Robotic Gripper for Payload Capture in Low Earth Orbit

Abstract

The consensus to a study phase for an IXV (Intermediate eXperimental Vehicle) successor, a preoperational vehicle called PRIDE (Programme for Reusable In-orbit Demonstrator in Europe), has been recently enlarged, as approved during last EU Ministerial Council. One of the main project task consists in developing PRIDE to conduct on orbit servicing activity with no docking. PRIDE would be provided with a robotic manipulator system (arm and gripper) able to transfer payloads, such as scientific payloads, from low Earth orbiting platforms to PRIDE payload bay. The platform is a part of a space tug designed to move small satellites and other payloads from Low Earth Orbits (LEO) to Geostationary orbit (GEO) and viceversa. A study on this robotic technology is here presented. This research is carried out by Politecnico di Torino and Thales Alenia Space Italy (Grasping Manipulator Design), and by Thales Alenia Space Italy and Amet (PRIDE Robotics System Design). The system configuration of the robotic manipulator is first described in terms of volumes and masses. The assumed housing payload bay requirements in terms of volume (<100 l) and mass (<50 kg) combined with the required overall arm dimensions (4 m length), as defined following the stated mission scenario, and mass of the payload (5–30 kg) force to developing an innovative robotic manipulator with the task-oriented end effector. It results in a 7 degree-of-freedom arm to ensure a high degree of dexterity and a dedicate end-effector designed to grasp the payload interface. The gripper concept here developed consists in a multi-finger hand able to lock both translational and rotational payload degrees of freedom through an innovative under actuation strategy to limit its mass and volume. While in the literature in usual actuation architectures, underactuated systems have been realized where the first (nearest) phalanx closure led afterwards to the closure of the second (distal) one using the loading of a torsional springs and mechanical linkages, this system presents a new underactuation strategy. In this case the distal phalanx closes before the nearest one, allowing to grasp the handle side and limiting the handle length and volume. This concept will allow the distal phalanx to move independently from the nearest one. A configuration study on the payload handle interface has also been performed. Moreover, trade-off studies, computer aided design models, multibody and structural analysis of the whole system are shown to prove its feasibility. Finally, the concept of system control architecture, organized in three main blocks is defined: the Control Overall System Block, the Control Arm Block and the Control Robotic Hand Block.