Deep Cryogenic Vacuum-Ice Testing of Cryobots: Project PROMETHEUS

PROMETHEUS is a cryobot concept targeted for deployment on Ocean Worlds and consists of a fully-instru-mented science vehicle able to actively control descent through the ice shell and into the subsurface ocean. The concept employs closed-cycle hot water drilling (CCHWD) technology as the pri-mary means of penetrating ice and making forward and turning progress. A “passive” (i.e. purely conductive) heat transfer system enables penetration starting on the surface where liquid water cannot exist until borehole closure is achieved and the sys-tem proceeds inside a melt water “bubble”. PROMETHEUS is compatible with a small fission reactor (the NASA Kilopower design) and employs a vertical motion control system (VMCS) using a trailing tether frozen into the ice to guard against falling through voids and enabling controlled entry into the sub-ice ocean. The design is capable of achieving a 20 km descent through a Europan ice profile in under a year and under 650 kg vehicle mass, including reactor mass. This paper details ex-perimental tests in 80K ice and vacuum of scaled versions of the PROMETHEUS vehicle.