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Fluid properties of refrigerant-21 were investigated at temperatures from the freezing point to 423 Kelvin and at pressures to 1.38 x 10 to the 8th power N/sq m (20,000 psia). The fluid properties included were: density, vapor pressure, viscosity, specific heat, thermal conductivity, thermal expansion coefficient, freezing point and bulk modulus. Tables of smooth values are reported.
System analyses are presented for electrically sustained, collision dominated plasma centrifuges, in which the plasma rotates under the influence of the Lorentz forces resulting from the interaction of the current density fields with an external magnetic field. It is shown that gas discharge centrifuges are technically feasible in which the plasma rotates at speeds up to 1 million cm/sec. The associated centrifugal forces produce a significant spatial isotope separation, which is somewhat perturbed in the viscous boundary layers at the centrifuge walls. The isotope separation effect is the more pronounced. The induced magnetic fields have negligible influence on the plasma rotation if the Hall coefficient is small. In the technical realization of collision dominated plasma centrifuges, a trade-off has to be made between power density and speeds of rotation. The diffusion of sputtered atoms to system surfaces of ion propulsion systems and the deposition of the atoms are treated theoretically by means of a simple model which permits an analytical solution. The problem leads to an inhomogeneous integral equation.
A program is described which extends the differential equation solving capability of MACSYMA to power series solutions and is available via the SHARE library. The program is directed toward those classes of equations with variable coefficients (in particular, those with singularities) and uses the method of Frobenius. Probably the most important distinction between this package and others currently available or being developed is that, wherever possible, this program will attempt to provide a complete solution to the equation rather than an approximation, i.e., a finite number of terms. This solution will take the form of a sum of infinite series.
Accurate information about wind action on antennas is required for reliable prediction of antenna pointing errors in windy weather and for the design of an antenna controller with wind disturbance rejection properties. The wind tunnel data obtained 3 years ago using a scaled antenna model serves as an antenna industry standard, frequently used for the first purpose. The accuracy of the wind tunnel data has often been challenged, since they have not yet been tested in a field environment (full-aized antenna, real wind, actual terrain, etc.). The purpose of this investigation was to obtain selected field measurements and compare them with the available wind tunnel data. For this purpose, wind steady-state torques of the DSS-13 antenna were measured, and dimensionless wind torque coefficients were obtained for a variety of yaw and elevation angles. The results showed that the differences between the wind tunnel torque coefficients and the field torque coefficients were less than 10 percent of their values. The wind-gusting action on the antenna was characterized by the power spectra of the antenna encoder and the antenna torques. The spectra showed that wind gusting primarily affects the antenna principal modes.
A previous analysis of turbulent heat transfer and flow with variable fluid properties in smooth passages is extended to flow over a flat plate at high Mach numbers, and the results are compared with experimental data. Velocity and temperature distributions are calculated for a boundary layer with appreciative effects of frictional heating and external heat transfer. Viscosity and thermal conductivity are assumed to vary as a power or the temperature, while Prandtl number and specific heat are taken as constant. Skin-friction and heat-transfer coefficients are calculated and compared with the incompressible values. The rate of boundary-layer growth is obtained for various Mach numbers.
A bootstrap configuration has been proposed for multistage pulse-tube coolers that, for instance, provide final-stage cooling to temperatures as low as 20 K. The bootstrap configuration supplants the conventional configuration, in which customarily the warm heat exchangers of all stages reject heat at ambient temperature. In the bootstrap configuration, the warm heat exchanger, the inertance tube, and the reservoir of each stage would be thermally anchored to the cold heat exchanger of the next warmer stage. The bootstrapped configuration is superior to the conventional setup, in some cases increasing the 20 K cooler's coefficient of performance two-fold over that of an otherwise equivalent conventional layout. The increased efficiency could translate into less power consumption, less cooler mass, and/or lower cost for a given amount of cooling.
A renewed interest in lunar exploration has spawned an array of development efforts for lunar surface assets. These systems depend on the reliable operation of mechanisms and components that may be susceptible to performance degradations or failure due to dust. The Uniform Dust Deposition System was developed at the NASA Glenn Research Center to provide repeatable, uniform, and automated deposition of simulants on surfaces of interest for dust mitigation testing. The system is capable of depositing simulants on test articles up to 60 cm in diameter and 15 cm high in a dry air environment with less than 1 percent relative humidity while keeping users safe from aerosolized dust. The automation of the system allows for high testing throughput while not sacrificing test quality and allows the user to reduce data in parallel. The additional development of a simulant preparation technique complements the repeatability of the deposition physics during testing. The system includes an imaging subsystem that leverages the power of machine learning to count simulant particles and measure their size, thereby allowing for accurate predictions of surface deposition densities (coefficient of determination R^(2) = 0.93) from images alone. The coverage of dust on a surface was shown to be uniform (coefficient of variation CV < 0.11), allowing developers to accurately evaluate the performance of their technology with a prescribed amount of lunar simulant, information that can be used to develop and refine models. The accuracy of the system is currently less than desired for a single deposition run, with a standard deviation (SD) ranging from 18 to 24 mg, or 0.839 to 1.184 mg/sq. cm , for a 5-cm-diameter area. However, the accuracy can be improved by performing multiple deposition runs to build dust to a desired level. Testing has shown that a SD of 0.2 to 0.6 mg, or 0.076 to 0.227 mg/sq. cm, can be achieved for a 5-cm-diameter area using this technique.
The availability of accurate and reliable rainfall data that are applicable to various phenomenological, climatological, and modeling studies is important, especially in the Philippines, which is considered to be highly vulnerable to natural hazards and a changing climate. The presented strategy involved constructing a dataset consisting of synoptic data, automatic rain gauge (ARG) measurements, and satellite data that are co-registered, consistent, and formatted in the same manner. Although sparse in number, the synoptic stations provide the most accurate rainfall information and were used as the baseline for creating the dataset. The ARGs that are within a distance of 1 km to the synoptic stations were used to determine the correction factors needed to make the synoptic and ARG data consistent. Subsequently, the corrected ARGs were used to make the satellite IMERG data consistent with both ARG and synoptic data. In case of the latter, only IMERG pixels with at least 10 ARGs within the relatively large footprint of the satellite sensor were used in estimating the required correction parameters derived from a combination of a power transform and linear regression correction techniques. The final results show good agreement of synoptic and corrected ARG data with correlation coefficients of 0.94 and 0.97 for the 10 day and monthly data, respectively, and improvement in the linear regression slope from 0.67 to 0.90 for 10 day data, and 0.70 to 0.94 for monthly data. In addition, the corrected ARG data agree well with the corrected IMERG data, with correlation coefficients of 0.88 and 0.93 for the 10 day and monthly data, respectively, and an improvement in slope from 0.66 to 0.87 for 10 day data, and 0.74 to 0.99 for monthly data. The merit of using a combined dataset is illustrated through comparative analyses of the IMERG data and spatially interpolated synoptic and ARG data. The results show general agreements in spatial patterns of rainfall across the datasets, especially in areas where in situ measurements are recorded. The observed discrepancy when ground data is limited emphasizes the need for satellite IMERG data to obtain the true spatial patterns of rainfall distribution.
In the presence of rain, the radar return powers from a three-frequency radar, with center frequency at 22.235 GHz and upper and lower frequencies chosen with equal water vapor absorption coefficients, can be used to estimate water vapor density and parameters of the precipitation. A linear combination of differential measurements between the center and lower frequencies on one hand and the upper and lower frequencies on the other provide an estimate of differential water vapor absorption. Conversely, the difference in radar reflectivity factors (in dB) between the upper and lower frequencies is independent of water vapor absorption and can be used to estimate the median mass diameter of the hydrometeors. For a down-looking radar, path-integrated estimates of water vapor absorption may be possible under rain-free as well as raining conditions by using the surface returns at the three frequencies. Cross-talk or interference between the precipitation and water vapor estimates depends on the frequency separation of the channels as well as on the phase state and the median mass diameter of the hydrometeors. Simulations of the retrieval of water vapor absorption show that the largest source of variability arises from the variance in the measured radar return powers while the largest biases occur in the mixed-phase region. Use of high pulse repetition frequencies and signal whitening methods may be needed to obtain the large number of independent samples required. Measurements over a fractional bandwidth, defined as the ratio of the difference between the upper and lower frequencies to the center frequency, up to about 0.2 should be passible in a differential frequency mode, where a single transceiver and antenna are used. Difficulties in frequency allocation may require alternative choices of frequency where the water vapor absorptions at the low and high frequencies are unequal. We consider the degradation in the retrieval accuracy when the frequencies are not optimum.
Rate coefficients for the O(+) + N2 atom transfer and O(+) + O2 charge transfer reactions are determined at thermal energies between 300 K and 900 K difference in a heated drift tube mass spectrometer apparatus. At 300 K the values K(O(+) + N2) = (1.2 plus or minus 0.1) x 10 to the negative 12 power cubic cm/sec and k(O(+) + O2) = (2.1 plus or minus 0.2) x 10 to the negative 11 power cubic cm/sec were obtained, with a 50% difference decrease in the reaction rates upon heating to 700 K. These results are in good agreement with heated flowing afterglow results, but the O(+) + O2 thermal rate coefficients are systematically lower than equivalent Maxwellian rates inferred by conversion of nonthermal drift tube and flow drift data.
A voltage-controlled 8415-MHz FET oscillator stabilized by a dielectric resonator is described. The oscillator provides over 3.2-MHz linear electronic tuning range with a flat power output equal to +1.8 dBm (27 C, nominal), a single-sideband noise-to-carrier ratio of -68 dBc/Hz at 1 kHz off carrier, and a frequency-temperature coefficient of 0.54 parts per million/C over a -24 C to 75 C range. The oscillator withstood 150 Krads (Si) of gamma radiation with no significant performance degradation. The overall performance of the FET oscillator is far superior in many ways to that of an equivalent bipolar oscillator for space applications. For space applications, the FET dielectric resonator oscillator (DRO) is preferred over bipolar DRO because of its lower DC power consumption, better thermal frequency stability, linear electronic tunability, and higher RF output power capability.
Measurements can be made of Very Long Baseline Interferometer (VLBI) phase scintillations due to plasma turbulence in the solar corona and solar wind. These measurements provide information on the spectrum and intensity of density fluctuations with scale sizes of a few hundred to several thousand kilometers. If we model the spatial power spectrum of the density fluctuations as P(sub delta n)(q) = C(sup 2)(sub N) q(sup -alpha), where q is the spatial wavenumber, these observations yield both alpha and the path-integrated value of C(sup 2)(sub N). The recently completed Very Long Baseline Array (VLBA) is capable of making such measurements over the heliocentric distance range from a few solar radii to 60 solar radii and beyond. This permits the determination with the same technique and instrument of the radial evolution of turbulent characteristics, as well as their dependence on solar wind transients, sector structure, etc. In this paper we present measurements of 13 sources observed at a wide range of solar elongations, and at different times. These observations show that the coefficient C(sup 2(sub N), depends on heliocentric distance as approximately C(sup 2)(sub N) varies as (R/Solar Radius)(sup -3.7). The radio derived power spectral characteristics are in agreement with in situ measurements by the Helios spacecraft for regions of slow solar wind, but fast solar wind does not have large enough density fluctuations to account for the magnitude of the observed scintillations. The observed radial dependence is consistent with a WKB-type evolution of the turbulence with heliocentric distance. Our data also show indication of turbulence enhancement associated with solar wind transients.
A computer-simulation study was undertaken to investigate the application of Fuel Conservative Guidance (FCG) techniques, developed at NASA Ames Research Center, to improve the fuel efficiency and minimize recovery time of powered-lift short-takeoff-and-landing (STOL) airplanes operating from aircraft carriers at sea. The FCG system consists of a set of algorithms whose coefficients and parameters limits match those of the Quiet Short-Haul Research Aircraft. When a flightpath is specified by a set of initial conditions for the aircraft and a set of positional waypoints with associated airspeeds, the FCG synthesizes the necessary guidance commands to capture the specified path at any specified waypoint and to optimize fuel consumption and time fo fly along the path. Closed-form expressions are developed for calculating the altitude profile synthesized by the algorithm. Results of this simulation study show that when restrictions on the approach flightpath imposed for manual operation are removed completely, fuel consumption during the approach was reduced by as much as 38 percent (434 lb of fuel) and the time required to fly the flightpath was reduced by as much as 28 percent (209 sec). Savings because of FCG were produced by: (1) shortening the total flight time and distance, and (2) keeping the airspeed high as long as possible to minimize time spent flying in a powered-lift mode.
An order of magnitude study of the ratios of successive polynomial derivatives yields information about the number of roots at an approached root point and the approximate location of a root point from a nearby point. The location approximation improves as a root is approached, so a powerful convergence procedure becomes available. These principles are developed into a computer program which finds the roots of polynomials with real number coefficients.
Information on the cosmic-ray diffusion coefficient, kappa, derived from near-earth observations of the solar modulation of galactic electron fluxes and from the near-earth power spectra of the interplanetary magnetic field, has been used to study the heliocentric radial dependence of kappa, and to derive limits on the spatial extent of the solar modulation region. Representing kappa, as a separable function of radius r and rigidity, and assumming kappa(r) proportional to r to the n-th power, we can place a limit on the power law exponent, n not greater than 1.2. The distance of the modulation boundary is a function of n, and, e.g., for n = 0, falls into the range of 6-25 AU.
Methods of predicting integral parameters and skin friction coefficients of turbulent boundary layers developing over moving ground planes were evaluated. The three methods evaluated were: relative integral parameter method; relative power law method; and modified law of the wall method.
Simple method prevents loosening due to thermal mismatch. Four segment die pushed outward against tubing wall by tapered ram. Boss on each segment of die produces dimple in wall. Ram driven by commercial pneumatic cylinder powered by air at 250 psi. Method applicable to brazing of heat exchanges, thrust chambers, and other assemblies in which thermal expansion coefficients of materials differ significantly.
Vacuum metal-organic-chemical-vapor-deposition (MOCVD) is a new fabrication process with improved safety and easier scalability due to its metal rather than glass construction and its uniform multiport gas injection system. It uses source materials more efficiently than other methods because the vacuum molecular flow conditions allow the high sticking coefficient reactants to reach the substrates as undeflected molecular beams and the hot chamber walls cause the low sticking coefficient reactants to bounce off the walls and interact with the substrates many times. This high source utilization reduces the materials costs power device and substantially decreases the amounts of toxic materials that must be handled as process effluents. The molecular beams allow precise growth control. With improved source purifications, vacuum MOCVD has provided p GaAs layers with 10-micron minority carrier diffusion lengths and GaAs and GaAsSb solar cells with 20% AMO efficiencies at 59X and 99X sunlight concentration ratios. Mechanical stacking has been identified as the quickest, most direct and logical path to stacked multiple-junction solar cells that perform better than the best single-junction devices. The mechanical stack is configured for immediate use in solar arrays and allows interconnections that improve the system end-of-life performance in space.