Research On Reentry Guidance Method For Reusable Launch Vehicle

Reusable Launch Vehicle(RLV) is a main development trend of space transportation system, the initial reentry segment is the first phase of the whole entry process with an extremely complex flight environment, RLV in this phase encounters severe flight constraints which threaten the flight safety, at the same time RLV needs to complete the mission meeting all the requirements, these demand highly for the safety and reliability of the reentry guidance. In this paper, the nominal trajectory design and the guidance law are discussed.In this paper, a motion model of three-degrees-freedom is presented to describe the motion of RLV in reentry segment. The lift-to-drag ratio and balance ability are analyzed due to the aerodynamic layout of RLV, making the basis for the design of nominal trajectory and the guidance law.In this paper, the angle of attack profile is planned according to its affects to overall constraints. The initial flightpath angle-velocity range is determined by the influence on the reentry flight safety. In order to ensure the safety of the reentry flight, the reentry corridor is formed in the drag acceleration-velocity profile to describe overall constraints, the influence of uncertainty on reentry corridor is also analyzed. Finally, a segmented design method is adopted to define the nominal trajectory due to the reentry flight mission. Then, a complete nominal trajectory design method is formed. Finally, the validity and the robustness of the nominal trajectory are proved through the simulation.In this paper, the reentry guidance is divided into longitudinal guidance and lateral guidance because of the characteristics of reentry flight. The nominal trajectory is tracked by controlling the size of the bank angle, which ensure the safety of reentry and achieve the goal of longitudinal guidance. And a series of bank angle reversals is controlled to cover the azimuth requirement of the terminal area energy management phase. However sometimes this goal cannot be achieved due to uncertainties. The range correction scheme is designed to solve this problem, the nominal trajectory is updated with real-time feedback according to distance deviation. The simulation results show the range correction scheme and the reentry guidance strategy are correct and robust.