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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Phase-ambiguity resolution for QPSK modulation systems. Part 2: A method to resolve offset QPSK

Part 2 presents a new method to resolve the phase-ambiguity for Offset QPSK modulation systems. When an Offset Quaternary Phase-Shift-Keyed (OQPSK) communications link is utilized, the phase ambiguity of the reference carrier must be resolved. At the transmitter, two different unique words are separately modulated onto the quadrature carriers. At the receiver, the recovered carrier may have one of four possible phases, 0, 90, 180, or 270 degrees, referenced to the nominally correct phase. The IF portion of the channel may cause a phase-sense reversal, i.e., a reversal in the direction of phase rotation for a specified bit pattern. Hence, eight possible phase relationships (the so-called eight ambiguous phase conditions) between input and output of the demodulator must be resolved. Using the In-phase (I)/Quadrature (Q) channel reversal correcting property of an OQPSK Costas loop with integrated symbol synchronization, four ambiguous phase conditions are eliminated. Thus, only four possible ambiguous phase conditions remain. The errors caused by the remaining ambiguous phase conditions can be corrected by monitoring and detecting the polarity of the two unique words. The correction of the unique word polarities results in the complete phase-ambiguity resolution for the OQPSK system.

Nguyen, Tien Manh↗
NASA NTRS1989

Digitally modulated bit error rate measurement system for microwave component evaluation

The NASA Lewis Research Center has developed a unique capability for evaluation of the microwave components of a digital communication system. This digitally modulated bit-error-rate (BER) measurement system (DMBERMS) features a continuous data digital BER test set, a data processor, a serial minimum shift keying (SMSK) modem, noise generation, and computer automation. Application of the DMBERMS has provided useful information for the evaluation of existing microwave components and of design goals for future components. The design and applications of this system for digitally modulated BER measurements are discussed.

Shalkhauser, Mary Jo W.↗
NASA NTRS1989

Space module assembly apparatus with docking alignment flexibility and restraint

A berthing mechanism especially for use in berthing and compliant air-tight securing between manned space vehicle and modules is disclosed. The interface is provided by a pair of annular rings, one of which is typically, mechanically attached to the vehicle and the other to the module to which it is to be docked and secured. One of the two rings is attached to a base by resilient bellows. The facing surface of one annular ring is joined to a base by a cable laced through alternating pulleys attached circumferentially so that the interface surface of that ring may be tilted to accommodate angular misalignment as the annular rings are brought into docking (berthing) contact. Interleaving guide flanges with chambered sides provide at least some rotational mialignmnet correction. A plurality of electromechanical actuator/attenuator units provide means for extending one annular ring toward the other in the final stages of docking, for absorbing the initial docking shock and for drawing the annular rings into tight interface contact. Locking hooks provide for securing the interfaces.

Willie D Whitaker↗
NASA NTRS1989

Interfacing modules for integrating discipline specific structural mechanics codes

An outline of the organization and capabilities of the Engine Structures Computational Simulator (Simulator) at NASA Lewis Research Center is given. One of the goals of the research at Lewis is to integrate various discipline specific structural mechanics codes into a software system which can be brought to bear effectively on a wide range of engineering problems. This system must possess the qualities of being effective and efficient while still remaining user friendly. The simulator was initially designed for the finite element simulation of gas jet engine components. Currently, the simulator has been restricted to only the analysis of high pressure turbine blades and the accompanying rotor assembly, although the current installation can be expanded for other applications. The simulator presently assists the user throughout its procedures by performing information management tasks, executing external support tasks, organizing analysis modules and executing these modules in the user defined order while maintaining processing continuity.

Endres, Ned M.↗
NASA NTRS1988

Operation of a deformable mirror device as a Fourier plane phase modulating filter

The operation of a deformable mirror device (DMD) as a Fourier plane phase modulating filter is described. An analysis of the optical characteristics of the DMD elements as phase modulators is summarized. Analytical and experimental results indicating the existence of a quasi-phase-only operational mode are presented. These results are used to specify the mirror deflection required to implement a binary phase-only image correlation operation. An optical correlator system is implemented using the DMD Fourier plane filter and experimental results from this system are compared with computer simulations of the correlator operation.

Florence, James M.↗
NASA NTRS1989

Studies with spike initiators - Linearization by noise allows continuous signal modulation in neural networks

It is shown that noise can be an important element in the translation of neuronal generator potentials (summed inputs) to neuronal spike trains (outputs), creating or expanding a range of amplitudes over which the spike rate is proportional to the generator potential amplitude. Noise converts the basically nonlinear operation of a spike initiator into a nearly linear modulation process. This linearization effect of noise is examined in a simple intuitive model of a static threshold and in a more realistic computer simulation of spike initiator based on the Hodgkin-Huxley (HH) model. The results are qualitatively similar; in each case larger noise amplitude results in a larger range of nearly linear modulation. The computer simulation of the HH model with noise shows linear and nonlinear features that were earlier observed in spike data obtained from the VIIIth nerve of the bullfrog. This suggests that these features can be explained in terms of spike initiator properties, and it also suggests that the HH model may be useful for representing basic spike initiator properties in vertebrates.

Yu, Xiaolong↗
NASA NTRS1988

U.S. Laboratory Module - Its capabilities and accommodations to support user payloads

The U.S. Laboratory Module of the Space Station is discussed, focusing on user accommodations. The configuration and subsystems capabilities of the module are described, including the power, thermal, environmental control, and data management subsystems, the vacuum system, process materials management, and laboratory support equipment. The experimental facilities included in the laboratory are listed. The experiment operations planned for the laboratory are examined and compared with the experimental activities in other manned space laboratories.

Powell, Luther E.↗
NASA NTRS1989

Joint-transform correlator systems using deformable-mirror spatial light modulators

Two joint-transform correlator systems based on deformable-mirror-device (DMD) spatial light modulators and CCD video cameras are described. The system designs provide for real-time correlation between video-formatted input scenes and stored reference images. The DMD light modulators are used exclusively for inputting data in the optical stages of these systems, and the CCD cameras are used to provide the critical square-law detection required in joint-transform achitectures. Experimental verification of the functionality of these DMD/CCD joint-transform systems is also presented.

Florence, James M.↗
NASA NTRS1988

A review of test results on solar thermal power modules with dish-mounted Stirling and Brayton cycle engines

This paper presents results of development tests of various solar thermal parabolic dish modules and assemblies that used dish-mounted Brayton or Stirling cycle engines for production of electric power. These tests indicate that early modules achieve net efficiencies up to 29 percent in converting sunlight to electricity, as delivered to the grid. Various equipment deficiencies were observed and a number of malfunctions occurred. The performance measurements, as well as the malfunctions and other test experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.

Jaffe, Leonard D.↗
NASA NTRS1989

A new calculation of the cosmic-ray antiproton spectrum in the Galaxy and heliospheric modulation effects on this spectrum using a drift plus wavy current sheet model

The expected interstellar antiproton spectrum arising from cosmic-ray interactions in the Galaxy is recalculated, and the modulation of both antiprotons and protons is calculated using a two-dimensional modulation model incorporating gradient and curvature drifts and a wavy current sheet as well as the usual diffusion, convection, and energy-loss effects. Significant differences in the antiproton/proton ratio for different solar magnetic field polarities are predicted as well as a 'low-energy' component for antiprotons below about 1 GeV.

Webber, W. R.↗
NASA NTRS1989

On the ability of rough surface scattering approximations to predict hydrodynamic modulation of the ocean radar cross section - A numerical study

Scattering from the ocean surface at microwave frequencies is often described by the Bragg scattering model or the two-scale model. Here, the ability of these models to predict cross section modulation is investigated by comparing Bragg and two-scale cross-sections with cross sections calculated by a numerical electromagnetic approach. The numerical method is used as the standard of comparison. For slightly rough surfaces, the Bragg model is found to be very accurate, but for much rougher surfaces, the two-scale model is superior and should be used for calculating both the absolute cross section and the change in cross section due to spatial or temporal modulation of the ocean wave height spectrum. These results are relevant to the interpretation of SAR images of ocean surface phenomena which perturb the wave height spectrum at ripple wavelengths.

Durden, Stephen L.↗
NASA NTRS1990

Optical Modulation Via The Photorefractive Effect

Rotation of polarization and use of analyzer yield large variations in intensity. Experiments show one beam of light used to change intensity of another beam via photorefractive effect in GaAs. Each beam causes polarization of other beam to rotate. Rotation detected by passing modulated beam through analyzer. Results agree closely with predictions of theory of photorefractive effect. Modulation scheme works with other photorefractive materials of similar crystallographic symmetry.

Cheng, Li-Jen↗
NASA NTRS1990

Improved Photovoltaic-Driven Quantum Light Modulator

Additional features increase sensitivity and utility. Modifications proposed to improve device described in "Photovoltaic-Driven Multiple-Quantum-Well Modulator" (NPO-16914) and "Strain-Layer-Superlattice Light Modulator" (NPO-16915). Resembles prior devices of this general type but includes active region using quantum state filling and more optimum structure. Exploits quantum well equivalent of Moss-Burnstein shift.

Maserjian, Joseph↗
NASA NTRS1990

Ball-Pass Cage-Modulation Detector

Ball-pass cage-modulation detector puts out signal useful in detecting incipient failure of bearing in rotating machine. Part of system of electronic equipment measuring various components of vibrations in such bearings. Bearing sensor - strain gauge or deflectometer on bearing housing - measures deflections of housing as balls pass by. Output of sensor filtered to extract ball-pass cage modulation, indicative of wear in bearing.

Randall, Richard L.↗
NASA NTRS1989

MT's algorithm: A new algorithm to search for the optimum set of modulation indices for simultaneous range, command, and telemetry

MT's algorithm was developed as an aid in the design of space telecommunications systems when utilized with simultaneous range/command/telemetry operations. This algorithm provides selection of modulation indices for: (1) suppression of undesired signals to achieve desired link performance margins and/or to allow for a specified performance degradation in the data channel (command/telemetry) due to the presence of undesired signals (interferers); and (2) optimum power division between the carrier, the range, and the data channel. A software program using this algorithm was developed for use with MathCAD software. This software program, called the MT program, provides the computation of optimum modulation indices for all possible cases that are recommended by the Consultative Committee on Space Data System (CCSDS) (with emphasis on the squarewave, NASA/JPL ranging system).

Nguyen, Tien Manh↗
NASA NTRS1990

Monitoring of catalyst performance in CO2 lasers using frequency modulation spectroscopy with diode lasers

Closed-cycle CO2 laser operation with removal of O2 and regeneration of CO2 can be achieved by catalytic CO-O2 recombination. Both parametric studies of the optimum catalyst formulation and long-term performance tests require on line monitoring of CO, O2 and CO2 concentrations. There are several existing methods for molecular oxygen detection. These methods are either intrusive (such as electrochemical method or mass spectrometry) or very expensive (such as CARS, UV laser absorption). Researchers demonstrated a high-sensitivity spectroscopic measurement of O2 using the two-tone frequency modulation spectroscopy (FMS) technique with a near infrared GaAlAs diode laser. Besides its inexpensive cost, fast response time, nonintrusive measurements and high sensitivity, this technique may also be used to differentiate between isotopes due to its high spectroscopic resolution. This frequency modulation spectroscopy technique could also be applied for the on-line monitoring of CO and CO2 using InGaAsP diode lasers operation in the 1.55 microns region and H2O in the 1.3 microns region. The existence of single mode optical fibers at the near infrared region makes it possible to combine FMS with optical fiber technology. Optical fiber FMS is particularly suitable for making point-measurements at one or more locations in the CO2 laser/catalyst system.

Wang, Liang-Guo↗
NASA NTRS1990

An expert system to advise astronauts during experiments: The protocol manager module

Perhaps the scarcest resource for manned flight experiments - on Spacelab or on the Space Station Freedom - will continue to be crew time. To maximize the efficiency of the crew and to make use of their abilities to work as scientist collaborators as well as equipment operators, normally requires more training in a wide variety of disciplines than is practical. The successful application of on-board expert systems, as envisioned by the Principal Investigator in a Box program, should alleviate the training bottleneck and provide the astronaut with the guidance and coaching needed to permit him or her to operate an experiment according to the desires and knowledge of the PI, despite changes in conditions. The Protocol Manager module of the system is discussed. The Protocol Manager receives experiment data that has been summarized and categorized by the other modules. The Protocol Manager acts on the data in real-time, by employing expert system techniques. Its recommendations are based on heuristics provided by the Principal Investigator in charge of the experiment. This prototype was developed on a Macintosh II by employing CLIPS, a forward-chaining rule-based system, and HyperCard as an object-oriented user interface builder.

Haymann-Haber, Guido↗