Liu Luhua

Nonlinear hierarchy-structured predictive control design for a generic hypersonic vehicle

A hierarchy-structured predictive controller is designed and analyzed for rotation motion dynamics of a generic hypersonic vehicle (GHV). This vehicle model has fast variability, is highly nonlinear, and includes uncertain parameters. The controller contains two subsystems, the inner-fast-loop nonlinear generable predictive controller (NGPC) and the outer-slow-loop NGPC, both of which are designed by the closed-form optimal generable predictive control method. Thus, the heavy on-line computational burden in the classical predictive control method is avoided. The hierarchy structure of the control system decreases the relative degree of each subsystem and helps increase the dynamic response speed of the attitude controller. In order to improve the robustness of the control system, a feedback correction algorithm is proposed that corrects the calculation error between the predictive model and the real dynamic model. Simulation studies are conducted for the trimmed cruise conditions of an altitude of 33.5 km and Mach 15 to investigate the responses of the vehicle to the step commands of angle of attack, sideslip angle, and bank angle. The simulation studies demonstrate that the proposed controller is robust with respect to the parametric uncertainties and atmospheric disturbance, and meets the performance requirements of GHV with acceptable control inputs.

Research on strategy to decrease wind load of solid rocket with multiple-stage boosters

For solid rocket Hying in the endoatmosphere, the disturbance of wind field movement on ballistic trajectory cannot be neglected. This paper presents the dynamical model of solid rocket, selects a typical wind field model and analyzes the effects on ballistic characteristics in boost phase caused by wind field disturbance. And then a coefficient is introduced to reflect the degree of wind field disturbance and used as a basic reference to research the transmission mechanism of the effects on angle of attack and aerodynamic loads of the wind field disturbance. At last, this paper proposes a strategy to decrease wind load and the simulations show the efficiency of the proposed strategy.

Research on solar sail halo orbits around artificial lagrange point

The successful launch of the first satellite around the collinear libration point—International Sun-Earth Explorer-3(ISEE-3), undrawed the prelude of the mission around the libration point. And now, along with the development of the technology of low thrust propulsion and the renaissance of the technology of the solar sail, it has received considerable attention that how to utilize the solar sail in the space mission around the collinear libration point. This paper bases on the Circular Restricted Three-Body Problem(CRTBP), and takes the traditional L1 point as example, studies on the halo orbit around the traditional L1 point, and discusses the solar sail artificial L1 point, analyses the variation of the position of the artificial L1 point with the lightness number of the solar sail, and then investigates the solar sail halo orbit around the artificial L1 point, and compares it with the halo orbit around the traditional L1 point, at the end, analyses the effect of the difference of the lightness number and the out-of-plane amplitude on the orbit, and the variation of the orbit period with the lightness number.

Study on the Collision Avoidance Maneuver in the RVD Mission

The probability analysis of the collision and the plan of collision maneuver strategy in the rendezvous and docking (RVD) mission are studied in this paper. Firstly, the paper puts forward the uncertainty covariance by using the linear system theory under the Gaussian stochastic process conditions, and it gives the statistic characteristic of output stochastic states and probability density function at a given time. Secondly, the relationship between the collision probability and the disturbances which include initial states errors, control errors and environmental disturbances, is analyzed. Thirdly, effective strategies of collision avoidance in the RVD mission are provided to reduce the collision probability under the performances of energy expenditure and safety. At last, some conclusions and remarks of RVD collision avoidance are drawed