DESIGN OF AN INTEGRAL THERMAL PROTECTION SYSTEM FOR FUTURE SPACE VEHICLES By SATISH KUMAR BAPANAPALLI A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2007 1 © 2007 Satish Kumar Bapanapalli 2 To my loving wife Debamitra, my parents Nagasurya and Adinarayana Bapanapalli, brother Gopi Krishna and sister Lavanya 3 ACKNOWLEDGMENTS I would like to express my sincere gratitude to my advisor and mentor Dr. Bhavani Sankar for his constant support (financial and otherwise) and motivation throughout my PhD studies. He allowed me to work with freedom, was always supportive of my ideas and provided constant motivation for my research work, which helped me grow into a mature and confident researcher under his tutelage. I also thank my committee co-chair Dr. Rafi Haftka for his invaluable inputs and guidance, which have been instrumental for my research work. I am also grateful to him for getting my interest into the field of Structural Optimization, which I hope would be a huge part of all my future research endeavors. I am also thankful to Dr. Max Blosser (NASA Langley) for his crucial inputs in my research work, which kept us on track with the expectations of NASA. I sincerely thank my dissertation committee members Dr. Ashok Kumar and Dr. Gary Consolazio for evaluating my research work and my candidature for the PhD degree. I also would like to acknowledge Dr. Peter Ifju and Dr. Nam-Ho Kim for their useful inputs and comments. I am thankful to NASA, for their financial support through the CUIP Project, and the program manager Claudia Meyer. Thanks also go to all the past and current members of Center of Advanced Composites: Ryan, Jongyoon, Huadong, Oscar, Jianlong, Thi, Sujith and Ben, and other graduate students in the department: Christian, Tushar, Vijay, and Palani. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................9 ABSTRACT...................................................................................................................................11 CHAPTER 1 INTRODUCTION AND OBJECTIVES .............................................................................13 1.1 Introduction.......................................................................................................................13 1.2 Requirements of a Thermal Protection System ................................................................16 1.3 Objectives .........................................................................................................................19 1.4 Approach...........................................................................................................................20 1.4.1 The Optimization Problem .....................................................................................20 1.4.2 Geometry and Design Variables.............................................................................21 1.4.3 Analysis: Finite Element Methods .........................................................................21 1.4.4 Loads and Boundary Conditions ............................................................................22 1.4.5 Formulation of Constraints.....................................................................................22 1.4.6 Optimized Designs .................................................................................................23 2 BACKGROUND..................................................................................................................24 2.1 Approaches to Thermal Protection ...................................................................................24 2.1.1 Active TPS..............................................................................................................24 2.1.2 Semi-passive TPS...................................................................................................25 2.1.3 Passive TPS ............................................................................................................25 2.2 TPS and NASA.................................................................................................................27 2.3 Need for a load-bearing TPS: ITPS..................................................................................36 2.4 ITPS Design Challenges...................................................................................................38 2.5 Choice of Constraints .......................................................................................................41 2.6 Background on Corrugated-Core and Truss-Core Sandwich Structures..........................43 2.7 Background on Multi-Disciplinary Optimization and Response Surface Approximation Techniques.................................................................................................45 3 FINITE ELEMENT MODELS AND ANALYSES.............................................................49 3.1 Finite Element Analysis for Heat Transfer.......................................................................49 3.1.1 Incident Heat Flux and Radiation Equilibrium Temperature.................................49 3.1.2 Loads, Boundary Conditions and Assumptions .....................................................52 3.1.3 One-Dimensional and Two-Dimensional FE Models ............................................55 3.1.4 Temperature vs. Reentry Time and Temperature Distribution ..............................58 5 3.1.5 Obtaining Temperature Data from the FE Analysis...............................................61 3.2 Finite Element Buckling Analysis....................................................................................62 3.3 Stress and Deflection Analysis .........................................................................................68 4 RESPONSE SURFACE APPROXIMATIONS AND OPTIMIZATION PROCEDURE ......................................................................................................................69 4.1 Response Surface Approximations...................................................................................69 4.1.1 Response Surface Approximations for Maximum Bottom Face Sheet Temperature .................................................................................................................70 4.1.2 Response Surface Approximations for Buckling ...................................................70 4.1.3 Response Surface Approximations for Stress and Deflection................................71 4.2 Procedure for Generation of Response Surfaces Approximations ...................................71 4.3 Optimization Procedure....................................................................................................75 5 ITPS DESIGNS....................................................................................................................76 5.1 Selection of Loads, Boundary Conditions and Other Input Parameters...........................76 5.2 Corrugated-Core Designs .................................................................................................80 5.2.1 Accuracy of Response Surface Approximations....................................................83 5.2.2 Optimized Corrugated-Core Panel Designs ...........................................................86 5.2.3 Buckling Eigen Values, Deflections and Stresses at Different Reentry Times......90 5.2.4 Optimized Designs with Changed Boundary Conditions.......................................97 5.3 Truss-Core Structures for ITPS ........................................................................................98 6 EFFECT OF INPUT PARAMETERS ON THE ITPS DESIGN.......................................104 6.1 Sensitivity of ITPS Designs to Heat Transfer Parameters..............................................105 6.1.1 Changing the Emissivity of the Top Surface of ITPS ..........................................105 6.1.2 Allowing Heat Loss from the Bottom Face Sheet................................................106 6.1.3 Increasing the initial temperature of the structure................................................107 6.2 Sensitivity of ITPS Designs to Loads and Boundary Conditions...................................109 6.2.1 Effect of Boundary Conditions.............................................................................109 6.2.2 Increasing the Pressure Load on the Top Surface ................................................109 6.2.3 Increasing the In-Plane Load................................................................................110 7 CONCLUSIONS AND FUTURE WORK ........................................................................111 7.1 Conclusions.....................................................................................................................111 7.2 Future Work....................................................................................................................113 APPENDIX: MATERIAL PROPERTIES USED FOR THE RESEARCH WORK ..................116 LIST OF REFERENCES.............................................................................................................120