ENCELADUS CONTAINS THE BEST CHARACTERIZED OCEAN ENVIRONMENT BEYOND EARTH. WE PROPOSE TO INVESTIGATE LARGE-SIZED MISSION CONCEPTS THAT LEVERAGE THE ASTROBIOLOGICAL OPPORTUNITY ENCELADUS OFFERS TO SEARCH FOR BIOSIGNATURES AND CONSTRAIN THE PROCESSES THAT DRIVE OCEAN HABITABILITY AND PLUME ACTIVITY. OUR GOAL IS TO PROVIDE A PRIORITIZED SET OF SCIENCE OBJECTIVES THAT ENSURES EVEN A NON-DETECTION OF LIFE PROVIDES MEANINGFUL RESULTS. WHILE AN ORBITER WITH VARIOUS SMALL LANDERS AND SOLO ORBITERS WERE SOME OF THE CONCEPTS STUDIED IN 2010 THE INCREASED UNDERSTANDING OF THE ENCELADUS ENVIRONMENT FROM CASSINI EXTENDED MISSION DATA AND TECHNOLOGICAL ADVANCEMENTS IN INSTRUMENTS OVER THE LAST NINE YEARS MAKE A NEW EVALUATION ESSENTIAL FOR PROVIDING ACCURATE ASSESSMENTS TO THE NATIONAL ACADEMIES. SINCE THE LAST DECADAL SURVEY CASSINI PROVIDED MORE EVIDENCE THAT ENCELADUS OCEAN MEETS THE BASIC REQUIREMENTS FOR HABITABILITY: LIQUID WATER CHEMICAL BUILDING BLOCKS AND ENERGY SOURCES. THE INFERENCES FROM THE FRACTURE HISTORY AND GRAVITY FIELD OF A GLOBAL SUBSURFACE OCEAN WERE ED BY OBSERVATIONS OF PHYSICAL LIBRATION. SIMPLE AND COMPLEX ORGANICS HAVE BEEN DETECTED AMONGST THE WATER ICE AND VAPOR PLUME MATERIAL. THE PRESENCE OF SALTS SILICA AND MOLECULAR HYDROGEN IN THE PLUME SUGGEST THAT THE OCEAN IS GEOCHEMICALLY INTERACTING WITH A ROCKY CORE WHICH PROVIDES CHEMICAL ENERGY AKIN TO THE ACTIVITY THAT SUSTAINS ECOSYSTEMS AT EARTH S SEAFLOOR. BOTH THE EJECTION AND FALLOUT OF ENCELADUS PLUME MATERIAL HAVE BEEN MAPPED PROVIDING NEW INSIGHT INTO THE EASE OF ACCESSIBILITY OF FRESH OCEANIC MATERIAL BOTH IN FLIGHT AND ON THE SURFACE. RECENT INVESTMENT IN TECHNOLOGIES SUITABLE FOR SURFACE AND SUBSURFACE SCIENCE AT EUROPA (E.G. ICEE AND SESAME PROGRAMS) CAN BE LEVERAGED AT THE MORE RADIATION-BENIGN ENCELADUS SURFACE. THE EUROPA LANDER SCIENCE DEFINITION TEAM LAID THE GROUND WORK FOR DESIGNING BIOSIGNATURE DETECTION STRATEGIES AND IDENTIFYING COMPELLING LANDING SITES WITH LIMITED DATA. MARS2020 AND EXOMARS HAVE DRIVEN ADVANCEMENTS IN TECHNOLOGIES CAPABLE OF IDENTIFYING GEOCHEMICAL AND ISOTOPIC BIO-SIGNATURES. SAMPLE ACQUISITION SYSTEMS ARE ALSO CURRENTLY BEING STUDIED FOR COMET SAMPLE RETURN LUNAR LANDERS THE EUROPA LANDER STUDY AND A ROTORCRAFT ON TITAN. LESSONS LEARNED FROM THESE DEVELOPMENTS WILL FACILITATE PLANNING FOR SAMPLING AT ENCELADUS IN THE NEXT DECADE. THIS CONFLUENCE OF THE PROPERTIES OF THE OCEAN AND THE EASE OF ACCESS TO THE SAMPLES MAKES A PRESSING CASE FOR EXPLORING ENCELADUS IN THE NEXT DECADE. THE PLUMES ARE ACTIVE NOW AND HAVE BEEN SINCE AT LEAST VOYAGER A RETURN TO ENCELADUS AS SOON AS POSSIBLE ENSURES THE FRESHEST SAMPLES EVEN IN THE UNLIKELY EVENT THAT THE PLUMES BECOME INACTIVE. THE IMPERATIVE OF STUDYING ENCELADUS AS AN ASTROBIOLOGICAL TARGET WAS DEMONSTRATED IN THE NEW FRONTIERS 4 COMPETITION WITH TWO MEDIUM-CLASS MISSION CONCEPTS SUBMITTED FOR CONSIDERATION. BY INCLUDING EXTENSIVE PARTICIPATION FROM BOTH NF4 TEAMS AS WELL AS ADDITIONAL TEAM MEMBERS FROM A RANGE OF CAREER LEVELS PLANETARY SPECIALTIES AND MISSION EXPERTISE THIS PROPOSAL TAKES ADVANTAGE OF A CROSS-DISCIPLINARY POOL OF EXPERTISE TO REPRESENT THE INTERESTS OF THE BROADER ENCELADUS AND ASTROBIOLOGY COMMUNITIES. WITH DIRECT ACCESS TO FRESH PLUME SAMPLES AND THE HIGH HABITABLE POTENTIAL OF ITS OCEAN ENCELADUS THUS OFFERS THE UNIQUE AND UNPARALLELED POTENTIAL FOR ANSWERING THE FUNDAMENTAL QUESTIONS SURROUNDING LIFE ELSEWHERE IN THE SOLAR SYSTEM. IN THIS PROPOSAL WE SEEK TO PROVIDE OPTIONS FOR FULFILLING THAT POTENTIAL IN THE NEXT DECADE. SPECIFICALLY WE WILL ELUCIDATE THE SCIENCE COST ASSOCIATED WITH TRADES BETWEEN LANDER +/- ORBITER ARCHITECTURES IN THE $1-2.5B COST RANGE. WE WILL IDENTIFY THE KEY SCIENCE OBJECTIVES SPECIFICALLY ENABLED BY KEY RISKS ASSOCIATED WITH AND KEY TECHNOLOGIES REQUIRED FOR EACH ARCHITECTURE AND COMBINATIONS THEREOF. A SKELETON POINT DESIGN WILL BE EVALUATED FOR THE OPTION WITH GREATEST SCIENCE RETURN PER DOLLAR.