Zixuan Liang

Decoupling trajectory tracking for gliding reentry vehicles

A decoupling trajectory tracking method for gliding reentry vehicles is presented to improve the reliability of the guidance system. Function relations between state variables and control variables are analyzed. To reduce the coupling between control channels, the multiple-input multiple-output (MIMO) tracking system is separated into a series of two single-input single-output (SISO) subsystems. Tracking laws for both velocity and altitude are designed based on the sliding mode control (SMC). The decoupling approach is verified by the Monte Carlo simulations, and compared with the linear quadratic regulator (LQR) approach in some specific conditions. Simulation results indicate that the decoupling approach owns a fast convergence speed and a strong anti-interference ability in the trajectory tracking.

Decoupled three-dimensional entry trajectory planning based on maneuver coefficient

A rapid and decoupled three-degree-of-freedom trajectory planning approach is presented for maneuvering entry vehicles. A maneuver coefficient is defined to describe the lateral motion of a three-degree-of-freedom trajectory so that the designs for the longitudinal and lateral trajectories are decoupled. The longitudinal drag profile is planned according to the flight range that considers the maneuver coefficient. The lateral trajectory is controlled by an adjustable heading error corridor to achieve the required maneuver coefficient. The three-degree-of-freedom trajectory is finally generated based on the drag profile and the adjustable corridor. The trajectory planning algorithm is tested on two entry vehicles. Results indicate that this algorithm is capable of planning three-degree-of-freedom trajectories for nominal and maneuvering missions. The feasible region of the maneuver coefficient is investigated for each vehicle. The wide region demonstrates that the proposed planning algorithm is applicable and insensitive to estimation errors of the maneuver coefficient.

Onboard longitudinal trajectory planning for terminal area energy management of reusable launch vehicles

An onboard trajectory planning algorithm is presented in this paper for the terminal area energy management (TAEM) phase of a reusable launch vehicle (RLV). To satisfy the multiple constraints in the TAEM phase, a profile in the flight-path angle vs. range-to-go space is planned. The optimization of this flight-path angle profile is described as a one-parameter search problem and solved by the Newton iteration method. With the optimized flight-path angle profile, a satisfied longitudinal flight trajectory is generated based on the flight dynamics. Testing for the trajectory planning algorithm is performed in missions with different terminal flight-path angle constraints. The onboard algorithm is indicated effective to generate a constrained longitudinal flight trajectory in 0.5 seconds on a PC. The Monte Carlo simulations are employed in dispersed cases, and the planning algorithm is shown robust in trajectory generation with large initial condition errors of the TAEM phase.

Modeling method for gliding reentry vehicle via model migration

The development of gliding reentry vehicle is a process of small-batch and multi-batch. In order to reduce the cost of experiments and shorten the cycle of modeling of gliding reentry vehicles with similar shapes, the new method based on model migration is presented in this paper. Specifically, a method of assessing the similarity degree of the gliding reentry vehicles is explained; whether the model migration theory can be applied in the vehicle modeling depends on the degree. The aerodynamic coefficients of the base gliding reentry vehicle are partitioned by the linearity of itself, and the cluster centers of the intervals are obtained. The migration equations are given through the analysis of the relation of the cluster centers of aerodynamic coefficients of the base vehicle to the ones of the new vehicle. The advantage of the new method is verified by the simulation.

Fault-tolerant reconfigurable control for reusable launch vehicle using NESO

Reusable launch vehicle (RLV) has multiple different kinds of control effectors. These redundant effectors provide RLV the potential to maintain acceptable stability and performance even when some of them get failures. Proper control allocation and re-allocation after control effectors failure are necessary for RLV. A new fault-tolerant reconfigurable controller integrating control allocation is proposed in this paper. The new controller contains two parts: the basic controller and the compensated controller. The basic controller is designed to guarantee high performance without thinking the disturbances of the RLV. Nonlinear extended state observer (NESO) is used to estimate the disturbances. The compensated control uses the estimation to build the compensation command and eliminate the influence of disturbances. Control allocation is used to distribute the virtual control command to aerodynamic control effectors and reaction control system. After the fault is located, the re-allocation will be conducted to use the healthy control effectors to compensate the failed ones. Simulation results show that the proposed controller could achieve satisfactory performance dealing with the disturbances and control effector failures.

Trajectory tracking for RLV terminal area energy management phase based on LQR

A new longitudinal trajectory tracking law for the Terminal Area Energy Management (TAEM) phase of the Reusable Launch Vehicle (RLV) is presented in this paper. The conventional PID method controls the height and the velocity by the angle of attack and the angle of airbrake respectively, and no coupling is considered. To improve the tracking precision, the new tracking law is designed based on the linear quadratic regulator (LQR) theory where the coupling is taken into account. Finally, the trajectory tracking law based on the LQR is simulated and compared with the conventional method. Simulation results indicate the effectiveness and the robustness of the new tracking law.

Optimal bank reversal for high-lifting reentry vehicles

For high-lifting reentry vehicles, large tracking errors appear during the process of bank reversals, especially when the angular rate of the bank angle is low. An optimal bank reversal (OBR) approach is proposed in this paper mainly to solve this problem. The conventional bank reversal (CBR) which would cause large altitude tracking errors is simulated and analyzed on the high-lifting common aero vehicle (CAV) model. To minimize the tracking error during the bank reversal, a pre-control phase is added in the bank reversal process. This new OBR is designed based on the numerical trajectory prediction, and solved as a two-parameters optimization problem. Finally, in both nominal and dispersion cases, the CBR and the OBR approaches are simulated and compared. The proposed OBR approach is shown to own smaller altitude tracking errors during bank reversals, higher guidance precision for the terminal condition, and also good real-time performance.