11.2.2007 (Revision 1, Edited for Public Release) Saturn’s Active ENCELADUS Ice Moon Preface Upon the recommendation of the NASA Advisory Council Planetary Science Subcommittee and the Outer Planets Assessment Group (OPAG), NASA Headquarters (HQ) Planetary Science Divi- sion commissioned pre-Phase A studies of Flagship missions to Europa, Ganymede/Jupiter system, Enceladus, and Titan. The purpose of these studies is to inform near term strategic decisions for the next Flagship mission. NASA’s Goddard Space Flight Center (GSFC) was directed to conduct the Enceladus study. NASA HQ appointed an Enceladus Science Definition Team (SDT) consisting of members drawn from the science community. The Enceladus SDT developed the science objectives, prioritized sub- objectives, defined an example strawman payload, and worked with the mission design team to create the mission scenarios, concept of operations and instrument accommodation requirements. The SDT based science priorities on those recommended in the 2003 Decadal Survey for planetary science and on work performed by previous science teams in support of the JPL-led study documented in Titan and Enceladus $1B Mission Feasibility Report, JPL D-37401 (Reh et al. 2007). (The two SDT Co-Chairs provided a consolidated view of the SDT’s advice as input for this study.) The NASA GSFC assembled a mission design team (listed in Section 5) to develop mission ar- chitecture concepts to address the science goals identified by the SDT. A Champion Team (listed in Section 5), whose members have expertise in the keys areas required for this study, provided advice to the mission design team at critical decision points, and reviewed and endorsed this report. Relative to the initial edition of the report released 29 August 2007, this Revision 1 edition contains changes that permit the report to be released to the public. It also includes editorial corrections along with a few minor technical corrections which materially affect neither the results nor the recommenda- tions. ENCELADUS Table of Contents 1.0 Executive Summary . 1-1 1.1 Overview . .1-1 1.2 Enceladus Science . 1-1 1.2.1 Science Goals . 1-1 1.2.2 Measurement Requirements . .1-2 1.2.3 Instrument Types . 1-2 1.3 Mission Architecture Assessment . 1-2 1.3.1 Key Challenges to Studying Enceladus . 1-2 1.3.2 Technical Approach . 1-3 1.3.3 Architecture Trade Space . 1-3 1.3.4 Trade Space Concept Designs . .1-3 1.3.5 Remaining Architectures in Trade Space . .1-3 1.4 Cost . 1-3 1.5 Conclusions and Findings . 1-7 2.0 Enceladus Science Goals and Objectives . 2-1 2.1 Science Goals . 2-1 2.1.1 Introduction: The Importance of Enceladus . 2-1 2.1.2 Priority 1 Goals . 2-2 2.1.2.1 Biological Potential . 2-2 2.1.3 Priority 2 Goals . 2-4 2.1.3.1 Composition . .2-4 2.1.3.2 Cryovolcanism . .2-6 2.1.3.3 Tectonics . 2-7 2.1.3.4 Tidal Heating and Interior Structure . 2-8 2.1.4 Priority 3 Goals . 2-11 2.1.4.1 Saturn System Interaction . 2-11 2.1.4.2 Surface Processes . 2-12 2.1.5 Relationship to NASA Strategic Goals and Decadal Survey Goals . 2-14 2.1.5.1 The First Billion Years of Solar System History . 2-14 2.1.5.2 Volatiles and Organics: The Stuff of Life . 2-14 2.1.5.3 The Origin and Evolution of Habitable Worlds . 2-14 2.1.5.4 Processes: How Planetary Systems Work . 2-15 2.1.5.5 Relevance to Decadal Survey Large Satellites Sub-Panel Themes . 2-15 2.2 Measurement Requirements Overview . 2-17 2.2.1 Traceability Matrix . 2-17 2.2.2 Cassini’s Ability to Make These Measurements . 2-17 2.3 Instrument Types . 2-20 2.3.1 Orbiter Remote Sensing Instruments . 2-21 2.3.1.1 Thermal Mapper (Category 1) . 2-21 2.3.1.2 Near-IR Mapper (Category 1) . 2-21 2.3.1.3 Visible Mapper (Category 1) . 2-22 2.3.1.4 Framing Camera (Category 2) . 2-22 2.3.1.5 UV Spectrometer (Category 2) . 2-22 iii ENCELADUS 2.3.2 Orbiter Geophysics Instruments . 2-23 2.3.2.1 Laser Altimeter (Category 1) . 2-23 2.3.2.2 Radio Science (Category 1) . 2-23 2.3.2.3 Magnetometer (Category 1) . 2-24 2.3.2.4 Radar Sounder (Category 1 or 2) . 2-24 2.3.3 Saturn Orbiter In-Situ Instruments . 2-25 2.3.3.1 Ion and Neutral Gas Mass Spectrometer (Category 1) . 2-25 2.3.3.2 Dust Analyzer (Category 1) . 2-25 2.3.3.3 Low Energy Plasma Analyzer (Category 2) . 2-26 2.3.3.4 Energetic Particle Spectrometer (Category 2) . 2-26 2.3.4 Enceladus Orbiter In-Situ Instruments . 2-27 2.3.4.1 Gas Chromatograph Mass Spectrometer (Category 1) . 2-27 2.3.4.2 Dust Micro-Analyzer (Category 1) . 2-27 2.3.5 Enceladus Soft Lander Instruments . 2-28 2.3.5.1 Lander Camera (Category 1) . 2-28 2.3.5.2 Seismometer (Category 1) . 2-28 2.3.5.3 Radio Science (Category 1) . 2-29 2.3.5.4 Surface Chemistry Package and Oxidant Detector (Category 1) . 2-29 2.3.5.5 Laser Desorption Mass Spectrometer (Category 1) . 2-29 2.3.5.6 Magnetometer (Category 2) . 2-30 2.3.5.7 Tunable Laser Spectrometer (Category 2) . 2-30 2.3.6 Hard Lander Instruments (Category 2) . 2-31 2.3.7 Matrices Relating Instruments to Science Goals . 2-31 2.4 Science Evaluation of Architecture Trade Space . 2-31 2.4.1 Mission Configurations Not Chosen for Detailed Study . 2-31 2.4.1.1 Sample Return . 2-31 2.4.1.2 Dumb Impactors . 2-34 2.4.1.3 Saturn Orbiter Only (no landers) . 2-34 2.4.1.4 Single Flyby Missions . 2-35 2.4.1.5 Lander-Only Missions . 2-35 2.4.6 Missions Chosen for Detailed Study . 2-35 2.5 Plume Particle Sizes and Abundances: Potential Hazards and Sampling Opportunities . 2-35 2.6 References . 2-38 3.0 Mission Architecture Assessment. 3-1 3.1 Technical Approach . 3-1 3.1.1 Risk Reduction / Fact Finding Activities . 3-1 3.1.1.1 Key Challenges to Studying Enceladus . 3-1 3.1.1.2 Trajectory Work . 3-2 3.1.1.2.1 Gravity Assists to Saturn . 3-2 3.1.1.2.1.1 SEP Trajectories . 3-2 3.1.1.2.1.2 Chemical Propulsion Trajectories . 3-2 3.1.1.2.2 Saturn Orbit Insertion and Gravity Assists within the Saturn System . 3-3 3.1.1.2.3 Free Return Trajectories . 3-5 3.1.1.3 Aerocapture . ..