Actuators for fast capture are essential in the tasks of space structure assembly and space debris disposal. To avoid damage and rebound caused by collision, the mechanical devices for capture or docking impose very strict restrictions on the collision speed. The gripper made of soft material can realize compliant grasping, but its actuating speed and driving mode should adapt to the scenarios of grasping moving objects in space. By harnessing the rapid occurrence of structural instability and tuning its triggering conditions, we present a soft and bistable gripper for dynamic capture. The gripper deforms on the collision with other objects, and it absorbs the kinetic energy of the objects to trigger an instability, and then achieve fast grasping as well as cushioning. This process does not need any other input energy, and it greatly simplifies the conventional driving devices so as to realize the miniaturized and light-weight gripping actuation. The proper pre-deformation to the bistable structure of the gripper enables one to dynamically adjust the energy barrier for triggering the onset of instability to achieve the optimal grasping and buffering effect according to the kinetic characteristics of targets. After finishing one grasping task, the bistable gripper can automatically return to its initial state and release the target via a self-designed cable-driven mechanism. The ground-testing experiment demonstrates that the proposed soft gripper is capable to grasp, transfer, and release moving targets, and it thus possesses great potential to fulfill challenging operations in space missions.

The docking mechanism is a key component for on-orbit refueling technology. In this paper, the design and analysis of a novel floating docking mechanism for on-orbit berthing-based refueling is presented. Compared with traditional berthing and docking, the berthing here is high in success rate and low in impact, which is accomplished by stretching out a docking subassembly instead of pulling back the client spacecraft. However, the berthing also has two problems: initial deviations between two spacecraft and an additional force generated by a hard alloy refueling pipe, which both seriously affect the docking operation. Thus, the docking mechanism is designed to have alignment abilities and decrease the additional force as much as possible. Based on the principles above, we introduced spring pins and a helical refueling pipe to design a light, compact, and simple docking mechanism. To further reduce the additional force, we proposed an elliptical-helical pipe and analyzed its mechanical properties. Finally, simulations and experiments were conducted to validate the proposed mechanism. The results show that the proposed mechanism with an elliptical-helical pipe has a high tolerance for linear and angular misalignment and superior dynamic performance during docking.

A novel convertible unmanned aerial vehicle (UAV) with four tiltable rotors and a tandem-wing system has been developed. Considering the aerodynamic effect caused by the rotor-induced velocity, a mathematical model that contains the traditional free airstream analysis and rotor-induced effect analysis is proposed, from which the precise equilibrium point of the control inputs and states can be derived. Moreover, a control allocation algorithm is designed to provide the mapping relationship between traditional input variables and specific input variables of the UAV, so that the complicated mathematical model can be linearized for the design of model predictive control (MPC) system. In order to handle the control input constraints of the UAV system, an MPC system is applied for the trajectory tracking during the cruising phase. The simulation results demonstrate that the proposed model predictive control system has stability, accuracy without a random disturbance and quick response capabilities with a random disturbance during cruising trajectory tracking, which are in high demand for the quick UAV flight system.