Simple Method for Tethered Space Debris Retrieval

Space debris retrieval problem utilizing a tethered system in an elliptical orbit is studied in this paper.An analytical control law specified by a tether length rate for retrieval is derived from a dumbbell model of the system.The proposed control method can suppress large swings around the local vertical position of the tethered system.Under such a control strategy,the debris retrieval behaves in asymptotic stable motion towards the expected angle.The stability of the non-autonomous system during the retrieval control is analyzed using the Floquet theory.The result demonstrates that an orbital region exists,on which the retrieval process maintains asymptotically stable.The proposed analytical control law is validated via numerical simulations.

China＇s Choice of Analytical Models for Its Anti-Monopoly Law

Modem analytical models for anti-monopoly laws are a core element of the application of those laws. Since the Anti-Monopoly Law of the People＇s Republic of China was promulgated in 2008, law enforcement and judicial authorities have applied different analytical models, leading to divergent legal and regulatory outcomes as similar cases receive different verdicts. To select a suitable analytical model for China＇s Anti-Monopoly Law, we need to consider the possible contribution of both economic analysis and legal formalism and to learn from the mature systems and experience of foreign countries. It is also necessary to take into account such binding constraints as the current composition of China＇s anti-monopoly legal system, the ability of implementing agencies and the supply of economic analysis, in order to ensure complementarity between the analytical model chosen and the complexity of economic analysis and between the professionalism of implementing agencies and the cost of compliance for participants in economic activities. In terms of institutional design, the models should provide a considered explanation of the legislative aims of the law＇s provisions. It is necessary, therefore, to establish a processing model of behavioral classification that is based on China＇s national conditions, applies analytical models using normative comprehensive analysis, makes use of the distribution rule of burden of proof, improves supporting systems related to analytical models and enhances the ability of public authorities to implement the law.

Venus round trip using solar sail

Trajectory optimization and simulation is performed for Venus round trip (VeRT) mission using solar sail propulsion. Solar gravity is included but atmospheric drag and shadowing effects are neglected in the planet-centered escape and capture stages. The spacecraft starts from the Geostationary orbit (GEt) at a predetermined time to prepare a good initial condition for the Earth-Venus transfer, although the launch window is not an issue for spacecraft with solar sails. The Earth-Venus phase and the return trip are divided into three segments. Two methods are adopted to maintain the mission trajectory for the VeRT mis- sion and then compared through a numerical simulation. According to the first approach, Planet-centered and heliocentric ma- neuvers are modeled using a set of blended analytical control laws instead of the optimal control techniques. The second pro- cedure is the Direct Attitude Angle Optimization in which the attitude angles of the solar sail are adopted as the optimization variables during the heliocentric transfer. Although neither of the two methods guarantees a globally optimal trajectory, they are more efficient and will produce a near-optimal solution if employed properly. The second method has produced a better result for the minimum-time transfer of the VeRT mission demonstrating the effectiveness of the methods in the preliminary design of the complex optimal interplanetary orbit transfers.

Nonlinear optimal predictive controller for static var compensator to improve power system damping and to maintain voltage

The main objectives of this paper are to simul-taneously improve power system damping and to maintain voltage at the static var compensator(SVC)location bus simultaneously.A new controller for SVC with closed-form analytic solution nonlinear optimal predictive control(NOPC)law was presented.The controller does not require online optimization and the huge calculation burden can be avoided,so that the demand of real-time control can be sat-isfied.In addition,there are only two design parameters,which are the predictive period and control order;so it is easy to implement and test in practical use.Simulation results have shown that the controller can not only attenuate power system oscillation effectively but can also maintain voltage at the SVC bus location.