Design Considerations for a 2-DOF Robotic Gantry to Support a Mars Sample Return ConOps

In support of NASA's Mars Sample Return (MSR) campaign, the Jet Propulsion Laboratory (JPL) contracted Motiv Space Systems (Motiv) of Pasadena, CA to architect, develop, and qualify a 2-DOF Robotic Gantry, to serve as a critical element in the MSR mission Capture, Contain, and Return System (CCRS) Concept of Operations (ConOps). The primary function of the Gantry is to transfer the sample containment vessel from its on-orbit staging area to its location in the Earth Return Vehicle. The Gantry positions a JPL-designed End Effector (EE) within its allotted workspace while reacting the forces and moments associated with sample transfer. The Gantry configuration took on a variety of architectures throughout its development, including robotic arms and composite structures with serially mounted translating stages. The Gantry is made up of a rotary stage structure, designed to carry launch loads and maintain sufficient stiffness during operations, along with a translating linear stage that supports and positions the EE. A rotary stage actuator positions the rotary stage structure within a 270-degree range of motion. A motor-driven synchronization drive advances and positions the linear stage structure through approximately 500 mm range of motion. The system makes use of a kinematic arrangement of rolling elements, engineered and tested to sustain loads from launch and operations. Force and position sensors enable feedback telemetry. Power and signals are transmitted by an arrangement of flex-print cabling, used in twist-capsule and rolling loop arrangements. Two launch restraint systems, located on the rotary and linear stages, provide protection of the system's structure, mechanisms, and sensors during launch. Several key requirements drove the system's convergence: first-mode frequency, allocated mass, supported payload mass, the random vibration environment, linear force generation, interface accuracy, and overall packaging. This paper describes at a high-level the development of the Gantry system, from conception to near critical design completion, which satisfied most levied requirements. Motiv's solution, as presented in several technical and programmatic reviews, ultimately met most requirements. Unfortunately, the development effort was suspended in late 2023 due to funding uncertainty and the pursuit of alternate architectures for both CCRS and MSR. This paper serves in part to preserve the final Gantry configuration, as the system employed a variety of novel engineering approaches.