Optimal Trajectory Design And Characteristics Analysis For Manned Lunar Landing Mission With Emergency Return Capability

Manned lunar landing mission is a complicated system project charactered withadvanced technologies. During the manned lunar landing mission, the safety ofastronaut must be taken into account for missiondesign, due to the mission’s high risks.It should be ensured that the astronauts are able to abort the mission and return back tothe Earth at any time, when an emergency occurs. Taking the manned lunar missiontrajectory with emergency return capabilities as the research object, this dissertationmainly studies the emergency constraints analysis, orbit modeling and optimizationdesign, orbital characteristics analysis and so on. The main researches and results aresummarized as follows.The emergency conditions for manned lunar trajectory design are analyzed,and the trajectory optimization models with abort constraints are formulated. Thetrajectory for manned lunar mission is divided into several stages, then the abort modesafter the failed mission in different stage are researched and the trajectory plansconsidering emergency return capabilities are proposed. For the translunar and lunarlanding trajectories, which are effected greatly by emergency return conditions, theconstraints for trajectories design caused by mission abort are analyzed thoroughly. Byselecting the reasonable design variables and optimization objects, the manned lunarmission trajectory optimization models satisfying the emergency return constraints areestablished. So the trajectory design problem is transformed into one kind ofoptimization problem.By combining analytical method with numerical method, a serial trajectorydesign strategy from initial value design to precision solution is proposed, and thetranslunar trajectory satisfying the emergency constraints is designed. Firstly, threetranslunar trajectory modes consisting of free return trajectory strategy, midcoursemaneuver strategy and terminal maneuver strategy both based on free return trajectoryare given. Furthermore, the analytical model using patched-conic method and numericalmodel considering with various perturbations are established for the translunartrajectories. In terms of two mathematic models’ characteristics, a serial optimizationstrategy from initial value design to high accuracy solution is put forward, and thetranslunar trajectory parameters satisfying emergency return conditions are obtained.A rapid trajectory optimization approach for manned lunar landing usingGauss Pseudospectral Method (GPM) is developed. A three dimensional descentdynamics equation is derived. And an optimization design model for powered descenttrajectory with abort conditions is formulated. Considering the limitations of traditionaltrajectory optimization methods in initial guess determination and computationefficiency, a rapid trajectory optimization approach based on GPM, containing an initial guess generator, is proposed. Moreover, the validity, optimality and robustness of thismethod are validated. Finally, the trajectory parameters and control variables of lunarlanding mission are calculated by employing the proposed optimization method.A hybrid optimization method combining GPM and shooting method isproposed, and the optimal lunar e mergency ascent and rendezvous trajectory isdesigned. Firstly, the lunar emergency ascent and rendezvous trajectory is divided intotwo stages: emergency ascent stage and emergency rendezvous stage. Trajectory designmodels of both stages are established, and are optimized by the GPM and differentialevolution algorithm respectively. Furthermore the two stages of the trajectory arecombined, thus constructing a multistage nonlinear programming model with strictconstraints. And a hybrid optimization strategy combining GPM and shooting method isdesigned to obtain the optimal solution of the ascent and rendezvous trajectoryparameters satisfying the emergency constraints.With the background of strict requirements of manned lunar safety, thisdissertation successfully applies optimization methods to the trajectory design formanned lunar landing mission. In terms of the theoretical studies, many characteristicparameters, including the accessible range of lunar landing sites and fuel consumption,etc., are analyzed, which have some theoretical significance and application value forChina’s future manned lunar landing mission.