0 40 40 62 v 1 1 3 A pr 2 00 4 On the possibility of determining the Lense – Thirring effect to an accuracy of a few percent using Jason – 1

In this paper we show that by suitably combining the nodes Ω of the existing geodetic LAGEOS, LAGEOS II and Ajisai SLR satellites and of the radar altimeter Jason–1 satellite it would be possible to measure the general relativistic gravitomagnetic Lense–Thirring effect in the gravitational field of the Earth with a high accuracy and reliability. The proposal of introducing Jason–1 in such a combination comes from the fact that its orbit can be determined to the level of 1–cm (in the radial direction). This is of the same order of magnitude as that of the spherical SLR geodetic satellites. According to the recently released GGM01S GRACE–only Earth gravity model, the impact of the mismodelled even zonal harmonics of geopotential, which represent the major source of systematic error, amounts to 2.6%. This result will be further improved by the forthcoming new GRACE Earth gravity models. The non– gravitational perturbations on the geodetic satellites have very little impact because only the nodes would be analyzed. Moreover, a major role would be played by LAGEOS and, to a lesser extent, LAGEOS II because the coefficient of Ajisai's node is of the order of 10 −3. However, a major concern would be the assessment of the impact of the non–conservative accelerations on the Jason–1 node, even though it enters the combination with a coefficient of the order of only 10 −2. According to the present–day force models, the mismodelling in the non–conservative forces would, at worst, induce an aliasing signal with an amplitude of 4% of the Lense-Thirring effect over a time span of 2 years. However, an observational time span of just a few years could safely be adopted in order to fit and remove the residual long–period non–gravitational signals affecting Jason's node, which, in the case of the direct solar radiation pressure, have a main periodicity of approximately 120 days.