Novel reaction control techniques for redundant space manipulators: Theory and simulated microgravity tests $ Silvio Cocuzza a,n , Isacco Pretto a , Stefano Debei b a CISAS ‘‘G. Colombo’’—Center of Studies and Activities for Space, Universit  a degli Studi di Padova, via Venezia 15, Padova 35131, Italy b Deparment of Mechanical Engineering, Universit  a degli Studi di Padova, via Venezia 1, Padova 35131, Italy article info Article history: Received 11 March 2010 Accepted 9 June 2010 Available online 7 December 2010 Keywords: Space robot Reaction control Redundancy resolution Weighted pseudoinverse Constrained least squares Simulated microgravity test abstract This paper presents two novel redundancy resolution schemes aimed at locally minimizing the reaction torque transferred to the spacecraft during manipulator manoeuvres. The subject is of particular interest in space robotics because reduced reactions result in reduced energy consumption and longer operating life of the attitude control system. The first presented solution is based on a weighted Jacobian pseudoinverse and is derived by using Lagrangian multipliers. The weight matrix is defined by means of the inertia matrix which appears in the spacecraft reaction torque dynamics. The second one is based on a least squares formulation of the minimization problem. In this formulation the linearity of the forward kinematics and of the reaction torque dynamics equations with respect to the joint accelerations is used. A closed-form solution is derived for both the presented methods, and their equivalence is proven analytically. Moreover, the proposed solutions, which are suitable for real-time implementation, are extended in order to take into account the physical limits of the manipulator joints directly inside the solution algorithms. A software simulator has been developed in order to simulate the performance of the presented solutions for the selected test cases. The proposed solutions have then been experimentally tested using a 3D free-flying robot previously tested in an ESA parabolic flight campaign. In the test campaign the 3D robot has been converted in a 2D robot thanks to its modularity in order to perform planar tests, in which the microgravity environment can be simulated without time constraints. Air-bearings are used to sustain the links weight, and a dynamometer is used to measure the reaction torque. The experimental validation of the presented inverse kinematics solutions, with an insight on the effect of joint flexibility on their performance, has been carried out, and the experimental results confirmed the good performance of the proposed methods. In particular, two test cases have been analyzed in order to validate and evaluate the performance of both the unconstrained solution and the solution which takes into account the robot physical limits. & 2010 Silvio Cocuzza. Published by Elsevier Ltd. All rights reserved. 1. Introduction In the operating scenario of a space manipulator, the minimization of the dynamic disturbances transferred to the spacecraft is an important issue in order to maintain the antennas communication link, and in order to keep the orientation of pointing instrumentation and scanning devices. Reduced dynamic disturbances result in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/actaastro Acta Astronautica 0094-5765/$ - see front matter & 2010 Silvio Cocuzza. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2010.06.014 $ This paper was presented during the 60th IAC in Daejeon. n Corresponding author. Tel.: + 390498276798; fax: + 390498276788. E-mail addresses: silvio.cocuzza@unipd.it (S. Cocuzza), isacco.pretto@unipd.it (I. Pretto), stefano.debei@unipd.it (S. Debei). Acta Astronautica 68 (2011) 1712–1721