Research On The Orbit Determination And Parameters Solution Of Small Body Based On Astrometric Observations

In this paper,we systematically carry out a study on the orbit determination and parameters solution of small body based on astrometric observations,taking China first asteroid detection mission as a guide.Generally speaking,the ephemeris of asteroids is an important basis for asteroid detection mission planning and orbit designing.A high-precision ephemeris can ensure that the probe accurately enter the gravitational influence zone of the target object and perform such difficult operations as companion flight,orbit and soft landing on the target asteroid.Therefore,based on historical astronomical tracking data,we have calculated the precise numerical ephemeris of target objects for those asteroid detection mission.The work of this thesis are as following:（1）We have got the precise numerical ephemeris of near-Earth asteroid 2016HO3and main-belt active asteroid 311P.The differences between the obtained integral numerical orbit and the reference ephemeris from JPL are less than the precision of astronomical observation.By combining with the analysis of simulation orbit determination experiment,we explore the impact of different noise levels on the orbit determination precision of the optical simulation observations of main-belt asteroids,providing some references for China asteroid detection missions.（2）We aim to report integrated orbital fits for Triton based on all the available astrometric data from 1847 to 2020,including observations from Earth-based telescopes,Voyager 2,and the Hubble Space Telescope.We also estimate the Neptunian gravity using the motion of Triton.In our results,our new orbit model of Triton was well determined,with the deviations from NEP081 and NEP097 being less than 300km（about 15 mas）during the observation coverage period.The formal uncertainty of Triton’s position at initial epoch was reduced to about 3 km.（3）For natural satellites with long-time optical astrometric observations,we explore the possibility of astrometric data to solve the central celestial low-order gravity field.We also determined the gravitational field parameters of Neptune.The fitted GMs for Neptune are GMs=6836525.210±19.526 km³s^-2.The revised gravity model yielded J2=3401.655±1.850×10^-6,J4=33.294±10.000×10^-6.The astrometric observations showed little sensitivity to GMs and J4,but acted well on J2.Our analysis of the error due to a variation in the pole parameters using the Monte Carlo method showed that J2=3401.655±3.994×10^-6 is a more realistic error based on the published pole formal errors.