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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

LP-search and its use in analysis of the accuracy of control systems with acoustical models

The LP-search is proposed as an analog of the Monte Carlo method for finding values in nonlinear statistical systems. It is concluded that: To attain the required accuracy in solution to the problem of control for a statistical system in the LP-search, a considerably smaller number of tests is required than in the Monte Carlo method. The LP-search allows the possibility of multiple repetitions of tests under identical conditions and observability of the output variables of the system.

Sergeyev, V. I.↗
NASA NTRS2003

Robust Control for Microgravity Vibration Isolation using Fixed Order, Mixed H2/Mu Design

Many space-science experiments need an active isolation system to provide a sufficiently quiescent microgravity environment. Modern control methods provide the potential for both high-performance and robust stability in the presence of parametric uncertainties that are characteristic of microgravity vibration isolation systems. While H2 and H(infinity) methods are well established, neither provides the levels of attenuation performance and robust stability in a compensator with low order. Mixed H2/H(infinity), controllers provide a means for maximizing robust stability for a given level of mean-square nominal performance while directly optimizing for controller order constraints. This paper demonstrates the benefit of mixed norm design from the perspective of robustness to parametric uncertainties and controller order for microgravity vibration isolation. A nominal performance metric analogous to the mu measure, for robust stability assessment is also introduced in order to define an acceptable trade space from which different control methodologies can be compared.

Whorton, Mark↗
NASA NTRS2004

Robust Control for The G-Limit Microgravity Vibration Isolation System

Many microgravity science experiments need an active isolation system to provide a sufficiently quiescent acceleration environment. The g-LIMIT vibration isolation system will provide isolation for Microgravity Science Glovebox experiments in the International Space Station. While standard control system technologies have been demonstrated for these applications, modern control methods have the potential for meeting performance requirements while providing robust stability in the presence of parametric uncertainties that are characteristic of microgravity vibration isolation systems. While H2 and H infinity methods are well established, neither provides the levels of attenuation performance and robust stability in a compensator with low order. Mixed H2/mu controllers provide a means for maximizing robust stability for a given level of mean-square nominal performance while directly optimizing for controller order constraints. This paper demonstrates the benefit of mixed norm design from the perspective of robustness to parametric uncertainties and controller order for microgravity vibration isolation. A nominal performance metric analogous to the mu measure for robust stability assessment is also introduced in order to define an acceptable trade space from which different control methodologies can be compared.

Whorton, Mark S.↗
NASA NTRS1971

Pneumatic oscillator Patent

Development and characteristics of fluid oscillator analog to digital converter with variable frequency controlled by signal passing through conditioning circuit

Dustin, M. O.↗
NASA NTRS1975

Passenger ride quality response to an airborne simulator environment

The present study was done aboard a special aircraft able to effect translations through the center of gravity with a minimum of pitch and roll. The aircraft was driven through controlled motions by an on-board analog computer. The input signal was selectively filtered Gaussian noise whose power spectra approximated that of natural turbulence. This input, combined with the maneuvering capabilities of this aircraft, resulted in an extremely realistic simulation of turbulent flight. The test flights also included varying bank angles during turns. Subjects were chosen from among NASA Flight Research Center personnel. They were all volunteers, were given physical examinations, and were queried about their attitudes toward flying before final selection. In profile, they were representative of the general flying public. Data from this study include (1) a basis for comparison with previous commercial flights, that is, motion dominated by vertical acceleration, (2) extension to motion dominated by lateral acceleration, and (3) evaluation of various bank angles.

Wolf, T. D.↗
NASA NTRS1977

Low-cost high-performance VLF receiver front-end

A VLF receiver front end has been designed using standard linear IC's. The basic methods have been evaluated extensively on the omega 10.2-kHz channel but are readily adaptable to any other VLF frequency in the 10.2-20 kHz region. Applications for the modules exist in position location, time-frequency measurements, and signal propagation. The set provides control gates, zero-crossing signals, and analog outputs to interface with any type of digital logic, microprocessor, or analog signal processor.

Burhans, R. W.↗
NASA NTRS1977

Experimental study of pyroxene-liquid interaction in quartz-normative basalt 15597

Equilibrium and controlled cooling rate experiments on a synthetic analog of Apollo 15 quartz normative basalt 15597 are reported. While the partitioning of the major elements Ca, Mg, and Fe between pyroxene and liquid is rate independent, the K sub D parameter for Fe/Mg, which is calculated for low-Ca pyroxene, is temperature dependent. It is suggested that chemical trends observed in lunar pyroxenes are a consequence of three rate processes. The processes are (1) rate-dependent suppression of crystallization of other phases until lower temperature alters liquid composition and, therefore, the composition of the pyroxene that crystallizes; (2) the efficiency of fractional crystallization and the extent of crystal zoning are rate dependent; and (3) the partitioning of Al2O3, TiO2, and Cr2O3 between pyroxene and liquid depends on cooling rate.

Grove, T. L.↗
NASA NTRS1978

An acoustic range for the measurement of the noise signature of aircraft during flyby operations

The remotely operated multiple array acoustic range (ROMAAR), which has been developed to give direct measurement and display of aircraft noise in several measurement units during takeoff, landing, and flyby operations, is described. The ROMAAR, which provides information on the ground noise signature of aircraft, represents a unique combination of state-of-the-art digital and analog noise-recording methods, computer-controlled digital communication methods, radar tracking facilities, quick-look weather (profile) capabilities, and sophisticated data handling routines and facilities. The ROMAAR, which is operated by NASA, allows direct data feedback to the NASA Aircraft Noise Prediction Office. As many as 38 simultaneous noise measurements can be made for each aircraft overflight.

Hilton, D. A.↗
NASA NTRS1985

Miscibility Gap Systems

Immiscible droplets embedded in a host fluid in which a temperature gradient exists migrate toward the hot end of the host fluid because of the temperature dependence of the interfacial energy of the droplet. This thermocapillary migration effect was exploited in the design of a controllable heat valve which is the thermal analog of the electronic vacuum triode. Studies have also been made of test cells that could use thermocapillary migration to facilitate the study of condensation and dissolution kinetics in miscibility-gap solutions.

Schmid, L. A.↗
NASA NTRS1986

Reverse osmosis water purification system

A reverse osmosis water purification system, which uses a programmable controller (PC) as the control system, was designed and built to maintain the cleanliness and level of water for various systems of a 64-m antenna. The installation operates with other equipment of the antenna at the Goldstone Deep Space Communication Complex. The reverse osmosis system was designed to be fully automatic; with the PC, many complex sequential and timed logic networks were easily implemented and are modified. The PC monitors water levels, pressures, flows, control panel requests, and set points on analog meters; with this information various processes are initiated, monitored, modified, halted, or eliminated as required by the equipment being supplied pure water.

Ahlstrom, H. G.↗
NASA NTRS1988

Three-dimensional self-adaptive grid method for complex flows

A self-adaptive grid procedure for efficient computation of three-dimensional complex flow fields is described. The method is based on variational principles to minimize the energy of a spring system analogy which redistributes the grid points. Grid control parameters are determined by specifying maximum and minimum grid spacing. Multidirectional adaptation is achieved by splitting the procedure into a sequence of successive applications of a unidirectional adaptation. One-sided, two-directional constraints for orthogonality and smoothness are used to enhance the efficiency of the method. Feasibility of the scheme is demonstrated by application to a multinozzle, afterbody, plume flow field. Application of the algorithm for initial grid generation is illustrated by constructing a three-dimensional grid about a bump-like geometry.

Djomehri, M. Jahed↗
NASA NTRS1988

Three-dimensional self-adaptive grid method for complex flows

A self-adaptive grid procedure for efficient computation of three-dimensional complex flow fields is described. The method is based on variational principles to minimize the energy of a spring system analogy which redistributes the grid points. Grid control parameters are determined by specifying maximum and minimum grid spacing. Multidirectional adaptation is achieved by splitting the procedure into a sequence of successive applications of a unidirectional adaptation. One-sided, two-directional constraints for orthogonality and smoothness are used to enhance the efficiency of the method. Feasibility of the scheme is demonstrated by application to a multinozzle, afterbody, plume flow field. Application of the algorithm for initial grid generation is illustrated by constructing a three-dimensional grid about a bump-like geometry.

Djomehri, M. Jahed↗
NASA NTRS1995

Low Power Camera-on-a-Chip Using CMOS Active Pixel Sensor Technology

A second generation image sensor technology has been developed at the NASA Jet Propulsion Laboratory as a result of the continuing need to miniaturize space science imaging instruments. Implemented using standard CMOS, the active pixel sensor (APS) technology permits the integration of the detector array with on-chip timing, control and signal chain electronics, including analog-to-digital conversion.

Space Microelectronics Image Sensors APS Digital I↗
NASA NTRS1995

Low Power Camera-on-a-Chip Using CMOS Active Pixel Sensor Technology

A second generation image sensor technology has been developed at the NASA Jet Propulsion Laboratory as a result of the continuing need to miniaturize space science imaging instruments. Implemented using standard CMOS, the active pixel sensor (APS) technology permits the integration of the detector array with on-chip timing, control and signal chain electronics, including analog-to-digital conversion.

Space Microelectronics Image Sensors APS Digital I↗
NASA NTRS2005

A back-illuminated megapixel CMOS image sensor

In this paper, we present the test and characterization results for a back-illuminated megapixel CMOS imager. The imager pixel consists of a standard junction photodiode coupled to a three transistor-per-pixel switched source-follower readout [1]. The imager also consists of integrated timing and control and bias generation circuits, and provides analog output. The analog column-scan circuits were implemented in such a way that the imager could be configured to run in off-chip correlated double-sampling (CDS) mode. The imager was originally designed for normal front-illuminated operation, and was fabricated in a commercially available 0.5 pn triple-metal CMOS-imager compatible process. For backside illumination, the imager was thinned by etching away the substrate was etched away in a post-fabrication processing step.

Complementary Metal Oxide Semiconductor imager (CM↗
NASA NTRS2009

Validation through Full-Scale Flight Exploration

Objectives: a) Regain Stable Platform: 1) Metrics analogous to stability margins needed for adaptive control systems; 2) Avoid adverse structural interactions. b) Maneuverability: 1) Control vehicle within new constraints; 2) Respect structural limitations; 3) Inform pilot of new performance limitations. c) Provide ability to safely land airplane: 1) Develop safest recovery trajectory.

Bosworth, John T.↗