Special Coverage

Transducer-Actuator Systems for On-Machine Measurements and Automatic Part Alignment
Wide-Area Surveillance Using HD LWIR Uncooled Sensors
Heavy Lift Wing in Ground (WIG) Cargo Flying Boat
Technique Provides Security for Multi-Robot Systems
Bringing New Vision to Laser Material Processing Systems
NASA Tests Lasers’ Ability to Transmit Data from Space
Converting from Hydraulic Cylinders to Electric Actuators
Automating Optimization and Design Tasks Across Disciplines
Vibration Tables Shake Up Aerospace and Car Testing
Supercomputer Cooling System Uses Refrigerant to Replace Water

Hybrid Composite Structures Made From Polybenzoxazole Fibers

Strength-to-thickness ratios would be increased.

Hybrid composite-material (fiber/matrix) structures of a proposed type would incorporate recently developed polybenzoxazole (PBO) fibers that feature high strengths and high moduli of elasticity and which can be made in much thinner sections than are possible with graphite fibers. The PBO fibers could be used, for example, in skins, face sheets, or panels, any or all of which could be made as multiple-angle-ply layups.

Posted in: Briefs, TSP, Materials, Composite materials, Fibers, Materials properties
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A Mass-Spectrometer System for Detecting Gas Leaks

This versatile, expandable system can be controlled from a safe remote location.

The Hydrogen Umbilical Mass Spectrometer (HUMS) consists of an integrated sample delivery system, a commercial mass-spectrometer- based gas analyzer, and a set of calibration gas mixtures traceable to NIST (National Institute for Standards and Technology). The system, except for the calibration gas mixtures and the remote operator display, fits into a standard 24-in. wide, 6-ft high, 36-in. deep (0.61 by 1.83 by 0.91 m, respectively) equipment rack and is powered by 120-Vac, 30-A, 60-Hz source. It was designed to perform leak detection and measurement of cryogenic propellants (oxygen and hydrogen) from a remote location during shuttle-launch countdown. It is used specifically to sample the background gas surrounding the 17-in. (0.43-m) Orbiter-ET disconnect, looking for leakage of gaseous hydrogen. The capability to monitor shuttle purge gases and cryogenic hydrogen fill and drain line T-0 disconnect helium purge gas is incorporated into the shuttle installation on each Mobile Launch Platform (MLP).

Posted in: Briefs, TSP, Test & Measurement, Measurements, Spectroscopy, Spectroscopy, Gases
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Oscillator-Stability Analyzer Based on a Time-Tag Counter

This system would combine the best characteristics of prior single- and dual-mixer systems.

A proposed system for simultaneous characterization of the instability of several precise, low-noise oscillators of nominally equal frequency would be built around a commercially available time-tag counter. One of the oscillators would be deemed to be a reference oscillator, and each of the other oscillators would be compared with it by operation of a combination of hardware and software. In addition, without further modification of the hardware, any two nonreference oscillators could be compared with each other via software.

Posted in: Briefs, TSP, Electronics & Computers, Noise, Noise, Test equipment and instrumentation
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Flexible Carrier-Signal-Tracking Loop for a Transponder

This loop could be programmed for perfect or imperfect integration.

A proposed digital carrier-signal-tracking loop in a radio transponder could be programmed to operate in either a perfect-integration or an imperfect-integration mode. Although originally intended for use in a transponder aboard a spacecraft at a great distance from the Earth, the proposed loop might also be advantageously incorporated into terrestrial communication systems in which it is necessary to track the phases of received carrier signals.

Posted in: Briefs, TSP, Electronics & Computers, Radio equipment, Telecommunications systems, Radio equipment, Telecommunications systems
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Simplified Construction of Conical Log-Spiral Antenna

Mating parts align themselves during assembly.

An improved design for a conical log-spiral antenna (see Figure 1) simplifies construction and improves alignment. The radiating-element substructure of such an antenna must be properly aligned with the signal-feed substructure to obtain the correct impedance match for efficient coupling of the signal into or out of the antenna. This design provides for mating parts, the faying surfaces of which enforce alignment initially during construction and maintain alignment subsequently during use.

Posted in: Briefs, Electronics & Computers, Antennas, Antennas, Mountings, Parts
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Programming Language for Automated Scheduling and Planning

The ASPEN Modeling Language (AML) has been developed for use in the Automated Scheduling and Planning Environment (ASPEN) software system. As described in prior NASA Tech Briefs articles, ASPEN is an object-oriented system that contains a modular, reconfigurable, reusable set of components that implement the elements commonly found in complex automated-scheduling application programs. AML has a simple syntax that makes it easy for a user who lacks expertise in computer science and artificial intelligence to rapidly create a model of a spacecraft-operations domain for an ASPEN automated-scheduling application program. AML enables a user to construct a model, expressed as a plain-text file, that defines activities, resources, and states. A user can also modify a model without need to recompile ASPEN. AML encodes spacecraft operability constraints, flight rules, spacecraft hardware models, goals of scientific experiments, and operational procedures to enable the generation, by the automated-scheduling program, of low-level sequences of spacecraft operations.

Posted in: Briefs, TSP, Software, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware, Human machine interface (HMI), Aircraft operations, Terminology, Spacecraft
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Communication Software for Distributed Application Programs

The Task Remote Asynchronous Message Exchange Layer (Tramel) software reduces the costs of distributing application programs across computer networks, including the Internet. Tramel implements robust, reliable, simple, highly portable interprocess communication, such that distributed application programs can tolerate extreme deterioration of communication links and elements of such a program can be stopped, moved to other computers (including computers with different operating systems), and restarted, all while the program is running and without alteration of any source code or configuration file. Because Tramel is based on asynchronous message passing, it can tolerate extremely low link performance without sacrificing transaction concurrency or relying on a multithreading system. Tramel manages network connections for an application program, shielding the program from such details as processor architectures, operating systems, and communication protocols. At the same time, Tramel affords monitoring capabilities that can keep application-program elements informed of the current configuration of the program. Tramel can be executed on any of a variety of computers running the UNIX, VxWorks, or Windows NT operating system.

Posted in: Briefs, TSP, Software, Communication protocols, Computer software / hardware, Computer software and hardware, Communication protocols, Computer software / hardware, Computer software and hardware
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Software for Coordinating Multiple Exploratory Robots

A computer program coordinates the activities of multiple instrumented robotic vehicles of the "rover" type intended for use in scientific exploration. The program is a master/slave, distributed version of the ASPEN planning software, other versions of which have been reported in several prior NASA Tech Briefs articles. On the basis of an input set of goals and the initial conditions of each rover, the program generates a sequence of activities that satisfy the goals while obeying the resource constraints and rules of operation of each rover. The program includes a central planning subprogram that assigns goals to individual rovers in such a way as to minimize the total traversal time of all the rovers while maximizing the scientific return. The remainder of planning is distributed among the individual rovers: each rover runs a subprogram that plans its activities to attain the goal(s) assigned to it.

Posted in: Briefs, TSP, Software, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware, Robotics, Spacecraft
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Program Creates Code to Parse Text

Saxj is a computer program that facilitates the development of programs that parse textual input in the Java programming language. Saxj is a parser generator that creates static Java parsers in the same sense in which YACC, Bison, and YACC++ are static parser generators that create static C-language parsers. Saxj creates Java object-oriented parsers on the basis of grammar specifications. Saxj uses an algorithm of the "look-ahead 1 token, look right" [LALR(1)] type to convert a grammar specification into a parser. Saxj is built upon implementation of this algorithm by use of a library of Java classes. Grammar specifications in Saxj are intentionally similar to those in YACC, Bison, and YACC++, so that the documentation of Saxj can be nearly the same as that of YACC++. The various instantiations of the class of parsers contain a single definition of the parse table; it is in this sense that the parsers are characterized as static. All of the parsers generated by the YACC family are similarly static. A dynamic parser is feasible in the case of machine learning. Saxj can be used, for example, for writing compiler software, for interpreting sequences of computer-generated commands, and for general language parsing.

Posted in: Briefs, TSP, Software, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware
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Program Creates Java Lexical Analyzers

Luthorj is a computer program that creates static lexical analyzers in the Java programming language, in the same sense in which Flex and Lex create lexical analyzers in the C programming language. The majority of users of Luthorj are expected to be familiar with Lex, and Luthorj parses input files that are largely the same as Lex files. However, Luthorj is not merely a look-alike, Java version of Lex. The functionality of Luthorj is partly compatible with that of Flex, but Luthorj and Flex use different methods to provide similar functionality. The lexical analyzers created by Luthorj convert textual strings into tokens that, in turn, can be fed to parsers created by the Saxj program described in the preceding article. Luthorj converts input string specifications to lexical-analysis data structures by use of an algorithm that converts regular expressions to nondeterministic finite automata (NFA). The NFA are then mapped to deterministic finite automata (DFA). The combination of all DFA are represented as a transition table, which is stored in a file. The outputs of Luthorj are the transition table and the code to use it.

Posted in: Briefs, TSP, Software, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware
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