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The selection of a high-order programming language for a real-time distributed network simulation is described. The additional problem of implementing a language on a possibly changing network is addressed. The recently designed language ADA (trademarked by DoD) was chosen since it provides the best model of the underlying application to be simulated.
The tools, techniques, and aids needed to engineer, manage, and administer a large software-intensive task are themselves parts of a large softwaare base, and are incurred only at great expense. The needs of the software life cycle in terms of such supporting tools and methodologies are highlighted. The concept of a distributed network for engineering, management, and administrative functions is outlined, and the key characteristics of localized subnets in high-communications-traffic areas of software activity are discussed. A formal, deliberate, structured, systems-engineering approach for the construction of a uniform, coordinated tool set is proposed as a means to reduce development and maintenance costs, foster adaptability, enhance reliability, and promote standardization.
The primary objective of Task 3 is to provide additional analysis and insight necessary to support key design/programmatic decision for options quantification and selection for system definition. This includes: (1) the identification of key trade study topics; (2) the definition of a trade study procedure for each topic (issues to be resolved, key inputs, criteria/weighting, methodology); (3) conduct tradeoff and sensitivity analysis; and (4) the review/verification of results within the context of evolving system design and definition. The trade study topics addressed in this volume include space autonomy and function automation, software transportability, system network topology, communications standardization, onboard local area networking, distributed operating system, software configuration management, and the software development environment facility.
Multilevel optimization methods are being considered for the design of complex systems on distributed networks of computers or even parallel processors. An obstacle to the use of multilevel methods is that they can be computationally expensive because of the cycling necessary to account for the coupling between the subproblems. This research effort aims at increasing the efficiency of multilevel optimization by adapting two techniques that are widely used in conventional one-level optimization: constraint approximation and temporary constraint deletion. These improvements are implemented and tested on three-, ten- and 52-bar planar truss designs. The results show that for larger problems (approximately 100 design variables and larger), the cost of analysis dominates the total cost so that multilevel optimization is no more expensive than one-level optimization. If parallel processing is used or the analysis process itself is decomposed, then multilevel optimization stands to become more economical than one-level optimization.
The tools, techniques, and aids needed to engineer, manage, and administer a large software-intensive task are themselves parts of a large software base, and are incurred only at great expense. The needs of the software life cycle in terms of such supporting tools and methodologies are highlighted. The concept of a distributed network for engineering, management, and administrative functions is outlined, and the key characteristics of localized subnets in high-communications-traffic areas of software actively are discussed. A formal, deliberate, structured, systems-engineering approach for the construction of a uniform, coordinated tool set is proposed as a means to reduce development and maintenance costs, foster adaptability, enhance reliability, and promote standardization.
The present conference considers topics encompassing the fields of satellite communications technology, optical subsystems, transmitters and receivers, subsystems for pointing and tracking, onboard processing- and component-related technologies, fiber-optic distribution networks, and reliability-related considerations. Attention is given to lightwave technology in microwave systems, the status of CO2 laser technology and homodyne receiver concepts for communication satellite optical links, laser Doppler measurement techniques for spacecraft, fiber-optic gyros for space applications, integrated acoustooptic device modules for communication, signal processing and computing, radiation-hardened optoelectronic components, and radiation effects on fiber-optics.
Collection of computer programs developed for expert computer system performing complicated, tedious, and repetitive portions of analysis of telemetry data from spacecraft. Provides nonstop, accurate surveillance of incoming data, also frees operators to concentrate their expertise on unexpected abnormal operating conditions. When unable to explain discrepancies with certainty resulting from data out of synchronization or other falso-alarm conditions, triggers alarm devices to request assistance from designated individuals. Concept useful in such terrestrial systems as production lines, power-distribution networks, chemical processes, large airplanes, and other assemblies of interdependent equipment.
Modern spacecraft tracking and navigation require highly accurate Earth-orientation parameters. For near-real-time applications, errors in these quantities and their extrapolated values are a significant error source. A globally distributed network of high-precision receivers observing the full Global Positioning System (GPS) configuration of 18 or more satellites may be an efficient and economical method for the rapid determination of short-term variations in Earth orientation. A covariance analysis using the JPL Orbit Analysis and Simulation Software (OASIS) was performed to evaluate the errors associated with GPS measurements of Earth orientation. These GPS measurements appear to be highly competitive with those from other techniques and can potentially yield frequent and reliable centimeter-level Earth-orientation information while simultaneously allowing the oversubscribed Deep Space Network (DSN) antennas to be used more for direct project support.
The Control Structure Interaction Program is a technology development program for spacecraft that exhibit interactions between the control system and structural dynamics. The program objectives include development and verification of new design concepts (such as active structure) and new tools (such as a combined structure and control optimization algorithm) and their verification in ground and possibly flight test. The new CSI design methodology is centered around interdisciplinary engineers using new tools that closely integrate structures and controls. Verification is an important CSI theme and analysts will be closely integrated to the CSI Test Bed laboratory. Components, concepts, tools and algorithms will be developed and tested in the lab and in future Shuttle-based flight experiments. The design methodology is summarized in block diagrams depicting the evolution of a spacecraft design and descriptions of analytical capabilities used in the process. The multiyear JPL CSI implementation plan is described along with the essentials of several new tools. A distributed network of computation servers and workstations was designed that will provide a state-of-the-art development base for the CSI technologies.
The Space Station Freedom workstation system is a distributed network of computer based workstations that provides the man-machine interfaces for controlling space station systems. This includes control of external manipulator, robotic and free flyer devices by crewmembers in the space station's pressurized shirt-sleeve environment. These remotely controlled devices help minimize the requirement for costly crew extravehicular activity (EVA) time for such tasks as station assembly and payload support. Direct window views may be used for controlling some of the systems, but many activities will be remote or require levels of detail not possible by direct observation. Since controlling remote devices becomes more difficult when direct views are inadequate or unavailable, many performance enhancing techniques have been considered for representing information about remote activities to the operator. Described here are the telepresence techniques under consideration to support operations and training. This includes video enhancements (e.g., graphic and text overlays and stereo viewing), machine vision systems, remote activity animation, and force reflection representation.
A tuple space based object oriented model for knowledge base representation and interpretation is presented. An architecture for managing distributed knowledge agents is then implemented within the model. The general model is based upon a database implementation of a tuple space. Objects are then defined as an additional layer upon the database. The tuple space may or may not be distributed depending upon the database implementation. A language for representing knowledge and inference strategy is defined whose implementation takes advantage of the tuple space. The general model may then be instantiated in many different forms, each of which may be a distinct knowledge agent. Knowledge agents may communicate using tuple space mechanisms as in the LINDA model as well as using more well known message passing mechanisms. An implementation of the model is presented describing strategies used to keep inference tractable without giving up expressivity. An example applied to a power management and distribution network for Space Station Freedom is given.
In anticipation of the needs of future light-weight, low-power spacecraft, arcjet power electronics in the 100 to 400 W operating range were developed. Limited spacecraft power and thermal control capacity of these small spacecraft emphasized the need for high efficiency. Power topologies similar to those in the higher 2 kW and 5 to 30 kW power range were implemented, including a four transistor bridge switching circuit, current mode pulse-width modulated control, and an output current averaging inductor with an integral pulse generation winding. Reduction of switching transients was accomplished using a low inductance power distribution network, and no passive snubber circuits were necessary for power switch protection. Phase shift control of the power bridge was accomplished using an improved pulse width modulation to phase shift converter circuit. These features, along with conservative magnetics designs allowed power conversion efficiencies of greater than 92.5 percent to be achieved into resistive loads over the entire operating range of the converter. Electromagnetic compatibility requirements were not considered in this work, and control power for the converter was derived from AC mains. Addition of input filters and control power converters would result in an efficiency of on the order of 90 percent for a flight unit. Due to the developmental nature of arcjet systems at this power level, the exact nature of the thruster/power processor interface was not quantified. Output regulation and current ripple requirements of 1 and 20 percent respectively, as well as starting techniques, were derived from the characteristics of the 2 kW system but an open circuit voltage in excess of 175 V was specified. Arcjet integration tests were performed, resulting in successful starts and stable arcjet operation at power levels as low as 240 W with simulated hydrazine propellants.
This invention relates to a resource allocation in computer systems, and more particularly, to a method and associated apparatus for shortening response time and improving efficiency of a heterogeneous distributed networked computer system by reallocating the jobs queued up for busy nodes to idle, or less-busy nodes. In accordance with the algorithm (SIDA for short), the load-sharing is initiated by the server device in a manner such that extra overhead in not imposed on the system during heavily-loaded conditions. The algorithm employed in the present invention uses a dual-mode, server-initiated approach. Jobs are transferred from heavily burdened nodes (i.e., over a high threshold limit) to low burdened nodes at the initiation of the receiving node when: (1) a job finishes at a node which is burdened below a pre-established threshold level, or (2) a node is idle for a period of time as established by a wakeup timer at the node. The invention uses a combination of the local queue length and the local service rate ratio at each node as the workload indicator.
The design and performance is presented of the following Coplanar Waveguides (CPW) microwave distribution networks for linear as well as circularly polarized microstrip patches and dipole arrays: (1) CPW/Microstrip Line feed; (2) CPW/Balanced Stripline feed; (3) CPW/Slotline feed; (4) Grounded CPW/Balanced coplanar stripline feed; and (5) CPW/Slot coupled feed. Typical measured radiation patterns are presented, and their relative advantages and disadvantages are compared.
A globally distributed network of high-precision receivers which obtain data from the full Global Positioning System (GPS) configuration of 18 or more satellites may soon become an efficient and economical method for the rapid determination of short-term variations in earth orientation. A covariance analysis has been performed to evaluate the errors associated with GPS monitoring of earth orientation. Earth orientation parameters were modeled either as constants over observing windows of various lengths, or as stochastic process-noise variables. The sensitivity of earth orientation estimates to systematic errors in selected model parameters was also examined. GPS measurements appear to be highly competitive with those from other techniques, and have the potential to generate nearly continuous centimeter-level earth orientation information to aid both spacecraft navigation and the study of high-frequency earth orientation-related processes.
In anticipation of the needs of future light-weight low-power spacecraft, arcjet power electronics in the 100- to 400-W operating range were developed. Power topologies similar to those in the higher 2-kW and 5- to 30-kW power range were implemented, including a four-transistor bridge-switching circuit, current-mode pulse-width modulated control, and an output current averaging inductor with an integral pulse generation winding. Reduction of switching transients was accomplished using a low inductance power distribution network, and no passive snubber circuits were necessary for power switch protection. Phase shift control of the power bridge was accomplished using an improved pulse width modulation to phase shift converter circuit. These features, along with conservative magnetics designs, allowed power conversion efficiencies of greater than 92.5 percent to be achieved into resistive loads over the entire operating range of the converter.
The design and performance is presented of the following coplanar waveguides (CPW) microwave distribution networks for linear as well as circularly polarized microstrip patches and dipole arrays: (1) CPW/microstrip line feed; (2) CPW/balanced stripline feed; (3) CPW/slotline feed; (4) grounded CPW/balanced coplanar stripline feed; and (5) CPW/slot coupled feed. Typical measured radiation patterns are presented, and their relative advantages and disadvantages are compared.
"What if" questions answered exactly, without using "increment-and-reevaluate" approach, and without finite differencing of system analysis, by use of sensitivity analysis to calculate first derivatives of behaviors of coupled systems with respect to design variables. If problem strongly nonlinear, efficiency improved by making derivatives of higher orders available to search algorithms. Extension effected by recursive application of same implicit function theorem that underlies previous method. Useful in design calculations for almost any system, including structures, machines, and distribution networks. Feedback control of processes improved by inclusion of derivative terms of higher order.