Space stations and artificial satellites have been widely used in communications, navigation, meteorology, astronomical observation, military, etc. However, at the mercy of complex and changeable space environment, spacecrafts may be disabled due to functional module degradation, failure, and running out of fuel. These spacecrafts need to be repaired or restored to avoid becoming space debris. Thus, the on-orbit service technology is developed, which covers a wide range of fields such as on-orbit maintenance, on-orbit assembly, on-orbit detection, and space debris removal. On the other hand, the current space on-orbit operation tasks are tending to be lightweight, miniaturized, multimodule, and multifunctional, where the CubeSat, a small, low-cost satellite, was born and played an important role. In a research paper recently published in Space: Science & Technology, Jinguo Liu, Shenyang Institute of Automation, Chinese Academy of Sciences, combining the CubeSat technology, innovatively proposed a deployable 1 U-sized space robot, named Cubot, for the on-orbit tasks of space debris removal and space station auxiliary maintenance.
First of all, the system design of Cubot were introduced from three aspects. Firstly, the authors innovatively proposed a modular structure design method for the space manipulator, with the purpose of facilitating the configuration and application of the manipulator in CubeSat. Cubot is composed of three parts, including active joints, passive joints, and end effectors. The design parameters including rod length, passive joint number, and the size of end-effector can be adjusted flexibly and customized according to specific on-orbit missions. The link length and link offset can be confirmed according to required storage size. Thus, Cubot can be designed flexibly serving for suitable CubeSat space. Secondly, two working modes of Cubot for on-orbit service were introduced. Mode A was designed for space station on-orbit maintenance. Cubot can replace astronauts in space operations to reduce the risk of on-orbit missions. Mode B was designed for active removal of space debris. Relying on the CubeSat system, Cubot can complete the debris capturing in the range of low to high orbit. Although Cubot cannot capture the debris that is high spinning because the despinning device is not designed, Cubot is operable for the debris that is no spinning or low spinning that can keep relative status by the friction with gripper. In this way, Cubot can perform capture missions for many times, which reduces the launch cost greatly. Thirdly, the mechanism analysis was carried out for the two different configurations (deployment process and after deployment) of Cubot. During the deployment process, the passive joint can be regarded as an active joint with angular limitation, and the limiting angle was determined by the preset angle of the torsion spring. Therefore, the Cubot in the deployment process can be regarded as a 7-DOF manipulato
