Research On Guidance Algorithms Of Ascent And Rendezvous For Mars Sample Return

Mars Ascent Vehicle(MAV)design is closely related to trajectory design.However,the existing method mostly decoupled the staging optimization and trajectory optimization,resulting in computational inefficiency.A method of coupled staging-trajectory optimization with initial value generator is proposed in this paper for two-stage MAV design.The method consists of two parts as follow.The first is the staging optimization initial analytic algorithm for two-stage MAV.Ascent trajectory can be modeled as Hohmann-transfer-liked process with velocity loss estimations for drag,steering and gravity,and the resulting MAV staging design is used as the initial guess for the coupled staging-trajectory optimizer.The second is the coupled staging-trajectory multiphase optimization algorithm.Considering given vehicle,mission,path and control constraints,the objective of the optimization algorithm is to minimize the Gross Liftoff Mass(GLOM)of two-stage MAV,and the algorithm is based on Gauss Pseudospectral OPtimization Software(GPOPS-II).In addition,numerical simulations show that the error of GLOM in staging optimization initial analytic algorithm is within 1%,and taking this staging optimization initial result as the initial value of the coupled staging-trajectory multiphase optimization algorithm can increase the convergence rate by an order of magnitude.For Mars Sample Return Mission in the future,the Apollo derived ascent guidance algorithm,used for two stages solid rocket Mars Ascent Vehicle(MAV),ignore the atmosphere of Mars,and a noticeable deterioration in performance is presented when attitude control constraints are introduced.This paper presents an improved Apollo derived ascent guidance algorithm.An analytic estimator of velocity change due to atmosphere drag is applied to in-plane trajectory tracking control law,which will improve the precision of apogee altitude of ascent orbit.Meanwhile,insteading of time,velocity is used as the independent variable of out-of-plane control law,which result in the modification of orbit inclination tracking.In addition,numerical simulations show that the improved Apollo derived ascent guidance algorithm can significantly enhance guidance performance and narrow the orbit error of Orbiting Sample,which can make it easier to the Mars orbital rendezvous.Based on the theory of relative motion,this paper proposes the Mars intermediate guidance algorithm.The mechanism of this algorithm is that treating the original and modified trajectories as chief and deputy space objects respectively,establishing relative motion model and solving the correction speed by terminal relative state.Intermediate phase of Mars rendezvous has longer flight time and larger correction speed,resulting in the original J2 STM guidance method error is too large and the original method cann't be applied directly.A improved J2 STM guidance method is proposed,which based on the modified trajectory obtained by the lambert method,then solving the initial correction speed by original J2 STM method.In addition,numerical simulation show that the Mars intermediate guidance algorithm can significantly improve the guidance accuracy,and its compute efficiency is good.