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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Improving range resolution with a frequency-hopping technique

Range resolution of a conventional pulsed Doppler radar is determined by the scattering volume defined by the transmitted pulse shape. To increase the resolution, the length of the pulse must be reduced. Reducing the pulse length also reduces the transmitted power and hense the signal to noise ratio unless the peak power capability of the transmitter is greatly increased. Improved range resolution may also be attained through the use of various pulse coding methods, but such methods are sometimes difficult to implement from a hardware standpoint. The frequency-hopping (F-H) technique described increases the range resolution of pulse Doppler MST (mesosphere stratosphere troposphere) radar without the need for extensive modifications to the radar transmitter. This technique consists of sending a repeated sequence of pulses, each pulse in the sequence being transmitted at a unique radio frequency that is under the control of a microcomputer. This technique is discussed along with other radar parameters.

Stitt, G. R.↗
NASA NTRS2005

Airborne Shaped Sonic Boom Demonstration Pressure Measurements with Computational Fluid Dynamics Comparisons

The Shaped Sonic Boom Demonstration project showed for the first time that by careful design of aircraft contour the resultant sonic boom can maintain a tailored shape, propagating through a real atmosphere down to ground level. In order to assess the propagation characteristics of the shaped sonic boom and to validate computational fluid dynamics codes, airborne measurements were taken of the pressure signatures in the near field by probing with an instrumented F-15B aircraft, and in the far field by overflying an instrumented L-23 sailplane. This paper describes each aircraft and their instrumentation systems, the airdata calibration, analysis of the near- and far-field airborne data, and shows the good to excellent agreement between computational fluid dynamics solutions and flight data. The flights of the Shaped Sonic Boom Demonstration aircraft occurred in two phases. Instrumentation problems were encountered during the first phase, and corrections and improvements were made to the instrumentation system for the second phase, which are documented in the paper. Piloting technique and observations are also given. These airborne measurements of the Shaped Sonic Boom Demonstration aircraft are a unique and important database that will be used to validate design tools for a new generation of quiet supersonic aircraft.

Haering, Edward A., Jr.↗
NASA NTRS1972

Permutation codes for sources.

Source encoding techniques based on permutation codes are investigated. For a broad class of distortion measures it is shown that optimum encoding of a source permutation code is easy to instrument even for very long block lengths. Also, the nonparametric nature of permutation encoding is well suited to situations involving unknown source statistics. For the squared-error distortion measure a procedure for generating good permutation codes of a given rate and block length is described. The performance of such codes for a memoryless Gaussian source is compared both with the rate-distortion function bound and with the performance of various quantization schemes. The comparison reveals that permutation codes are asymptotically ideal for small rates and perform as well as the best entropy-coded quantizers presently known for intermediate rates. They can be made to compare favorably at high rates, too, provided the coding delay associated with extremely long block lengths is tolerable.

Berger, T.↗
NASA NTRS1972

Modular arithmetic weight and cyclic shifting.

This note shows that the modular arithmetic weight of an integer is invariant to the cyclic shifts of its radix-2 form. This result leads to a reduced search for the minimum weight codeword in a cyclic AN-code as well as to a better understanding of previous work.

Hartman, W. F.↗
NASA NTRS1975

The application of interactive graphics to large time-dependent hydrodynamics problems

A written companion of a movie entitled "Interactive Graphics at Los Alamos Scientific Laboratory" was presented. While the movie presents the actual graphics terminal and the functions performed on it, the paper attempts to put in perspective the complexity of the application code and the complexity of the interaction that is possible.

Gama-Lobo, F.↗
NASA NTRS1977

Backup flight control system functional evaluator software manual

The software for the Backup Flight Control System Functional Evaluator (BFCSFE) on a Data General Corporation Nova 1200 computer consists of three programs: the ground support program, the operational flight program (OFP), and the ground pulse code modulation (PCM) program. The Nova OFP software is structurally as close as possible to the AP101 code; therefore, this document highlights and describes only those areas of the Nova OFP that are significantly different from the AP101. Since the Ground Support Program was developed to meet BFCSFE requirements and differs considerably from the AP101 code, it is described in detail.

Helmke, C. A.↗
NASA NTRS1977

Controlled flexibility in technical editing - The levels-of-edit concept at JPL

The levels-of-edit concept, which can be used to specify the amount of editorial effort involved in the preparation of a manuscript for publication, is discussed. Nine types of editing are identified and described. These include coordination edit (preparing estimates, gathering cost data, monitoring production processes), policy edit, integrity edit (making sure that parts of a publication match in a physical or numerical sense), screening edit (ensuring that the quality of camera-ready copy is sufficient for external publication), copy clarification edit, format edit, mechanical style edit, language edit, and substantive edit (reviewing the manuscript for content coherence, emphasis, subordination and parallelism). These functions are grouped into five levels of edit. An edit-level number is assigned to each manuscript, providing a quantitative and qualitative indicator of the editing to be done which is clearly understood by authors, managers, and editors alike. In addition, clear boundaries are drawn between normal and extraordinary editing tasks. Individual organizations will group various edits in different ways to reflect their needs and priorities; the essential element of the system is unambiguous definition and coding of the types and amount of work to be done.

Buehler, M. F.↗
NASA NTRS1978

The STAGS computer code

Basic information about the computer code STAGS (Structural Analysis of General Shells) is presented to describe to potential users the scope of the code and the solution procedures that are incorporated. Primarily, STAGS is intended for analysis of shell structures, although it has been extended to more complex shell configurations through the inclusion of springs and beam elements. The formulation is based on a variational approach in combination with local two dimensional power series representations of the displacement components. The computer code includes options for analysis of linear or nonlinear static stress, stability, vibrations, and transient response. Material as well as geometric nonlinearities are included. A few examples of applications of the code are presented for further illustration of its scope.

Almroth, B. O.↗
NASA NTRS1980

Trophic classification of Tennessee Valley area reservoirs derived from LANDSAT multispectral scanner data

LANDSAT MSS data from four different dates were extracted from computer tapes using a semiautomated digital data handling and analysis system. Reservoirs were extracted from the surrounding land matrix by using a Band 7 density level slice of 3; and descriptive statistics to include mean, variance, and ratio between bands for each of the four bands were calculated. Significant correlations ( 0.80) were identified between the MSS statistics and many trophic indicators from ground truth water quality data collected at 35 reservoirs in the greater Tennessee Valley region. Regression models were developed which gave significant estimates of each reservoir's trophic state as defined by its trophic state index and explained in all four LANDSAT frames at least 85 percent of the variability in the data. To illustrate the spatial variations within reservoirs as well as the relative variations between reservoirs, a table look up elliptical classification was used in conjunction with each reservoir's trophic state index to classify each reservoir on a pixel by pixel basis and produce color coded thematic representations.

Meinert, D. L.↗
NASA NTRS1982

Image data compression application to imaging spectrometers

The potential of image data compression techniques to satisfy the anticipated requirements of imaging spectrometer missions is discussed. Noiseless coding, rate controlled compression, cluster compression, and error protection are addressed.

Rice, R. F.↗
NASA NTRS1982

Instrumentation, data acquisition and reduction for a large spaceborne helium dewar

The data acquisition system monitors five types of transducers: (1) platinum and germanium resistance thermometers; (2) superconducting liquid level indicators for both cryogen tanks; (3) pressure transducers for both tanks; (4) strain gauges at critical structural locations; and (5) flowmeters for monitoring cryogen tank boiloff which are linear voltage output transducers. All the transducers produce a voltage proportional to the parameter they measure; this is routed to a single six and one-half digit voltmeter by way of an 80-channel multiplexer. The data acquisition program has six main functions: (1) definition and modification of the channels to be stimulated; (2) sensor stimulation and measurement; (3) raw data storage; (4) raw data conversion; (5) real-time formatting and output of raw or converted data; and (6) editing. The heart of the program is a driver section that represents approximately 20 percent of the code. The driver mode sequences and controls the six main functions.

Brooks, W. F.↗
NASA NTRS1986

Viterbi algorithm on a hypercube: Concurrent formulation

The similarity between the Fast Fourier Transform and the Viterbi algorithm is exploited to develop a Concurrent Viterbi Algorithm suitable for a multiprocessor system interconnected as a hypercube. The proposed algorithm can efficiently decode large constraint length convolutional codes, using different degrees of parallelism, and is attractive for VLSI implementation.

Pllara, F.↗
NASA NTRS1986

A three-dimensional axisymmetric calculation procedure for turbulent flows in a radial vaneless diffuser

An analytical model is proposed to calculate the three-dimensional axisymmetric turbulent flowfield in a radial vneless diffuser. The model assumes that the radial and tangential boundary layer profiles are approximated by power law profiles. Then, using the integrated radial and tangential momentum and continuity equations for the boundary layer and corresponding inviscid equations for the core flow, there results six ordinary differential equation in six unknowns which are easily solved using a Runge-Kutta technique. A model is also proposed for fully developed flow. The results using this technique were compared with the results from a three-dimensional viscous, axisymmetric duct code and with experimental data and good quantitative agreement was obtained.

Schumann, L. F.↗
NASA NTRS1987

Digital modulation for an aeronautical mobile satellite system

A review is provided of radio technology, particularly signal modulation, in a satellite-based aeronautical communication system. The propagation environment is examined, and a generic signal-detection strategy is established. The following are then covered: signal bandwidth and carrier modulation; power performance; error detection and block coding; channel spacing; the modulator and demodulator; and coarse frequency error detection.

Davarian, F.↗