Tomasz Rybus

Trajectory Planning and Simulations of the Manipulator Mounted on a Free-Floating Satellite

This chapter focuses on the dynamics of a 6 DOF manipulator mounted on a satellite during an orbital servicing mission. Algorithm for computation of control torques applied in manipulator’s joints in various parts of orbital rendezvous maneuver is presented. This algorithm can be used to calculate manipulator’s control torques along with torques and forces for control of satellite’s orientation and position during complex maneuver or for controlling only the manipulator while taking into account additional 6 DOFs of the free-floating satellite. Simulation tool used for performing numerical simulations of orbital rendezvous and results of simulations of two parts of the possible maneuver (capturing of tumbling target satellite and positioning captured satellite for docking) are also presented.

Dynamic Simulations of Free-Floating Space Robots

This paper focuses on the dynamics of a 6-dof manipulator mounted on a free-flying servicer satellite during final part of an on-orbit rendezvous maneuver. Determination of reaction torques induced by the manipulator on the servicer satellite is critical for the development of the Guidance, Navigation and Control (GNC) subsystem. Presented in this paper is a path planning algorithm for capturing a tumbling target satellite, as well as simulation results of the capture maneuver and folding of the manipulator with the attached target satellite. The second part of this paper is focused on the presentation of our work leading to the construction of a planar air-bering test-bed for space manipulators.

Application of Rapidly-exploring Random Trees (RRT) algorithm for trajectory planning of free-floating space manipulator

Unmanned manipulator-equipped satellite could perform on-orbit servicing mission or could be used to remove large space debris from orbit. Planning a manipulator trajectory that will lead to a safe capture of a selected grasping point on the target object is a challenging task, as the satellite-manipulator system is in a free-floating state. Moreover, complicated structure of the target satellite (e.g., arrays of solar panels) results in obstacles that must be avoided by the satellite-manipulator system. In this paper we present application of Rapidly-exploring Random Trees (RRT) algorithm for trajectory planning of such system. This algorithm proved to be well suited for a considered case, as state of the satellite-manipulator system is highly dimensional (12 + 2n dimensions) and various constraints must be taken into account (e.g., joint limits and obstacles). Operation of the RRT algorithm is successfully demonstrated in a simplified simulation example.

Analyses of a Free-Floating Manipulator Control Scheme Based on the Fixed-Base Jacobian with Spacecraft Velocity Feedback

The control of a manipulator mounted on a free-floating satellite is a challenging task as dynamic interactions between the manipulator and the satellite must be taken into account. Various methods were proposed for control of such systems. In this study we focus on the Jacobian-based Cartesian control and analyze the control scheme based on the fixed-base Jacobian inverse with addition of satellite velocity feedback (i.e., feedback from measurements of manipulator-base velocity, which is resultant from manipulator motions and depends on system parameters). We show that in an ideal case this control may be equivalent to the well-known inverse dynamical Jacobian control. The presented control scheme is compared in numerical simulations with other Cartesian control algorithms and it is demonstrated that for nominal parameters its performance is similar to the performance of the inverse dynamical Jacobian control, while its computational complexity is significantly smaller. The algorithm described in this paper may prove useful for practical implementation on future satellite servicing missions.

Manipulator Mounted on a Satellite versus Manipulator Mounted on UAV Helicopter - Comparative Study

The free-floating satellite performing autonomous rendezvous and docking maneuver (RVD) to the uncontrolled target satellite is a topic of discussion especially in context of the path planning optimization, control algorithm design as well as approach to the testing procedure. In this paper we investigate the possibility of using an unmanned helicopter as a test platform for examination of control algorithms which could be used on the satellitemanipulator system. We are presenting the typical RVD maneuver in which uncontrolled tumbling satellite is captured by manipulator arm. Then, to prove the correct development of the simulation tool as well as the controller of the space robots (6+6 DoF) during RVD maneuver, the comparison of the simulation and testing of the helicopter equipped with manipulator arm (6+2 DoF) is performed. Additionally, design of a special lightweight manipulator applicable to UAV is presented.

Lie groups approach to space robots kinematics modelling

In this article we would like to present a geometric approach to model the velocity-level behaviour of the free-floating space manipulator system. Namely we will incorporate some concepts from the theory of Lie groups which have already proved useful in the kinematic and dynamic modelling of fixed-base manipulators. The treatment presented in this article allows obtaining general and coordinate-free kinematic expressions which relate Cartesian velocities of rigid bodies with joint-space velocities. Moreover due to the exponential map and product of exponentials formula we were able to obtain closed form expressions for derivatives of system’s equations with respect to the joint angles.

Ultra-Light Planetary Manipulator: Study and Development

The demand for the use of Planetary Manipulators is quite obvious in space exploration and in situ research. It can also be predicted that its role will expand in upcoming decades given the planned intensification of space exploration. This chapter presents the newly developed 3dof Ultra-Light Planetary Manipulator (ULPM) designated for extended servicing of exploration tools (e.g., penetrators, small rovers, etc.), or scientific instruments and sensors in planetary missions, where Mars and Moon are the mostly foreseen destinations. It combines new ideas and earlier achievements, both of which had influence on the concept and would demonstrate the technology. In consequence, a laboratory model device was successively developed. Two leading constraints determined the design: very low mass of the unit and long extension range of deployment of the servicing instruments. For those reasons, the utilization of the tubular boom mechanism was preferred. Integrated Ultra-Light Planetary Manipulator was tested in laboratory conditions in order to prove its operational functionality and performance. Particularly, it was examined what is the safety deployment distance for certain loads with acceptable stability of the flexible system structure. This topic was also one of the most important issues for performed analysis and manipulator’s dynamics simulations.

Numerical simulations and analytical analyses of the orbital capture manoeuvre as a part of the manipulator-equipped servicing satellite design

The lifetime of a considerable number of satellites is significantly shortened by malfunctions occurring during operational period; therefore, unmanned satellite servicing missions are considered. This paper presents an approach for analyses of various configurations and parameters of manipulator intended for on-orbit servicing. It is based on analytical method used to analyse workspace and singularities of the manipulator mounted on a free-floating satellite, and on numerical simulations of mission-specific manoeuvers (e.g., capture of malfunctioned satellite). The application of this approach to obtain parameters of the manipulator most suitable for defined servicing tasks is presented.

The prototype of space manipulator WMS LEMUR dedicated to capture tumbling satellites in on-orbit environment

Manipulator mounted on an unmanned chaser satellite could be used for performing orbital capture maneuver in order to repair satellites or remove space debris from orbit. Use of manipulators for such purposes is challenging, since the performed task need to be done autonomously, accurately and with robustness even if possible high disturbances appear e.g. due to contact between the manipulator arm end-effector and the target spacecraft. In this paper the WMS LEMUR manipulator developed by CBK PAN is presented with focus on tests performed in the platform-art© facility in GMV Spain.

Optimal detumbling of defunct spacecraft using space robots

Unmanned spacecraft equipped with manipulators could be used for on-orbit servicing or for capture and removal from orbit of large space debris. After grasping of tumbling target satellite with the manipulator both satellites connected by the manipulator begin to rotate around the common mass center. Changes of manipulator configuration would results in changes of combined moment of inertia and changes in rotational motion of such system. Two satellites connected by the manipulator can be considered as a one rigid body with variable inertia. In this paper we present application of Rapidly-exploring Random Trees (RRT) algorithm for planning changes of inertia tensor of such rotating body in order to minimize rotational kinetic energy and stabilize motion around one axis. Minimization of rotational energy is crucial for the detumbling phase of orbital capture maneuver. Results of numerical simulation is presented and possible directions of future work are indicated.