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Europa: Exploration of Under-Ice Regions with Ocean Profiling Agents

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Europa: Exploration of Under-Ice Regions with Ocean Profiling Agents EUROPA EXPLORATION OF UNDER-ICE REGIONS WITH OCEAN PROFILING AGENTS David W Allen, Matthew Jones, Leigh McCue, Craig Woolsey, and William B Moore Technical Report Number: VaCAS-2013-01 July 6, 2013 Contents List of Figures ........................................ vii List of Tables ........................................ x List of Abbreviations .................................... xii Executive Summary xiii 1 Introduction 1 1.1 Objectives ....................................... 1 1.1.1 Science Objectives .............................. 1 1.1.2 Mission Objectives .............................. 4 1.1.3 Planetary Protection ............................. 5 2 Europa 6 3 Mission Overview 9 3.1 Mission Phases .................................... 9 3.1.1 Launch from Earth .............................. 9 3.1.2 Transit to Europa ............................... 9 3.1.3 Surface Operations .............................. 11 3.1.4 Penetration of the Ice ............................. 12 3.1.5 Exploration of the Ocean ........................... 12 3.2 Previous and Upcoming Missions .......................... 12 3.2.1 Previous Missions .............................. 12 3.2.2 Juno ...................................... 14 3.2.3 Europa “Clipper” ............................... 14 ii 4 Fundamental Science 15 4.1 Biology ........................................ 15 4.2 Ocean Mechanics ................................... 16 4.3 Ocean/Ice Interaction ................................. 17 4.4 Ice Mechanics ..................................... 17 4.5 Ocean Floor Mechanics ................................ 18 4.6 Chemistry ....................................... 19 4.7 Surface Geology ................................... 19 4.8 Science Traceability Matrix .............................. 20 5 Value System Design 23 5.1 The Analytical Hierarchy Process .......................... 23 5.1.1 Example of AHP to a Basic System ..................... 23 5.2 System Description .................................. 25 5.3 Design Criteria .................................... 26 5.3.1 Hydrobot Performance ............................ 30 5.3.2 Hydrobot Science ............................... 31 5.3.3 Hydrobot Communication .......................... 31 5.3.4 Cryobot Performance ............................. 31 5.3.5 Cryobot Science ............................... 32 5.3.6 Cryobot Communication ........................... 32 5.3.7 Surface Unit Performance .......................... 32 5.3.8 Surface Unit Science ............................. 33 5.3.9 Surface Unit Communication ........................ 33 5.3.10 Landing System Performance ........................ 33 5.4 Complete Value System ................................ 34 6 Current State-of-the-Art Technologies and Development 37 6.1 Underwater Gliders .................................. 37 6.1.1 Principles of Operation ............................ 37 6.1.2 Examples ................................... 39 iii 6.1.3 Sensors .................................... 41 6.1.4 Power Systems ................................ 42 6.1.5 Performance Attributes ............................ 42 6.1.6 Performance Limitations ........................... 43 6.1.7 New Horizons ................................ 45 6.2 Melt Probes ...................................... 50 6.2.1 Principles of Operation ............................ 50 6.2.2 Examples ................................... 51 6.2.3 Performance ................................. 52 6.3 Spacecraft Power Sources ............................... 56 6.3.1 Nuclear Power Sources ............................ 56 6.3.2 Batteries ................................... 59 6.3.3 Fuel Cells ................................... 64 6.4 Hydrobot Sensor Packages .............................. 64 6.4.1 Package 3 ................................... 66 6.4.2 Package 2 ................................... 67 6.4.3 Package 1 ................................... 67 6.4.4 Science Traceability Matrix of Sensor Packages . 68 6.4.5 Data Rate ................................... 68 6.4.6 Sonar ..................................... 69 7 Design Alternatives 70 7.1 Transit and Landing .................................. 70 7.1.1 Launch Vehicles ............................... 71 7.1.2 Landing Systems ............................... 72 7.2 Surface Operation ................................... 72 7.2.1 Importance of RPS in Lander ........................ 73 7.2.2 Technology Needs for Lander ........................ 73 7.2.3 Communication ................................ 74 7.2.4 Science .................................... 74 iv 7.3 Ice Operation ..................................... 74 7.3.1 Payload Capacity ............................... 75 7.3.2 Power Source ................................. 75 7.3.3 Descent Time ................................. 76 7.3.4 Communication ................................ 78 7.3.5 Science .................................... 79 7.4 Ocean Operation ................................... 79 7.4.1 Hydrobot Design ............................... 79 7.4.2 Communication ................................ 83 7.4.3 Science .................................... 84 7.5 Evaluation of Design Alternatives .......................... 84 7.5.1 Transit and Landing ............................. 84 7.5.2 Surface Unit ................................. 86 7.5.3 Cryobot .................................... 88 7.5.4 Hydrobot ................................... 93 7.5.5 Communication Menu ............................ 96 8 Mission Architectures 98 8.1 Proposed Mission Architectures ........................... 98 8.2 Evaluation of Mission Architectures ......................... 100 9 Roadmap, Timeline, Notional Vehicle Design, and Proposed Concept of Operations 102 9.1 Roadmap and Timeline ................................ 102 9.2 Notional Design .................................... 103 9.2.1 Surface Unit with Landing System ...................... 103 9.2.2 Cryobot .................................... 103 9.2.3 Hydrobot ................................... 106 9.3 Proposed Concept of Operations ........................... 107 10 Conclusions 112 11 Acknowledgements 114 v A Other Ice-Covered Worlds 115 B Explanation of Science Traceability Matrix 117 B.1 Biology ........................................ 117 B.2 Ocean Mechanics ................................... 118 B.3 Ocean/Ice Interface .................................. 119 B.4 Ice Mechanics ..................................... 119 B.5 Ocean Floor ...................................... 120 B.6 Chemistry ....................................... 121 B.7 Surface Geology ................................... 121 C Explanation of the Value System 123 C.1 Notation ........................................ 123 C.2 Explanation of System Description .......................... 123 C.3 Design Criteria .................................... 128 C.3.1 Hydrobot Performance ............................ 128 C.3.2 Hydrobot Science ............................... 130 C.3.3 Hydrobot Communication .......................... 132 C.3.4 Cryobot Performance ............................. 133 C.3.5 Cryobot Science ............................... 135 C.3.6 Cryobot Communication ........................... 137 C.3.7 Surface Unit Performance .......................... 138 C.3.8 Surface Unit Science ............................. 140 C.3.9 Surface Unit Communication ........................ 142 C.3.10 Landing System Performance ........................ 143 Bibliography 154 vi List of Figures 0.1 The exploration of Europa’s ocean by biologically inspired hydrobots. Background image http://www.nasa.gov/images/content/206105main_pia10131. jpg. xiii 2.1 Europa’s interior structure (left) consisting of a metallic core, rock mantle, and water/ice shell [1]. The equilibrium temperature structure of the ice shell is shown on the right, for three different shell thicknesses: 20 km (black), 40 km (red), and 60 km (blue). ..................................... 7 2.2 An illustration of possible structures in the ice shell (after [2]). Warm upwellings and cold downwellings with scales of about 10 km result in lateral temperature variations of about 10 degrees C. Near the surface, re-freezing of impact- or friction- generated melts may leave lenses or sheets of precipitated salts. In warmer regions these may remain liquid as hyper-saline brines. 8 3.1 The configuration of the SLS. Image from NASA, available at http://www. nasa.gov/pdf/623766main_8143_Singer-AD_industry_day-021312_ FINAL3.pdf .................................... 10 3.2 Costs and masses of past and upcoming missions to the outer planets. 13 3.3 Powers and masses of missions to outer planets. 14 5.1 Legend for design criteria trees shown in Figures 5.2, 5.3, 5.4, and 5.5. 27 5.2 Design criteria tree for the hydrobot. The legend is shown in Figure 5.1. 27 5.3 Design criteria tree for the cryobot. The legend is shown in Figure 5.1. 28 5.4 Design criteria tree for the surface unit. The legend is shown in Figure 5.1. 29 5.5 Design criteria tree for the landing system. The legend is shown in Figure 5.1. 30 6.1 Free body diagram for wings-level gliding flight [3]. 38 6.2 Annotated schematic of the Virginia Tech underwater glider [4]. 41 vii 6.3 Neutral displacement of a cylindrical hull in water versus length. (Fineness ratio: l=d = 7) ........................................ 44 6.4 Drag polar for a model of the Slocum glider [3]. 45 6.5 Example of vehicle path optimization in a steady, uniform flow [5]. 46 6.6 Comparison of the relation of tail fin span and area with
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