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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

University resources sharing using the CTS

NASA-Ames Research Center and Stanford University in California, and Carleton University in Ottawa, Canada, are designing a curriculum-sharing experiment which will use compressed digital television. The experiment will permit evaluation of the potential of curriculum sharing by two universities which are geographically distant, but capable of transmitting and receiving television signals. The evaluation of the curriculum sharing per se will include inputs from faculty, staff and students at both institutions. Accessibility to and acceptability of each other's curriculum will be studied and recorded. Adjustments to differences in academic terms, class meeting times, teaching styles and similar issues will be closely monitored. It is hoped that this experiment will provide long-range planners the kind of information which they will need when designing large-scale educational telecommunications systems for the future.

Down, K. S.↗
NASA NTRS1979

Application of non-attenuating frequency radars for prediction of rain attenuation and space diversity performance

In order to establish transmitter power and receiver sensitivity levels at frequencies above 10 GHz, the designers of earth-satellite telecommunication systems are interested in cumulative rain fade statistics at variable path orientations, elevation angles, climatological regions, and frequencies. They are also interested in establishing optimum space diversity performance parameters. In this work are examined the many elements involved in the employment of single non-attenuating frequency radars for arriving at the desired information. The elements examined include radar techniques and requirements, phenomenological assumptions, path attenation formulations and procedures, as well as error budgeting and calibration analysis. Included are the pertinent results of previous investigators who have used radar for rain attenuation modeling. Suggestions are made for improving present methods.

Goldhirsh, J.↗
NASA NTRS1981

Telecommunications in cometary environments

Propagation effects on telecommunications in a cometary environment include those due to dust, the inhomogeneous plasma of the coma and tail, and ionization generated by impact of neutral molecules and dust on the spacecraft. Attenuation caused by dust particles is estimated to be on the order of 10 to the minus 5th power dB for the Halley Intercept Mission. Ionization generated by impact on the spacecraft is estimated to result in an electron content of 10 to the 12th power to 10 to the 13th power el/sq meters (3 eV electrons) along the telecommunications path. An estimate of the electron content due to Comet Halley itself is 10 to the 16th power to 10 to the 17th power el/sq meters, compared to a content of 10 to the 16th power to 10 to the 18th power el/sq meters for the Earth's ionosphere and 10 to the 17th power to 10 to the 18th power el/sq meters for the interplanetary medium. The electron content of the plasma near Comet Halley will cause excess range delay, and a Doppler shift of the signal from the spacecraft will occur in propagation to the rate of change of the path electron content. It is recommended that S and X down-link frequencies by employed to monitor the path electron content and amplitude scintillation and spectral broadening of the received signals. These measurements will provide a quantitative base of knowledge that will be valuable for radio science and telecommunications system design purposes.

Flock, W. L.↗
NASA NTRS1982

Intermodulation analysis

In single channel-per-carrier (SCPC) telecommunication system, hundreds of carriers are routed through common nonlinear satellite amplifiers causing intermodulation distortion. While development of nearly linear and efficient high-power amplifiers is essential to LMSS to reduce this distortion, some degree of intermodulation is unavoidable. An evaluation of the carrier-to-intermodulation ratio for each channel is an essential element in the design of such systems for optimum utilization of satellite power and bandwidth. The determination of channel distribution within the power amplifier bandwidth is considered.

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NASA NTRS1981

The estimation of convective precipitation from GOES imagery with the Griffith/Woodley technique

Improved rainfall monitoring using satellite and conventional data are described. A method was developed to: (1) provide rainfall evaluations more uniform, accurate and complete than can be derived from satellite or conventional data alone; (2) serve current operational environmental program in countries with special needs for improved rainfall data; (3) invoke either polar orbiting and/or geostationary imagery as the satellite inputs; (4) utilize global telecommunication system (GTS) SYNOP messages as the basic conventional data inputs; (5) be applicable to any and all types of weather situations in the operational areas; (6) be undemanding in hardware and software so as to be an option available for use even by nations or agencies with very limited financial resources.

Griffith, C. G.↗
NASA NTRS1983

Telemetry Modulation and Coping

Digital telemetry has supplanted analog telemetry for deep space communications. With digital telemetry, the telecommunications systems design engineer may use error correcting codes. This allows increased error protection at the cost of increased bandwidth. All science telemetry returned from the Voyager and Galileo spacecraft are protected by error correcting codes. Both the modulation and coding of digital telemetry for the deep space channel are considered. The descriptions include relative performance of some competing schemes. However, the treatment given here is, of necessity, cursory. A small class of modulation schemes has proven to be best for the deep space channel. The digital telemetry is either phase-shift-keyed onto a squarewave subcarrier and then phase modulated onto the carrier or the digital telemetry is directly phase modulated onto the carrier.

Kinman, P. W.↗
NASA NTRS1984

Earth orbiter into planetary orbiter - What's the problem?

A recent series of competitive design studies appears to have yielded positive results about the efficacy of adapting earth-orbiting spacecraft to perform planetary missions. The purpose of this paper is twofold: (1) to show the intrinsic attributes required to adapt an earth orbiter into a Martian orbiter compatible with the scientific requirements, and (2) to show the minimum requisite changes needed to make the adaptation. It is shown that major deficiencies of such conversion for earth-orbiting satellites lie in the not-unexpected inability of its telecommunications system to operate at Martian distances and its lack of an autonomous recovery system from anomalous performance. Since these deficiencies can be overcome without too great a financial or schedule penalty, the study shows that the adaptation can be made cost effectively.

Brodsky, R. F.↗
NASA NTRS1984

Natural radio noise - A mini-review

Natural radio noise in telecommunication systems can be accounted for by the contribution which it makes to antenna noise temperature. Attenuation due to water vapor and oxygen, clouds, and precipitation is accompanied by thermal noise which further degrades the applicable signal-to-noise ratio. Extraterrestrial noise may be of thermal or nonthermal origin and may cover a continuum of frequencies or occur at discrete frequencies. The spectral index n (the exponent giving the variation of noise power density with wavelength) is -2 for a black body and between 0 and -2 for thermal emission in general. The mechanism responsible for much of the extensive nonthermal extraterrestrial noise is synchrotron radiation, characterized by a positive spectral index.

Flock, W. L.↗
NASA NTRS1984

Activities of the Jet Propulsion Laboratory, 1 January - 31 December 1983

There are many facets to the Jet Propulsion Laboratory, for JPL is an organization of multiple responsibilities and broad scope, of diverse talents and great enterprise. The Laboratory's philosophy, mission, and goals have been shaped by its ties to the California Institute of Technology (JPL's parent organization) and the National Aeronautics and Space Administration (JPL's principal sponsor). JPL's activities for NASA in planetary, Earth, and space sciences currently account for almost 75 percent of the Laboratory's overall effort. JPL Research activities in the following areas are discussed: (1) deep space exploration; (2) telecommunications systems; (3) Earth observations; (4) advanced technology; (5) defense programs; and (6) energy and technology applications.

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NASA NTRS1986

Activities of the Jet Propulsion Laboratory

Work accomplished by the Jet Propulsion Laboratory (JPL) under contract to NASA in 1985 is described. The work took place in the areas of flight projects, space science, geodynamics, materials science, advanced technology, defense and civil programs, telecommunications systems, and institutional activities.

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NASA NTRS1987

Magellan - Communicating with a spacecraft at Venus

NASA's Magellan mission scheduled for launch in April 1989, using the Space Shuttle/Innertial Upper Stage configuration, will put a single spacecraft in orbit around Venus in order to map the planet's surface with SAR. The SAR's resolution will be enough to furnish surface details, and such geological features as tectonics, volcanic activity, surface faulting, and water and wind erosion. Attention is presently given to the telecommunications system that will be needed to transmit the 3.4 trillion bits of data which the SAR will acquire during the course of this mission.

Burow, Nathan A.↗
NASA NTRS1989

NASA ground communications

As part of the Communications Requirements and Constraints, NASA's two major Ground Data Networks were briefly described. The NASA Communication Network, called NASCOM, is the worldwide operational telecommunications system which interconnects as the tracking and telemetry acquisition sites, launch areas, mission and project control centers, data capture facilities, and network control centers in support of space flight. For the Space Station era, NASCOM plans are set for higher data rate service utilizing data packet switched technology. Increased use of fiber optics is expected in a much more diverse network topology. The second major ground network, the Program Support Communications Network (PSCN), interconnects all NASA Centers and NASA contractor locations for intercenter non-operation communications. The primary functions are to transport voice, video, data and facsimile information for intercenter coordination, and to provide user access to space science and applications data bases. For the Space Station era, PSCN plans address the significant increase in forecast requirements for science data distribution and access to the Numerical Aerodynamics Simulator, and increased use of the Video Teleconference System.

Roeder, John↗
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 NTRS1992

High-Quality TiS2 For Li/TiS2 Cells

Modified process for synthesis of battery-grade titanium sulfide (TiS2) yields substantially improved material for Li/TiS2 electrochemical cells. Includes all-vapor-phase reaction between sulfur and titanium. Product less dense and more homogeneous, consists of smaller particles of higher crystalline quality, and purer. Cells have high cathode utilization and long cycle life performance. Expected to find applications in rechargeable lithium batteries for spacecraft, military equipment, telecommunication systems, automobiles, and consumer products.

Huang, Chen-Kuo↗
NASA NTRS1991

Nonlinear optical properties of organic materials: A theoretical study

Replacement of electronic switching circuits in computing and telecommunication systems with purely optical devices offers the potential for extremely high throughput and compact information processing systems. The potential application of organic materials containing molecules with large nonresonant nonlinear effects in this area have triggered intensive research during the last decade. Interest on this area was due to two facts: (1) that many organic materials show nonlinearities that are orders of magnitude larger than those of conventional inorganic materials such as lithium niobate and potassium dihydrogen phosphate; and (2) that organic materials show much flexibility in terms of molecular designs. Some of the desirable characteristics that these materials should have are that they be transparent to the frequency of the incident laser and its second or third harmonic, that they have a high damage threshold, and, in the case of second-order effects, that their crystal structure or molecular orientation be accentric. Since polymeric assemblages can enhance the nonlinear response of organic molecules severalfold, efforts have been directed toward the synthesis of thin films with interpenetrating lattices of electroactive molecules. The goal of this theoretical investigation is to predict the magnitude of the molecular polarizabilities of organic molecules that could be incorporated into films. These calculations are intended to become a powerful tool to assist material scientists in screening for the best candidates for optical applications. The procedure that was developed for the present calculations is based on the static-field approach, and is a modification to the method developed by Dewar and Stewart, 1984 for calculating molecular linear polarizabilities.

Cardelino, Beatriz H.↗
NASA NTRS1991

A robust low-rate coding scheme for packet video

Due to the rapidly evolving field of image processing and networking, video information promises to be an important part of telecommunication systems. Although up to now video transmission has been transported mainly over circuit-switched networks, it is likely that packet-switched networks will dominate the communication world in the near future. Asynchronous transfer mode (ATM) techniques in broadband-ISDN can provide a flexible, independent and high performance environment for video communication. For this paper, the network simulator was used only as a channel in this simulation. Mixture blocking coding with progressive transmission (MBCPT) has been investigated for use over packet networks and has been found to provide high compression rate with good visual performance, robustness to packet loss, tractable integration with network mechanics and simplicity in parallel implementation.

Chen, Y. C.↗
NASA NTRS1992

The investigation of bandwidth efficient coding and modulation techniques

The New Mexico State University Center for Space Telemetering and Telecommunications systems has been, and is currently, engaged in the investigation of trellis-coded modulation (TCM) communication systems. In particular, TCM utilizing M-ary phase shift keying is being studied. The study of carrier synchronization in a TCM environment, or in MPSK systems in general, has been one of the two main thrusts of this grant. This study has involved both theoretical modelling and software simulation of the carrier synchronization problem.

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NASA NTRS1990

NASA/NSF Workshop on Antarctic Research

Viewgraphs that accompanied an Ames Research Center presentation address Ames' currently-supported life sciences activities. These include crew factor issues such as human, automation, and telecommunication systems; strategic behavior and workloads; sleep, fatigue, and circadian rhythms; and virtual reality and spatial instrumentation. The need, background, and examples of pertinent research are provided.

Connors, Mary M.↗