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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Circumstellar matter in the binary V Puppis

Results are reported for Copernicus observations of the double-lined binary V Puppis in the wavelength region from 1155 to 1310 A with a resolution of 0.2 A. The sharp-lined UV absorption spectrum is found to provide a line of sight dominated by an apparently 'textbook' H II region in a Stromgren sphere surrounding the stars. Several characteristics of this H II region are deduced by analyzing absorption features arising from excited fine-structure states of N II and Si II. Evidence is given for the presence of a normal interstellar H I region containing H2 and a separate H I region which could be the transition zone of the H II region. A possible blueshifted N V feature is noted in absorption. It is suggested that the H(+) emission measure and a characteristic size and shape for the H II region can probably be determined by optical observations of Balmer recombination lines within about 1 deg of V Puppis.

York, D. G.↗
NASA NTRS1978

Photoelectric photometry of J V

UBV photometry of J V (Amalthea) near greatest western elongation shows this satellite to be about one magnitude fainter than previously believed. It is observed to be very red, having a B-V color index near + 1.5 mag. Unlike the Galilean satellites, J V appears to be a low-albedo object.

Millis, R. L.↗
NASA NTRS1979

Nike Black Brant V high altitude dynamic instability characteristics

Flight experience on the Nike Black Brant V has demonstrated the existence of plume induced flow separation over the fins and aft body of the Black Brant V motor. Modelling of the forces associated with this phenomenon as well as analysis of the resultant vehicle coning motion and its effect on the velocity vector heading are presented. A summary of Nike Black Brant V flight experience with high altitude dynamic instability is included.

Montag, W. H.↗
NASA NTRS1979

A correlation between auroral kilometric radiation and inverted V electron precipitation

The paper discusses the direct relationship between the auroral kilometric radiation (AKR) power flux observed by the eccentric orbiting Hawkeye spacecraft and energetic electron precipitation in the nighttime auroral zone measured by the low-altitude polar orbiting AE-D spacecraft. The results of this study show that AKR is more closely associated with inverted V electron precipitation than with plasma sheet precipitation. It is found that as the observed AKR power flux increases, so does the simultaneously observed peak energy in inverted V electron precipitation increase. There is an evidence that suggests that the efficiency of generating AKR from inverted V particle participation ranges from 1/100,000% to a maximum efficiency of about 1%.

Green, J. L.↗
NASA NTRS1980

The influence of a voltage ramp on the measurement of I-V characteristics of a solar cell

For efficiency and convenience the voltage applied to a Si solar cell is often fairly rapidly driven from zero to the open circuit value typically at a common rate of 1 V per millisecond. During this time the values of current are determined as a function of the instantaneous voltage thus producing an I-V characteristic. The present paper shows that the customary expressions for the current as a function of cell parameters still remain valid provided that the diffusion length in the expression for the dark current is changed from its steady state value L to the effective diffusion length L1 given by L1 = L(1 + qV/kT.tau) to the -1/2, where V is the ramp rate considered constant and tau is the lifetime of minority carriers. This result is true to a very good approximation provided that low level injection prevails.

Von Roos, O.↗
NASA NTRS1982

Use of the Charge/Discharge (C/D) ratio to aument voltage limit (V sub T) charge control in the ERBS spacecraft

A 50-ampere hour nickel cadmium cell test pack was operated in a power profile simulating the orbit of the Earth Radiation Budget Satellite (ERBS). The objective was to determine the ability of the temperature compensated voltage limit (V sub T) charge control system to maintain energy balance in the half sine wave-type current profile expected of this mission. The four-cell pack (50 E) was tested at the Naval Weapons Support Center (NWSC) at Crane, Indiana. The ERBS evaluation test consisted of two distinct operating sequences, each having a specific purpose. The first phase was a parametric test involving the effect of V sub T level, temperature, and Beta angle on the charge/discharge (C/D) ratio, an indicator of the amount of overcharge. The second phase of testing made use of the C/D ratio limit to augment the V sub T charge limit control. When the C/D limit was reached, the current was switched from the taper mode to a C/67 (0.75 A) trickle charge. The use of an ampere hour integrator limiting the overcharge to a C/67 rate provided a fine tuning of the charge control technique which eliminated the sensitivity problems noted in the initial operating sequence.

Halpert, G.↗
NASA NTRS1982

3-D supersonic combustion experiments with hydrogen in V-trough

Both supersonic blowdown and free jet wind tunnels were used in oil flow visualization and hydrogen gas burning tests of 60- and 90-deg V-shaped trough combustion characteristics. Oil dots showed that mass outflow from the reattachment region at the bottom of the V-trough dominated flow behavior, and occupied the trough's entire length and 10% of its cross-section. Intermingled vortex pairs were also found to superimpose themselves upon the outflow, and hydrogen burning within troughs reduced missile base drag by 25%. The troughs were aligned so that their long dimensions were parallel to the airflow, and the two top edges of the V section were mounted flush with respect to the upstream flat surfaces. Step heights tested ranged from 3.4 mm to 6.25 cm.

Friedberg, R. A.↗
NASA NTRS1982

E/B - V/ extinction values for 24 planetary nebulae derived from IUE data

Excellent agreement was found for E(B - V) values for nine planetary nebulae observed in common by IUE and ANS, derived from a strong 2200A absorption feature. E(B - V) values for seven additional objects with moderately strong 2200A absorption were determined. A third group of eight planetary nebulae for which the 2200A absorption feature is marginal or absent had E(B - V) extinctions determined from the observed He II I(1640A)/I(4686A) ratio. A comparison with optical and radio data is included.

Feibelman, W. A.↗
NASA NTRS1983

A split delta-V technique for drift control of geosynchronous spacecraft

A split-delta-V technique is presented for the east-west stationkeeping of geosynchronous spacecraft using the linearized optimal transfer strategies for near-circular coplanar orbits. The maneuvers are carried out by taking advantage of the dynamics of the spacecraft in order to cancel out the effect of the drift accumulated between successive impulsive delta-V's. A stability analysis is then carried out in order to determine the effect of implementing a series of precanned maneuvers at the end of each drift cycle in an autonomous mode by taking into account initial orbit determination uncertainties and execution errors emanating from each delta-V. It is shown that small tolerance deadbands are violated after only a few cycles and the system is unstable.

Kechichian, F. A.↗
NASA NTRS1983

Simulation of auroral current sheet equilibria and associated V-shaped potential structures

Results from numerical simulations of auroral current sheet equilibria and associated V-shaped potential structures are presented. It is shown that with allowance for both hot magnetospheric ion and cold ionospheric ion populations, the perpendicular potential drop, Phi(m), associated with a non-neutral auroral current sheet is critically controlled by the temperature of the 'heated' ionospheric ions. The heating is caused by the wave turbulence excited by the auroral current sheet. In the presence of heated ionospheric ions, a relatively large variation in the temperature of the hot magnetospheric ion population causes a very small variation in the potential drop Phi(m). The perpendicular potential drop acts to produce a V-shaped double layer with multiple potential steps parallel to the magnetic field when a zero potential boundary condition is imposed at the ionospheric boundary. Outside the V-shaped potential structure, ionospheric return currents develop self-consistently.

Singh, N.↗
NASA NTRS1982

Use of column V alkyls in organometallic vapor phase epitaxy (OMVPE)

The use of the column V-trialkyls trimethylarsenic (TMAs) and trimethylantimony (TMSb) for the organometallic vapor phase epitaxy (OM-VPE) of III-V compound semiconductors is reviewed. A general discussion of the interaction chemistry of common Group III and Group V reactants is presented. The practical application of TMSb and TMAs for OM-VPE is demonstrated using the growth of GaSb, GaAs(1-y)Sb(y), Al(x)Ga(1-x)Sb, and Ga(1-x)In(x)As as examples.

Ludowise, M. J.↗
NASA NTRS1984

Laboratory discharge studies of a 6 V alkaline lantern-type battery Eveready Energizer no. 528, under various ambient temperatures (-15 deg C and + 22 deg C) and loads (30 omega and 60 omega)

The voltages of two Eveready No. 528 batteries, one the test battery, the other the control battery, were simultaneously recorded as they were discharged across 30 omega loads using a dual chart recorder. The test battery was initially put in a freezer at -15 + or - 3 C. After its voltage had fallen to .6 V, it was brought back out into the room at 22 + or - 3 C. A second run was made with 60 omega loads. Assuming a 3.0 V cut-off, the total energy output of the test battery at -15 C was 26 WHr 30 omega and 35 WHr 60 omega, and the corresponding numbers for the control battery at 22 C were 91 WHr and 100 WHr. When the test battery was subsequently allowed to warm up, the voltage rose above 4 V and the total energy output rose to 80 WHr 30 omega and 82 WHR 60 omega.

Ahrens, S. T.↗
NASA NTRS1983

Simulation of the Galileo spacecraft axial - Delta-V algorithm

Preliminary results are presented from the analysis of the Galileo spacecraft axial delta-V algorithm. The Galileo spacecraft is a dual spin interplanetary spacecraft which will study the four Galilean moons of Jupiter as well as the Jovian environment and atmosphere. In order to achieve orbit about Jupiter and accurately deliver the probe to the planet's upper atmosphere, the Galileo spacecraft must be capable of performing many trajectory corrections or delta-V maneuvers. Twelve 10 Newton thrusters and one 400 Newton engine are utilized for this purpose. There are many maneuver modes and control algorithms available to the spacecraft. In this paper only the analysis of the axial delta-V algorithm will be discussed. The analysis consists of two parts: an analytic study and a simulation study. The analytic results are based on rigid body dynamics, while the simulation includes the first order effect of the flexible magnetometer boom and nutation damper. The simulation utilizes a program developed at JPL which allows flexible body effects to be simulated by modeling a collection of rigid bodies attached together by hinges, springs and dampers. In this preliminary study of the Galileo only two rigid bodies were used in the simulation, but many more can and will be used in the final tests. In this analysis, the algorithm appears to be working correctly and the analytic and simulation results agree very well.

Longuski, J. M.↗
NASA NTRS1985

Determination of inverted-V stability from Dynamics Explorer satellite data

The longevity of a number of inverted-V electron precipitation events was measured by comparing electron distributions acquired from the two Dynamics Explorer spacecraft during close proximity passes through the southern auroral zone. Common events were identified in the two data sets for time separations up to 18 min. The maximum energy attained within an inverted-V sometimes varied between observations indicating growth or decay of the event. The number of events increasing in energy was roughly equal to those exhibiting decreasing energy, suggesting similar time scales for growth and decay. Observations closely spaced in time (minutes) had some events not in common, implying either a sudden cessation of the event or a limited spatial extent precluding observation by one of the two spacecraft due to its orbital displacement. A statistical study of 28 close proximity passes showed that the number of matched inverted-V events exceeded those which were unmatched. This was not true for comparisons of random pairs of electron distribution plots for the two spacecraft. This implies that the close proximity events observed by both spacecraft were not just random coincidences.

Thieman, J. R.↗
NASA NTRS1987

A V-grooved AlGaAs/GaAs passivated PN junction

A passivated, V-grooved GaAs solar cell offers important advantages in terms of improved optical coupling, higher short circuit current, and increased tolerance to particle radiation when compared to the planar cell configuration. An AlGaAs epilayer has been deposited on a p-type GaAs epilayer grown on an n-type V-grooved GaAs surface using MOCVD. A wet chemical etching process was used to produce a V-pattern with a 7.0 micron periodicity. Reflectivity measurements substantiate the expected decrease in solar reflectance. Scanning electron microscopy techniques were used to confirm the presence of the AlGaAs layer and verify the existence of a pn junction.

Bailey, Sheila G.↗
NASA NTRS1988

Temporal and spatial relationships between O V and Fe XXI emissions in solar flares

The temporal-spatial structure of simple solar flares observed with the Ultraviolet Spectrometer and Polarimeter of the Solar Maximum mission satellite has been studied in order to investigate the relationships between the impulsive O V and the gradual Fe XXI emissions. The point-like flares are characterized by the cotemporal evolution of the O V and Fe XXI emissions. The simple loop flares have a much larger spatial extent and show two distinctive phases: an initial impulsive phase with its emission localized in loop footpoints, and a gradual phase with its emission distributed in the loop. The temporal evolution of the Fe XXI and O V emissions in a flare is found to be closely related to its spatial structure.

Cheng, Chung-Chieh↗
NASA NTRS1987

A V-grooved AlGaAs/GaAs passivated pn junction

A passivated, V-grooved GaAs solar cell offers important advantages in terms of improved optical coupling, higher short-circuit current, and increased tolerance to particle radiation when compared to the planar cell configuration. An AlGaAs epilayer has been deposited on a p-type GaAs epilayer grown on an n-type V-grooved GaAs surface using MOCVD. A wet chemical etching process was used to produce a V-pattern with a 7.0-micron periodicity. Reflectivity measurements substantiate the expected decrease in solar reflectance. Scanning electron microscopy techniques were used to confirm the presence of the AlGaAs layer and verify the existence of a pn junction.

Bailey, S. G.↗
NASA NTRS1988

Discovery of very high velocity outflow in V Hydra - Wind from an accretion disk in a binary?

High-resolution observations of lines from the CO v = 1-0 vibration-rotation band at 4.6 microns, taken with the FTS/KPNO 4-m telescope, are reported for the carbon-rich red giant V Hydra, which is surrounded by an extended expanding molecular envelope resulting from extensive mass loss. The spectrum shows, in addition to the expected absorption at the outflow velocity of the envelope, absorption extending up to 120 km/s bluewards of the stellar velocity. A comparison of the spectrum observed at two epochs shows that the high-velocity absorption features change with time. It is suggested that the observed high-velocity features in V Hydra arise in a high-velocity polar outflow from an accretion disk in a binary system, as proposed in the mass-loss model for bipolar envelopes by Morris (1988).

Sahai, R.↗