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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Maximum theoretical angular accuracy of planar and linear arrays of sensors

The maximum theoretical accuracy in the angular location of a radiating object that can be obtained by using a planar or linear array is studied. The elements are assumed to have identical radiation patterns and the complex voltages observed at their ports are assumed to be subject to phase measurement errors, having normal probability density. An optimum scheme for the statistical extraction of the parameters defining the direction is established noting that the presence of thermal noise does not affect the structure of the estimator. Comparisons with the conventional multiple interferometric techniques are made.

Borgiotti, G. V.↗
NASA NTRS1977

On the maximum off-axis gain of symmetrical pencil-beam antennas

For a general class of symmetrical pencil-beam antennas, the gain at a given off-axis angle can be maximized by choosing the proper antenna size. The maximum gain at the given angle relative to the on-axis gain is independent of the given angle and dependent only on the main-beam pattern. It is computed here for four commonly used gain functions. Its value, in all cases, is close to 4 dB. This result is important in the definition of service areas for communication and broadcast satellites.

Sawitz, P. H.↗
NASA NTRS1977

Comparison of Estimated with Measured Maximum Instantaneous Distortion Using Flight Data from an Axisymmetric Mixed Compression Inlet

YF-12C flight-measured inlet dynamic distortion data are compared with predictions made on the basis of the method reported by Melick et al. (1976). The YF-12C aircraft is a twin engine aircraft capable of speeds above 3. The inlets have a translating spike to control the inlet throat area. A bypass system is used to control the terminal shock of the inlet for operation in the mixed compression mode. The dynamic data were obtained with the aid of 24 high frequency response total pressure sensors. The model of Melick et al. is discussed along with the computer program used to implement the model. It is found that the predictions of maximum instantaneous distortion are within 20 percent of the measured values, which had been obtained at Mach numbers of 1.8, 2.1, 2.5, and 3.0.

Brilliant, H. M.↗
NASA NTRS1977

Further observations on maximum likelihood estimates of stability and control characteristics obtained from flight data

A maximum likelihood estimation method for flight test data is described. Flight results based on 3000 maneuvers from 30 aircraft on the effect of resolution and sampling rate on the estimates, on understanding the discrepancies previously observed in the magnitude of the Cramer-Rao bounds, on the scale effects on the derivative estimates obtained from dynamic aircraft flight maneuvers, and on the analysis of lateral-directional maneuvers obtained in turbulence, are presented.

Iliff, K. W.↗
NASA NTRS1977

DSN telemetry system performance using a maximum likelihood convolutional decoder

Results are described of telemetry system performance testing using DSN equipment and a Maximum Likelihood Convolutional Decoder (MCD) for code rates 1/2 and 1/3, constraint length 7 and special test software. The test results confirm the superiority of the rate 1/3 over that of the rate 1/2. The overall system performance losses determined at the output of the Symbol Synchronizer Assembly are less than 0.5 db for both code rates. Comparison of the performance is also made with existing mathematical models. Error statistics of the decoded data are examined. The MCD operational threshold is found to be about 1.96 db.

Benjauthrit, B.↗
NASA NTRS1977

Onboard magnetic field modeling for Solar Maximum Mission /SMM/

Analysis and simulation results are presented for magnetic field models for use in attitude acquisition onboard Solar Maximum Mission (SMM). A study was made of the degree of the spherical harmonic expansion of the magnetic field required, considering mission requirements, modeling errors, and magnetometer quantization and biases. It is shown that a fifth-degree field is sufficient to provide two-degree roll angle determination accuracy with a residual magnetic bias of 10 milligauss. Also, a spherical harmonic expansion for the McIlwain L-parameter is included for the first time. This parameter will be telemetered to ground with experimental data. The fifth-degree expansion will provide the L-parameter to within two percent of accepted values. The additional onboard computational burden is the storage of 36 coefficients and an increase of about 15% in computation time. Prototype flight code was developed which is anticipated to require about 2000 bytes of core storage and 30 milliseconds of computation time per orbit point on the NSSC-1 computer.

Headrick, R. D.↗
NASA NTRS1978

Flying-hot-wire study of two-dimensional mean flow past an NACA 4412 airfoil at maximum lift

Hot-wire measurements have been made in the boundary layer, the separated region, and the near wake for flow past an NACA 4412 airfoil at maximum lift. The Reynolds number based on chord was about 1,500,000. The main instrumentation was a hot-wire probe mounted on the end of a rotating arm. A digital computer was used to control synchronized sampling of hot-wire data at closely spaced points along the probe arc. Ensembles of data were obtained at several thousand locations in the flow field. The data include intermittency, two components of mean velocity, and twelve mean values for double, triple, and quadruple products of two velocity fluctuations. The data are available on punched cards in raw form and also after use of smoothing and interpolation routines to obtain values on a fine rectangular grid aligned with the airfoil chord. The data are displayed in the paper as contour plots.

Coles, D.↗
NASA NTRS1978

Estimating maximum instantaneous distortion from inlet total pressure rms measurements

In the present paper, a new mathematical model of inlet turbulence is developed by application of basic fluid dynamics and statistical concepts. The model provides an understanding of the turbulent inlet flow as well as a means of describing the flow in quantitative terms. Specifically, the maximum instantaneous distortion produced by inlet unsteady flow can be estimated by the simple measurement of rms data. Practical application of these techniques leads to a data/acquisition/reduction system that is at least one, and maybe two, orders of magnitude less expensive than conventional methods. Each data point can be reduced in terms of the mean strength of the turbulent vortices. By storing these two parameters (that are representative of the unsteady flow with the steady state information), the maximal instantaneous distortion can be reconstructed for other distortion factors at any time subsequent to the test.

Melick, H. C., Jr.↗
NASA NTRS1978

Attitude control algorithms for the Solar Maximum Mission

Algorithms for onboard attitude control of the Solar Maximum Mission (SMM) are discussed and test results are presented. The algorithms include: despin and sun acquisition, control of pitch and yaw (sun pointing) to 5 arc-sec accuracy and roll (around the sun line) to 0.1 deg, time-optimal and constant-rate slew sequences, attitude maintenance during orbit night and sun reacquisition at orbit dawn, momentum unloading, and gyro drift calibration. The tests were performed on the SMM Software Development and Validation Facility at the NASA Goddard Space Flight Center with a FORTRAN prototype version of the onboard software.

Markley, F. L.↗
NASA NTRS1979

Maximum-likelihood data decoder

Digital convolutional decoder circuit for data communication receiver employs Viterbi decoding algorithm to quickly and efficiently decode data on basis of "maximum likelihood" computations.

Alberda, M. E.↗
NASA NTRS1979

A maximum likelihood convolutional decoder model vs experimental data comparison

This article describes the comparison of a maximum likelihood convolutional decoder (MCD) prediction model and the actual performance of the MCD at the Madrid Deep Space Station. The MCD prediction model is used to develop a subroutine that has been utilized by the Telemetry Analysis Program (TAP) to compute the MCD bit error rate for a given signal-to-noise ratio. The results indicate that that the TAP can predict quite well compared to the experimental measurements. An optimal modulation index also can be found through TAP.

Chen, R. Y.↗
NASA NTRS1979

Optimization of multi-element airfoils for maximum lift

Two theoretical methods are presented for optimizing multi-element airfoils to obtain maximum lift. The analyses assume that the shapes of the various high lift elements are fixed. The objective of the design procedures is then to determine the optimum location and/or deflection of the leading and trailing edge devices. The first analysis determines the optimum horizontal and vertical location and the deflection of a leading edge slat. The structure of the flow field is calculated by iteratively coupling potential flow and boundary layer analysis. This design procedure does not require that flow separation effects be modeled. The second analysis determines the slat and flap deflection required to maximize the lift of a three element airfoil. This approach requires that the effects of flow separation from one or more of the airfoil elements be taken into account. The theoretical results are in good agreement with results of a wind tunnel test used to corroborate the predicted optimum slat and flap positions.

Lawrence E Olson↗
NASA NTRS1979

Approximate maximum likelihood decoding of block codes

Approximate maximum likelihood decoding algorithms, based upon selecting a small set of candidate code words with the aid of the estimated probability of error of each received symbol, can give performance close to optimum with a reasonable amount of computation. By combining the best features of various algorithms and taking care to perform each step as efficiently as possible, a decoding scheme was developed which can decode codes which have better performance than those presently in use and yet not require an unreasonable amount of computation. The discussion of the details and tradeoffs of presently known efficient optimum and near optimum decoding algorithms leads, naturally, to the one which embodies the best features of all of them.

Greenberger, H. J.↗
NASA NTRS1979

Maximum likelihood estimation for life distributions with competing failure modes

Systems which are placed on test at time zero, function for a period and die at some random time were studied. Failure may be due to one of several causes or modes. The parameters of the life distribution may depend upon the levels of various stress variables the item is subject to. Maximum likelihood estimation methods are discussed. Specific methods are reported for the smallest extreme-value distributions of life. Monte-Carlo results indicate the methods to be promising. Under appropriate conditions, the location parameters are nearly unbiased, the scale parameter is slight biased, and the asymptotic covariances are rapidly approached.

Sidik, S. M.↗
NASA NTRS1979

Wing shape optimization for maximum cross-country speed, with mathematical programming

A computer program was developed to calculate numerically the speed and circling polars of an aircraft when the lift and drag characteristics of the wing airfoils are known. The planform of the wing is described by variables which are optimized so that the cross-country speed of the glider is maximum for the particular type of thermal model. Two thermal models are compared and shown that with a greater wing area than now normally used the performance can be increased.

Helwig, G.↗
NASA NTRS1977

A GSTDN/TDRSS compatible RF system for the Solar Maximum Mission /SMM/

The Solar Maximum Mission (SMM) is a major NASA observatory to be launched in late 1979. SMM will be supported by NASA's existing Ground Spaceflight Tracking and Data Network (GSTDN) and the planned Tracking and Data Relay Satellite System (TDRSS). Design of a GSTDN/TDRSS compatible RF system for SMM poses multiple problems related to the complex nature of the observatory command, telemetry, and tracking support requirements and the fundamental differences in signal design, antenna characteristics, data rates, and link performance criteria for GSTDN vs. TDRSS support. The RF system described in this paper achieves full compatibility with a minimum of hardware complexity by use of an integrated antenna system, the NASA standard S-Band transponder, and utilization of both the single access and multiple access support capabilities of the TDRSS to handle both real time data and tape recorder dumps.

Heffernan, P. J.↗