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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The baseband processor in future satellite communication systems

This paper provides a description of a baseband processor planned for satellite communication systems operating in Ka band. The satellite based interconnection of individual earth terminals is described in terms of uplink and downlink message formats, and the on-board processing signal flow. Advanced technology requirements and developments are reviewed including current activity in custom large scale integrated circuit development.

Thomas, R. E.↗
NASA NTRS1985

The role of unneutralized surface ions in negative potential arcing

The observed arcing on negatively biased solar arrays exposed to plasma environments is shown to be due to an effective charge layer on the interconnect formed by ion collection from the plasma. Time scales to form this layer are shown to be in agreement with experimental observations. A quantitative theory is presented which predicts arcing threshold dependence on plasma density and external potentials. After breakdown, the discharge process is modeled as space charge limited transport to nearby coverslips. Peak currents and decay times predicted by this model are compared with experimental observations.

Jongeward, G. A.↗
NASA NTRS1986

Optical techniques to feed and control GaAs MMIC modules for phased array antenna applications

A complex signal distribution system is required to feed and control GaAs monolithic microwave integrated circuits (MMICs) for phased array antenna applications above 20 GHz. Each MMIC module will require one or more RF lines, one or more bias voltage lines, and digital lines to provide a minimum of 10 bits of combined phase and gain control information. In a closely spaced array, the routing of these multiple lines presents difficult topology problems as well as a high probability of signal interference. To overcome GaAs MMIC phased array signal distribution problems optical fibers interconnected to monolithically integrated optical components with GaAs MMIC array elements are proposed as a solution. System architecture considerations using optical fibers are described. The analog and digital optical links to respectively feed and control MMIC elements are analyzed. It is concluded that a fiber optic network will reduce weight and complexity, and increase reliability and performance, but higher power will be required.

Bhasin, K. B.↗
NASA NTRS1986

Radiative transfer in a sphere illuminated by a parallel beam - An integral equation approach

The problem of multiple scattering of nonpolarized light in a planetary body of arbitrary shape illuminated by a parallel beam is formulated using the integral equation approach. There exists a simple functional whose stationarity condition is equivalent to solving the equation of radiative transfer and whose value at the stationary point is proportional to the differential cross section. The analysis reveals a direct relation between the microscopic symmetry of the phase function for each scattering event and the macroscopic symmetry of the differential cross section for the entire planetary body, and the interconnection of these symmetry relations and the variational principle. The case of a homogeneous sphere containing isotropic scatterers is investigated in detail. It is shown that the solution can be expanded in a multipole series such that the general spherical problem is reduced to solving a set of decoupled integral equations in one dimension. Computations have been performed for a range of parameters of interest, and illustrative examples of applications to planetary problems as provided.

Shia, R.-L.↗
NASA NTRS1986

Evaluating the performance of multicomputer configurations

Steps to optimize the performance of a multicomputer system (MCS) are discussed. Three aspects are emphasized: (1) the interconnection scheme that ties all the processors together, (2) the scheduling and mapping of the algorithm on the architecture, and (3) the mechanism for detecting parallelism and partitioning the algorithm into modules which achieve computational speedup when run on an MCS. Mapping and scheduling issues are addressed, and an application example is given.

Agrawal, D. P.↗
NASA NTRS1986

Modeling, estimation and identification methods for static shape determination of flexible structures

This paper outlines methods for modeling, identification and estimation for static determination of flexible structures. The shape estimation schemes are based on structural models specified by (possibly interconnected) elliptic partial differential equations. The identification techniques provide approximate knowledge of parameters in elliptic systems. The techniques are based on the method of maximum-likelihood that finds parameter values such that the likelihood functional associated with the system model is maximized. The estimation methods are obtained by means of a function-space approach that seeks to obtain the conditional mean of the state given the data and a white noise characterization of model errors. The solutions are obtained in a batch-processing mode in which all the data is processed simultaneously. After methods for computing the optimal estimates are developed, an analysis of the second-order statistics of the estimates and of the related estimation error is conducted. In addition to outlining the above theoretical results, the paper presents typical flexible structure simulations illustrating performance of the shape determination methods.

Rodriguez, G.↗
NASA NTRS1986

Attitude and articulation control concepts for the Earth Observing System

A study of pointing requirements and control approaches for the Earth Observing System, EOS, is presented. The proposed instrument set includes several massive instruments with varied articulation requirements, and pointing control requirements in several cases tighter than 0.01 degrees. Approaches to multipayload control and stability are explored, including: (a) the use of interconnected but dynamically isolated payload modules on a large platform, each with independent inertial control, and (b) precision basebody control of smaller platforms, with momentum compensated articulation and on-orbit dynamic balancing of spin-scan instruments. Results from multibody spacecraft models highlight potential payload dynamic interaction problems and suggest the need for dynamic isolation and disturbance rejection control techniques.

Bell, C. E.↗
NASA NTRS1985

NASA'S communications programs - 1985

NASA's communications program was restructured in 1979 to develop selective high risk technology forced on relief of the orbit and frequency congestion and on developing new and affordable service. The central theme of the current technology thrust is one of developing interconnectivity technology and architecture to convert the present era of bent pipe satellite utilization to one using nodal points in space for both space and earth based information gateways and interfaces to terrestrial communication systems.

Lovell, R. R.↗
NASA NTRS1987

Maximum-Likelihood Decoder on a Hypercube Multiprocessor

Efficient parallel processing used to implement complex decoders. Hypercube multiprocessor connection scheme practical to decode long convolutional codes with efficient use of hardware. Hypercube design reduces both communication time among processors and space needed for interconnection. Decoding concept applicable to concurrent processing of digital signals using convolutional codes for error correction.

Pollara, F.↗
NASA NTRS1987

Electronic Power Switch for Fault-Tolerant Networks

Power field-effect transistors reduce energy waste and simplify interconnections. Current switch containing power field-effect transistor (PFET) placed in series with each load in fault-tolerant power-distribution system. If system includes several loads and supplies, switches placed in series with adjacent loads and supplies. System of switches protects against overloads and losses of individual power sources.

Volp, J.↗
NASA NTRS1987

Real-Time Simulation Clock

Fiber-optic network delivers time signals to widely separated simulator sites. Real-time digital flight simulation used to support variety of research programs. Majority of research involves man-in-the-loop simulation requiring interconnection of digital computers, simulation cockpits, control consoles, graphics subsystems, and related equipment. Real-time simulation subsystem consists of several CYBER(R) computers and over 20 simulation sites. Allows for several simultaneous simulation jobs on one CYBER(R) as well as any combination of sites in each integrated simulation job.

Bennington, Donald R.↗
NASA NTRS1987

Trifluorophenylethylidene Condensation Polyimides

Report describes synthesis and properties of trifluorophenylethylidene (3F) condensation polyimides. Properties of these new polymers make suitable thermal-control coatings, interlayer dielectrics in advanced wafer chips, and electronic-multilevel-interconnection layers.

Alston, William B.↗
NASA NTRS1987

Solar-Powered Sensor Module

Hybrid sensor module with no external electrical interconnections includes optical data link. Measures such parameters as temperature, acceleration, and strain. Module transmits measurement data to central unit and receives control signals via light beams.

Johnson, J. Michael↗
NASA NTRS1987

PCACE-Personal-Computer-Aided Cabling Engineering

PCACE computer program developed to provide inexpensive, interactive system for learning and using engineering approach to interconnection systems. Basically database system that stores information as files of individual connectors and handles wiring information in circuit groups stored as records. Directly emulates typical manual engineering methods of handling data, thus making interface between user and program very natural. Apple version written in P-Code Pascal and IBM PC version of PCACE written in TURBO Pascal 3.0

Billitti, Joseph W.↗
NASA NTRS1986

A design concept for an MMIC microstrip phased array

A conceptual design for a microstrip phased array with monolithic microwave integrated circuit (MMIC) amplitude and phase controls is described. The MMIC devices used are 20 GHz variable power amplifiers and variable phase shifters recently developed by NASA contractors for applications in future Ka band advanced satellite communication antenna systems. The proposed design concept is for a general NxN element array of rectangular lattice geometry. Subarray excitation is incorporated in the MMIC phased array design to reduce the complexity of the beam forming network and the number of MMIC components required. The proposed design concept takes into consideration the RF characteristics and actual phyical dimensions of the MMIC devices. Also, solutions to spatial constraints and interconnections associated with currently available packaging designs are discussed. Finally, the design of the microstrip radiating elements and their radiation characteristics are examined.

Lee, R. Q.↗
NASA NTRS1986

Evaluation of reliability modeling tools for advanced fault tolerant systems

The Computer Aided Reliability Estimation (CARE III) and Automated Reliability Interactice Estimation System (ARIES 82) reliability tools for application to advanced fault tolerance aerospace systems were evaluated. To determine reliability modeling requirements, the evaluation focused on the Draper Laboratories' Advanced Information Processing System (AIPS) architecture as an example architecture for fault tolerance aerospace systems. Advantages and limitations were identified for each reliability evaluation tool. The CARE III program was designed primarily for analyzing ultrareliable flight control systems. The ARIES 82 program's primary use was to support university research and teaching. Both CARE III and ARIES 82 were not suited for determining the reliability of complex nodal networks of the type used to interconnect processing sites in the AIPS architecture. It was concluded that ARIES was not suitable for modeling advanced fault tolerant systems. It was further concluded that subject to some limitations (the difficulty in modeling systems with unpowered spare modules, systems where equipment maintenance must be considered, systems where failure depends on the sequence in which faults occurred, and systems where multiple faults greater than a double near coincident faults must be considered), CARE III is best suited for evaluating the reliability of advanced tolerant systems for air transport.

Baker, Robert↗
NASA NTRS1987

Advanced space communications architecture study. Volume 2: Technical report

The technical feasibility and economic viability of satellite system architectures that are suitable for customer premise service (CPS) communications are investigated. System evaluation is performed at 30/20 GHz (Ka-band); however, the system architectures examined are equally applicable to 14/11 GHz (Ku-band). Emphasis is placed on systems that permit low-cost user terminals. Frequency division multiple access (FDMA) is used on the uplink, with typically 10,000 simultaneous accesses per satellite, each of 64 kbps. Bulk demodulators onboard the satellite, in combination with a baseband multiplexer, convert the many narrowband uplink signals into a small number of wideband data streams for downlink transmission. Single-hop network interconnectivity is accomplished via downlink scanning beams. Each satellite is estimated to weigh 5600 lb and consume 6850W of power; the corresponding payload totals are 1000 lb and 5000 W. Nonrecurring satellite cost is estimated at $110 million, with the first-unit cost at $113 million. In large quantities, the user terminal cost estimate is $25,000. For an assumed traffic profile, the required system revenue has been computed as a function of the internal rate of return (IRR) on invested capital. The equivalent user charge per-minute of 64-kbps channel service has also been determined.

Horstein, Michael↗
NASA NTRS1987

Advanced space communications architecture study. Volume 1: Executive summary

The technical feasibility and economic viability of satellite system architectures that are suitable for Customer Premise Service (CPS) communications is investigated. System evaluation is performed at 30/20 GHz (Ka-band); however, the system architectures examined are equally applicable to 14/11 GHz (Ku-band). Emphasis is placed on system that permit low cost user terminals. Frequency Division Multiple Access (FDMA) is used on the uplink, with typically 10,000 simultaneous accesses per satellite, each of 64 kbps. Bulk demodulators onboard the satellite, in combination with a baseband multiplexer, convert the many narrowband uplink signals into a small number of wideband data streams for downlink transmission. Single hop network interconnectivity is accomplished through use of downlink scanning beams. Each satellite is estimated to weigh 5600 lb and consume 6850W of power; the corresponding payload totals are 1000 lb and 5000W. Nonrecurring satellite cost is estimated at $110 million, with the first unit cost at $113 million. In large quantities, the user terminal cost estimate is $25,000.

Horstein, Michael↗