Research Of Mars Probe Navigation And Control Methods

The goal of Chinese first Mars exploration mission in 2020 is to orbit,land and patrol.The probe arrived at Mars after a flight of 6.5 months,undergoing the Earth-Mars transfer,the mid-course correction and the deep space maneuver.The braking capture is carried out when it reaches the near-Mars point,and its hyperbolic orbit becomes an ellipsoid with respect to the Mars.After an entry,descent and landing process,the lander rover will make a soft landing and carry out 3-month inspecting detection.Besides,the orbiter will carry out the relay and remote sensing exploration for about two years.Focusing on the vital navigation and control technologies of the Mars probe,the main research results are summarized as follows.1.According to the high precise dynamical modes,the long-term orbit evolution is analyzed on the influence of the gravitational field of Mars spherical perturbation.And the short-term,long-period and long-term effects of all kinds of perturbation on the probe’s orbit are depicted.Thus,the time and space model has been established for the navigation design.As to the optimized selection of control strategies,the particle swarm optimization is utilized to analyze the capture control strategies under the conditions of different attitude benchmarks and describe the capture control errors under the condition of different engine shutdown times.Thus,the design basis of the capture control strategies has been established.2.According to the high-precise dynamical model in the Earth-Mars transfer stage,the launch window design method is proposed based on the conic stitching.According to the constraints of exploration objects,mission objectives,window characteristics and carrying capacity,the launch window parameters in July 2020 are verified,and the optimal three-pulse parameters for deep space maneuvering are obtained.Meanwhile,five sets of orbit control strategies in the approaching-Mars stage are optimized,and the orbit deviation under different execution errors during the inclination control is calculated.Under the nominal launch window conditions,the asteroids that may rendezvous with the probe are searched and listed day by day.3.As the autonomous orbit prediction in different flight stages,the Chebyshev polynomial fitting and harmonic decomposition of on-board real-time orbit recursive calculation methods are studied.The simulation results show the optimality of Chebyshev polynomial in the orbit fitting effects.Considering the characteristics of orbit perturbation,the real-time orbit recursive method of harmonic decomposition is more suitable for orbit with high eccentricities.The Chebyshev polynomial piecewise fitting method,with less calculation costs and fitting errors less than 10km is suitable for real-time recursive calculation in the Earth-Mars transfer stage.4.For the cooperative navigation,the principles of precise orbit determination,the observation model of autonomous orbit determination and the initial orbit determination are presented respectively.Thus,the cooperative navigation under the conditions of the optimal estimation error covariance feedback coefficient is given.It is verified that the cooperative navigation has double advantages of high precision respectively in short and long arc.As the optical autonomous navigation precision is limited by the different choice of three goals,the continuous and stable one-way Doppler measurement between the observation site on the Earth and the Mars probe is utilized to form a new integrated navigation scheme.The autonomous navigation precision is significantly higher than that of pure optical navigation,which provides a useful reference for the design of the integrated navigation scheme.5.According to the two-way range and velocity measurements,and VLBI measurements,the orbit calculation in the Earth-Mars transfer stage is finished.(1)It breaks through the deep space measurement fusion,establishes the average distance change rate model considering the correction of the uplink carrier frequency deviation,and refines the spatial error correction models such as atmospheric refraction,zero value and clock difference of deep space ranging.(2)A precise time and space framework is constructed,and the Pathfinder orientation parameter model is implemented.Considering the effects of the precession and nutation,the high-precision transformation of Mars fixed coordinate system is realized.(3)The orbital dynamics model is refined to establish the non-spherical gravitational perturbation and the Mars satellite gravitational perturbation model.(4)The precise solar measurement model is established,which improves the calculation accuracy of time and distance parameters,increases the gravitational delay correction of general relativity,optimizes the tropospheric correction model of velocity measurements,and realizes the accurate calculation of theoretical observations such as range/velocity/VLBI measurements under the condition of large delay.