We recommend the establishment of a dedicated Ocean Worlds Exploration Program within NASA to provide sustained funding support for the science, engineering, research, development, and mission planning needed to implement a multi-decadal, multi-mission program to explore Ocean Worlds for life and understand the conditions for habitability. The two new critical flagship missions within this program would 1) land on Europa or Enceladus in the decade 2023-2032 to investigate geophysical and geochemical environments while searching for biosignatures, and 2) access a planetary ocean to directly search for life in the decade 2033-2042. The technological solutions for a landed mission are already in-hand, evidenced by the successful delta-Mission Concept Review of the Europa Lander pre-flight project in the fall of 2018. Following an initial landed mission, an ocean access mission will require substantial research, development, and analog testing this decade to enable the initiation of a pre-flight project at the start of the following decade. This ambitious goal could not have been put forward with comparable, requisite credibility in any preceding decade. Both science and technology have now matured so that we may prioritize the direct search for signs of life, applying lessons learned from planetary and Earth exploration to in situ investigations of worlds where water and life are most likely to exist today. This new era of planetary investigation will require significant support for cross-disciplinary research and development, bringing together planetary scientists and engineers with those that study the Earth. To chart these new waters, a diversity of disciplines must be accompanied by a diversity of experience, skill, and perspective. All facets of this Ocean Worlds Exploration Program must actively ensure equitable access and inclusion across the spectrum of contributors in Planetary Science, Exploration, and Astrobiology. Hence, we recommend an Ocean Worlds Exploration Program that includes specific initiatives designed to entrain and retain scientists and technologists from historically under-represented groups and to support a healthy work-life balance that enables equitable participation from across the entire community.

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As an initial step toward in situ exploration of the interiors of Ocean Worlds to search for life using cryobot architectures, we test how various communication tethers behave under potential Europa-like stress conditions. By freezing two types of pretensioned insulated fiber optic cables inside ice blocks, we simulate tethers being refrozen in a probe’s wake as it traverses through an Ocean World’s ice shell. Using a cryogenic biaxial apparatus, we simulate shear motion on preexisting faults at various velocities and temperatures. These shear tests are used to evaluate the mechanical behavior of ice, characterize the behavior of communication tethers, and explore their limitations for deployment by a melt probe. We determine (a) the maximum shear stress tethers can sustain from an ice fault, prior to failure (viable/unviable regimes for deployment), and (b) optical tether performance for communications. We find that these tethers are fairly robust across a range of temperature and velocity conditions expected on Europa (T = 95–260 K, velocity = 5 × 10−7 m s−1 to 3 × 10−4 m s−1). However, damage to the outer jackets of the tethers and stretching of inner fibers at the coldest temperatures tested both indicate a need for further tether prototype development. Overall, these studies constrain the behavior of optical tethers for use at Ocean Worlds, improve the ability to probe thermomechanical properties of dynamic ice shells likely to be encountered by landed missions, and guide future technology development for accessing the interiors of (potentially habitable ± inhabited) Ocean Worlds.