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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

The R-Shell approach - Using scheduling agents in complex distributed real-time systems

Large, complex real-time systems such as space and avionics systems are extremely demanding in their scheduling requirements. The current OS design approaches are quite limited in the capabilities they provide for task scheduling. Typically, they simply implement a particular uniprocessor scheduling strategy and do not provide any special support for network scheduling, overload handling, fault tolerance, distributed processing, etc. Our design of the R-Shell real-time environment fcilitates the implementation of a variety of sophisticated but efficient scheduling strategies, including incorporation of all these capabilities. This is accomplished by the use of scheduling agents which reside in the application run-time environment and are responsible for coordinating the scheduling of the application.

Natarajan, Swaminathan↗
NASA NTRS1994

Real-time tracking of objects for space applications using a laser range scanner

Real-time tracking of multiple targets and three dimensional object features was demonstrated using a laser range scanner. The prototype was immune to ambient illumination and sun interference. Tracking error feedback was simultaneously obtained from individual targets, global predicted target position, and the human operator. A more complete study of calibration parameters and temperature variations on the scanner is needed to determine the exact performance of the sensor. Lissajous patterns used in three-dimensional real-time tracking prove helpful given their high resolution. The photogrammetry-based Advanced Space Vision System (ASVS) is discussed in combination with the laser range scanner.

Blais, F.↗
NASA NTRS1994

An architecture for real-time vision processing

To study the feasibility of developing an architecture for real time vision processing, a task queue server and parallel algorithms for two vision operations were designed and implemented on an i860-based Mercury Computing System 860VS array processor. The proposed architecture treats each vision function as a task or set of tasks which may be recursively divided into subtasks and processed by multiple processors coordinated by a task queue server accessible by all processors. Each idle processor subsequently fetches a task and associated data from the task queue server for processing and posts the result to shared memory for later use. Load balancing can be carried out within the processing system without the requirement for a centralized controller. The author concludes that real time vision processing cannot be achieved without both sequential and parallel vision algorithms and a good parallel vision architecture.

Chien, Chiun-Hong↗
NASA NTRS1994

ControlShell: A real-time software framework

The ControlShell system is a programming environment that enables the development and implementation of complex real-time software. It includes many building tools for complex systems, such as a graphical finite state machine (FSM) tool to provide strategic control. ControlShell has a component-based design, providing interface definitions and mechanisms for building real-time code modules along with providing basic data management. Some of the system-building tools incorporated in ControlShell are a graphical data flow editor, a component data requirement editor, and a state-machine editor. It also includes a distributed data flow package, an execution configuration manager, a matrix package, and an object database and dynamic binding facility. This paper presents an overview of ControlShell's architecture and examines the functions of several of its tools.

Schneider, Stanley A.↗
NASA NTRS1994

A Prototype Lisp-Based Soft Real-Time Object-Oriented Graphical User Interface for Control System Development

A prototype Lisp-based soft real-time object-oriented Graphical User Interface for control system development is presented. The Graphical User Interface executes alongside a test system in laboratory conditions to permit observation of the closed loop operation through animation, graphics, and text. Since it must perform interactive graphics while updating the screen in real time, techniques are discussed which allow quick, efficient data processing and animation. Examples from an implementation are included to demonstrate some typical functionalities which allow the user to follow the control system's operation.

Litt, Jonathan↗
NASA NTRS1992

Performance comparison of token ring protocols for hard-real-time communication

The ability to guarantee the deadlines of synchronous messages while maintaining a good aggregate throughput is an important consideration in the design of distributed real-time systems. In this paper, we study two token ring protocols, the priority driven protocol and the timed token protocol, for their suitability for hard real-time systems. Both these protocols use a token to control access to the transmission medium. In a priority driven protocol, messages are assigned priorities and the protocol ensures that messages are transmitted in the order of their priorities. Timed token protocols do not provide for priority arbitration but ensure that the maximum access delay for a station is bounded. For both protocols, we first derive the schedulability conditions under which the transmission deadlines of a given set of synchronous messages can be guaranteed. Subsequently, we use these schedulability conditions to quantitatively compare the average case behavior of the protocols. This comparison demonstrates that each of the protocols has its domain of superior performance and neither dominates the other for the entire range of operating conditions.

Kamat, Sanjay↗
NASA NTRS1994

Automated Test Environment for a Real-Time Control System

An automated environment with hardware-in-the-loop has been developed by Rocketdyne Huntsville for test of a real-time control system. The target system of application is the man-rated real-time system which controls the Space Shuttle Main Engines (SSME). The primary use of the environment is software verification and validation, but it is also useful for evaluation and analysis of SSME avionics hardware and mathematical engine models. It provides a test bed for the integration of software and hardware. The principles and skills upon which it operates may be applied to other target systems, such as those requiring hardware-in-the-loop simulation and control system development. Potential applications are in problem domains demanding highly reliable software systems requiring testing to formal requirements and verifying successful transition to/from off-nominal system states.

Hall, Ronald O.↗
NASA NTRS1994

Single Stage Rocket Technology's real time data system

The Single Stage Rocket Technology (SSRT) Delta Clipper Experimental (DC-X) Program is a United States Air Force Ballistic Missile Defense Organization (BMDO) rapid prototyping initiative that is currently demonstrating technology readiness for reusable suborbital rockets. The McDonnell Douglas DC-X rocket performed technology demonstrations at the U.S. Army White Sands Missile Range in New Mexico from April-October in 1993. The DC-X Flight Operations Control Center (FOCC) contains the ground control system that is used to monitor and control the DC-X vehicle and its Ground Support Systems (GSS). The FOCC is operated by a flight crew of three operators. Two operators manage the DC-X Flight Systems and one operator is the Ground Systems Manager. A group from McDonnell Douglas Aerospace at KSC developed the DC-X ground control system for the FOCC. This system is known as the Real Time Data System (RTDS). The RTDS is a distributed real time control and monitoring system that utilizes the latest available commercial off-the-shelf computer technology. The RTDS contains front end interfaces for the DC-X RF uplink/downlink and fiber optic interfaces to the GSS equipment. This paper describes the RTDS architecture and FOCC layout. The DC-X applications and ground operations are covered.

Voglewede, Steven D.↗
NASA NTRS1994

Graphic Server: A real time system for displaying and monitoring telemetry data of several satellites

Known as a Graphic Server, the system presented was designed for the control ground segment of the Telecom 2 satellites. It is a tool used to dynamically display telemetry data within graphic pages, also known as views. The views are created off-line through various utilities and then, on the operator's request, displayed and animated in real time as data is received. The system was designed as an independent component, and is installed in different Telecom 2 operational control centers. It enables operators to monitor changes in the platform and satellite payloads in real time. It has been in operation since December 1991.

Douard, Stephane↗
NASA NTRS1994

Real-time remote scientific model validation

This paper describes flight results from the use of a CLIPS-based validation facility to compare analyzed data from a space life sciences (SLS) experiment to an investigator's preflight model. The comparison, performed in real-time, either confirms or refutes the model and its predictions. This result then becomes the basis for continuing or modifying the investigator's experiment protocol. Typically, neither the astronaut crew in Spacelab nor the ground-based investigator team are able to react to their experiment data in real time. This facility, part of a larger science advisor system called Principal Investigator in a Box, was flown on the space shuttle in October, 1993. The software system aided the conduct of a human vestibular physiology experiment and was able to outperform humans in the tasks of data integrity assurance, data analysis, and scientific model validation. Of twelve preflight hypotheses associated with investigator's model, seven were confirmed and five were rejected or compromised.

Frainier, Richard↗
NASA NTRS1994

A real-time algorithm for integrating differential satellite and inertial navigation information during helicopter approach

A real-time, high-rate precision navigation Kalman filter algorithm is developed and analyzed. This Navigation algorithm blends various navigation data collected during terminal area approach of an instrumented helicopter. Navigation data collected include helicopter position and velocity from a global position system in differential mode (DGPS) as well as helicopter velocity and attitude from an inertial navigation system (INS). The goal of the Navigation algorithm is to increase the DGPS accuracy while producing navigational data at the 64 Hertz INS update rate. It is important to note that while the data was post flight processed, the Navigation algorithm was designed for real-time analysis. The design of the Navigation algorithm resulted in a nine-state Kalman filter. The Kalman filter's state matrix contains position, velocity, and velocity bias components. The filter updates positional readings with DGPS position, INS velocity, and velocity bias information. In addition, the filter incorporates a sporadic data rejection scheme. This relatively simple model met and exceeded the ten meter absolute positional requirement. The Navigation algorithm results were compared with truth data derived from a laser tracker. The helicopter flight profile included terminal glideslope angles of 3, 6, and 9 degrees. Two flight segments extracted during each terminal approach were used to evaluate the Navigation algorithm. The first segment recorded small dynamic maneuver in the lateral plane while motion in the vertical plane was recorded by the second segment. The longitudinal, lateral, and vertical averaged positional accuracies for all three glideslope approaches are as follows (mean plus or minus two standard deviations in meters): longitudinal (-0.03 plus or minus 1.41), lateral (-1.29 plus or minus 2.36), and vertical (-0.76 plus or minus 2.05).

Hoang, TY↗
NASA NTRS1993

Multi-layer holographic bifurcative neural network system for real-time adaptive EOS data analysis

Optical data processing techniques have the inherent advantage of high data throughout, low weight and low power requirements. These features are particularly desirable for onboard spacecraft in-situ real-time data analysis and data compression applications. the proposed multi-layer optical holographic neural net pattern recognition technique will utilize the nonlinear photorefractive devices for real-time adaptive learning to classify input data content and recognize unexpected features. Information can be stored either in analog or digital form in a nonlinear photofractive device. The recording can be accomplished in time scales ranging from milliseconds to microseconds. When a system consisting of these devices is organized in a multi-layer structure, a feedforward neural net with bifurcating data classification capability is formed. The interdisciplinary research will involve the collaboration with top digital computer architecture experts at the University of Southern California.

Liu, Hua-Kuang↗
NASA NTRS1995

Importance of real gas effects in entry technology

Critical issues concerning real gas effects in hypervelocity flows where the thermochemical nonequilibrium effects are pronounced, are described. Emphasis is on the development and validation of benchmark analysis tools. Approaches to develop and/or enhance phenomenological models, including test techniques to acquire databases, and incorporate them into computational flow field simulation codes are described. The performance characteristics of shock tubes, ballistic ranges and arc heated wind tunnels, state of the art diagnostics are included. The following aerothermodynamic phenomena are discussed: aerodynamic parameters, viscous interactions, turbulent transition, forebody heating/heat transfer, radiative heating, Lee-Base flows and low density real gas.

Deiwert, George S.↗
NASA NTRS1994

Recovering the real density field of galaxies from redshift space

This paper proposes a number of methods for recovering the true, real-space large-scale density distributions from redshift data sets. On the largest scales, the effects of peculiar velocities is to compress the galaxy clustering along the line of sight and consequently the density gradient in the radial direction is enhanced in comparison with the density gradient perpendicular to the line of sight. We calculate the relation between the density gradients in real and redshift space in the linear regime and show that it is a simple function of the density parameter, Omega. By considering the anisotropy of density gradients in redshift space it is possible, in principle, to obtain information about the value of Omega. Using N-body simulations we examine different methods for correcting the effects of large-scale velocities to obtain the true density distributions. We derive the peculiar velocity field from the redshift data and iterate to place each galaxy at a distance consistent with its measured redshift and its derived velocity. Linear theory, as well as second-order solutions for the peculiar velocity field are tested. The density distributions in low-density regions predicted by both linear theory and second-order theory are similar, and in good agreement with the true density field in the simulation. The use of the second-order corrections improves the prediction of the density field in high-density regions.

Gramann, Mirt↗
NASA NTRS1995

A Real-Time Nonvolatile Residue (NVR) Monitor

New development and application of device described in "Surface-Acoustic-Wave Piezoelectric Microbalance," (LAR-14476). Active sensing element of Real-Time NVR Monitor comprises pair of piezoelectric surface-acoustic-wave resonators resonating at frequency of 200 MHz. Bare, uncoated resonator exposed to atmosphere and directly in contact with airborne volatile and nonvolatile materials leaving residues on surface. Resonant frequency of exposed resonator decreases with increasing mass of adsorbed residue; resulting beat frequency between two resonators increases with mass and serves as sensitive real-time indication of airborne contaminants or non-volatile residue.

Bowers, William D.↗
NASA NTRS1995

Real-time design with peer tasks

We introduce a real-time design methodology for large scale, distributed, parallel architecture, real-time systems (LDPARTS), as an alternative to those methods using rate or dead-line monotonic analysis. In our method the fundamental units of prioritization, work items, are domain specific objects with timing requirements (deadlines) found in user's specification. A work item consists of a collection of tasks of equal priority. Current scheduling theories are applied with artifact deadlines introduced by the designer whereas our method schedules work items to meet user's specification deadlines (sometimes called end-to-end deadlines). Our method supports these scheduling properties. Work item scheduling is based on domain specific importance instead of task level urgency and still meets as many user specification deadlines as can be met by scheduling tasks with respect to urgency. Second, the minimum (closest) on-line deadline that can be guaranteed for a work item of highest importance, scheduled at run time, is approximately the inverse of the throughput, measured in work items per second. Third, throughput is not degraded during overload and instead of resorting to task shedding during overload, the designer can specify which work items to shed. We prove these properties in a mathematical model.

Goforth, Andre↗
NASA NTRS1995

In-flight demonstration of a Real-Time Flush Airdata Sensing (RT-FADS) system

A prototype real-time flush airdata sensing (RT-FADS) system has been developed and flight tested at the NASA Dryden Flight Research Center. This system uses a matrix of pressure orifices on the vehicle nose to estimate airdata parameters in real time using nonlinear regression. The algorithm is robust to sensor failures and noise in the measured pressures. The RT-FADS system has been calibrated using inertial trajectory measurements that were bootstrapped for atmospheric conditions using meteorological data. Mach numbers as high as 1.6 and angles of attack greater than 45 deg have been tested. The system performance has been evaluated by comparing the RT-FADS to the ship system airdata computer measurements to give a quantitative evaluation relative to an accepted measurement standard. Nominal agreements of approximately 0.003 in Mach number and 0.20 deg in angle of attack and angle of sideslip have been achieved.

Whitmore, Stephen A.↗
NASA NTRS1996

Development of a real-time transport performance optimization methodology

The practical application of real-time performance optimization is addressed (using a wide-body transport simulation) based on real-time measurements and calculation of incremental drag from forced response maneuvers. Various controller combinations can be envisioned although this study used symmetric outboard aileron and stabilizer. The approach is based on navigation instrumentation and other measurements found on state-of-the-art transports. This information is used to calculate winds and angle of attack. Thrust is estimated from a representative engine model as a function of measured variables. The lift and drag equations are then used to calculate lift and drag coefficients. An expression for drag coefficient, which is a function of parasite drag, induced drag, and aileron drag, is solved from forced excitation response data. Estimates of the parasite drag, curvature of the aileron drag variation, and minimum drag aileron position are produced. Minimum drag is then obtained by repositioning the symmetric aileron. Simulation results are also presented which evaluate the affects of measurement bias and resolution.

Gilyard, Glenn↗