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All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

The Langley Research Center CSI phase-0 evolutionary model testbed-design and experimental results

A testbed for the development of Controls Structures Interaction (CSI) technology is described. The design philosophy, capabilities, and early experimental results are presented to introduce some of the ongoing CSI research at NASA-Langley. The testbed, referred to as the Phase 0 version of the CSI Evolutionary model (CEM), is the first stage of model complexity designed to show the benefits of CSI technology and to identify weaknesses in current capabilities. Early closed loop test results have shown non-model based controllers can provide an order of magnitude increase in damping in the first few flexible vibration modes. Model based controllers for higher performance will need to be robust to model uncertainty as verified by System ID tests. Data are presented that show finite element model predictions of frequency differ from those obtained from tests. Plans are also presented for evolution of the CEM to study integrated controller and structure design as well as multiple payload dynamics.

Belvin, W. K.↗
NASA NTRS1973

Photoemission from CsI - Calculation.

Calculations of optical and photoemission spectra for CsI based on first-order allowed transitions between Bloch-wave states are discussed. The calculations, utilizing energy-band data for CsI published by Onodera (1968), were performed by computer sampling of regions in the Brillouin zone. The photoelectric spectra of CsI, calculated on the basis of an interpolated band scheme, display features which are in general agreement with the experimentally determined photoelectric energy distribution curves.

Distefano, T. H.↗
NASA NTRS1982

Quantum efficiency of opaque CsI photocathodes with channel electron multiplier arrays in the extreme and far ultraviolet

The arrays are overcoated with a CsI photocathode in the VUV. The measurements are part of the development program for the Extreme Ultraviolet Explorer. Monochromatic light from a hollow cathode discharge source passing through a McPherson grazing incidence monochromator is used to illuminate the CsI photocathode. The beam diameter is kept small (approximately 2 mm) to confine it within the individual thickness strips. A bias grid is used to produce a 50-V/mm electric field to guarantee collection of all photoelectrons emitted by the CEMA (channel electron multiplier array) webbing. The CEMAs are operated with a gain of 2-3 x 10 to the 6th and are moderately saturated. A channeltron secondary transfer standard is used to determine the absolute QE in the EUV, whereas an NBS calibrated windowed photodiode is used to measure the FUV absolute QE. It is noted that the CsI gives a factor of 3 increase in the QE in the EUV and a factor of 50-5000 in the FUV.

Martin, C.↗
NASA NTRS1989

Stability and implementation of partitioned CSI solution procedures

A partitioned procedure developed for the efficient solution of control-structure interaction (CSI) problems is presented with emphasis on its computational stability, implementation aspects, and accuracy characteristics. The partitioned CSI procedure proposed here can facilitate the use of large-scale structural analysis for control-structure interaction problems. It is anticipated that real-time CSI simulations will become routine if adequate advances are made in the construction of reduced-order observers and, for some time variant problems, if substantially faster parallel solution procedures for the Riccati equations become available.

Park, K. C.↗
NASA NTRS1991

The photoelectric effect from CsI by polarized soft X-rays

Studies of the polarization dependence of the photoelectric effect produced by soft X-rays from CsI indicate that the geometrical effects in these experiments can often mimic the polarization signature. This paper presents a detailed calculation of these geometrical effects that are produced when the X-ray beam is not precisely aligned on a rotatable plane photocathode. The experimentally observed geometrical effects were used to precisely determine the realignment of the incident beam of polarized X-rays on a rotatable photocathode. The results allow determinations of the true polarization dependence of the photoemission from CsI. It is shown that the photoelectric effect in CsI depends on the polarization state of the X-rays.

Shaw, Ping S.↗
NASA NTRS1992

Beam, plate, and shell finite elements for CSI design code

Efficient triangular plate bending finite elements (with 6 degree-of-freedom per node) are surveyed. The most promising element will be selected, coded, and implemented into the current Control Structures Interactions (CSI) Design Code. Numerical example, v.i.a. CSI Design Code will be conducted to confirm the efficiency and accuracy of the selected plate bending element. Procedures to further enhance the computations of the CSI design code will be recommended.

Nguyen, Duc T.↗
NASA NTRS1993

Integrated design of the CSI evolutionary structure: A verification of the design methodology

One of the main objectives of the Controls-Structures Interaction (CSI) program is to develop and evaluate integrated controls-structures design methodology for flexible space structures. Thus far, integrated design methodologies for a class of flexible spacecraft, which require fine attitude pointing and vibration suppression with no payload articulation, have been extensively investigated. Various integrated design optimization approaches, such as single-objective optimization, and multi-objective optimization, have been implemented with an array of different objectives and constraints involving performance and cost measures such as total mass, actuator mass, steady-state pointing performance, transient performance, control power, and many more. These studies have been performed using an integrated design software tool (CSI-DESIGN CODE) which is under development by the CSI-ADM team at the NASA Langley Research Center. To date, all of these studies, irrespective of the type of integrated optimization posed or objectives and constraints used, have indicated that integrated controls-structures design results in an overall spacecraft design which is considerably superior to designs obtained through a conventional sequential approach. Consequently, it is believed that validation of some of these results through fabrication and testing of a structure which is designed through an integrated design approach is warranted. The objective of this paper is to present and discuss the efforts that have been taken thus far for the validation of the integrated design methodology.

Maghami, Peiman G.↗
NASA NTRS1993

Evaluation of CSI enhancements for jitter reduction on the EOS AM-1 observatory

A collaborative study between the Goddard Space Flight Center and the Langley Research Center is now underway to investigate the application of Control-Structure Integration (CSI) technologies to the EOS AM-1 spacecraft. Preliminary GN&C pointing studies of EOS AM-1, performed in 1991 and 1992, have indicated the potential for low pointing jitter and stability margins. Hence, a detailed baseline and CSI enhanced jitter assessment has been undertaken. This paper describes the spacecraft jitter pointing requirements, finite element models, and on-board disturbances. The jitter assessment approach being used by the NASA LaRC and various tools developed for efficient simulation and analysis of jitter are presented. In addition, preliminary results are given to show the potential need of CSI technologies for improving pointing performance of the spacecraft.

Belvin, W. K.↗
NASA NTRS1991

Controls-Structures Interaction (CSI) technology program summary. Earth orbiting platforms program area of the space platforms technology program

Control-Structures Interaction (CSI) technology embraces the understanding of the interaction between the spacecraft structure and the control system, and the creation and validation of concepts, techniques, and tools, for enabling the interdisciplinary design of an integrated structure and control system, rather than the integration of a structural design and a control system design. The goal of this program is to develop validated CSI technology for integrated design/analysis and qualification of large flexible space systems and precision space structures. A description of the CSI technology program is presented.

Newsom, Jerry R.↗
NASA NTRS1993

Dynamic tests on the NASA Langley CSI evolutionary model

A modal analysis study, representing one of the anticipated 'Cooperative Spacecraft Structural Dynamics Experiments on the NASA Langley CSI Evolutionary Model', was carried out as a sub-task under the NASA/DLR collaboration in dynamics and control of large space systems. The CSI evolutionary testbed (CEM) is designed for the development of Controls-Structures Interaction (CSI) technology to improve space science platform pointing. For orbiting space structures like large flexible trusses, new identification challenges arise due to their specific dynamic characteristics (low frequencies and high modal density) on the one hand, and the limited possibilities of exciting such structures and measuring their responses on orbit on the other. The main objective was to investigate the modal identification potential of several different types of forcing functions that could possibly be realized with on-board excitation equipment using a minimum number of exciter locations as well as response locations. These locations were defined in an analytical test prediction process used to study the implications of measuring and analyzing the responses thus produced. It turned out that broadband excitation is needed for a general modal survey, but if only certain modes are of particular interest, combinations of exponentially decaying sine functions provide favorable excitation conditions as they allow to concentrate the available energy on the modes being of special interest. From a practical point-of-view structural nonlinearities as well as noisy measurements make the analysis more difficult, especially in the low frequency range and when the modes are closely spaced.

Troidl, H.↗
DOE OSTI2021

Reaction losses of charged particles in CsI(Tl) crystals

To efficiently detect energetic light charged particles, it is common to use arrays of energy-loss telescopes involving two or more layers of detection media. As the energy of the particles increases, thicker layers are usually needed. However, carrying out measurements with thick-telescopes may require corrections for the losses due to nuclear reactions induced by the incident particles on nuclei within the detector and for the scattering of incident particles out of the detector, without depositing their full energy in the active material. In this paper, we develop a method for measuring such corrections and determine the reaction and out-scattering losses for data measured with the silicon-CsI(Tl) telescopes of the newly developed HiRA10 array. Here, the extracted efficiencies are in good agreement with model predictions using the GEANT4 reaction loss algorithm for Z = 1 and Z = 2 isotopes. After correcting for the HiRA10 geometry, we obtain a general function that describes the loss of efficiency due to reaction losses in CsI(Tl) crystals as a function of range.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Monte Carlo simulation of the passage of $\gamma$-rays and $\alpha$-particles in CsI

In this work, theoretical and computational methods for simulating the creation of ionization tracks by fast ions in solids were applied to the passage of a-particles in CsI, an inorganic scintillator commonly used for radiation detection. The methods were implemented in a Monte Carlo program to simulate the interaction of $\alpha$-particles, with incident energies of up to 1 MeV, with CsI. The simulations followed the fate of individual electron-hole pairs and thus allowed for a detailed description of the microscopic structure of ionization tracks created by incident radiation. Simulations were also performed with $\gamma$-rays of the same energy to compare and contrast the ionization tracks obtained with both types of particle. Intrinsic properties such as the mean energy per electron-hole pair, Fano factor, maximum theoretical light yield, and spatial distributions of electron-hole pairs were computed for both $\alpha$-particles and $\gamma$-rays. $\alpha$-particles created cylindrical tracks that were initially aligned with the incident direction and with initial radii of a few nanometers, whereas $\gamma$-rays showed significant scattering, resulting in probability distributions with lower intensities and much greater radial extents.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1978

Design data brochure for CSI series V solar heating system

Generalized information on system configuration, system sizing, and mechanical layout is presented to assist the architect or designer in preparing construction drawings and specifications for the installation of the CSI integrated solar heating systems. Efficiency in space utilization of a full length collector and the importance of proper sizing of the collector array are among the topics discussed. Details of storage and transport subsystems are provided along with drawings and specifications of all components of the CSI system.

Source record↗
NASA NTRS1988

Further investigation of CsI-coated microchannel plate quantum efficiencies

Previously, pulse-counting detection efficiencies measured for CsI-coated microchannel plate (MCP) detectors (two-stage chevron configuration with a single collecting anode) have been reported to be 15-20 percent near Lyman-alpha (1216 A), compared to typical 65 percent quantum yields of opaque CsI photocathodes. To investigate the possibility that an improvement in quantum yield could result from use of MCPs with a bias angle of about 25 deg instead of 8 deg as used previously, the previous measurements were reported with new MCPs having the larger bias angle. No significant improvement in detection efficiency was achieved; the new detector tests still yielded maximum efficiencies of the order of 20 percent near 1216 A.

Carruthers, George R.↗
NASA NTRS1989

ASCIE: An integrated experiment to study CSI in large segmented optical systems

A description of the advanced structures/control integrated experiment (ASCIE) experimental setup, a generic test bed for several essential technologies was presented. In particular its multi-input, multi-output, non-collocated control system and its complex structural dynamics, characteristic of large segmented systems make it an ideal test bed for Control-Structure Interaction (CSI) experiments. The high accuracy of its measurement system will make it possible to investigate the dynamics of microvibrations and its implication for the CSI phenomenon.

Aubrun, Jean-Noel↗
NASA NTRS1991

Implementation of the Lanczos eigen-solver for the CSI code on high performance computers

The focus of this research is to implement a Lanczos algorithm for the Control-Structure Integration (CSI) code which can exploit both parallel and vector capabilities provided by modern, high performance computers. A partial restoring orthogonality scheme is also developed and incorporated into the basic Lanczos algorithm. The numerical performance of the proposed parallel-vector Lanczos algorithm is demonstrated by solving for the frequencies and mode shapes of the Phase Zero CSI model. The superior performance of the Lanczos algorithm is illustrated in tabular form.

Nguyen, Duc T.↗
NASA NTRS1991

Langley's CSI evolutionary model: Phase O

A testbed for the development of Controls Structures Interaction (CSI) technology to improve space science platform pointing is described. The evolutionary nature of the testbed will permit the study of global line-of-sight pointing in phases 0 and 1, whereas, multipayload pointing systems will be studied beginning with phase 2. The design, capabilities, and typical dynamic behavior of the phase 0 version of the CSI evolutionary model (CEM) is documented for investigator both internal and external to NASA. The model description includes line-of-sight pointing measurement, testbed structure, actuators, sensors, and real time computers, as well as finite element and state space models of major components.

Belvin, W. Keith↗
NASA NTRS1992

CSI computer system/remote interface unit acceptance test results

The validation tests conducted on the Control/Structures Interaction (CSI) Computer System (CCS)/Remote Interface Unit (RIU) is discussed. The CCS/RIU consists of a commercially available, Langley Research Center (LaRC) programmed, space flight qualified computer and a flight data acquisition and filtering computer, developed at LaRC. The tests were performed in the Space Structures Research Laboratory (SSRL) and included open loop excitation, closed loop control, safing, RIU digital filtering, and RIU stand alone testing with the CSI Evolutionary Model (CEM) Phase-0 testbed. The test results indicated that the CCS/RIU system is comparable to ground based systems in performing real-time control-structure experiments.

Sparks, Dean W., Jr.↗