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 Kostas NanosPostdocoral Fellow
Phone:+(30) 210-772-2643 Olga ChristidiPhD Student
   Georgios RekleitisPostdoctoral Fellow
Dedicated- Flat granite table 2.2m x 1.8m Ilias Patsiaouras
Research Fellow
Equipment:- Two autonomous space robots (active) & one passive Nikolena ChristofiDiploma Student
 - External camera above table Zisis MitrosResearch Assosiate



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


During this test the robot performed relatively well, by accomplished a predefined set of motions. On the  upper right corner you can see the picture from the camera located above the table. This test was performed to evaluate the performance of some robot subsystems.

During system tests the robot presented a malfunction, when one thruster didn't shut down. This resulted the robot to spin uncontrollably. This situation, is a common malfunction in real satellites. The video shows how reliably the hovering robot emulates the real motion.


Preliminary structural tests

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.

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.


10 Most Recent Publications - For older publications see here

 Rekleitis, G. and Papadopoulos, E., "On-orbit Cooperating Space Robotic Servicers Handling a Passive Object," accepted for publication, IEEE Transactions on Aerospace and Electronic Systems (TAES), June 2014.
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. 5-116
Machairas, K., Andreou, S., Paraskevas, I.  and Papadopoulos, E., “Extending the NTUA Space Robot Emulator for Validating Complex On-Orbit Servicing Tasks,” 12th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘13), ESA, ESTEC, Noordwijk, The Netherlands, May 15-17, 2013.
 Kalgreadis, A., Paraskevas, I., Flessa, T.  and Papadopoulos, E., “Localization of the NTUA Emulator Space Robot Using a Discrete Extended Kalman Filter, Data Fusion & Feedback Delay Compensation,” 12th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘13), ESA, ESTEC, Noordwijk, The Netherlands, May 15-17, 2013.
 Rekleitis, G. and Papadopoulos, E., “A Comparison of the Use of a Single Large vs a Number of Small Robots in On-Orbit Servicing,” 12th Symposium on Advanced Space Technologies in Robotics and Automation, (ASTRA ‘13), ESA, ESTEC, Noordwijk, The Netherlands, May 15-17, 2013.
 Paraskevas, I. and Papadopoulos, E., “On the Use of the Center of Percussion for Space Manipulators during Impacts,” Proc. IEEE International Conference on Robotics and Automation (ICRA '13), May 6-10, 2013, Karlsruhe, Germany.
 Papadopoulos, E., Paraskevas, I., and Flessa, Th., “Miniaturization and Micro/ Nanotechnology in Space Robotics,” in NanoRobotics: Current Approaches and Techniques, Mavroidis C. and Ferreira A. (Editors), Springer, 2013. 
 Flessa, T., Paraskevas, I., and Papadopoulos, E., “Localization and Fuel Management Techniques Using the NTUA Space Servicer Emulator System,” 11th International Symposium on Artificial Intelligence, Robotics and Automation in Space, (i-SAIRAS), 4-6 September 2012, Turin, Italy.
Nanos, K. and Papadopoulos, E., “On Cartesian Motions with Singularities Avoidance for Free-floating Space Robots,”. IEEE International Conference on Robotics and Automation (ICRA '12), May 14-18 2012, St. Paul, MN, USA.
 Rekleitis, G. and Papadopoulos, E., “On On-Orbit Passive Object Handling by Cooperating Space Robotic Servicers,” Proc. of the 2011 International Conference on Intelligent Robots and Systems (IROS '11), September 2011, San Francisco, CA, USA.

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