Tethered-satellite systems have great potential in completing various space missions. However, existing researches mainly focus on the deployment of satellites in a circular orbit, whereas deployment in an elliptical orbit, especially with disturbances, is rarely studied. This study develops a new control strategy to deploy tethered satellites in a low-eccentricity elliptical orbit that also considers system uncertainties and external disturbances. First, the periodical solution of the librational motion of a tethered-satellite system in an elliptic orbit is calculated. Because there is no fixed equilibrium point for deployment in elliptical orbits, the periodical solution is set as the end condition for deployment. After that, the controllability of the system is verified and an open-loop tension-control law is optimized by particle swarm optimization (PSO) and the Nelder-Mead method. To eliminate effects from uncertainties in initial states and errors from the deployment mechanism, an adaptive sliding mode controller is designed to achieve high-precision trajectory tracking. The performance of the proposed controller is compared quantitatively with a proportion-derivative (PD) controller and normal sliding mode controller. Furthermore, Monte Carlo simulations are conducted to demonstrate the effectiveness and robustness of the proposed controller when subjected to uncertain initial states. The simulation results indicate that the proposed control strategy enables the stable deployment of tethered-satellite systems despite the uncertainties and perturbations.

Spinning electrodynamic tether systems are considered ideal platforms for payload transportation, removal of space debris, artificial gravity, and so on, for they provide a propellantless solution to orbital maneuver and good centrifugal stability. However, all spinning electrodynamic tether systems have to transition into a spinning state from the equilibrium state, during which tethers are likely to become deformed because of Lorentz forces. This paper studies tether deformation during such a transition process. Two open-loop programs are proposed in the Lagrangian model as the reference trajectories of acceleration under different mission backgrounds. The dynamic characteristic of tether is studied in a more accurate model with distributed parameters (bead model). Considering the significant tether deformation in the case of high electrical current, an optimal controller is proposed based on Bellman dynamic programming. Numerical results indicate that the proposed control laws can ensure a safe transition of the proposed tether system into a spin and limit tether deformation to a reasonable level.

The research elaborates on the mechanical properties at the Al (111)/6H-SiC (0001) interface based on the density functional theory. Because of the difference in atom category at the interface of 6H-SiC (0001), it takes the C-terminated interface and Si-terminated interface into account. As indicated by the gross energy computing results at the two interfaces, the C-terminated Al (111)/6H-SiC (0001) interface demonstrates a greater adhesion force than the Si-terminated counterpart. Throughout detailed analysis on the bonding mechanism, surface hybridization and charge transfer at the Al (111)/6H-SiC (0001) reaction interface, the research reveals its strong covalent characteristics. According to the comparative study on the ideal tensile strength and general stacking fault energy at varying cleavage surfaces, a conclusion can be fitly reached that the fracture at the Al (111)/6H-SiC (0001) interface is easily seen in Al-Al bonds in the Al matrix instead of C(Si)-Al bonds at the interface. Despite the greater adhesion energy of the C-Al bond than the Si-Al bond, Al-Al bonds close to the C-terminated Al (111)/6H-SiC (0001) interface easily fracture due to the low ideal tensile strength.

This paper mainly studies the spin-up control of a spinning electrodynamic tether formation (SEDTF) consisting of three linearly distributed nano-satellites connected by two tethers. The main challenge of the spin-up process is that, due to the coupling effect of two tethers, more significant tether deformation and attitude disturbance on tethered nano-satellites emerge than that of a single tether system. To deal with this problem, the dynamic model is first established for analyzing flexible tether motions and attitude motions of three nano-satellites. A sliding mode control strategy is then proposed for the spin-up process: 1) Considering the underactuation problem of the tether system, a sliding mode controller with an adaptive law is proposed to track spinning motion and stabilize tether deformation by adjusting only electrical current; 2) Considering the disturbance of constantly oscillating tension force, a sliding mode controller with a fixed-time prescribed performance is proposed to ensure a fast stabilization of attitude motions. Numerical results validate a synchronized spin-up of a SEDTF. Under the regulation of the proposed control strategy, tether deformations are reduced to an insignificant level, and attitude motions of nano-satellites are stabilized around designated orientations.