In-Orbit Dynamics of Large Space Structures with Surface Robotics

Large space structures (LSSs), with potential lengths ranging from 50 meters to several kilometers, are critical for future applications such as space-based solar power satellites, orbital habitats, and in-space infrastructure. Their dynamics, particularly under external orbital forces and surface robotic activity, pose significant challenges to structural stability and control. This paper presents a dynamic modelling approach to evaluate the vibrational response of a long, slender beam-like structure in Low Earth Orbit (LEO), incorporating both non-uniform gravity gradient forces and the transient loading effect of a moving robotic mass. A simply supported boundary condition at the beam’s center is assumed to approximate the fixed orbital position of the structure’s centroid under Keplerian motion, where the central hub remains in stable orbit while the rest of the structure extends freely. Initially, characteristic equation solutions are used to compute the first three natural frequencies and mode shapes of the unloaded beam, followed by dynamic simulations using ordinary differential equations (ODEs) to analyze time-domain responses under two distinct scenarios: distributed orbital forcing and robotic motion. For the gravity gradient excitation, the beam exhibits symmetric modal deformation dominated by the first mode, with a damped dynamic behavior settling into a steady-state shape. In contrast, the robotic forcing induces asymmetric, continuously shifting deflections that activate higher-order modes and result in sustained vibrations. These contrasting behaviors reveal key insights into the modal sensitivity and dynamic stability of LSS platforms under realistic in-orbit operational loads. The results serve as a foundation for future work on nonlinear modelling, active damping, and robotic interaction control strategies, with implications for the safe assembly and operation of next-generation orbital structures.