Mission Design and Technology for a Titan Aerobot Balloon System (TABS) Mission Design und Technologie für ein Titan Aerobot Ballon-System (TABS) A thesis accepted by the Faculty of Aerospace Engineering and Geodesy of the Universität Stuttgart in partial fulfillment of the requirements for the degree of Doctor of Engineering Sciences (Dr.-Ing.) By Jaime Esper Born in Colombia Main referee: Prof. Dr. rer. nat. Hans-Peter Röser Co-referees: Prof. Michael W. Plesniak, Ph.D. Prof. Dr. –Ing. Stefanos Fasoulas Date of Defense: 28 March 2012 Institute of Space Systems University of Stuttgart 2012 Dedication In living memory of my father Dr. Alfredo Esper, who instilled in me a deep sense of awe and admiration for nature, and a curiosity to always reach for the stars. To my family, whose love gives warmth and meaning to my journey. ii Table of Contents Dedication …………………………………………………………………………………………………... ii List of Figures ………………………………………………………………………………………………. v List of Tables ……………………………………………………………………………………………….. vi Acronyms …………………………………………………………………………………………………… vi Abstract / Kurzfassung …………………………………………………………………………………….. vii 1.0 Introduction and Background …………………………………………………………………………… 1 1.1 Research Plan ………………………………………………………………………………….. 1 1.2 Technology Functional Areas …………………………………………………………………. 1 1.3 Dissertation Methodology/Outline …………………………………………………………….. 6 2.0 Scientific Objectives and Science Instruments .......................................................................................... 7 3.0 Mission Design .......................................................................................................................................... 7 3.1 Design Approach ......................................................................................................................... 7 3.2 Trajectory Design ........................................................................................................................ 7 3.3 Trajectory Computation ............................................................................................................... 9 3.4 Trajectory Correction Maneuvers ................................................................................................ 18 3.5 Entry Flight Path Angle ............................................................................................................... 18 4.0 Communications ........................................................................................................................................ 19 4.1 Link Analysis and TABS Antenna Sizing ................................................................................... 19 4.2 Onboard Storage, Downlink Duty Cycle, and Total Data ........................................................... 22 4.3 Carrier Spacecraft Flyby and Relay Communications ................................................................ 24 4.4 Communications Summary ......................................................................................................... 25 5.0 TABS Buoyant Gas System ....................................................................................................................... 26 5.1 Hydrogen Balloon (baseline) ....................................................................................................... 26 5.2 Montgolfier Balloon .................................................................................................................... 28 5.3 Comparison of Different Balloon Types ..................................................................................... 29 5.3.1 Super Pressure Hydrogen versus Montgolfier Balloons ............................................ 29 5.3.2 Super Pressure Hydrogen versus Helium Balloons ................................................... 31 5.4 TABS H2 Tank Sizing ................................................................................................................. 33 5.4.1 Primary Spherical Tank Sizing .................................................................................. 33 5.4.2 Primary Toroidal Tank Sizing ................................................................................... 35 5.4.3 Auxiliary Toroidal Tank Sizing ................................................................................. 36 5.5 Tank Gas Flow Rate and Balloon Inflation Time ....................................................................... 37 6.0 Entry Probe ................................................................................................................................................ 40 6.1 Instrument Platform Size ............................................................................................................. 40 6.2 High Gain Antenna ...................................................................................................................... 40 6.3 Aeroshell Geometry and Size ...................................................................................................... 41 6.4 Payload Thermal Control ............................................................................................................. 42 6.5 Aft Component Accommodation ................................................................................................. 42 6.6 Probe Layout and Overall Dimension .......................................................................................... 43 6.7 Vehicle Aerodynamic Stability Considerations ........................................................................... 43 6.8 Deployment Scheme and Operational Configuration .................................................................. 45 6.9 Entry Probe Equipment List ......................................................................................................... 48 7.0 Aerothermodynamic Entry Analysis .......................................................................................................... 51 7.1 Titan's Atmospheric Model .......................................................................................................... 52 7.1.1 Atmospheric Scale Height .......................................................................................... 52 7.1.2 Exponential Atmospheric Model ................................................................................ 53 iii 7.1.3 Atmospheric Model Comparisons .............................................................................. 55 7.1.4 Flow Regime Estimation ............................................................................................ 56 7.2 Aerodynamics .............................................................................................................................. 57 7.2.1 Aerodynamic Loading and Velocity Evolution .......................................................... 57 7.2.2 Dynamic Pressure ....................................................................................................... 58 7.2.3 Entry Flight Time ....................................................................................................... 59 7.3 Aerothermodynamics ................................................................................................................... 60 7.3.1 Total Convective Heat Load and Body Average Heating Rate .................................. 61 7.3.2 Stagnation Point Heating – Convective ...................................................................... 62 7.3.3 Stagnation Point Heating – Radiative ......................................................................... 64 7.3.4 Total Heat Input at the Stagnation Point ..................................................................... 67 7.3.5 Thermal Protection System (TPS) Requirements ....................................................... 68 7.4 Aerothermodynamic Model Validation Based on Huygens Results ............................................ 72 7.4.1 Entry Aerodynamics .................................................................................................... 72 7.4.2 Entry Aerothermodynamics ......................................................................................... 75 7.4.3 Summary Results and Comparison .............................................................................. 81 8.0 Decelerator System Sizing and Balloon Inflation ....................................................................................... 83 8.1 Drogue Decelerator Sizing ............................................................................................................ 83 8.2 Main Parachute Sizing and Balloon Inflation ............................................................................... 87 9.0 Carrier Spacecraft ........................................................................................................................................ 93 9.1 Interface Structure and TABS Accommodation ........................................................................... 93 9.2 Carrier Spacecraft (CS) Sizing ...................................................................................................... 93 9.3 Chemical Propulsion System (CHEM) ......................................................................................... 98 9.4 Solar Electric Propulsion (SEP) Module ....................................................................................... 100 9.5 Solar Array ...................................................................................................................................