Lightning and related phenomena in isolated thunderstorms and squall line systems
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Rust, W. D.↗
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Results for “isolate”
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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Electrical isolation design of photovoltaic modules
A method was developed for calculating the magnitude and location of the maximum electric field for a family of solar-cell-like shapes. Simple formulas for use by photovoltaic module designers were developed. They provide quantitative information on the effects of the cell shape, cell thickness, and pottant thickness on the electrical stress intensification at the cell edge. A method for calculating the lines of force for three-dimensional electric fields was developed and applied to a geometry of interest to the photovoltaic program.
Kallis, J. M.↗
Future payload isolation and pointing system technology
Pointing requirements for spaceborne scientific instruments are getting progressively more stringent. At the same time the instruments are likely to fly in an increasingly disturbance rich environment characterized by large basebody and instrument to instrument dynamic interactions. It is not clear that current state-of-the-art pointing technology will be able to adequately address the needs of the mid 1990's. Design options to meet these needs are suggested herein including an innovative 'softmount' concept. The advantages of the softmount approach as compared to the traditional gimbal architecture are illustrated through a planar stability and disturbance response analysis.
Laskin, R. A.↗
Robust detection-isolation-accommodation for sensor failures
The results of a one year study to: (1) develop a theory for Robust Failure Detection and Identification (FDI) in the presence of model uncertainty, (2) develop a design methodology which utilizes the robust FDI ththeory, (3) apply the methodology to a sensor FDI problem for the F-100 jet engine, and (4) demonstrate the application of the theory to the evaluation of alternative FDI schemes are presented. Theoretical results in statistical discrimination are used to evaluate the robustness of residual signals (or parity relations) in terms of their usefulness for FDI. Furthermore, optimally robust parity relations are derived through the optimization of robustness metrics. The result is viewed as decentralization of the FDI process. A general structure for decentralized FDI is proposed and robustness metrics are used for determining various parameters of the algorithm.
Weiss, J. L.↗
Performance characteristics of an isolated coannular plug nozzle at transonic speeds
The Langley 16-Foot Transonic Tunnel was used to evaluate the performance characteristics of a coannular plug nozzle at static conditions (Mach number of 0) and at Mach numbers from 0.65 to 1.20. Jet total pressure ratio was varied from 1.0 (jet off) to 10.0. Thirty-seven configurations generated by the combination of three geometric variables - plug angle, shroud boattail length (fixed exit radius), and shroud extension length - were tested.
Mercer, C. E.↗
Future payload isolation and pointing system technology
An overview is presented of the technology associated with the precision pointing of future spaceborne science instruments. High-level architectural options for dealing with the precision pointing problem are considered, and a representative NASA mission set for the 1990s is given. Pointing accuracy and stability requirements are extracted from the mission requirements, with the sub-0.1 arcsec stability requirement emerging as the primary driver. The state of the art of current technology is assessed, including an evaluation of gimbal systems, suspension systems, and actuator and sensor component technology. Areas where the technology needs to be pushed to satisfy future requirements are identified, and some promising design options are proposed.
Laskin, R. A.↗
Monolithic Isolated Single-Mode Ring Laser
MISER uses four-sided ring to lase nonreciprocally. Laser concept provides very-compact, efficient, and stable source of coherent radiation. Lasers of single, very-stable frequency desirable for number of purposes. Frequency stability makes possible coherent detection of laser radiation with low-bandwidth detector, useful for communications. Allows very-high-resolution spectroscopy. Any application where desired to use laser in way microwaves used traditionally enhanced if frequency very stable.
Kane, T. J.↗
EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude
The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.
Schwartz, Daniel A.↗
Initial investigations into the damping characteristics of wire rope vibration isolators
Passive dampers composed of coils of multi-strand wire rope are investigated. Analytical results range from those produced by complex NASTRAN models to those of a Coulomb damping model with variable friction force. The latter agrees well with experiment. The Coulomb model is also utilized to generate hysteresis loops. Various other models related to early experimental investigations are described. Significant closed-form static solutions for physical properties of single-and multi-strand wire ropes are developed for certain specific geometries and loading conditions. NASTRAN models concentrate on model generation and mode shapes of 2-strand and 7-strand straight wire ropes with interfacial forces.
Cutchins, M. A.↗
Prototype fault isolation expert system for spacecraft control
A program which illustrates how an expert system might perform fault handling for a satellite propulsion subsystem is discussed. The program runs on a VAX 11/780 under VMS with a VT100 interface and is written in FRANZ/LISP. The program presents a series of menus to the user. Once the user selects from the menu, the program simulates the behavior of the hydrazine propulsion system under the fault condition, detects the presence of the fault, and then determines what set of actions to perform in implementing the fault workaround.
Truszkowski, Walt↗
Laser induced fluorescence and phosphorescence of matrix isolated glyoxal - Evidence for exciplex formation in the A 1Au and a 3Au states
Laser-induced fluorescence and phosphorescence as well as infrared and visible absorption spectra of glyoxal in Ar, N2, and CO matrices are presented and analyzed. Glyoxal in its first excited electronic state is shown to form an exciplex with its nearest neighbors in all three matrices, and transitions normally forbidden dominate the emission spectra. The spectral characteristics of these complexes are similar to those of the Ar-glyoxal complex found in supersonic beam experiments. Due to the matrix cage effect, no vibrational predissociation is observed. The phosphorescence lifetime is determined and an upper limit is given for the fluorescence lifetime. This, in combination with the relative intensities of fluorescence and phosphorescence, can be used to place limits on the quantum yields of the various relaxation processes.
Van Ijzendoorn, L. J.↗
Fault detection, isolation, and reconfiguration in the fault tolerant multiprocessor
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Lala, J. H.↗
Boundary-layer effects on the flowfield about isolated flow-through nacelles
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Compton, William B., III↗
Kinetic isolation tether experiment
Progress was made on the analysis of tether damping and on experimentation of the control system on the laboratory simulator. The damping analysis considers the dynamics of a long tether connecting two spacecraft in Earth orbit, one of the spacecraft having dominant mass. In particular, it considers the material damping of the tether. The results show that, with properly chosen tether material and braiding structure, longitudinal vibration of the tethered system is well damped. A particularly effective method of implementing attitude control for tethered satellites is to use the tether tension force to generate control torques by moving the tether attach point relative to the satellite center of mass. A scaled, one dimensional laboratory simulation of the KITE mission was built and preliminary experiments of the proposed attitude control system were performed. The simulator was built to verify theoretical predictions of attitude controllability, and to investigate the technological requirements in order to implement this concept. A detailed description of the laboratory apparatus is provided, and in addition, the results of the preliminary experiments are presented and discussed.
Powell, J. David↗
Studies of isolated neutron stars, pulsars and pulsar-driven nebulae with the advanced X-ray astrophysics facility (AXAF)
The AXAF will signal a revolution in the understanding of neutron stars, pulsars, and Crab Nebula-type supernova remnants. The mission will provide vital and detailed observational data relevant to the physics of superdense matter inside neutron stars, to the acceleration and radiation of nonthermal particles in their magnetospheres, and to the processes whereby these relativistic particles and magnetic fields fuel the surrounding synchrotron nebulosities on scales of parsecs. Highlights of the results should include (1) detection of thermal surface emission from neutron stars, (2) greatly enlarged samples of pulsars that emit magnetospheric (nonthermal) X-rays, and (3) high resolution (spatial and spectral) maps of the nebulae powered by slowing pulsars. The AXAF will extend these studies to external galaxies, being capable of detection of young pulsars and remnants in normal galaxies like M31, in starburst systems like M82, and probably even in galaxies as distant as the Virgo cluster.
Wilson, A. S.↗
Isolation and elimination of waste products
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Borschenko, V. V.↗
FIESTA: An operational decision aid for space network fault isolation
The Fault Tolerance Expert System for Tracking and Data Relay Satellite System (TDRSS) Applications (FIESTA) is a fault detection and fault diagnosis expert system being developed as a decision aid to support operations in the Network Control Center (NCC) for NASA's Space Network. The operational objectives which influenced FIESTA development are presented and an overview of the architecture used to achieve these goals are provided. The approach to the knowledge engineering effort and the methodology employed are also presented and illustrated with examples drawn from the FIESTA domain.
Lowe, Dawn↗
Isolated testing of highly maneuverable inlet con cepts
Ten percent scale models of a Mach 2.2 two dimensional inlet and a Mach 2.0 axisymmetric inlet were tested in the NASA Lewis Research Center 8'x6' Supersonic Wind Tunnel as part of a cooperative effort with the McDonnell Aircraft Company. The objective of this effort was to test methods designed to increase the maneuvering performance of fighter aircraft inlets. Maneuvering improvement concepts were tested up to 40-deg angle of attack for Mach numbers of 0.6 and 0.9, and up to 25 deg for Mach numbers 1.2 and 1.4. Maneuvering improvement concepts included a rotating cowl lip, auxiliary inlets aft of the inlet throat, and a retracting centerbody for the axisymmetric inlet. Test results show that the rotating cowl design was effective in improving subsonic maneuvering performance for both inlets. Auxiliary inlets did not produce significant performance increases for either model. The retracted centerbody resulted in some performance benefits at high angles of attack. None of the maneuvering improvement concepts were effective at Mach 1.2 and 1.4.
Norby, W. P.↗