Modeling and Validation of a Cryobot Architecture for Accessing the Subsurface of Ocean Worlds

Abstract:

Space faring nations have begun to turn their attention to ocean worlds, with the ultimate goal of delivering a life detection payload to its subsurface ocean. To achieve this goal, an ice probe, or cryobot, must be designed and built to overcome a significant set of challenges. Beginning its journey on a frigid surface, exposed to vacuum and radiation, the cryobot must operate for several years, meeting and overcoming hazards on route until reaching its aqueous target many kilometers below.

We consider a cryobot architecture that utilizes a radioisotope thermal power source at its core, providing both electrical power for the operation of onboard systems and the heat required to melt the surrounding ice and allow the probe to descend. The choice of radioisotope power, rather than a fission reactor, is driven by considerations of keeping landed mass realistic and utilizing components with high technology readiness. The architecture is augmented by critical technologies that enable both cutting and water jetting for descent. The cutter can enhance progress during the initiation phase, when the cryobot will be sublimating rather than melting ice, or to penetrate through dust layers. Water jetting improves descent time, and has been demonstrated to move cuttings past the probe.

The cryobot architecture must close around an acceptable time to reach the ocean and is critically dependent on the heat density of the radioisotope source and the dimensions of the overall system, as well as the structure of the ocean world ice shell. The calculation of this time is achieved by modeling the cryobot performance against homogeneous far-field conditions and then integrating the results over a range of possible ice shells to quantify the uncertainty. A range of models are being developed to provide high-fidelity, accurate prediction of the Cryobot descent rate for a given set of ice shell characteristics. Models range from extensions to classical thermodynamic ones to grid-based models that consider the Cryobot, fluid-thermal environment. These models are compared at discrete points to find consistency between the mathematical-physical predictions. There is then a campaign of lab and field experiments to begin validation of the system. We will report on the status of these models and discuss progress towards validation of the results.