Vertical Motion Control System for Cryobots

This proposal responds to NASA SBIR 2023 Focus Area 4: Robotic Systems for Space Exploration. The subtopic S13.01 describes a need for technologies that provide improved robotic mobility for ocean world deep ice drilling and sub-ice ocean access. In particular, the need for innovations concerning “tethers and tether play-out and retrieval systems” are mentioned, as are component technologies for subsurface ocean access systems for ocean worlds like Europa and Enceladus. We propose to develop a Vertical Motion Control System (VMCS) which will pay out, and when needed spool in, an onboard tether from an ice penetrating robot (cryobot) on an ocean world. Ocean worlds remain of critical interest for astrobiology, however these off-world bodies of water are difficult to access as they lie below kilometers of ice. Any cryobot mission runs the risk of premature termination if the vehicle encounters an open void, water-filled cavity, or sub-surface ocean due to uncontrolled free fall of the vehicle. A VCMS is a means of proactively controlling the cryobot's descent. This will be of particular utility at the ice-ocean interface where the cryobot can convert to a defacto instrumented sonde for depth-registered characterization of the subsurface ocean. There are further advantages to a VCMS being bi-directional, the most obvious use of which would be to retreat upward through the ice column in the event that an impassable object is encountered and to then use steering hot water jets. This proposal addresses robotic mobility and access to sampling by offering a solution to one of the critical hurdles for cryobots capable of melt-penetration deep drilling of ice on Europa or Enceladus. We are proposing a VMCS consisting of a parallel-axis spooler, and a levelwind system, sized for a 1.6-mm-diameter Vectran tether (tensile strength: 4,315 N). For a 15-km mission, this spooler is 54 cm long. This design can be modified for shorter or longer tether lengths as needed.

The Vertical Motion Control System an enables robotic exploration missions on icy ocean worlds. Any ice-penetrating cryobot mission in a thick ice shell risks free fall and subsequent mission failure if the vehicle encounters an open void, water-filled cavity, or sub-surface ocean. The VMCS will proactively control the vehicle descent speed and mitigate these hazards. The VMCS could also enable a robotic explorer to descend into and ascend out of fissures on Enceladus, or a robot that “rappels” into cave skylight openings on Mars or the Moon.

The VMCS can be built into scientific instrumentation and sampling packages to enable onboard, load bearing tether spooling and make possible deployment through or operation within physically-constrained environments such as ice boreholes. Mobile robotics that employ strength and/or data tethers such as Autonomous Underwater Vehicles, Remotely Operated Vehicles, and aerial drones may also benefit.

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