Trajectory Optimization And Guidance Of Deep Space Exploration Reentry

The reentry of the deep space exploration capsule is a critial step ofhuman-rated deep space travel. It directly determines whether the spacecraft andastronauts could land on touch-down zone safely. Due to the characteristics of thisprocess such as giant energy, strictly constraint conditions and difficulty to recycleetc, the main work of this thesis is focused on the trajectory optimization and preciseguidance.First, based on a few simple hypotheses, the spacecraft’s motion equations inthe reentry coordinate system are established according to the Newton’s Second Law.To facilitate numerical simulation, the motion equations are transformed intodimensionless form, which also provides the basis for the research in the sequel. Astrategy is proposed for the reentry of deep space exploration vehicle.Second, according to the simulation of the reentry process, the optimization isfocused on the first segment of reentry process. Further analysis indicates that theoptimization could be focused on the longitudinal profile. Dynamic constraintconditions are changed into static terminal constraint conditions, then a SequentialWeight-Increasing Factor Technique (SWIFT) is used in static constrainedoptimization, and simulation of optimal planning is made on a simplified model.For the standard guidance law for the first segment of reentry process, a newmethod is presented to determine the landing point of standard trajectory. Thismethod helps to design the standard trajectory in longitudinal profile and lateralprofile completely independently, which could bring some convenience in trajectorydesign. The gain coefficients of standard gudiance are determined by setting out alinear quadratic optimal performance index and then solving Riccati equation.During the simulation experiment with initial errors, it’s found that the effect ofguidance is not good enough. So we make some improvement on the guidance lawand reach satisfactory results in the simulation for the same conditions.Finally, according to characteristics of the second segment, apredicator-corrector guidance law is presented and simulated. After further analysisof the scheme of reentry, the simulation is conducted for the whole process.