Development of miniature robotic manipulators to enable SmallSat clusters

This paper presents the concept to provide a robust and scalable robotic solution to enable SmallSat clusters via Cluster Forming On-board Robotic Manipulators (C-FORM). Instead of dedicated launches of large science instruments, small science satellites could be piggybacked as secondary payloads. After deployment, the SmallSats will rendezvous. Miniature robot arms will deploy and perform docking to a second SmallSat, similar to robotic docking on the ISS or space shuttle. This docking method accommodates uncertainty in GNC while reducing risk of spacecraft collision through increased separation distance. Docking will be repeated until the cluster is completely formed, amplifying their capabilities. These clusters would be scalable in both the number and size of the cluster elements. The formation will be maintained without expending energy or fuel. This work addresses technology development areas of creating large, scalable structures in space. This assembly method allows for very small packing volumes that reduces mass and cost. Increased separation distance between cluster elements provide larger aperture per SmallSat, reducing number of total elements. It also enables scalable large structures that can be reconfigurable. Precise relative repositioning can accommodate alignment errors or thermal drift in addition to enabling variable baseline instruments. Individual cluster elements could be grossly repositioned to provide hardware reconfiguration. Applications include large, scalable RF and optical apertures, interferometry, in-space assembly, close formation flying, scanning and fixed "stare" imagers, and mother-daughter spacecraft. Four aspects addressed in this paper include the robotic arm, end effector, SmallSat bus, and rendezvous. The robotic arm is designed to meet SmallSat size (< 0.5U), weight (< kg), actuation, and power (≈ 15 W) (SWAP) constraints. The actuators can be driven using SmallSat processing and motor drivers. Manipulator position can be held without use of power. By maintaining these constraints, the miniature robotic arm can be used as a payload of a variety of science SmallSats. Accounting for general SmallSat bus trends, capabilities, and interfaces help to provide minimal integration efforts across different platforms. The compact end effector is designed to accommodate any positioning uncertainty and relative spacecraft motion during docking. After docking, the end effector remains engaged without the use of power. Docking can be released to allow for gross hardware reconfiguration. Modularity was another important aspect of the end effector design. While the focus of this work is on docking, modularity allows for a wide range of potential applications. A representative SmallSat bus was designed using COTS components. Finally, rendezvous and relative control of two SmallSats was investigated.