Multi-Axis Selective Decoupling Framework for Free-Floating Space Manipulators

Daegyun Choi; Donghoon Kim

cs.ROAug 14, 2026

Multi-Axis Selective Decoupling Framework for Free-Floating Space Manipulators

Authors: Daegyun Choi, Donghoon Kim

Organizations: Postdoctoral Researcher, Department of Aerospace Engineering & Engineering Mechanics, University of Cincinnati, Cincinnati, OH 45221, USA. · Associate Professor, Department of Aerospace Engineering & Engineering Mechanics, University of Cincinnati, Cincinnati, OH 45221, USA.

Abstract

Free-floating space manipulator systems face operational challenges due to dynamic coupling. While traditional reactionless manipulation eliminates base disturbances, enforcing the null-space projections across all rotational axes imposes excessive constraints on the system and drastically reduces the available workspace. To address this limitation, this work proposes a multi-axis selective decoupling framework that nullifies momentum transfer exclusively along mission-critical directions. By leveraging a directionally constrained sub-coupling matrix, the framework relaxes the null-space constraints. Numerical simulations confirm that this approach mathematically eliminates constrained directional disturbances along the targeted axes while preserving the remaining degrees of freedom, enabling the manipulator to execute task-space operations successfully.

Figures & tables

Body	Mass (kg)	Length (m)	Inertia (kg $\cdot$ m 2 )
Base	$2550.0$	–	diag([ $6200$ , $3540$ , $7090$ ])
Link 1	$35.0$	$0.35$	Calculated as solid cylinders with the given link length and a radius of 0.1 m [ 6 ]
Link 2	$22.5$	$0.87$
Link 3	$21.9$	$0.63$
Link 4	$16.5$	$0.26$
Link 5	$26.0$	$0.28$

Table 1: Kinematic and Dynamic Parameters of the Reference SMS Model

Figure 1: Visual Representation of ETS-VII

Parameter (unit)		Value
All cases	Simulation time (s)	$150$
	Time interval (s)	$0.1$
	Initial base states	zeros
	Initial joint rates	zeros
	Tracking gain	$0.05$
	Max. joint rate (deg/s)	$5$

Table 2: Simulation Parameters

Panel of Figure 2 — Figure 2: Time History of Joint States, Base Attitude, and Base Angular Velocity (Case 1)

Figure 3: Time History of Constrained Disturbance Angular Velocity (Case 1)

Panel of Figure 4 — Figure 4: Time History of Joint States, Base Attitude, and Base Angular Velocity (Case 2)

Figure 5: Time History of Constrained Disturbance Angular Velocity (Case 2)

Panel of Figure 6 — Figure 6: Time History of Joint States, Base Attitude, and Base Angular Velocity (Case 3)

Figure 7: Time History of Constrained Disturbance Angular Velocity (Case 3)

Robotic Control

Robotic control studies how machines use sensing and computation to produce reliable movement and interaction in changing environments.

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More than a Manipulator: Planning Propellant-Free Attitude Maneuvers for Free-Floating Spacecraft

Harsh G. Bhundiya, Avi Soval, Keenan Albee

Department of Astronautical Engineering, University of Southern California, Los Angeles, CA 90089 · Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, CA 90089 · Departments of Astronautical, Aerospace and Mechanical, and Electrical and Computer Engineering, University of Southern California, Los Angeles, CA 90089

Spacecraft Attitude Determination Space Robotics Robotics Robotic Manipulation

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Spacecraft attitude control is traditionally achieved using momentum exchange devices or propellant-consuming thrusters. Meanwhile, a growing number of missions require robotic manipulators, which are typically treated as disturbance sources to be rejected rather than as actuators for spacecraft reorientation. This work investigates the use of manipulator motions for propellant-free attitude control by formulating a trajectory optimization problem with critical joint and collision avoidance constraints. Using an interior point solver for the resulting nonlinear program, complex slew and detumble trajectories are demonstrated for a range of spacecraft-manipulator systems with varying kinematic complexity and mass properties. The achievable control authority is compared directly with that of reaction wheel arrays via momentum and torque envelopes, demonstrating the potential for manipulators to serve as redundant or even primary attitude control systems. This work provides a framework for using manipulators as multipurpose attitude control actuators, with particularly promising applications in in-space assembly and manufacturing when grasping payloads with high relative mass fractions.

Abstract

Robotic Control

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