Docking and reconfiguration of modular spacecraft: preliminary SWARM testing at MSFC

Abstract

On-orbit servicing and assembly is a critical enabling technology for the advancement of large scale structures in space. The goal of the SWARM project (Synchronized Wireless Autonomous Reconfigurable Modules) is to develop and mature algorithms for autonomous docking and reconfiguration, to be used as the building blocks for autonomous servicing and assembly. Algorithms for approach, docking, and reconfiguration have been implemented and tested through a demonstration of the assembly of two telescope sub-apertures at Marshall Space Flight Center (MSFC) in July 2006. The algorithms developed for reconfiguration set the mass properties based on the configuration. Updatable parameters include the location of sensors and receivers with respect to the geometric center, thruster locations, and control gains specific to each configuration. To test these algorithms in a 2D environment, a ground testbed was developed to provide multiple docking ports and modular payload attachments. Hardware components include nodes, Universal Docking Ports, posts, sub-aperture mirrors, and a SPHERES satellite as the assembler tug. Testing at MSFC successfully demonstrated relative docking and reconfiguration. Valuable information was gained about the performance of the docking under friction, sensitivity to estimator initialization, thrust authority needed for different phases of the test, and control when CM changes during the test.