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At least 1,117 records · Page 62

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NASA NTRS1988

Experimental studies of active members in control of large space structures

Intelligent structures for precision spacecraft applications are structural systems incorporating sensors, actuators, and built-in electronic logic that facilitate self-monitoring of structure responses to disturbances. Attention is presently given to adaptive structures, in which the electronic logic need not be integral to the structure. Active members are used to replace selected passive members of truss-type structures; the sensors employed allow measurement of the elastic strain and deformation experienced by the structure. Two struss-type testbed structures are described.

Fanson, J. L.↗

NASA NTRS1988

Noise-margin limitations on gallium-arsenide VLSI

Two factors which limit the complexity of GaAs MESFET VLSI circuits are considered. Power dissipation sets an upper complexity limit for a given logic circuit implementation and thermal design. Uniformity of device characteristics and the circuit configuration determines the electrical functional yield. Projection of VLSI complexity based on these factors indicates that logic chips of 15,000 gates are feasible with the most promising static circuits if a maximum power dissipation of 5 W per chip is assumed. While lower power per gate and therefore more gates per chip can be obtained by using a popular E/D FET circuit, yields are shown to be small when practical device parameter tolerances are applied. Further improvements in materials, devices, and circuits wil be needed to extend circuit complexity to the range currently dominated by silicon.

Long, Stephen I.↗

NASA NTRS1989

Timing Sampler For Delay Measurements

Integrated circuit called timing sampler used to measure delays in complementary metal oxide/silicon logic gates. Circuit chip contains chains of inverters and metal traces having minimum parasitic delays (delay chains), circuits to compare pulse timings, and output multiplexer. Timing sampler enables delay measurements for both positive and negative logic-level transitions by use of variety of circuit geometries representing tentative practical designs.

Blaes, Brent R.↗

NASA NTRS1989

Asymmetrical SRAM Cells For Radiation Tests

Features of circuits altered to increase or decrease sensitivity to radiation. State-space analysis used to analyze single-event-upset behavior of memory cell. When voltage on node a is set at one of indicated initial values Vao and then released, voltages on nodes a and b then follow indicated trajectory to final logic "one" or logic "zero" state. Ability to do this important for design of radiation-detecting integrated circuits (deliberately made more sensitive to ionizing radiation) and "radiation-hardened" integrated circuits - those intended to be relatively invulnerable to intense radiation.

Buehler, Martin G.↗

NASA NTRS1989

Correction And Use Of Jitter In Television Images

Proposed system stabilizes jittering television image and/or measures jitter to extract information on motions of objects in image. Alternative version, system controls lateral motion on camera to generate stereoscopic views to measure distances to objects. In another version, motion of camera controlled to keep object in view. Heart of system is digital image-data processor called "jitter-miser", which includes frame buffer and logic circuits to correct for jitter in image. Signals from motion sensors on camera sent to logic circuits and processed into corrections for motion along and across line of sight.

Diner, Daniel B.↗

NASA NTRS1988

Computerized monitoring and control of experiments in space

The computer subsystem of the Villanova University GAS (Get Away Special) experiment apparatus is discussed. The function of the computer subsystem is to provide data acquisition and control system support to the experiments. The computer subsystem will provide high availability, low power consumption and highly reliable data retention. The general layout of the subsystem provides for redundant processing units, control modules, and multiple data acquisition modules. Each of the two redundant processing units will be composed of a microprocessor, control logic, PROM, RAM, non-volitile memory, timers, self-check logic and data ports to the data acquisition and control modules. One unit will control the experiment while the other shadows the primary unit operation. The data acquisition module gathers data from the experiment. The data is transfered to the processing unit in digital form. The control module validates the data, decodes it and executes the command.

Janisch, Thomas V.↗

NASA NTRS1986

Rdesign: A data dictionary with relational database design capabilities in Ada

Data Dictionary is defined to be the set of all data attributes, which describe data objects in terms of their intrinsic attributes, such as name, type, size, format and definition. It is recognized as the data base for the Information Resource Management, to facilitate understanding and communication about the relationship between systems applications and systems data usage and to help assist in achieving data independence by permitting systems applications to access data knowledge of the location or storage characteristics of the data in the system. A research and development effort to use Ada has produced a data dictionary with data base design capabilities. This project supports data specification and analysis and offers a choice of the relational, network, and hierarchical model for logical data based design. It provides a highly integrated set of analysis and design transformation tools which range from templates for data element definition, spreadsheet for defining functional dependencies, normalization, to logical design generator.

Lekkos, Anthony A.↗

NASA NTRS1988

Transformational derivation of programs using the Focus system

A program derivation support system called Focus is being constructed. It will formally derive programs using the paradigm of program transformation. The following issues are discussed: (1) the integration of validation and program derivation activities in the Focus system; (2) its tree-based user interface; (3) the control of search spaces in program derivation; and (4) the structure and organization of program derivation records. The inference procedures of the system are based on the integration of functional and logic programming principles. This brings about a synthesis of paradigms that were heretofore considered far apart, such as logical and executable specifications and constructive and transformational approaches to program derivation. A great emphasis has been placed, in the design of Focus, on achieving small search spaces during program derivation. The program manipulation operations such as expansion, simplification and rewriting were designed with this objective. The role of operations that are expensive in search spaces, such as folding, has been reduced. Program derivations are documented in Focus in a way that the high level descriptions of derivations are expressed only using program level information. All the meta-level information, together with dependencies between derivations of program components, is automatically recorded by the system at a lower level of description for its own use in replay.

Reddy, Uday S.↗

NASA NTRS1987

SOLON: An autonomous vehicle mission planner

The State-Operator Logic Machine (SOLON) Planner provides an architecture for effective real-time planning and replanning for an autonomous vehicle. The highlights of the system, which distinguish it from other AI-based planners that have been designed previously, are its hybrid application of state-driven control architecture and the use of both schematic representations and logic programming for the management of its knowledge base. SOLON is designed to provide multiple levels of planning for a single autonomous vehicle which is supplied with a skeletal, partially-specified mission plan at the outset of the vehicle's operations. This mission plan consists of a set of objectives, each of which will be decomposable by the planner into tasks. These tasks are themselves comparatively complex sets of actions which are executable by a conventional real-time control system which does not perform planning but which is capable of making adjustments or modifications to the provided tasks according to constraints and tolerances provided by the Planner. The current implementation of the SOLON is in the form of a real-time simulation of the Planner module of an Intelligent Vehicle Controller (IVC) on-board an autonomous underwater vehicle (AUV). The simulation is embedded within a larger simulator environment known as ICDS (Intelligent Controller Development System) operating on a Symbolics 3645/75 computer.

Dudziak, M. J.↗

NASA NTRS1987

A framework for qualitative reasoning about solid objects

Predicting the behavior of a qualitatively described system of solid objects requires a combination of geometrical, temporal, and physical reasoning. Methods based upon formulating and solving differential equations are not adequate for robust prediction, since the behavior of a system over extended time may be much simpler than its behavior over local time. A first-order logic, in which one can state simple physical problems and derive their solution deductively, without recourse to solving the differential equations, is discussed. This logic is substantially more expressive and powerful than any previous AI representational system in this domain.

Davis, E.↗

NASA NTRS1988

A simulation-based fault injection experiment to evaluate self-test diagnostics for a fault-tolerant computer

The design and results of a fault injection experiment conducted in the Airlab facility at NASA-Langley using a logic network simulator are described. An attempt was made to determine the effectiveness of the diagnostic self-test sequences used to detect failures in the communicator/interstage (C/I) of a fault-tolerant processor (FTP). Identification of the undetected faults in the C/I Status Register logic resulted in changes in the diagnostic test sequences implemented for the FTP.

Baker, Robert L.↗

NASA NTRS1988

The design of radiation-hardened ICs for space - A compendium of approaches

Several technologies, including bulk and epi CMOS, CMOS/SOI-SOS (silicon-on-insulator-silicon-on-sapphire), CML (current-mode logic), ECL (emitter-coupled logic), analog bipolar (JI, single-poly DI, and SOI) and GaAs E/D (enhancement/depletion) heterojunction MESFET, are discussed. The discussion includes the direct effects of space radiation on microelectronic materials and devices, how these effects are evidenced in circuit and device design parameter variations, the particular effects of most significance to each functional class of circuit, specific techniques for hardening high-speed circuits, design examples for integrated systems, including operational amplifiers and A/D (analog/digital) converters, and the computer simulation of radiation effects on microelectronic ISs.

Kerns, Sherra E.↗

NASA NTRS1989

A programmable CCD driver circuit for multiphase CCD operation

A programmable CCD (charge-coupled device) driver circuit was designed to drive CCDs in multiphased modes. The purpose of the drive electronics is to operate developmental CCD imaging arrays for NASA's tiltable moderate resolution imaging spectrometer (MODIS-T). Five objectives for the driver were considered during its design: (1) the circuit drives CCD electrode voltages between 0 V and +30 V to produce reasonable potential wells, (2) the driving sequence is started with one input signal, (3) the driving sequence is started with one input signal, (4) the circuit allows programming of frame sequences required by arrays of any size, (5) it produces interfacing signals for the CCD and the DTF (detector test facility). Simulation of the driver verified its function with the master clock running up to 10 MHz. This suggests a maximum rate of 400,000 pixels/s. Timing and packaging parameters were verified. The design uses 54 TTL (transistor-transistor logic) chips. Two versions of hardware were fabricated: wirewrap and printed circuit board. Both were verified functionally with a logic analyzer.

Ewin, Audrey J.↗

NASA NTRS1990

Upper-Bound Estimates Of SEU in CMOS

Theory of single-event upsets (SEU) (changes in logic state caused by energetic charged subatomic particles) in complementary metal oxide/semiconductor (CMOS) logic devices extended to provide upper-bound estimates of rates of SEU when limited experimental information available and configuration and dimensions of SEU-sensitive regions of devices unknown. Based partly on chord-length-distribution method.

Edmonds, Larry D.↗

NASA NTRS1990

Exact Chord-Length Distribution For SEU Calculations

Computed rates of SEU's more accurate. Exact integral chord-length distribution derived for use in calculations of rates of single-event upsets (SEU's) (changes in logic states) caused by impingement of cosmic rays or other ionizing radiation on electronic logic circuits.

Buehler, Martin G.↗

NASA NTRS1990

Temperature Dependence Of Single-Event Effects

Report describes experimental study of effects of temperature on vulnerability of integrated-circuit memories and other electronic logic devices to single-event effects - spurious bit flips or latch-up in logic state caused by impacts of energetic ions. Involved analysis of data on 14 different device types. In most cases examined, vulnerability to these effects increased or remain constant with temperature.

Coss, James R.↗

NASA NTRS1989

Simulation of shuttle flight control system structural interaction with RMS deployed payloads

A simulation of the system made up of the Orbiter, Remote Manipulator System (RMS), and payload grappled by the RMS was completed. The simulation was used to study the stability of this overall system when its attitude is under control of the Orbiter's on-orbit Flight Control System (FCS). The simulation was also used to study the dynamics of the system when the RMS and its associated command software are in active control of the relative Orbiter to payload position and orientation. The simulation models all of the following elements: RMS boom bending (represented by two cubic bending models); RMS boom torsion; RMS joint gearbox compliance (represented by a non-linear wind-up model); flexibility at the RMS to Orbiter interface; flexibility at the RMS to payload interface; joint motor dynamics; joint servo-loop dynamics; RMS on-board computer command logic; data transfer delays between the RMS sensor and the RMS on-board computer and between the RMS on-board computer and RMS joint servos; on-orbit flight control nonlinear control logic; and the Reaction Control System (both Primary and Vernier) jet forces and moments.

Turnball, Joe↗

NASA NTRS1989

Stress in dilute suspensions

Generally, two types of theory are used to describe the field equations for suspensions. The so-called postulated equations are based on the kinetic theory of mixtures, which logically should give reasonable equations for solutions. The basis for the use of such theory for suspensions is tenuous, though it at least gives a logical path for mathematical arguments. It has the disadvantage that it leads to a system of equations which is underdetermined, in a sense that can be made precise. On the other hand, the so-called averaging theory starts with a determined system, but the very process of averaging renders the resulting system underdetermined. A third type of theory is proposed in which the kinetic theory of gases is used to motivate continuum equations for the suspended particles. This entails an interpretation of the stress in the particles that is different from the usual one. Classical theory is used to describe the motion of the suspending medium. The result is a determined system for a dilute suspension. Extension of the theory to more concentrated systems is discussed.

Passman, Stephen L.↗