DIRECT-SOLAR-RADIATION AND INDIRECT-SOLAR-RADIATION EFFECTS ACTING ONLAGEOS AND THE GRAVITOMAGNETIC EXPERIMENT

The LAGEOS tracking data show that the residuals on the along-track ac celeration have a secular drag of about -3.4.10(-12) m/s2 and signatur es whose periods are represented by linear combinations of the longitu de 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 e ffect due to the solar heating is a probable mechanism able to explain the signatures occurring together with the Earth's and LAGEOS anisotr opic optical properties. The paper has been focused to correct and imp rove the Yarkovsky-Schach model. In particular the approximation, as m ade in the old model, that the eclipse intersection is the same for tw o orbits on end is not applicable. Furthermore, the effects induced by the atmosphere and by the disklike Sun on the solar radiation have be en considered and discussed. It turns out that the sensitivity of the Yarkovsky-Schach model to the corrections discussed is of about 20%. F inally, a brief review and discussion are given about the non-conserva tive effects (thermal thrust and solar-radiation pressure) and how the y affect the detection of the Lense-Thirring gravitomagnetic effect by using a twin-LAGEOS satellite injected in an orbit of supplementary i nclination.