Implementable program for efficient ocean-world exploration

The next US planetary Decadal Survey's mission priorities will emerge in 2022-23. Current US law requires NASA to implement a "virtual" Ocean Worlds Exploration Program (OWEP) using a mix of mission classes. NASA and ESA are currently developing large missions to explore Europa and Ganymede, respectively; NASA is also formulating concepts for a potential large mission to search for biosignatures on the Europa surface. Small-class mission concepts for Titan and Enceladus were proposed in 2010 and 2014, but not selected; NASA awarded 25M in 16 technology-development projects pertinent to Europa and other ocean worlds; recently NASA evaluated four medium-class OWEP mission in the New Frontiers program and has advanced one to Phase A. OWEP technical challenges are formidable: 1) almost a dozen diverse ocean worlds of varying priority, with key pieces of the ocean-world scientific puzzle are distributed among them; 2) power limitations at the Jovian and Saturnian ocean worlds; 3) standard launch and in-space propulsion impose half-decade (to Jupiter) or decade-long (to Saturn) transfers; and 4) the oceans are beneath kilometers of cryogenic ice.A virtual program of disparate initiatives is unlikely to cohere into an efficient OWEP. First, OWEP technologies outside the framework of individual missions have uncertain funding; the 25M allocated in FY17 is but a small down-payment, and enhanced investment would compete against many other solar system objectives. Second, the medium-class OWEP mission concepts compete against unrelated science objectives in a selection process whose outcome cannot be predicted. The MEP (Mars Exploration Program) offers one successful exemplar for a strategic program. Yet none of six key conditions underpinning the MEP over the past 15 years apply to a virtual OWEP. In particular, NASA has no mission-opportunity class comparable to the MEP backbone of MGS, Odyssey, and MRO: directed, medium-class missions supporting broader strategic objectives. Progress would be fastest if NASA could adapt three MEP program characteristics: 1) major technology investments separate from mission projects; 2) directed medium-class missions that conduct pivotal investigations on a sustained roadmap; and 3) multi-mission technical infrastructure that "lowers the bar" for individual missions. The most important OWEP example is space transportation, e.g., heavy-lift launch, and high-power solar-electric propulsion, to minimize trip times into Saturn and Jupiter orbit. This analysis treats the governing programmatic constraints, technical uncertainties, and policy gaps for an OWEP, then lays out multiple options for maximizing progress on the highest priority science objectives.