Model Evaluation of a Transformable CubeSat for Nonholonomic Attitude Reorientation Using a Drop Tower
Yuki Kubo, Tsubasa Ando, Hirona Kawahara, Shu Miyata, Naoya Uchiyama, Kazutoshi Ito, Yoshiki Sugawara
TL;DR
The paper presents a drop-tower based methodology to evaluate a numerical model of a transformable, four-body CubeSat capable of nonholonomic attitude reorientation via sequential joint actuation. By designing a PSO-optimized four-stroke maneuver and accounting for modeling errors through COM-offset compensation, the authors demonstrate that the numerical model replicates the robot's motion within roughly $0.3$–$0.5$ degrees and can be further improved post-test. Results indicate a measured reorientation of $${23.3}^{\circ}$$ versus a design target of $${26.1}^{\circ}$$, with post-hoc compensation reducing attitude error to about $${0.24}^{\circ}$$, illustrating the utility of ground testing for ground-truthing on-orbit performance. The work also discusses differences between ground and orbital demonstrations, offering a pathway to extend the methodology to a 3U transformable CubeSat with potential feedback control and higher-end IMUs to boost precision and agility.
Abstract
This paper presents a design for a drop tower test to evaluate a numerical model for a structurally reconfigurable spacecraft with actuatable joints, referred to as a transformable spacecraft. A mock-up robot for a 3U-sized transformable spacecraft is designed to fit in a limited time and space of the microgravity environment available in the drop tower. The robot performs agile reorientation, referred to as nonholonomic attitude control, by actuating joints in a particular manner. To adapt to the very short duration of microgravity in the drop tower test, a successive joint actuation maneuver is optimized to maximize the amount of attitude reorientation within the time constraint. The robot records the angular velocity history of all four bodies, and the data is analyzed to evaluate the accuracy of the numerical model. We confirm that the constructed numerical model sufficiently replicates the robot's motion and show that the post-experiment model corrections further improve the accuracy of the numerical simulations. Finally, the difference between this drop tower test and the actual orbit demonstration is discussed to show the prospect.