Citation: Zhang, L. Configuration
Optimization for Free-Floating Space
Robot Capturing Tumbling Target.
Aerospace 2022, 9, 69. https://
doi.org/10.3390/aerospace9020069
Academic Editor: Mikhail Ovchinnikov
Received: 23 December 2021
Accepted: 25 January 2022
Published: 26 January 2022
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Article
Configuration Optimization for Free-Floating Space Robot
Capturing Tumbling Target
Long Zhang
Key Laboratory of Space Utilization, Technology and Engineering Center for Space Utilization, Chinese Academy
of Sciences, Beijing 100094, China; zhanglong@csu.ac.cn
Abstract:
The maximum contact force is one of the most important indicators for contact problems.
In this paper, the configuration optimization is conducted to reduce the maximum contact force for
a free-floating space robot capturing tumbling target. First, the dynamics model of a free-floating
space robot is given, with which the inertial properties perceived at the end-effector can be derived.
Combing the inertial properties of the contact bodies, a novel concept of integrated effective mass
is proposed. It tries to transform the complex contact process into the energy change of a virtual
single body with integrated effective mass. On this basis, a more general continuous contact model is
established, which is also suitable for non-central collisions between space robot and the tumbling
target. Thereafter, the maximum contact force is derived as an important indicator for the null-space
optimization method to reduce the maximum contact force. Finally, numerical simulations with a
3-degree-of-freedom free-floating space robot and a 7-degree-of-freedom free-floating space robot,
as the research objects, are carried out respectively and the results show the effectiveness of the
method proposed.
Keywords:
free-floating space robot; configuration optimization; maximum contact force; integrated
effective mass; tumbling target capture
1. Introduction
Due to the characteristics of microgravity, high vacuum, and strong radiation in space,
astronauts carrying out space missions will face extremely high risks. Space robots, with
their outstanding advantages in terms of strong adaptability to the space environment and
freedom from physiological conditions, have gradually become the main force in space
exploration [
1
–
3
]. In recent years, with the continuous development of space exploration,
capturing non-cooperative targets has attracted much attention, as the technique is expected
to be applied for functions such as the removal of debris from orbit and servicing broken
satellites for repair [4–6].
Scholars have conducted research on related technologies in the capture of non-
cooperative targets. It is generally known that an entire capture task contains three phases:
the target-chasing control phase, which is also called the pre-contact phase; the contact
phase between the target and end-effector of the space robot; and the stabilization control
phase of tumbling motion, which is also called the post-contact phase [
7
,
8
]. Most research
focuses on the pre-contact phase to optimize the capture configuration or follow an optimal
trajectory [
9
–
12
], and the post-contact phase to detumble the non-cooperative target or
reduce the base attitude disturbance [
13
–
16
]. In this paper, based on the analysis of the
contact phase, which emphasizes contact modelling, the capture configuration is optimized
to minimize the maximum contact force.
For the contact-modelling problem, there are generally two different approaches
from the perspective of whether the contact process is assumed to be continuous or not.
The first approach is usually called discrete contact dynamics modelling method, which
assumes that the contact is an instantaneous phenomenon, and that the configuration
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