Dynamics and nonlinear control of space electromagnetic docking

Space electromagnetic docking technology, free of propellant and plume contamination, offers continuous, reversible and synchronous controllability, which is widely applied in the future routine on-orbit servicing missions. Due to the inherent nonlinearities, couplings and uncertainties of an electromagnetic force model, the dynamics and control problems of them are difficult. A new modeling approach for relative motion dynamics with intersatellite force is proposed. To resolve these control problems better, a novel nonlinear control method for soft space electro-magnetic docking is proposed, which combines merits of artificial potential function method, Lyapunov theory and extended state observer. In addition, the angular momentum management problem of space electromagnetic docking and approaches of handling it by exploiting the Earth＇s magnetic torque are investigated. Finally, nonlinear simulation results demonstrate the feasibility of the dynamic model and the novel nonlinear control method.

ZnS-assisted evolution of N,S-doped hierarchical porous carbon nanofiber membrane with highly exposed Fe-N_(4)/C_(x) sites for rechargeable Zn-air battery

Binder-free bifunctional electrocatalysts are attractive for rechargeable Zn-air batteries(ZABs)in gridscale energy storage and flexible electronics,but suffering from the sluggish mass transport and inadequate catalytic capability.Herein,we propose a scalable approach of in-situ engineering highly exposed Fe-N_(4)/Cxsites on the N,S-doped porous carbon nanofiber membrane as a binder-free air electrode catalyst for ZABs.ZnS nanospheres are firstly used as integrated structure-directing agents to facilitate the electronic modulation of Fe-N_(4)/Cxsites by S doping and construct the hierarchical macro/meso/micropores at high temperature.Neither additional step for removal of ZnS nanospheres nor doping process is required,significantly simplifying the pore formation process and improving the S doping efficiency.Benefiting from the enhanced intrinsic activity of high-density Fe-N_(4)/Cxsites(23.53μmol g^(-1))and the optimized mass transport of carbon nanofibers,as-synthesized electrocatalyst shows a positive half-wave potential of 0.89 V for oxygen reduction reaction and a small overpotential of 0.47 V at 10 m A cm^(-2)for oxygen evolution reaction.When used as the air cathode catalyst for ZABs,it delivers a high specific capacity of 699 m Ah g^(-1)at 5 m A cm^(-2),a large peak power density of 228 m W cm^(-2)and a prolonged cycling over 1000 h.At 10 m A cm^(-2),a robust structure with atomically dispersed Fe is also remained after cycling for 420 h.Due to the flexible properties of the electrocatalyst,as-assembled quasi-solid-state ZAB shows stable cycling over 90 h at alternately flat/bent states,demonstrating great prospects in flexible electronic device applications.

Efficient electrocatalytic overall water splitting and structural evolution of cobalt iron selenide by one-step electrodeposition

Developing bifunctional electrocatalysts with both high catalytic activity and high stability is crucial for efficient water splitting in alkaline media.Herein,a Fe-incorporated dual-metal selenide on nickel foam(Co_(0.9)Fe_(0.1)-Se/NF) is synthesized via a facile one-step electrodeposition method.As-synthesized materials could serve as self-supported bifunctional electrocatalysts with excellent catalytic activity towards oxygen evolution reaction(OER) and hydrogen evolution reaction(HER) in alkaline media.Experimental results show that delivering a 10 mA cm^(-2) water splitting current density only requires a cell voltage of 1.55 V.In addition,a very stable performance could be kept for about 36 hours,indicating their excellent working stability.Moreover,by means of phase analysis,we have identified that the evolution of the synthesized Co_(0.9)Fe_(0.1)-Se/NF experiences two entirely different processes in HER and OER,which hydroxide and oxyhydroxide are regarded as the real active sites,respectively.This work may pave the way to further understanding the relationships between the reactivity and stability of chalcogenide-based electrocatalysts and facilitating the rational design of efficient electrocatalysts for future renewable energy system applications.

A physics-informed deep learning framework for spacecraft pursuit-evasion task assessment

Qualitative spacecraft pursuit-evasion problem which focuses on feasibility is rarely studied because of high-dimensional dynamics,intractable terminal constraints and heavy computational cost.In this paper,A physics-informed framework is proposed for the problem,providing an intuitive method for spacecraft threat relationship determination,situation assessment,mission feasibility analysis and orbital game rules summarization.For the first time,situation adjustment suggestions can be provided for the weak player in orbital game.First,a dimension-reduction dynamics is derived in the line-of-sight rotation coordinate system and the qualitative model is determined,reducing complexity and avoiding the difficulty of target set presentation caused by individual modeling.Second,the Backwards Reachable Set(BRS)of the target set is used for state space partition and capture zone presentation.Reverse-time analysis can eliminate the influence of changeable initial state and enable the proposed framework to analyze plural situations simultaneously.Third,a time-dependent Hamilton-Jacobi-Isaacs(HJI)Partial Differential Equation(PDE)is established to describe BRS evolution driven by dimension-reduction dynamics,based on level set method.Then,Physics-Informed Neural Networks(PINNs)are extended to HJI PDE final value problem,supporting orbital game rules summarization through capture zone evolution analysis.Finally,numerical results demonstrate the feasibility and efficiency of the proposed framework.