Reassessment of the error modelling of non-gravitational perturbations on LAGEOS II and their impact in the Lense ?Thirring derivation ? Part II

We have studied LAGEOS II perturbative effects due to thermal thrust radiation and due to the asymmetric refectivity of the satellite hemispheres.In particular,the perturbations due to the so-called Earth-Yarkovsky effect and Yarkovsky –Schach effect have been analysed —together with the Asymmetric Refectivity effect —in the satellite eccentricity vector excitations,argument of perigee rate and also in its node and inclination excitations.A realistic simulation of these e ects via a numerical integration of LAGEOS II for a time span of about 7 yr has confirmed the validity of our analytical models,providing additional important information on the actual behaviour of the satellite in the presence of these perturbations.The agreement between the numerical results —as for the Fourier analysis in the analysed elements —and the real data (e.g.,the orbital elements residuals)is quite good.The analysis of LAGEOS II orbital residuals —over a 4.7-yr period —has allowed us to estimate the Yarkovsky –Schach parameters,as well as the parameter of its asymmetric reflectivity effect.In comparison with previous results for these parameters in the case of LAGEOS,our values are close to those of Slabinski (Cel.Mech.66 (1997)131)and about a factor of 2 smaller than those of Metris et al.(J.Geophys.Res.102 (B2)(1997)2711)with regard to the Yarkovsky –Schach effect,while the value obtained for the asymmetric reflectivity parameter is close to that of Scharroo et al.(J.Geophys.Res.96 (1991)729).We have veri ed that,similar to what happens for the effects of the visible radiation,also in the case of thermal thrust eclipses modelling is more important for the node and inclination excitations than it is for the eccentricity excitations or perigee rate e ects.We nally give our conclusions on the use of LAGEOS II perigee and node for General Relativistic studies.In particular,we confirm their use for geometrodynamics tests in the Earth ’s surroundings,as in the case of the Lense–Thirring effect derivation.