Stability analysis and testing of a docking simulator

M. Zebenay, T. Boge, D. Choukroun

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

The European Proximity Operation Simulator (EPOS) aims, among other objectives, at performing tests for verification and validation of the docking phase of an on-orbit servicing mission. The simulator includes two robots, equipped with very accurate position controllers, holding a docking interface, a probe element, and (virtual) satellites. A key feature of the simulator set-up is a feedback loop that is closed on the real force and torque sensed at the docking interface during the contact with the probe and that is used to drive a free-floating bodies numerical simulation. The high stiffness of the controlled robots causes the contact dynamics to be quicker than the robots' dynamics. This leads to inconsistencies in the docking simulation results and to potential instability and damage of the closed-loop system. This work presents a novel mitigation strategy to the given challenge, accompanied with a stability analysis and validating experiments. The high stiffness issue is addressed by combining a virtual stiffness and damping in the software with a real stiffness in the hardware, designing, thus, a "hybrid" docking simulator. Nonlinear state-space modeling of the closed-loop system is performed for the three dimensional case, where the tracking robots system is approximated as a pure delay. A linearized model is developed for the two dimensional case and a simplified expression is obtained by defining as states the depth and the rate of penetration along the normal to the contact surface. A stability analysis is then performed, easily extending previous results obtained in single-dimension, which provides stability regions as a function of the contact stiffness and damping, the tracking robots time delay, and the satellites masses. The design of a hardware compliance device is presented and the effective stiffness along the normal to the contact surface is developed. The proposed hybrid contact dynamics model and the accompanying analysis are envisioned to enable safe and flexible docking simulation. The proposed simulator shall enable the emulation of a desired contact dynamics for any stiffness and damping characteristics within the stability region.

Original languageEnglish
Title of host publication54th Israel Annual Conference on Aerospace Sciences 2014
PublisherTechnion – Israel Institute of Technology
Pages572-608
Number of pages37
ISBN (Print)9781632662651
StatePublished - 1 Jan 2014
Event54th Israel Annual Conference on Aerospace Sciences, IACAS 2014 - Tel-Aviv and Haifa, Israel
Duration: 19 Feb 201420 Feb 2014

Publication series

Name54th Israel Annual Conference on Aerospace Sciences 2014
Volume1

Conference

Conference54th Israel Annual Conference on Aerospace Sciences, IACAS 2014
Country/TerritoryIsrael
CityTel-Aviv and Haifa
Period19/02/1420/02/14

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