Soft-Robotic Rover with Electrodynamic Power Scavenging

The purpose of studying the capabilities of Electrodynamic Tethers (EDT) and Soft Robotics is to ascertain the feasibility of using cross-cutting EDT and soft robotics technologies to achieve future NASA mission objectives with mass and power budgets orders of magnitude lower than conventional spacecraft. In this context, the Phase I study focuses on three technological elements: the design of a soft-robotic rover that can operate in extraterrestrial oceans, demonstrating feasibility of electrodynamic tethers for power scavenging in the Europa environment, and utilizing electrolysis to power biomimetic propulsion. The Phase I results show that a soft robotic, underwater rover has many advantages over a traditional view of autonomous underwater vehicles. Many of these advantages stem from its ability to collapse or expand the body, which carries two key benefits: (i) cost savings in transport and (ii) buoyancy control. Furthermore, this rover's material offers properties that enable it to survive most oceanic conditions, withstand a likely radiation environment, and retard ice formation. The use of these soft robots under water is very attractive because buoyancy enables very large robots without the need for skeletal structures that limit their shape-changing ability. The prime limitation of soft robots for underwater exploration is their nascent state of development, an issue that this study has begun to address and that we hope to continue in Phase II. The theoretical calculations and experimental investigation on electrodynamic tethers discussed in this report show that their use in saltwater environments is feasible. However, magnetohydrodynamic effects require attention, which will be a priority in Phase II. A possible approach involves magnetic shielding of a portion of the EDT array to generate significant current from imposed alternating magnetic fields. The Phase I experiments show that this approach may enable enough power to be generated for a soft robotic rover of the scale contemplated here. This power is in the range of 1mW to 1W and determines the time required to collect and transmit science data. The interface between the EDT and rover resembles a fuel cell. This tehnology generates the gases required to power the actuators and recombines these gases, if needed, to extract electricity for several subsystems. For example, there exist science instruments that complement the low mass and low power of our rover and still return substantial new science data. Examples include miniature mass spectrometers, voltammeters, magnetometers, pressure sensors, temperature sensors, and other MEMS and soft sensors. Such a sensor suite can be used to determine chemical-composition data of nutrient particulates in the ocean, magnetic-field specifics, and pressure and temperature gradients. Designing a soft robotic rover for a mission to the Europan ocean requires a holistic view of the entire mission--for example, accommodating issues of radiation exposure during transit, conditions in the ocean, and conditions during travel through ice. The Phase I study did not concentrate on EDL or passage through the ice, as explained in the Phase I proposal, because JPL and others are already looking into those aspects of a mission. We incorporated these concepts into a general system architecture. The Europa environment is poorly understood due to the limited scientific data from which to draw conclusions. A mission centered on the proposed soft-rover technology holds promise for answering these conjectures with science data bolstering some definitive answers about the unique Europa environment. Despite these uncertainties, a soft rover has high potential of being capable of surviving in Europa's subsurface ocean environment. Phase I explored the concept of an eel- or squid-inspired rover. A key conclusion is that a buoyancy-controlled underwater glider may be the best use of a soft actuator's capabilities. The Phase I report summarizes mathematical models of buoyancy and underwater gliding for such a system. Additionally, the Phase I work shows that a rover can use hydrogen fuel for combustion powered hydrojetting. The combination of a buoyancy controlled glider and combustion powered hydrojetting can complement slow, long-duration, underwater exploration with the ability for rapid movements when necessary. As both buoyancy control and hydrojetting use fuel generated from sea water, the in-situ use of resources substantially reduces the launched system mass necessary [1]. These results point to the real utility of both an EDT energy harvesting system and an underwater soft robotic rover. The integration of the two systems via a fuel cell for in-situ resource use motivates further study in a proposed Phase II project.