. For orbits of 18-day duration, little distinction can be made between the results derived from the PGS gravity fields. It is also found that the geomagnetic field is an influential factor in the atmospheric modeling during this time period. Seasat altimeter measurements are used to determine the accuracy of the altimeter measurement time tag and to evaluate the orbital accuracy.

Schutz, B. E.↗