Miniaturizing Docking and Undocking through DockSat

Abstract

This project involves a 2U and 1U CubeSat that are launched together. The CubeSats are initially attached using a novel docking mechanism. The CubeSats will separate after being released from the deployer followed by rendezvous and re-docking maneuvers with one another. Multiple undocking and re-docking demonstrations will be attempted, with increasing separation distance between the satellites at each iteration. Docking demonstrations will commence once the joined satel-lites have deployed from the CubeSat deployer, and both chaser and target have been fully commissioned. Both the 1U target and the 2U chaser will have a docking interface. An undocking and re-docking experiment will involve an initial satellite release by the docking adapters. Initial relative velocity will be imparted by a combination of spring force and electromagnets. An electric thruster on the 2U satellite will bring the satellites closer together, while visual-based pose estimation will provide feedback for the control system. The 1U satellite will maintain a stable attitude while the rendezvous and proximity operations are taking place. The final close approach and docking will be assisted by electromagnets built into the docking system on each satellite. The projects primary goal is to demonstrate critical technolo-gies for reconfigurable satellites and in-orbit servicing. The technologies that will be demonstrated include vision-based pose estimation and navigation, modular and dynamic reconfigurable spacecraft, and trajectory planning with electric thrusters. In addition, the project has the objective of establishing a sus-tainable CubeSat program at Stellenbosch University, through which post-graduate students can gain experience in satellite design and integration. In this paper, we include the conceptual design of the mission including the definition of the major subsystems, mass budget as well as simulations of the undock and re-dock demonstration to show the mission feasibility. Three components required for the mission have been identified that require the most additional research and development. The docking mechanism is designed to be androgynous with servo-actuated latches and a vision system for multiple separations and docking procedures. Elec-tromagnets are also added to the mechanism and the behavior is modeled for initial separation and final close-proximity control. Additionally, a practical statistical model of the proposed elec-tric thruster is constructed and used in simulation to obtain an expectation of the chasers trajectory tracking performance.