http://yetl.yabesh.ir/yetl1/handle/yetl/19011 2026-04-23T21:58:26Z http://yetl.yabesh.ir/yetl1/handle/yetl/4309168 Improved Reinforcement Learning–Based Method for Emergency Mission Planning to Remove Space Debris Mingze Zhou; Tianxi Liu; Cheng Wei; Yao Yu; Jingjing Yin; Xingjian Wang A mission planning method with an online optimization mechanism based on improved reinforcement learning was proposed to address the task planning problem of space debris removal tools utilizing stochastic maneuvering strategy and target selection strategy in active space debris removal scenarios. The primary objective of this method is to enhance the efficiency of space debris removal operations within a specified timeframe. The initial steps involve establishing working models for lasers and onorbit working vehicles, as well as formulating an optimized reinforcement learning improvement approach. Subsequently, a reinforcement learning training module dedicated to space debris removal tasks was introduced. This module focuses on training the maneuver location and work objectives of the two space debris removal tools while learning the optimal strategy for achieving a successful removal rate. The trained decision-making strategy is then integrated into an optimizer to analyze the cost consumption associated with the planning outcomes. The key finding of this study is the development of a stable space debris removal strategy through the training of the removal tool. By choosing an appropriate agent, the agent-based optimization process achieves a 100% space debris removal rate, leading to cost savings in ground-based movement of removal tools and improved mission planning. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4309167 Homotopy Method with Initial Costate Evaluation for Low-Thrust Fuel-Optimal Homoclinic Halo Orbit Transfer Jixin Ding; Xue Bai; Ming Xu The problem of transferring a spacecraft between Halo orbits around Sun–Earth libration points using low-thrust propulsion is considered in this paper. The complete dynamics is established using Pontryagin’s maximum principle (PMP) within the framework of the Sun–Earth circular restricted three-body problem (CRTBP), incorporating both state and costate variables. To solve the nonsmooth shooting equations with discrete bang-bang control, a homotopy continuation method is introduced, continuing the smooth energy-optimal controls to the discrete fuel-optimal control. Additionally, a particle swarm optimization (PSO) algorithm is employed to estimate initial costate values for energy-optimal problems, addressing the challenge of nonphysical initial costate estimation. Finally, the effectiveness of the homotopy algorithm, in conjunction with PSO costate initial evaluation, is demonstrated through numerical verifications of homoclinic Halo transfers, where multirevolution transfer and parameter analysis are subsequently considered. The proposed homotopy algorithm, supported by parallel computation, generates the global distribution of feasible transfer windows for different initial and end positions of Halo orbits, distributing to the selection of suitable one concerning fuel consumption, time, and their combination. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4309165 Design, Modeling, and Ground Test of a Tethered CubeSat with a Rotational Net Wenjun Hu; Yueneng Yang; Zhiyang Liu Tethered CubeSats are one of the main techniques used in active space debris removal. In this work, a tethered CubeSat was designed for space debris removal using a rotational deployment of the net structure. Firstly, the system composition and prototype of the CubeSat were designed. Secondly, the structure and workflow design of the payload are introduced. Thirdly, the dynamic model for the rotational deployment of the flexible network and the corresponding finite element calculation model were established. Finally, a ground experimental verification of the rotational deployment process of a flexible net was performed. The results demonstrate that the satellite payload designed in this study undergoes stable net structure deployment in ground environments. The maximum deployment area can reach 85.2% of the total area of the net structure. The design of the payload in this paper can serve as a reference for tethered CubeSat design in space debris removal missions. As the space environment becomes more congested, the need for effective debris mitigation and removal strategies will increase in importance. The European Space Agency (ESA) has planned to launch a space robot in 2025 to carry out the world’s first space debris removal mission, known as ClearSpace-1. The National Aeronautics and Space Administration (NASA) has proposed a project named Optical Removal of Ionospheric Neutrals (ORION) to clear space debris. Although flexible net capture is a common method for removing space debris, it is prone to entanglement during deployment, which can hinder the successful execution of the debris capture mission. This paper designed a satellite payload for space debris removal. The payload consists of a rope net device rotated by centrifugal force, which effectively avoids the entanglement issues associated with the flexible net. The research presented in this paper can serve as a valuable reference for space debris removal using the flexible net capture method. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4309164 Virtual Frequency Fusion Technique: Detecting Multiple Damages via Broadband Lamb Wave Field Using Scanning Laser Vibrometry M. Kannusamy; Saptarshi Sasmal; Santosh Kapuria This article presents an efficient frequency fusion method by virtual acquisition of multifrequency guided wave velocity data for robust and accurate localization of multiple damages in plate-like structures. Lamb waves are actuated by applying voltage excitation to piezoelectric patch transducers affixed on the plate, and the velocity response is measured using the noncontact scanning laser Doppler vibrometer (SLDV). The results show that the usual root mean square (RMS) and weighted RMS maps of the velocity field measured using a single narrowband pulse excitation of a given central frequency may not accurately localize multiple damages. To overcome this challenge, we propose a fusion method in the form of the product of normalized reciprocal root mean square (rRMS) maps at multiple narrowband excitation frequencies for combining the measurement data from the different excitation frequencies. However, SLDV measurements at multiple narrowband frequencies would be tedious, time-consuming, and expensive. This difficulty is eliminated by virtually computing the velocity fields at various narrowband frequencies from a single physical measurement using broadband excitation. The efficacy of the proposed method is verified through the experimental investigation on an aluminum plate with multiple damages of different shapes and orientations for two different damage scenarios. The method could identify all damages accurately and clearly through sharp peaks in the rRMS amplitude at the damage locations without any accompanying ripples near them. On the other hand, the RMS and weighted RMS maps do not perform as well even after applying fusion of multiple frequencies. 2025-01-01T00:00:00Z