Research On Capture And Braking Of Mars Probe

Deep space exploration has been one of hot topics for aerospace powers in the 21 st century.Due to its shorter distance and many similarities to Earth,Mars became one of the primary targets.China will also launch its own Mars probe around 2020.Capture and brake are key techniques for mission success.This paper aims to deal with problems regarding capture strategy,error propagation,fault preplan,aerobraking.The main research results are as follows.1.Establishing the dynamical model for Mars capture and braking.In order to describe probe's dynamical model,time and space systems are introduced and calculation of ephemeris is derived.The force imposed on probe includes Mars nonspherical gravity,third body gravity such as Sun and Mars satellites and atmospheric resistance.2.To solve the capture and brake problem of Mars probe,this paper establishes the model of finite-thrust,involving three different strategies.Multi-objective particle swarm optimization algorithm is used to minimize both fuel consumption and periapsis distance error,and method of uniform design is applied to initialize particle populations.After simulation,Pareto-optimal set and Pareto front are obtained.It's indicated that capture strategy of fixed-direction thrust produced smaller periapsis distance error,whereas capture process where thrust direction is anti-parallel to velocity saves more fuel due to less gravity loss.Periapsis height is increased for strategy with constant rotation rate of thrust,and fuel consumption is moderate because of small angle between thrust direction and reverse direction of velocity vector.The idea of two optimized objectives can provide more comprehensive decision-making information than single objective of fuel consumption.3.Error propagation analysis of capture for Mars exploration is an important issue to be considered,which has a direct impact on the success of the task.In terms of three different capture strategies,considering many sources of error such as the initial state error,model error,execution error,applying Covariance Analysis Describing Equation Technique(CADET)to establish propagation equations of states' mean and standard deviation value.When simulating the whole capture process,considering one simulation error each time and combined errors at last,and results of CADET are compared with Monte Carlo method.It shows that CADET can yield high-precision results along with lower computation cost,demonstrating its better engineering application value,which can serve as a reference for the implementation plan of orbit capturing phase of Chinese incoming Mars exploration.4.To minimize fuel cost and maximize payload,aerobraking is used to transfer the probe from elliptic orbit to target orbit.Regarding the allowable maximum dynamic pressure at periapsis as the constraint,minimum height where periapsis should hold is obtained via Newton iteration.An aerobraking plan is proposed,where periapsis is lifted to a safe altitude via increasing velocity at the apoapsis.The last entry angle is optimized to ensure that the final apoapsis height is met.The simulation shows the validity of proposed plan and maximum dynamic pressure during the aerobraking process is satisfied.To sum up,this thesis analyses key problems regarding capture and braking of Mars probe,maximizing fuel cost and increasing the success rate,which can provide significant reference for Mars exploration mission.