Ground Demonstration on the Autonomous Docking of Two 3U CubeSats Using a Novel Permanent Magnet Docking Mechanism

Abstract

Small spacecraft autonomous rendezvous and docking is an essential technology for future space structure assembly missions. A novel magnetic capture and latching mechanism is analyzed that allows for docking of two CubeSats without precise sensors and actuators. The proposed magnetic docking hardware not only provides the means to latch the CubeSats but it also significantly increases the likelihood of successful docking in the presence of relative attitude and position errors. The simplicity of the design allows it to be implemented on many CubeSat rendezvous missions. A CubeSat 3-DOF ground demonstration effort is on-going at NASA Langley Research Center that enables hardware-in-the loop testing of the autonomous approach and docking of a follower CubeSat to an identical leader CubeSat. The test setup consists of a 3 meter by 4 meter granite table and two nearly frictionless air bearing systems that support the two CubeSats . Four cold-gas on-off thrusters are used to translate the follower towards the leader, while a single reaction wheel is used to control the attitude of each CubeSat. An innovative modified pseudo inverse control allocation scheme was developed to address interactions between control effectors. The docking procedure requires relatively high actuator precision, a novel miminal impulse bit mitigation algorithm was developed to minimize the undesirable deadzone effects of the thrusters. Simulation of the ground demonstration shows that the Guidance, Navigation, and Control system along with the docking subsystem leads to successful docking under 3-sigma dispersions for all key system parameters. Extensive simulation and ground testing will provide sufficient confidence that the proposed docking mechanism along with the choosen suite of sensors and actuators will perform successful docking in the space environment.

Underactuated Microsatellite Electromagnetic Docking Control Using Disturbance Observer-Based Sliding Mode Controller

“…The actuators of magnet-based docking are of three basic types: electromagnets, permanent magnets [19], [20] and tethered electromagnets [21]. The permanent magnets are simple to implement but usually provide a hard docking; and tethered electromagnetic docking (TED) tolerates failures but requires complex mechanical structure.…”

An Innovative Control Allocation Scheme to Address Reaction Thruster Interactions on a 3U CubeSat

“…The assembly of multiple small scale spacecrafts in space into large structures such as a space telescope or solar panels could be tremendously beneficial for the science and engineering communities. The Onorbit Autonomous Assembly of Nano-satellites (OAAN) team [1][2][3] at NASA Langley Research Center aims to demonstrate autonomous rendezvous and docking of two 3U CubeSats. The philosophy of the OAAN mission is to use the minimal suite of sensors and actuators while still meeting the mission objectives.…”