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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Origin of hot ions observed in a modified Penning discharge

Ions with a Maxwellian energy distriubtion and kinetic temperatures ranging from below 100 eV to several keV are observed in a steady state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.5 to 10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow (0.1 to 1.0 MHz) spoke consists of ions whose measured thermal velocity is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic turbulence and ion thermalization. The anode sheath thickness is smaller than the ion gyrodiameter in this plasma. Thus the ions are in the electric field of the sheath for only a fraction of their orbit, and their E/B drift (spoke) velocity is smaller than that of the electrons.

Roth, J. R.↗
NASA NTRS1971

Effects of surface roughness on the photometric properties of Mars

Starting with a macroscopically flat surface, which at each point scatters according to the Minnaert law with exponent k, the photometric effects of increasing the large-scale roughness of the Martian surface were investigated. The photometric properties of macroscopically rough surfaces can still be described by the Minnaert law, but with an exponent k star, in general not equal to k. Therefore observed values of the Minnaert exponent cannot be used to infer the small-scale surface properties of Mars (or of any planet) unless proper allowance is made for the photometric effects of large-scale roughness. The azimuthal dependence of k star provides a sensitive test for the importance of these effects.

Veverka, J.↗
NASA NTRS1971

Laboratory evaluation of Fecker and Loral optical IR PWI systems

A previous flight test of two electro-optical pilot warning indicators, using a flashing xenon strobe and silicon detectors as cooperative elements, pointed out several design deficiencies. The present laboratory evaluation program corrected these faults and calibrated the sensitivity of both systems in azimuth elevation and range. The laboratory tests were performed on an optical bench and consisted of three basic components: (1) a xenon strobe lamp whose output is monitored at the indicator detector to give pulse to pulse information on energy content at the receiver; (2) a strobe light attenuating optical system which is calibrated photometrically to provide simulated range; and (3) a positioning table on which the indicator system under study is mounted and which provides spatial location coordinates for all data points. The test results for both systems are tabulated.

Gorstein, M.↗
NASA NTRS1971

A note on the effect of reflected solar radiation on airborne and ground measurements in the thermal infrared

The magnitude of thermal solar radiation reflected from water surfaces is considered. It is shown both theoretically and by field observation that, for instruments with small fields of view, the reflected thermal solar radiation can contribute significantly to the measured energy. Comparison of thermal scanner data taken from aircraft at a 16 deg azimuth angle from the mirror point of the sun over the open ocean with data taken at a 164 deg anzimuth angle from the mirror point of the sun at the same angle from nadir is indicative of a difference of 2.8 K in the equivalent black body radiation temperature. Observations taken from a surface vessel into sunglint 80 deg from nadir are indicative of an equivalent black body radiation temperature that is 34 K warmer than the temperature obtained at a similar nadir angle away from the sunglint.

Whitehead, V. S.↗
NASA NTRS1971

Integrated operations/payloads/fleet analysis. Volume 5: Mission, capture and operations analysis

The current baseline mission model consists of the DOD Option B prepared for space transportation system mission analysis and a NASA model prepared for the integrated operations /payloads/ fleet analysis. Changes from the previous mission model are discussed, and additional benefits of the reusable space shuttle system are identified. The methodology and assumptions used in the capture analysis are described, and satellite and launch vehicle traffic models for the current and low cost expendable launch vehicle systems and the reusable space shuttle system are presented. The areas of fleet sizing, limitations and abort modes, system ground support requirements, and ground support systems assessment are covered. Current and extended launch azimuth limitations used for both ETR and WTR are presented for the current and low cost expendable vehicles and also the reusable space shuttle system. The results of a survey of launch support capability for the launch vehicle fleets are reported.

Source record↗
NASA NTRS1971

Discrete ordinate theory of radiative transfer. 2: Scattering from maritime haze

Discrete ordinate theory was used to calculate the reflected and transmitted radiance of photons which have interacted with plane parallel maritime haze layers. The results are presented for three solar zenith angles, three values of the surface albedo, and a range of optical thicknesses from very thin to very thick. The diffuse flux at the lower boundary and the cloud albedo were tabulated. The forward peak and other features in the single scattered phase function caused the radiance in many cases to be very different from that for Rayleigh scattering. The variation of the radiance with both the zenith or nadir angle and the azimuthal angle is more marked, and the relative limb darkening under very thick layers is greater, for haze than for Rayleigh scattering. The downward diffuse flux at the lower boundary for A = O is always greater and the cloud albedo is always less for haze than for Rayleigh layers.

Kattawar, G. W.↗
NASA NTRS1972

On obtaining lunar mission launch opportunities

A general procedure for predicting launch opportunities for the RAE-B lunar orbiter mission is presented. It is shown that knowledge of the earth-moon distance and lunar phase and declination are sufficient to determine launch periods consistent with present mission constraints and to approximately predict launch, transfer, and arrival parameters such as park orbit coast time, the possiblity of shadows in all phases of the mission, arrival energy, and the amount of sunlit orbit time in the lunar orbit. Constraints on RAE-B include bounds on the spin axis-sun angle in the translunar trajectory, an upper limit on the arrival energy, and a minimum time for sunlight duration in lunar orbits are being considered for the mission. Comparisons are made of relevant parameters for the two cases. The general features of launch, transfer, and arrival parameters are discussed and are shown to be a function of lunar declination, flight time, and launch azimuth.

Swartwood, H., Jr.↗
NASA NTRS1971

Almucantar radio telescope report 1: A preliminary study of the capabilities of large partially steerable paraboloidal antennas

The almucantar radio telescope development and characteristics are presented. The radio telescope consists of a paraboloidal reflector free to rotate in azimuth but limited in altitude between two fixed angles from the zenith. The fixed angles are designed to provide the capability where sources lying between two small circles parallel with the horizon (almucantars) are accessible at any one instant. Basic geometrical considerations in the almucantar design are presented. The capabilities of the almucantar telescope for source counting and for monitoring which are essential to a resolution of the cosmological problem are described.

Usher, P. D.↗
NASA NTRS1972

A comparison of coupling efficiencies for a Stix coil and an m equals 1 coil

This theoretical and experimental study compares the ion-cyclotron wave generating characteristics of a Stix coil (which generates waves with azimuthal mode number m = 0) with those of a coil which produces primarily m = + or -1 ion-cyclotron modes. The theoretical work of J.E. Hipp, which predicted very good coupling for the m = 1 coil, was extended to determine the scaling laws for plasma column radius and coil wavelength. Experimentally, an m = 1 coil and an m = 0 coil were used to generate ion-cyclotron waves on a beam generated plasma column with electron density = 10 to the 12th power/cu cm. Coupling resonances with peak efficiencies of approximately 40 to 50 percent were measured for both coils in low power (approximately 10k W) experiments. For equal power transfer to the plasma, the m = 0 coil voltage was more than a factor of two greater than that for the m = 1 coil.

Sigman, D. R.↗
NASA NTRS1972

New experiments on the effect of clock shifts on homing in pigeons

The effect of clock shifts as an experimental tool for predictably interfering with the homing ability of birds is discussed. Clock shifts introduce specific errors in the birds' sun azimuth compass, resulting in corresponding errors during initial orientation and possibly during orientation enroute. The effects of 6 hour and 12 hour clock shifts resulted in a 90 degree deviation and a 180 degree deviation from the initial orientation, respectively. The method for conducting the clock shift experiments and results obtained from previous experiments are described.

Schmidt-Koenig, K.↗
NASA NTRS1969

Identification of atmospheric structure by coherent microwave sounding

Two atmospheric probing experiments involving beyond-the-horizon propagation of microwave signals are reported. In the first experiment, Doppler-shift caused by the cross path wind is measured by a phase lock receiver with the common volume displaced in azimuth from the great circle. Variations in the measured Doppler shift values are explained in terms of variations in atmospheric structure. The second experiment makes use of the pseudorandom sounding signal used in a RAKE communication system. Both multipath delay and Doppler shift are provided by the receiver, permitting the cross section of the atmospheric layer structure to be deduced.

Birkemeier, W. P.↗
NASA NTRS1972

Polar cap electric field distributions related to the interplanetary magnetic field direction

The correlations between the azimuthal direction of the interplanetary magnetic field and the most simple polar cap signatures are discussed. Only the spatial distribution of the dawn-dusk polar cap field is considered. For each OGO 6 traverse across the northern or southern polar cap, the simultaneous values of the interplanetary magnetic field in solar-equatorial coordinates were recorded by the Explorer 33 magnetometer. Histograms of these values are presented and are discussed. The high degree of correlation with the longitudinal angle indicates that the relative geometry of the interplanetary magnetic field and magnetospheric magnetic fields must be fundamental to explaining the distribution of polar cap electric fields. The sign of the solar-equatorial component perpendicular to the sun-earth line appears to be a more critical parameter than the sign of the component toward the sun. The Svalgaard-Mansurov correlation and the correspondence between fast convection and parallel magnetospheric and interplanetary magnetic fields are described.

Heppner, J. P.↗
NASA NTRS1972

Magnetic field signatures of substorms on high latitudes field lines in the nighttime magnetosphere

Two types of magnetic field changes are repeatedly observed in the high latitude nightside magnetosphere in association with magnetic substorms. One type is characterized by sudden decrease in the field strength, accompanied by an abrupt perturbation in the field declination angle. These changes are attributed to field aligned-sheet currents flowing on the high latitude boundary of an expanding plasma sheet following substorms. Single sheets of field-aligned currents on this boundary tend to flow toward the earth in the morning quadrant and away in the evening. Multiple sheets of current may also occur, with the direction of the high latitude sheet generally being the same as for a single sheet. A second type of field change is a decrease in field inclination during substorms. This is regarded as a manifestation of the changing field configuration during substorms and can be described in terms of azimuthal currents.

Fairfield, D. H.↗
NASA NTRS1972

Optimum runway orientation relative to crosswinds

Specific magnitudes of crosswinds may exist that could be constraints to the success of an aircraft mission such as the landing of the proposed space shuttle. A method is required to determine the orientation or azimuth of the proposed runway which will minimize the probability of certain critical crosswinds. Two procedures for obtaining the optimum runway orientation relative to minimizing a specified crosswind speed are described and illustrated with examples. The empirical procedure requires only hand calculations on an ordinary wind rose. The theoretical method utilizes wind statistics computed after the bivariate normal elliptical distribution is applied to a data sample of component winds. This method requires only the assumption that the wind components are bivariate normally distributed. This assumption seems to be reasonable. Studies are currently in progress for testing wind components for bivariate normality for various stations. The close agreement between the theoretical and empirical results for the example chosen substantiates the bivariate normal assumption.

Falls, L. W.↗
NASA NTRS1972

Tracking coverage of the Radio Astronomy Explorer-B

Launch and arrival parameters for the Radio Astronomy Explorer-B mission were revised to provide better tracking station coverage of the transfer trajectory. It is shown that changing the launch azimuth and flight time is sufficient to provide postinjection tracking by Tananarive and Carnarvon, and redundant lunar orbit insertion coverage by command stations. These changes can be made with no significant influence on the other parameters and without sacrificing many launch opportunities. All acceptable launch opportunties during the RAE-B launch period are tabulated together with pertinent launch and arrival parameters.

Swartwood, H., Jr.↗
NASA NTRS1971

Analysis of pilot warning indicator performance in terminal area traffic.

Three pilot warning indicator concepts for collision hazard avoidance are analyzed using computer fast-time simulation. A hazard measure is defined based on a 1/2-g maximum horizontal acceleration, a maximum climb or dive angle of 10 deg for each aircraft, and a 20-sec warning time, through escape completion. The traffic model is based on flight tracks recorded in the Atlanta terminal area over an 11 hr period during August 1967. The basic PWI concept studied alarms on range to flashing beacons mounted on intruder aircraft as a function of relative azimuth and elevation. The alarm-hazard epoch ratio is about 17/1 to maintain the missed-alarm rate below 10%. Beacon vignetting or range-rate discrimination are shown to reduce the false-alarm rate by about 75%.

Ruetenik, J. R.↗
NASA NTRS1971

Origin of hot ions observed in a modified Penning discharge.

Ions with a Maxwellian energy distribution and kinetic temperatures ranging from below 100 eV to several keV have been observed in a steady-state modified Penning discharge. Observations in the plasma, with capacitive probes at several azimuthal locations, are consistent with the existence of two distinct spokes rotating with different velocities in the sheath between the plasma and the anode ring. The faster (0.5-10 MHz) spoke consists of electrons rotating with the E/B drift velocity. The slow (0.1-1.0 MHz) spoke consists of ions, the measured thermal velocity of which is directly proportional to the spoke velocity. The interaction of the two spokes is apparently responsible for the observed electrostatic ?turbulence' and ion thermalization. The anode sheath thickness is smaller than the ion gyrodiameter in this plasma. Thus the ions are in the electric field of the sheath for only a fraction of their orbit, and their E/B drift (spoke) velocity is smaller than that of the electrons.

Roth, J. R.↗
NASA NTRS1971

Average solar wind proton properties from Pioneers 6 and 7.

Distributions and average values for the proton speed, azimuthal and polar flow directions, and the proton temperature and density in the solar wind are presented. The data are obtained from the Ames plasma probes on Pioneers 6 and 7. The time periods covered include Dec. 18, 1965 to mid-February 1966, and mid-August to mid-October 1966. The distributions of the parameters, except for the polar flow direction, are skewed, partially because of stream-stream interactions in the solar wind. The average values of the basic plasma parameters from the two spacecraft are different which could be due partially to different solar activity at the two times, and partially to sector and beam structure dependence.

Mihalov, J. D.↗