Design & Testing of TRL5 IPEx Actuators

NASA is advancing In-Situ Resource Utilization (ISRU) by focusing on missions aimed at establishing sustainable infrastructure on the Moon and Mars. On the Moon, regolith serves as the most abundant resource. To support ISRU objectives, a 30-kg-class robot called ISRU Pilot Excavator (IPEx) is being developed to excavate 10,000 kg of lunar regolith during a future technology demonstration mission. IPEx uses novel excavation tools, called bucket drums, which are hollow cylinders with scoops staggered around the outside. Regolith is collected with the scoops and flows into the drum where it is captured by an internal baffle system. The excavator can then transport the regolith in the drum and reverse the direction of the drum rotation to dispense the regolith out. IPEx uses two sets of bucket drums that dig simultaneously in opposing directions and results in counteracting excavation forces. This combination of bucket drum excavation tools and counteracting excavation forces enables low mass robotic excavators to effectively dig in reduced gravity environments. This is a significant departure from terrestrial excavators that rely on high mass to produce tractive forces to counteract the forces of excavation. IPEx is made up of several custom actuators that all need to be verified for their intended application. This paper focuses on the initial design, testing and modifications of three actuators: the mobility actuator, the shoulder actuator, and the excavation actuator. Each actuator was tested under four separate test profiles: ambient motor characterization, hot and cold motor characterization, accelerated life test (ALT), and concept of operations (ConOps) test. The motor characterization tests enabled derivation of torque equations for each actuator to estimate output torque without implementing sensors. The accelerated life tests were successful for each actuator and verified the motors' ability to survive the mission. For the ConOps test, only the bucket drum actuator performed a complete ConOps without the need to restart the test. Overall, the first series of testing resulted in various failure modes and minor design alterations for each actuator. The test results, failure modes, and design alterations are highlighted within this paper. This paper focuses on discussing the mobility, excavation, and shoulder actuator design, testing principles, and results that qualified it as a TRL 5 system.