The Electro Dynamic Tether (EDT) system has been demonstrated to be inherently unstable due to a continuous energy input from Lorentz force. Previous studies have made some progress in understanding the instability of the EDT system, while the degree of instability remains insufficiently explored. It is known that strong instability degree means short time before the system turns unstable, which is detrimental to on-orbit mission. Therefore, it is of great significance to evaluate the instability degree of EDT system in depth. The novelty of this paper lies in obtaining the analytical solution of Instantaneous Equilibrium Points (IEPs) under given system parameters, analyzing the distribution characteristics of IEPs, as well as revealing the impact of IEPs on stability. Therefore, a rapid assessment method of the EDT system’s instability degree is proposed. Compared with the numerical method, the obtained analytical solution of IEPs shows higher efficiency and accuracy. Additionally, two theorems are proven to preliminarily determine the existence of IEPs. According to the IEP distribution and dynamics simulation on typical initial parameters, it is found that the system exhibits lower instability degree within the IEP zones, and there exists a specific central IEP zone with the lowest instability degree near the origin of the parameter-state plane. Priority should be given to choose the initial parameters within this region to gain lower instability degree.

In recent years, the rapid development of mega-constellations has significantly exacerbated the deterioration of the space debris environment, posing substantial and escalating threats to the safety of spacecraft. This study aims to explore the complex evolution of the space debris environment and assess the collision risks associated with spacecraft. First, a space debris environment topological network model is proposed, which incorporates interdisciplinary methods from topological networks, fluid mechanics, and spacecraft dynamics. This model enables a structured representation of the relationships among space objects and provides rapid predictions of the space debris environment. Then, a collision probability algorithm based on the topological network model is introduced. This algorithm inherits the efficiency advantages of the topological network model and has been validated for reliability through comparison with the classical ESA’s DRAMA software. Finally, based on the above models, the collision risks of constellation satellites in Low Earth Orbit (LEO) are analyzed, including both operational and deorbit processes. The study reveals that constellation satellites face a much higher risk of internal collisions with satellites from the same constellation during operations than that with other space objects. Additionally, during the satellite deorbit process, the collision risk peaks when satellites traverse the operational region of Starlink satellites.

The drag balloon is one of the primary devices for deorbiting of low Earth orbit spacecraft at the end of their life. Since the thin membrane sphere must be stored in a confined space for an extended period before use, achieving high-density and low-damage folding and smooth inflation and deployment is crucial for its operation. Considering the drag balloon is mostly composed of a certain number of bonded valves, an optimal valve configuration design method that considers shape stability and cost efficiency is firstly proposed. Furthermore, for the single petal structure, a symmetrical parallel z-type folding scheme is proposed, and methods for quantifying the folded volume and damage are provided. Then, to increase the folding-deployment ratio and reduce crease damage, an optimized folding scheme for the drag balloon is presented, and simulation of a sphere of 6-meter diameter is conducted. Based on this scheme, the effects of valve configuration, inflation speed, and initial internal pressure and temperature on the smooth deployment of the drag balloon are analyzed. The results show that the proposed folding scheme can achieve high-density and low-damage folding of the drag balloon. Additionally, by increasing the number of valves, slowing down the inflation speed, avoiding excessive vacuum, and reducing direct sunlight exposure, the attitude oscillation during the deployment process can be effectively mitigated, speeding up the attainment of a stable state.

With the escalating frequency of space activities, particularly the launch of constellation satellites, the amount of space debris experienced gradually increases, posing threats to the safety and sustainability of the space environment. To counteract the growth of debris, active deorbit devices are imperative for spacecrafts. In low Earth orbit (LEO), the drag sail device has emerged as a highly effective solution due to its ability to increase the spacecraft’s windward area, facilitating rapid deorbit by leveraging atmospheric drag as the primary perturbation. In this study, recent developments of membrane drag sail deorbit technology for LEO satellites are summarized, as well as the current problems such as attitude instability, dangerous space environment, and folding and unfolding issues. Moreover, crucial technologies such as modeling and simulation of deorbit efficiency, attitude stabilization, collision risk analysis and protection design, sail surface atomic oxygen protection design, and folding and unfolding of the drag sail are discussed. Finally, the development trends and technology applications of membrane drag sail deorbit for LEO satellites are presented.

In the field of active deorbiting technologies, the electrodynamic tether has garnered attention due to its cost-effectiveness, light weight, and low fuel consumption. In this study, to address the low success rate of the deployment mechanisms used in previous in-orbit experiments, a novel deployment mechanism with a size of 2 U and a weight 2.3 kg based on pusher motors is proposed. In order to achieve a smooth tether deployment without rupture and rebound, an optimization method was proposed for springs, and tether within the deployment mechanism. Finally, simulation and ground ejection experiment were conducted with the objective of deploying a 50-m tether. In the experiment, the top plate was ejected with a kinetic energy of 2.3 J, and the tether was successfully unfolded. The experimental results indicate that the device is capable of deploying a tether of at least 50 m, demonstrating the effectiveness of the optimization method.

Electrodynamic tether (EDT) is a key prospective technique for space-debris removal without the use of propellant. However, there are 2 main shortcomings of the classical EDT system. One is that the conductive tether with a single wire should exceed several kilometers to produce the expected force, which increases the risk of collision and damage. The other is the heavy current or high voltage caused by the overlong tether, which may even melt itself. Therefore, a novel electrodynamic multi-tether (EMT) system has been proposed here to overcome the above disadvantages of the classical EDT system. The EMT system has multi tethers connecting the 2 end bodies, which has more complex dynamic behaviors than the EDT system. In order to promote the application of the EMT system, this paper will pay attention to the dynamic modeling and analysis of the EMT system, to reveal the primary dynamic characteristics. Firstly, the dynamic equation of the novel EMT system was established. Secondly, the linear assumption and vibration theory were utilized to illustrate its primary dynamic characteristic. Finally, the expressions of the vibration period and critical current of tether were given and numerical simulations were conducted to verify these analyses. The results showed that the tether libration equation can be simplified when the size of main satellite is much smaller than that of tether. Besides, the tether will go tumbling immediately when the practical current exceeds the critical current.