Orbit adjustment and pointing control of drag-free spacecraft prior to scientific measurement mode

• A velocity-measurement-independent integral sliding mode adaptive control law within a cascaded framework is proposed to address the fast orbit control problem under uncertain space disturbances and nonholonomic constraints, featuring simple structure and direct effectiveness. • A high-precision, low-computational-cost attitude correction scheme is developed based on the kinematic mapping between the acquisition camera’s observed image position and the satellite/MOSA attitude, solving the inter-satellite link acquisition problem under large systematic errors. • A dual-optical-path cooperative image feedback pointing control strategy based on target optical path relative trajectory prediction is presented to achieve synchronous and stable pointing control of triple-satellite inter-satellite links, providing a reference for space-based gravitational wave detection missions. • The effectiveness and reliability of the proposed acquisition and tracking control scheme are comprehensively verified through physical experiments on a three-axis air-bearing table. In this study, we investigate the rapid formation initialization and inter-satellite laser link acquisition and tracking control for LISA/TianQin-like drag-free spacecraft operating in scientific preparation mode. First, an integral sliding mode adaptive motion controller is formulated to resolve the rapid formation adjustment problem for the under-actuated situation with orbit thrusters operating in a single direction relative to the body-fixed frame, wherein a nonlinear observer is synthesized to obviate the need for orbital velocity measurements in the control law. Second, concerning the capture of inter-satellite laser links subsequent to formation establishment, the kinematic mapping between camera image outputs and spacecraft/MOSA (Moving Optical Sub-Assembly) attitude is leveraged to transform boresight pointing errors into attitude offset corrections, yielding a computationally efficient high-precision target attitude determination for inner-satellite links. Third, for synchronized steady-state tracking following the capture of dual-target optical paths, a cooperative spacecraft/MOSA attitude control scheme is developed based on extended image-space kinematics integrated with dual-optical-path visual feedback. Stability analyses are conducted for our proposed strategies, and their efficacy is substantiated through numerical simulations and hardware-in-the-loop experiments contextualized within the TianQin mission framework.