Research Of Guidance And Control Technologies For Reusable Launch Vehicle Sub-orbital Ascent Flight

Reusable launch vehicle (RLV) sub-orbital flight is an important part of RLV demonstration, advanced guidance and control is one of the key technologies to carry out RLV demonstration. RLV launched at low altitude, and ultimately achieved height of 75km, Mach 6. The flight envelope is large, having strong flying constraints, atmospheric density and fly motion states change quickly in flight process, aerodynamic characteristics is complex and uncertainties are high, all above bring a great challenge to guidance and control system design. Around this problem, this paper will address the ascent trajectory optimization, guidance law, control law and allocation design.The nonlinear and multi-constraint features make ascending trajectory optimization difficult to solve. So a strategy for trajectory design based on pitch angle (power climbing) and attack angle (unpower climbing) is proposed, it simplifies the design parameters and has a strong physical concepts. In the trajectory parameters optimization, an optimization framework based on particle swarm optimization algorithm is built, convergence speed is fast, final altitude and velocity of the trajectory meet the mission requirements well, satisfying the dynamic pressure, overload and thermal constraints.Trajectory tracking in sub-orbital flight should be where the engine and aerodynamic have ability to change the trajectory state, proposing a new guidance problem, so in this paper, feedback linearization techniques is used for the nominal altitude tracking, the difficult of the non-linear relationship between the altitude and attitude tracking is solved, and the end altitude within allowed deviation is guaranteed. By feedback linearization technique, the tracking guidance law can be designed by linear system theory, easily for engineering realization.In the control law design, in order to improve the RLV strongly nonlinear attitude tracking capabilities and the robustness of the control system, a control system structure based on trajectory linearization is involved. This structure consists of forward and feedback control law, forward control law is to provide forward control torque which can improve the system dynamic fast-track performance, the state feedback control provides bias torque control system to ensure the stability and robustness. In the feedback control system robust validation, this paper uses a less conservative analysis ofμ, by which the control system stability margin is analyzed, and RLV model parameters under the robust perturbation are also assessed.For the diversity and complexity of control mechanism in the control allocation, this paper presents a mixed programming method. According to their own characteristics, the aerodynamic control surfaces and reaction control system (RCS) control allocation is used by different strategies to achieve optimal control output. The mixed programming allocation makes the control torque tracked well, and provides a coordinate work of control mechanisms with different characteristics.Finally, this paper has set up a simulation platform for RLV carried out a sub-orbital ascent flight of the whole non-linear process. Simulation results show that the guidance and control strategy are rational and correct, and a monte-carlo simulation verifies the guidance and control system robustness for the RLV's uncertainty of aerodynamic, quality, and thrust.