Application Of Celestial Body Flyby In Deep Space Exploration

Beginning with the exploration of the moon,deep space exploration starts in the middle of last century.Since then all the planets and some of their moons have been visited.Different from the lunar exploration,the distance from the earth most targets in deep space exploration is very large,which means long time of flight and huge consumption of fuel.When designing transfer trajectories to the moon,we can use two impulses transfer strategy to make the direct transfer.In the interplanetary space,however,while this method can still be used in the exploration of Mars or Venus,generally it cannot be used for other planets as the fuel consumption exceeds the ability of launch vehicles.One viable manner is to make use of the flyby of some celestial bodies to accelerate the probe,namely the gravity assist technology.Compared with traditional trajectory,the trajectory with planetary gravity assists saves both fuel and time considerably.It keeps the fuel consumption in a low level therefore makes some missions possible,so the importance of this technology is self-evident.With the background of deep space exploration and the theme of celestial body gravity assists,this paper studies the issues of gravity assist trajectory in the interplanetary space and lunar swing by trajectory in the Sun-Earth-Moon system.For gravity assist trajectory design in the interplanetary space,we should determine the sequence of gravity assists at first.A graphic method which can determine the sequence from the standpoint of energy and give all the possible sequences is studied.Then based on the patched conic method,each segment can be solved separately.Restricting the range of their transfer time,the optimization algorithm can search for the trajectory with minimum fuel consumption.Then the maximum reflection angle criteria is checked later.Once the judgement was passed through it would be a feasible result.This method can determine the trajectory from the Earth to Jupiter or Saturn effectively;For the lunar swing by trajectory in the Sun-Earth-Moon system,the manned lunar exploration trajectory,namely cis-lunar free return trajectory,is studied first with a new algorithm.The result is very well.Then we apply this trajectory for saving energy in geostationary satellites launching missions.Studies show that it can save much energy when the inclination angle of geostationary transfer orbit is high.At last,double lunar swing by trajectory which can keep the orientation of the line of apsides in the Sun-Earth line orientation,which is useful in the continuous study of the earth's magnetotail is studied.This trajectory is another application of the patched conic method,but more meticulous and complex.The major innovations of the thesis are as follows:1.Based on the Earth to Mars transfer trajectory design with bidirectional patching,an innovative midway trajectory correction method,which differs from correction method based on the B plane greatly,is proposed.This method integrates backwards from the target to the probe;2.In the earth to the moon transfer trajectory design,previous initial guess of the hyperbolic orbit around the moon is complex and unsolvable sometimes using the method based on the velocity difference at the influence sphere boundary of the moon,a new initialization method is proposed in this paper and it can reduce the process and avoid unsolvable situation;3.Proposing a way to solve the multiple gravity assist trajectory in the interplanetary space based on the differential evolution algorithm,the algorithm is lean,efficient and easy to converge.The optimal trajectory can be found rapidly through only a few loops.So it's a very good method to design preliminary transfer trajectories;4.The method of cis-lunar free return trajectory design is enriched.A new way based on the one-way integration is proposed to search for the free return trajectories with a fixed perilune height,with no middle patch point requirement.The method has a strong constraint condition,analyzes influence factors completely,it has certain reference value to the trajectory design of manned lunar explorations.