The project "Enceladus Explorer" (EnEx) aims to design a mission to the Saturnian icy moon Enceladus, as well as to develop an operable drilling technique to penetrate the icy surface of the moon using the "IceMole", a novel maneuverable subsurface ice melting probe for clean sampling and in-situ analysis of ice and subglacial liquids. The presumed ocean of liquid water under Enceladus' thick ice crust would make a prime target in the search for extraterrestrial life and would be more easily accessible near one of the recently discovered plumes of water vapor on the moon's south pole. The general mission concept therefore, is to land EnEx at a safe distance from an active plume. The IceMole would then be deployed, melting its way through the ice crust to a water-bearing crevasse at a depth of 500 - 1000 m for an in situ examination for the presence of microorganisms. The project is sponsored by the German Aerospace Center (DLR) and is carried out by a research consortium of seven German universities. In this context our institute is responsible for the overall mission and system design of the EnEx spacecraft. Extensive research was performed on the expected terrain and conditions to be encountered by a lander on the south polar terrain of Enceladus, and detailed description is given. The mission payload, the IceMole is also described. Various mission architecture and operational concepts have been developed and traded-off for the critical mission elements. These include the propulsion method and trajectories followed, the primary lander power source, whether to use a separate orbiter and lander or a single orbilander, and elements of the landing system, such as the landing gear and GNC and hazard avoidance algorithms and sensors to be used. From the options chosen for each element, a reference system is devised, comprising an orbiter and a legged lander, carrying an Americium powered ASRG power source, and the appropriate sensors needed for autonomous, safe landing. The system reaches Enceladus using the Am-241 ASRGs to power electric thrusters. A reference scenario is derived, where the system uses electric propulsion to reach the Saturn system and capture in orbit around it, and then shave-off enough orbital energy to capture in orbit around Enceladus. The lander then lands autonomously while avoiding hazards and IceMole operations are initiated. Once operations are concluded, the spacecraft and orbiter are disposed of according to the relevant planetary protection guidelines.
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