The rapidly expanding space economy and ambitious future exploration goals necessitate capabilities beyond simply launching monolithic spacecraft. On-orbit servicing (OOS), which includes inspection, repair, refueling, upgrading, and debris removal, is becoming increasingly vital for sustaining and enhancing space assets [1, 2, 10, 58, 60]. A critical subset of OOS is on-orbit assembly (OOA), the process of constructing larger structures in space from smaller components launched separately [7, 8, 9]. OOA is essential for building systems that are too large or complex to fit within existing launch vehicle fairings, such as large telescopes [7, 45, 46, 55, 56, 57, 88, 89, 90, 91], solar power stations [9], and future habitats or propellant depots [11, 12, 13]. Space robotics plays a central and indispensable role in enabling OOA, providing the dexterity, precision, and operational capability to perform complex manipulation and joining tasks in the challenging space environment [2, 21]. This article reviews the state of the art in robotic technologies applied to on-orbit assembly. We examine the key robotic systems and their capabilities developed through various international programs and missions. We detail significant past and current projects that have demonstrated or are developing OOA technologies, highlighting the progress made. Finally, we discuss the key technical challenges that remain and outline future directions in this transformative field, drawing upon a comprehensive body of research and development [1-93].

Space Robotics, On-Orbit Assembly, Space Technology, Robotics in Space, Autonomous Systems, Space Exploration

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