National Technical University of Athens - School of Mechanical Engineering
Control Systems Lab
Evangelos Papadopoulos Research Group

Research ID Current Researchers
Location:  Building M, Basement, Room -104 Georgios Rekleitis Postdoctoral Fellow
Phone: +(30) 210-772-2643 Kostas Nanos Postdoctoral Fellow
Olga Christidi PhD Student
Dedicated - Flat granite table 2.2m x 1.8m Fotini Xydi Diploma Student
Equipment: - Two autonomous space robots (active) & one passive Nikos Mavrikis Diploma Student
- PhaseSpace MoCap System Panagiotis Mavridis Diploma Student
- External camera above table



On Orbit Servicing (OOS) is a relatively new concept that aims at two important goals: (a) at an investment risk reduction through the reuse and maintenance of serviced orbital systems (e.g. damaged or run-out of fuel satellites) and (b) at an astronaut personal risk reduction, by partially relieving them from highly risky Extra Vehicular Activities. To this end, OOS must be able to achieve, mostly without human interference, missions such as: re- and de-orbiting, salvage, inspection, maintenance, repair and retrofit of orbiting space structures. The study and analysis of various systems towards the realization of Space Robotics and Robotic OOS is a major area of interest of our laboratory. The theoretical research on Space Robotics conducted at the lab aims at various goals, including:

  • Modeling and analysis of a system of cooperating free-flying robots manipulating a passive object in space as well as the development of control methodologies for the system.Analysis of impact minimization strategies with an uncontrolled free-floating object.
  • Study of a free floating space manipulator, focused at the dynamics, path planning and control of the manipulator in the presence of angular momentum and flexibilities which both affect its behavior.
  • Analysis and design of a novel reactionless satellite appendage pointing mechanism.
  • Analysis of the impact of a space robot with its target using the percussion point of its manipulators.
  • Modeling, control and evaluation of a robotic system for autonomous capturing of orbital debris.

A planar space emulator has also been developed in our laboratory, based on the motion of robotic systems on a horizontal plane, achieved by the use of air bearings. This 2D practically frictionless motion is as close as possible to the actual space motion without external disturbances, counteracting the gravity effect and making it the most realistic emulation in 2D. Light weight and small size were major considerations during the design of the robotic mechanisms. Compact solutions for the various issues of the mechanism, especially on the transmission system for the motion of the manipulators, were derived, in order to obtain a compact and lightweight robot. Autonomy, a key factor in the validity of the emulator, is achieved in three ways: propulsion autonomy, computational power autonomy and electrical autonomy. This system has the capability to produce experimental results in order to further test control strategies developed in our laboratory, but also to test new ideas. Currently the planar space emulator is comprised by two robots.



Robot during evaluation tests

During Development

Videos - More Videos can be found  here

Contact dynamics experiments for on-orbit robotic docking, during ESA's COMRADE Project, using the PIAP Gripper in the CSL 2D Space Robotics Emulator.

Contact dynamics experiments for on-orbit robotic docking, during ESA's COMRADE Project, using the PIAP Gripper in the CSL 2D Space Robotics Emulator.

On orbit robotic docking emulation in 2D, side and top views. Two satellite robot mockups sliding on air-bearings, practically without friction, on the CSL/NTUA 2D Space Emulator. Contact dynamics experiments for on-orbit robotic refueling tasks.
Contact dynamics experiments for on-orbit robotic refueling tasks. Experimental Identification of NTUA's Space Emulator Cepheus
Basic Motions of robot (open-loop control) with extended explanations. Reduced version of this video has been presented in Space Simulators Workshop during IROS 2011. Preliminary structural tests

Selected Publications - For complete publications list see here

Nanos, K. and Papadopoulos, E., “On the Dynamics and Control of Free-floating Space Manipulator Systems in the Presence of Angular Momentum,” Frontiers: Robotics & AI - Space Robotics, DOI: 10.3389/frobt.2017.00026, accepted, June 2017.
Tomassini, A., Suatoni, M., Avilés, M., Solway, N., Coxhill, I., Paraskevas, I., Rekleitis, G., Papadopoulos, E., Krenn, R., Brito, A., Sabbatinelli, B., Wollenhaupt, B., Vidal, C., Aziz, S., and Visentin, G., “Towards a Standardized Grasping and Refuelling On-orbit Servicing for GEO Spacecraft,” Acta Atronautica, Vol. 134, May 2017, pp. 1–10.
Christidi-Loumpasefski, O., Nanos, K., and Papadopoulos, E., “On Parameter Estimation of Space Manipulator Systems Using the Angular Momentum Conservation,” Proc. IEEE International Conference on Robotics and Automation (ICRA '17), Singapore, May 29-June 3, 2017.
Mitros, Z., Rekleitis, G., Patsiaouras I., and Papadopoulos, E., “Impedance control design for on-orbit docking using an analytical and experimental approach,” 25th Mediterranean Conference on Control and Automation (MED ‘17), Valletta, Malta, July 3-6, 2017. 
Paraskevas, I. and Papadopoulos, E., “Parametric sensitivity and control of on-orbit manipulators during impacts using the Centre of Percussion concept,” Control Engineering Practice, vol. 47, February 2016, pp. 48-59.
Mitros, Z., Paraskevas, I. and Papadopoulos, E., “On Robotic Impact Docking for On Orbit Servicing,” 24th Mediterranean Conference on Control and Automation (MED ‘16), Athens, Greece, June 21-24, 2016.
Nanos, K. and Papadopoulos, E., “On the Dynamics and Control of Flexible Joint Space Manipulators,” Control Engineering Practice, vol. 45, December 2015, pp. 230-243.
Nanos, K. and Papadopoulos, E., "Avoiding Dynamic Singularities in Cartesian Motions of Free-floating Manipulators," IEEE Transactions on Aerospace and Electronic Systems (TAES), vol. 51, no. 3, July 2015, pp. 2305 - 2318.
Rekleitis, G. and Papadopoulos, E., "On-orbit Cooperating Space Robotic Servicers Handling a Passive Object," IEEE Transactions on Aerospace and Electronic Systems (TAES), vol. 51, no 2, April 2015, pp. 802 - 814.
Rekleitis, G. and Papadopoulos, E., “On Controller Parametric Sensitivity of Passive Object Handling in Space by Robotic Servicers,” Proc. of the 2014 International Conference on Intelligent Robots and Systems (IROS '14), Chicago, Illinois, Sept. 14–18, 2014, USA.

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