Cryo-Compatible Robotic Actuators with Use of Superconducting Materials

This paper outlines a conceptual design for a superconducting electric motor to enable actuation of small robotic vehicles and manipulators in Permanently Shadowed Regions (PSRs) of the Moon. The design takes advantage of high-temperature superconductors (HTS) whose critical temperature is higher than the seasonal range encountered in lunar PSRs, eliminating the need for a cryocooler. The paper focuses on a 40Nm direct drive motor for a rover comparable in size to the Mars Exploration Rovers (MER), enabling wheel actuation without a gearbox at ground speeds encompassing MER-like and Endurance operations. It is shown that a superconducting motor is viable for this application, offering continuous driving times of about 4 hours at full torque, and in excess of 44 hours at medium to low torques, with winding temperature as the limiting factor. This performance is compatible with long-distance lunar exploration. The HTS motor is about 30% lighter than a copper-wound equivalent motor, and operates at efficiencies as high as 99.89%. A discussion of focus areas for motor control electronics and system-level trades is also included.