Return to Europa: Overview of the Jupiter Europa Orbiter Mission

摘要

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, Galileo supplied fascinating new insights into that satellite's secrets. The Jupiter Europa Orbiter (JEO) would be the NASA-led portion of the Europa Jupiter System Mission (EJSM), an international mission with orbiters developed by NASA, ESA and possibly JAXA. JEO would address a very important subset of the complete EJSM science objectives and is designed to function alone or in conjunction with ESA's Jupiter Ganymede Orbiter (JGO). The JEO mission concept uses a single orbiter flight system which would travel to Jupiter by means of a multiple-gravity-assist trajectory reaching Jupiter and perform a multi-year study of Europa and the Jupiter system, including 30 months of Jupiter system science and a comprehensive Europa orbit phase of 9 months. The JEO mission science objectives, as defined by the international EJSM Science Definition Team, include: A. Europa's Ocean: Characterize the extent of the ocean and its relation to the deeper interior B. Europa's Ice Shell: Characterize the ice shell and any subsurface water, including their heterogeneity, and the nature of surface-ice-ocean exchange C. Europa's Chemistry: Determine global surface compositions and chemistry, especially as related to habitability D. Europa's Geology: Understand the formation of surface features, including sites of recent or current activity, and identify and characterize candidate sites for future in situ exploration E. Jupiter System: Understand Europa in the context of the Jupiter system In concert with achieving these science objectives, NASA has provided study guidelines, including: (1) Launch no earlier than 2020, with preferred flight times to Jupiter of < 7 years (2) Use the 34m DSN station network for primary science downlink (3) Carry robust margins in all areas (technical and financial) The primary challenge of a Europa orbital mission is to perform in Jupiter's radiation environment, radiation damage being the life limiting parameter for the flight system. Designing for reliability and long life requires key knowledge of the environment, understanding of available hardware, conservative hardware and software design approaches, and a management structure that elevates the importance of radiation issues to the project office level. Instilling a system-level radiation-hardened-by-design approach very early in the mission concept would mitigate the pervasive mission and system level impacts (including trajectory, configuration, fault protection, operational scenarios, and circuit design) that can otherwise result in run-away cost and mass growth. This paper will address the mission concept developed by a joint JPL and APL team to address the science objectives as defined by an international Science Definition Team formed in 2008 while designing for the Jupiter environment and meeting NASA guidelines.