Direct- and indirect-solar-radiation effects acting on LAGEOS and the gravitomagnetic experiment

The LAGEOS tracking data show that the residuals on the along-track acceleration have a secular drag of about −3.4·10−122}m/s2 and signatures whose periods are represented by linear combinations of the longitude of the LAGEOS node and of the Sun. Thermal thrust due to the Earth’s infra-red radiation (Rubincam effect), charged- and neutral-particle drag seem to explain the overall secular drag. The Yarkovsky-Schach effect due to the solar heating is a probable mechanism able to explain the signatures occurring together with the Earth’s and LAGEOS anisotropic optical properties. The paper has been focused to correct and improve the Yarkovsky-Schach model. In particular the approximation, as made in the old model, that the eclipse intersection is the same for two orbits on end is not applicable. Furthermore, the effects induced by the atmosphere and by the disklike Sun on the solar radiation have been considered and discussed. It turns out that the sensitivity of the Yarkovsky-Schach model to the corrections discussed is of about 20%. Finally, a brief review and discussion are given about the non-conservative effects (thermal thrust and solar-radiation pressure) and how they affect the detection of the Lense-Thirring gravitomagnetic effect by using a twin-LAGEOS satellite injected in an orbit of supplementary inclination.