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Dive into the research topics where John D. Johnston is active.

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Featured researches published by John D. Johnston.


Journal of Spacecraft and Rockets | 2002

Corner Wrinkling of a Square Membrane Due to Symmetric Mechanical Loads

Joseph R. Blandino; John D. Johnston; Urmil K. Dharamsi

Thin-e lm membrane structures are under consideration for use in many future gossamer spacecraft systems. Examples include sunshields for large-aperture telescopes, solar sails, and membrane optics. The development of capabilitiesfortesting and analyzing pretensioned,thin-e lm membranestructuresisanimportantand challenging aspectofgossamerspacecrafttechnologydevelopment.Resultsarepresentedfromexperimentalandcomputational studies performed to characterize the wrinkling behavior of thin-e lm membranes under mechanical loading. The test article is a 500-mm-square Kapton ® membrane subjected to symmetric corner loads. Data are presented for loads ranging from 0.49 to 4.91 N. The experimental resultsshow that as theload increases the number of wrinkles increases, while the wrinkle amplitude decreases. The computational model uses a e nite element implementation of Stein‐Hedgepeth membrane wrinkling theory to predict the behavior of the membrane. Comparisons were made with experimental results for the wrinkle angle and wrinkled region. There was reasonably good agreement between the measured wrinkle angle and the predicted directions of the major principle stresses. The shape of the wrinkled region predicted by the e nite element model matches that observed in the experiments; however, the size of the predicted region is smaller that that determined in the experiments.


Journal of Guidance Control and Dynamics | 1998

Thermally Induced Attitude Dynamics of a Spacecraft with a Flexible Appendage

John D. Johnston; Earl A. Thornton

The performance of a significant number of spacecraft has been impacted negatively by attitude disturbances resulting from thermally induced deformations of flexible appendages. Motions of flexible appendages such as deployable booms and solar arrays result in disturbance torques reacting on the main body of a spacecraft and may have a significant effect on the attitude dynamics and control of the vehicle. The effects of thermally induced structural disturbances of a flexible appendage on the attitude dynamics of a simple spacecraft are investigated. The governing equations, including transient thermal effects, are formulated using a generalized form of Lagranges equations for hybrid coordinate dynamical systems. An approximate solution based on modal expansion is presented for the case of a step change in solar heating that simulates an orbital eclipse transition. Analytical models are presented for the thermal-structural response of two types of flexible appendages: a thin-walled boom with tip mass and a solar panel. Numerical results demonstrate that the attitude response of the system consists of a slowly developing pointing error and superimposed oscillations whose magnitude is related to the ratio of the thermal and structural response times of the flexible appendage.


Journal of Spacecraft and Rockets | 2000

Thermally Induced Dynamics of Satellite Solar Panels

John D. Johnston; Earl A. Thornton

Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.


Journal of Spacecraft and Rockets | 2006

Analytical and Experimental Characterization of Gravity Induced Deformations In Subscale Gossamer Structures

John D. Johnston; Joseph R. Blandino; Kiley McEvoy

The development of gossamer space structures such as solar sails and sunshields presents many challenges due to their large size and extreme flexibility. The post-deployment structural geometry exhibited during ground testing may significantly depart from the in-space configuration due to the presence of gravity-induced deformations (gravity sag) of lightly preloaded membranes. This paper describes a study carried out to characterize gravity sag in two subscale gossamer structures: a single quadrant from a 2 m, 4 quadrant square solar sail and a 1.7 m membrane layer from a multi-layer sunshield The behavior of the test articles was studied over a range of preloads and in several orientations with respect to gravity. An experimental study was carried out to measure the global surface profiles using photogrammetry, and nonlinear finite element analysis was used to predict the behavior of the test articles. Comparison of measured and predicted surface profiles shows that the finite dement analysis qualitatively predicts deformed shapes comparable to those observed in the laboratory. Quantitatively, finite element analysis predictions for peak gravity-induced deformations in both test articles were within 10% of measured values. Results from this study provide increased insight into gravity sag behavior in gossamer structures, and demonstrates the potential to analytically predict gravity-induced deformations to within reasonable accuracy.


43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | 2002

The Effect of Asymmetric Mechanical and Thermal Loading on Membrane Wrinkling

Joseph R. Blandino; John D. Johnston; Jonathan J. Miles; Urmil K. Dharamsi

Effect of Asymmetric Mechanical and Thermal Loading on Membrane WrinklingJoseph R. Blandino*James Madison UniversityJohn D. Johnston**NASA Goddard Spaceflight CenterJonathan J. Miles*.**James Madison UniversityUrmil K. Dharamsi ....James Madison UniversityAbstractLarge, tensioned membranes are being considered forfuture gossamer spacecraft systems. Examples includesunshields, solar sails, and membrane optics. In manycases a relatively flat membrane with minimal _wrinkling is desired. Developing methods to predictand measure membrane wrinkling is important to thefuture development of gossamer spacecraft. Numericaland experimental data are presented for a 0.5 m square,tensioned membrane. The membrane is subjected tosymmetric and asymmetric mechanical loading. Dataare also presented for a symmetrically loadedmembrane subjected to spot heating in the center. Thenumerical model shows good agreement with theexperiment for wrinkle angle data. There is alsoreasonable agreement for the wrinkled area for bothisothermal and elevated temperature tests.IntroductionMembrane structures typically exhibit nonlinearbehavior when loaded. Since a membrane structurecannot support compressive stresses, local buckling orwrinkling often occurs. At ambient temperature thewrinkle pattern is dependent upon both the membraneand loading geometry. At elevated temperature thewrinkle pattem may also be a function of the materialproperties and the residual stress state of the membrane.The coefficient of thermal expansion will cause thematerial to expand, while heating may relieve any.residual stress from the membrane that was createdduring manufacturing. Quantifying the wrinklingbehavior of a membrane poses many challenges, bothexperimentally and analytically. Th e purpose of thispaper is to present both experimental and computationaldata quantifying the wrinkling behavior of a squaremembrane subjected to symmetric and asymmetricmechanical loading as well as non-uniform thermalloading.


Journal of Thermophysics and Heat Transfer | 1995

Thermal response of radiantly heated spinning spacecraft booms

John D. Johnston; Earl A. Thornton

This article describes a study of the thermal response of radiantly heated spacecraft booms spinning about their principal axis. Thermally induced structural disturbances occur as the result of uneven solar heating and can reduce the pointing accuracy of a spin-stabilized spacecraft and in extreme cases affect the stability of the entire vehicle. The thermal response of radiantly heated spinning circular cross-sectional tubes is investigated using analytical, computational, and experimental approaches. An approximate analytical solution for the transient thermal response is presented. A finite element formulation is developed to evaluate the effects of natural convection, internal radiation, and temperature-dependent material properties on the thermal response. An experimental program undertaken to validate the analytical and computational models is described. The results of laboratory experiments conducted in the atmosphere are presented for a range of tube spin rates. Predictions from finite element analysis correlate well with experimental data and verify important aspects of spinning tube thermal behavior. Key aspects of the thermal behavior of radiantly heated spinning tubes are identified as 1) the independence of the tube average temperature of spin rate, 2) a decrease in the difference between maximum and minimum temperatures around the tube circumference with increasing spin rate, and 3) a shift in the steady-state temperature distribution in the direction of tube rotation.


intersociety energy conversion engineering conference | 1996

An evaluation of thermally-induced structural disturbances of spacecraft solar arrays

John D. Johnston; Earl A. Thornton

Spacecraft have experienced attitude disturbances as a result of thermally-induced motions of flexible appendages for over 30 years. Thermally-induced deformations of appendages such as deployable booms and solar arrays may result in significant disturbance torques. These effects lead to a decrease in pointing accuracy, an increase in pointing jitter and in extreme cases may affect the stability of the entire spacecraft. Examples of recent satellites whose performance has been degraded by thermally-induced structural disturbances are the Hubble Space Telescope (HST) and the Upper Atmosphere Research Satellite (UARS). This paper presents an evaluation of thermally-induced structural disturbances of solar arrays, including: (1) identification of disturbances sources and classifications; (2) assessment of the susceptibility of different types of solar array to the disturbances; and (3) discussion of potential methods for mitigating the effects of the disturbances.


Archive | 2003

STRUCTURAL ANALYSIS AND TESTING OF A SUBSCALE SUNSHIELD MEMBRANE LAYER

John D. Johnston; Joseph R. Blandino; Jonathan T. Black; Richard S. Pappa


44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference | 2003

Structural Analysis and Testing of a 1/20th Scale NGST Sunshield Membrane Layer

John D. Johnston; Joseph R. Blandino; Jonathan T. Black; Richard S. Pappa


Fifth International Conference on Space | 1996

Recent Progress in Thermally Induced Vibrations Research

John D. Johnston; Richard S. Foster; David L. Eby; Earl A. Thornton

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Kiley McEvoy

James Madison University

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Jonathan T. Black

Air Force Institute of Technology

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