A comparative assessment of gravitational field modeling methods for binary asteroid landing

The tradeoff between accuracy and efficiency in gravitational field modeling for binary asteroid landing is one of the challenges in dynamical analyses.Four representative gravitational modeling methods are employed and compared in this study.These are the sphere-sphere model,ellipsoid-sphere model,inertia integral-polyhedron method,and finite element method.This study considers the differences between these four models,particularly their effects on the landing dynamics of a lander.A framework to simulate the coupled orbit-attitude motion of a lander in a binary system is first established.Numerical simulations are then performed on the natural landings on the second primary of the(66391)Moshup-Squannit system.The results show significant differences in the final landing dispersions,settling time,and sliding distance when applying the simplified models.On the basis of the modeling accuracy and computational efficiency,the finite element method should be chosen for future missions.

Construction of Earth's gravitational field model from CHAMP,GRACE and GOCE data

The basic principle of spectral combination method is discussed,and the general expressions of the spectral weight and spectral combination of the united-processing of various types of gravimetric data are shown.What＇s more,based on degree error RMS of potential coefficients,the detailed expressions of spectral combination formulae and the corresponding spectral weights in the Earth＇s gravitational field model（EGM） determination using GOCE ＋ GRACE and CHAMP ＋ GRACE ＋ GOCE are derived.The fundamental situation that ulux-champ2013 s,tongji-GRACE01,go-cons-gcf-2-tim-r5 constructed respectively by CHAMP,GRACE,GOCE data and go-cons-gcf-2-dir-r5 constructed by syncretic processing of GRACE,GOCE and LAGEOS data are explained briefly,the degree error RMS,cumulative geoid height error and cumulative gravity anomaly error of these models are calculated.A syncretic model constructed from CHAMP,GRACE and GOCE data,which is expressed by champ ＋ grace ＋ goce,is obtained based on spectral combination method.Experimentation results show that the precision of CHAMP data model is the lowest in satellite-only models,so it is not needed in the determination of syncretic models.The GRACE data model can improve the GOCE data model in medium-long wavelength,so the overall precision of syncretic model can be improved.Consequently,as many types of gravimetric data as possible should be combined together in the data processing in order to strengthen the quality and reliability with widening scope and improve the precision and spatial resolution of the computational results.

The Spherically-Symmetric Pressure Free Collapse of the White-Black Hole

The vector model for gravitational field is a modified theory of gravitational field. In this model, the gravitational field is a vector field and its source is the gravitational mass of matter. This model predicts the existence of a new universal object after the black hole disappeared. It is named the white-black hole （or white hole） in the vector model for the gravitational field. The white- black hole has many interesting properties different from that of black hole in Einstein＇s theory of gravity. This paper presents an investigation of the spherically-symmetric pressure free collapse of a white-black hole in the vector model for gravitational field from the point of view of an observer at infinity and on its surface. The obtained results have many interesting differences compared with that in the spherically-symmetric pressure free collapse of black holes. In addition, the metric of space-time of the white-black hole in modified Eddington-Finkelstein coordinates and modified Kruskal-Szekeres coordinates are found.