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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Departures from hydrostatic equilibrium in the global distribution of thermospheric argon

This report describes the application of a three-dimensional two-component model to the distribution of argon in the upper atmosphere of the earth. The Cira (1972) model is used to specify the background gas density and the temperature as functions of altitude, latitude, local time, and day of the year. Emphasis is placed on examining the effects of departures from hydrostatic equilibrium on the argon density distribution. Such effects are found to be significant, producing a strong summer argon bulge. Comparisons of the model results with observational data are discussed.

Straus, J. M.↗
NASA NTRS1977

Steady state, exposure age, and growth of agglutinates in lunar soils

Mineralogical evolution of lunar soils as a function of agglutinate content can be described with the help of a two-component model. Steady-state condition of exposed lunar soils can be achieved only by the balance of comminution, agglutination, and replenishment processes. Rate of replenishment depends on the meteoroid flux and the nature of the substrate which varies both in space and time. Rates of agglutination and comminution depend not only on the micrometeoritic flux but also on the chemical and modal composition of an exposed soil. It is concluded from modeling the above that steady-state condition of lunar soils is independent of its maturity or exposure age. Agglutinate content of a lunar soil can be used to estimate the relative exposure age of the soil only if the soil is in a non-steady-state condition.

Basu, A.↗
NASA NTRS1978

The moon - Composition determined by nebular processes

The Ganapathy-Anders seven-component model is used as the basis for an analysis of conditions in the early solar nebula as they pertain to the formation of the moon. Calculations incorporating improved geological data and petrological constraints are presented in terms of a model moon which meets trace element restrictions and conforms to known parameters of heat flow, density, and moment of inertia ratio, ie., 40 ppb U, and a core of 2% by weight. It is noted that a melt of the model composition approximates that of Apollo 15 green glass, together with a residuum of olivine, plus 3-4% spinel.

Morgan, J. W.↗
NASA NTRS1978

On-orbit experience with the HEAO attitude control subsystem

The first satellite (HEAO-1) in the High Energy Astronomy Observatory Program series was launched successfully on Aug. 12, 1977. To date it has completed over nine months of orbital operation in a science data gathering mode. During this period all attitude control modes have been exercised and all primary mission objectives have been achieved. This paper highlights the characteristics of the attitude control subsystem design and compares the predicted performance with the actual flight operations experience. Environmental disturbance modeling, component hardware/software characteristics, and overall attitude control performance are reviewed and are found to compare very well with the prelaunch analytical predictions. Brief comments are also included regarding the operations aspects of the attitude control subsystem. The experience in this regard demonstrates the effectiveness of the design flexibility afforded by the presence of a general purpose digital processor in the subsystem flight hardware implementation.

Hoffman, D. P.↗
NASA NTRS1979

Investigation of the asymmetric aerodynamic characteristics of cylindrical bodies of revolution with variations in nose geometry and rotational orientation at angles of attack to 58 degrees and Mach numbers to 2

Wind-tunnel tests were conducted to investigate the side forces and yawing moments that can occur at high angles of attack and zero sideslip for cylindrical bodies of revolution. Two bodies having several tangent ogive forebodies with fineness ratios of 0.5, 1.5, 2.5, and 3.5 were tested. The forebodies with fineness ratios of 2.5 and 3.5 had several bluntnesses. The cylindrical afterbodies had fineness ratios of 7 and 13. The model components - tip, forebody, and afterbody - were tested in various rotational positions about their axes of symmetry. Most of the tests were conducted at a Mach number of 0.25, a Reynolds number of 0.32 x 10 to the 6th power, and with the afterbody that had a fineness ratio of 7 and with selected forebodies. The effect of Mach number was determined with the afterbody that had a fineness ratio of 13 and with selected forebodies at mach numbers from 0.25 to 2 at Reynolds number = 0.32 X 10 to the 6th power. Maximum angle of attack was 58 deg.

Kruse, R. L.↗
NASA NTRS1978

Period variations in pulsating X-ray sources. II - Torque variations and stellar response

A statistical description of variations in the torque acting on a rotating neutron star is developed in terms of stationary random processes and is used to calculate the torque power spectrum, stellar response power spectrum, and the total mean square variation in the crustal angular velocity of the star. The response of a star with a finite frequency internal mode is calculated with the aid of phenomenological equations which correspond to a generalized two-component model of the star. The form of the stellar response functions is examined in a number of limiting cases of physical interest, and the dependence of the response power on both the period of observation and the time over which fluctuating torques have been acting is discussed.

Lamb, F. K.↗
NASA NTRS1980

Simulation of a navigator algorithm for a low-cost GPS receiver

The analytical structure of an existing navigator algorithm for a low cost global positioning system receiver is described in detail to facilitate its implementation on in-house digital computers and real-time simulators. The material presented includes a simulation of GPS pseudorange measurements, based on a two-body representation of the NAVSTAR spacecraft orbits, and a four component model of the receiver bias errors. A simpler test for loss of pseudorange measurements due to spacecraft shielding is also noted.

Hodge, W. F.↗
NASA NTRS1979

The chemical components of highlands breccias

Component models for polymict highlands breccias are considered, where rocks are assumed to be mixtures of end-members unaffected by such processes as fumarolic volatiles and impact-induced volatilization. Evidence points to pristine norites as substantial contributors to highlands breccias; the bulk major element compositions of breccias average noritic anorthosite, and norites are the second-most abundant of pristine samples. In addition, plots of element abundances in breccias indicate that KREEP in highlands breccias is not of Apollo 14 composition but is higher in Ti and Sc, and probably lower in incompatibles.

Ryder, G.↗
NASA NTRS1980

Chemical fractionations in meteorites. XI - C2 chondrites

Measurements of the compositions of 20 trace elements in the representative C2 chondrites Boriskino, Cold Bokkeveld, Erakot, Essebi, Haripura, Santa Cruz and Al Rais are reported. The contents of Ag, Au, Bi, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Sn, Te, Tl, U, and Zn were determined by radiochemical neutron activation analysis. The siderophile abundances of the C2 chondrites are found to be less uniform than those of other carbonaceous chondrites, while the C2R chondrite Al Rais is systematically lower in 12 volatiles than the C2M chondrites. Enrichment of Bi and Tl found in Erakot and Haripura indicate the possible presence of the late condensate mysterite. Volatile abundances are shown to agree with matrix contents for meteorites that have suffered little aqueous alteration, however to be 20-30% lower for the more altered meteorites. Finally, the decline of element abundance with volatility is shown to be consistent with the sigmoid curve explained by the two-component model.

Wolf, R.↗
NASA NTRS1980

Variability of the solar flux in the far ultraviolet 1175-2100 A

An attempt is made to correlate available observations within the framework of a simple two-component model of the full-disk flux which divides the solar surface into quiet and active areas with a constant average contrast factor for the intensity at a particular wavelength. The expected range of variability over the solar cycle of the far UV flux is examined within the 1175-2100 A wavelength range. Two possible indices of solar variability, the calcium plage index and the Zurich sunspot number, are investigated as guides to the fraction of disk covered by active regions and the possible resulting flux variability. In addition, contrast factors I(plage)/I(quiet region) are determined for various lines and continua, and the fraction of the disk covered by plages at various times is estimated. Results are in good agreement with the L-alpha fluxes of Vidal-Madjar (1975) and the broadband observations by Hinteregger (1979), but disagree with the flux variability reported by Heath and Thekaekara (1977) over the 1700-3000 A range.

Cook, J. W.↗
NASA NTRS1980

Measurements of quiescent prominence spectra - Ca/+/ double-lambda 8542, 8498 and He lambda 4471, Ti/+/ lambda 4468

High-dispersion measurements of the line profiles of the Ca(+) lines at 8542 and 8498 A and the He 4471-A, Ti(+) 4468-A line pair in the spectra of quiescent solar prominences are presented. The measured Ca(+) and He line profiles are found to be accurately described by the two-component model of Landman et al. (1977) and Landman and Mongillo (1979) in which the prominence along the line of sight consists of a low-temperature region surrounded by high-temperature material representing contributions from the prominence/corona interface; the Ti(+) lines are too weak to distinguish among different models. The Ca(+) data allow a constant infrared line source function for the low-temperature region of 50,000 ergs/sq cm per sec per ster per A to be calculated, which is in disagreement with the previous Ca(+) excitation equilibrium calculations but is consistent with generally accepted values of the electron density and temperature. The integrated intensity ratio of 0.048 between Ti(+) and He emission indicates a low-temperature region temperature of 6620 K and microturbulence of 5.1 km/sec and high-temperature microturbulence of 11 km/sec for Ca(+) and 20 km/sec for He. The results exclude macroturbulence as a possible explanation of the generally observed wing enhancements.

Landman, D. A.↗
NASA NTRS1981

Model aerodynamic test results for two variable cycle engine coannular exhaust systems at simulated takeoff and cruise conditions. Comprehensive data report. Volume 3: Graphical data book 1

A graphical presentation of the aerodynamic data acquired during coannular nozzle performance wind tunnel tests is given. The graphical data consist of plots of nozzle gross thrust coefficient, fan nozzle discharge coefficient, and primary nozzle discharge coefficient. Normalized model component static pressure distributions are presented as a function of primary total pressure, fan total pressure, and ambient static pressure for selected operating conditions. In addition, the supersonic cruise configuration data include plots of nozzle efficiency and secondary-to-fan total pressure pumping characteristics. Supersonic and subsonic cruise data are given.

Nelson, D. P.↗
NASA NTRS1981

Hybrid and electric advanced vehicle systems (heavy) simulation

A computer program to simulate hybrid and electric advanced vehicle systems (HEAVY) is described. It is intended for use early in the design process: concept evaluation, alternative comparison, preliminary design, control and management strategy development, component sizing, and sensitivity studies. It allows the designer to quickly, conveniently, and economically predict the performance of a proposed drive train. The user defines the system to be simulated using a library of predefined component models that may be connected to represent a wide variety of propulsion systems. The development of three models are discussed as examples.

Hammond, R. A.↗
NASA NTRS1982

Evaluation of automated decisionmaking methodologies and development of an integrated robotic system simulation. Volume 1: Study results

A variety of artificial intelligence techniques which could be used with regard to NASA space applications and robotics were evaluated. The techniques studied were decision tree manipulators, problem solvers, rule based systems, logic programming languages, representation language languages, and expert systems. The overall structure of a robotic simulation tool was defined and a framework for that tool developed. Nonlinear and linearized dynamics equations were formulated for n link manipulator configurations. A framework for the robotic simulation was established which uses validated manipulator component models connected according to a user defined configuration.

Lowrie, J. W.↗
NASA NTRS1983

Model aerodynamic test results for a refined actuated inlet ejector nozzle at simulated takeoff and cruise conditions

Wind tunnel model tests were conducted to demonstrate the aerodynamic performance improvements of a refined actuated inlet ejector nozzle. Models of approximately one-tenth scale were configured to simulate nozzle operation at takeoff, subsonic cruise, transonic cruise and supersonic cruise. Variations of model components provided a performance evaluation of ejector inlet and exit area, forebody boattail angle and ejector inlet operation in the open and closed mode. Approximately 700 data points were acquired at Mach numbers of 0, 0.36, 0.9, 1.2, and 2.0 for a wide range of nozzle flow conditions. Results show that relative to two ejector nozzles previously tested performance was improved significantly at takeoff and subsonic cruise performance, a C sub f of 0.982, was attained equal to the high performance of the previous tests. The established advanced supersonic transport propulsion study performance goals were met or closely approached at takeoff and supersonic cruise.

Nelson, D. P.↗
NASA NTRS1983

Time-resolved spectrophotometry of the emission lines in the galactic X-ray source H2252-035

The galactic X-ray source H2252-035 has been the object of a concentrated observational effort, since Griffiths et al. (1980) have identified it with a cataclysmic variable-like spectrum. Since the observed 859 s periodicity corresponds to the beat frequency between the X-ray and orbital periods, it has been interpreted as related to a reprocessing of the X-ray flux into optical emission in some region of the system which is rotating with the orbital period and heated by beamed X-ray emission from the compact star. In connection with the present investigation, H2252-035 has been observed with a 120 inch (3 m) telescope and image dissector scanner on 1980 September 9/10 and on 1981 September 20/21. At a time resolution of approximately 2 minutes, four bright emission lines showed short time-scale flickering and a pronounced orbital period variation in phase with the continuum modulation. A two-component model for the line emission region is proposed.

Clarke, J. T.↗
NASA NTRS1983

Aerodynamic characteristics, including effect of body shape, of a Mach 6 aircraft concept

Longitudinal aerodynamic characteristics for a hydrogen-fueled hypersonic transport concept at Mach 6 are presented. The model components consist of four bodies with identical longitudinal area distributions but different cross-sectional shapes and widths, a wing, horizontal and vertical tails, and a set of wing-mounted nacelles simulated by slid bodies on the wing upper surface. Lift-drag ratios were found to be only sightly affected by fuselage planform width or cross sectional shape. Relative distribution of fuselage volume above and below the wing was found to have an effect on the lift-drag ratio, with a higher lift drag ratio produced by the higher wing position.

Riebe, G. D.↗
NASA NTRS1984

Trace elements in rims and interiors of Chainpur chondrules

Trace elements were measured in the rims and interiors of nine chondrules separated from the Chainpur LL-3 chondrite. Whole rock samples of Chainpur and samples of separated rims were also measured. Chondrule rims are moderately enriched in siderophile and volatile elements relative to the chondrule interiors. The enriched volatile elements include the lithophilic volatile element Zn. The moderate enrichment of volatiles in chondrule rims and the lack of severe depletion in chondrules can account for the complete volatile inventory in Chainpur. These results support a three-component model of chondrite formation in which metal plus sulfide, chondrules plus rims and matrix silicates are mixed to form chondrites.

Wilkening, L. L.↗