Planning for in-Space Robotic Assembly of Modular CubeSats

Abstract

As the space industry continues to grow, developments such as the proliferation of small satellites have lowered the barrier to entry to space, making it faster and easier to launch payloads into orbit. However, the need for rapid deployment in space remains, particularly for rapid replacement of satellites that are nodes in larger constellations or supporting time-sensitive missions such as natural disaster monitoring. On-orbit assembly provides a solution to meet this demand. This thesis describes the development of Orbital Locker, a robotic system designed to enable the autonomous in-space assembly and deployment of modular satellites. The concept of operations involves a free-flying satellite that acts as a storage ``locker'', carrying modular CubeSat components and assembling and deploying them on request. Orbital Locker is an initial small-scale demonstration that is intended to be scaled up, consisting of a Cartesian gantry robot, and CubeSat modules dimensioned such that three modules stack to form a 1U CubeSat. The focus of this thesis is the software architecture of the system including module identification and assembly planning, and assembly testing in microgravity. Module identification makes use of fiducial markers to localize modules within the Locker, tracking the inventory of parts available. The assembly planner uses a graph-based method to optimize the steps required to assemble a desired satellite. It first generates a graph representation of possible assembly states and then uses a graph search algorithm to find the optimal sequence. Results from microgravity testing of the autonomous assembly on a ZeroG flight are presented, where a 1U CubeSat form factor was assembled in 72 seconds. Throughout this work, emphasis is placed on the extensibility of the system to support future scaled-up systems containing a larger inventory of modules.