A critical approach to the concept of a polar, low–altitude LARES satellite

According to very recent developments of the LARES mission, which would be devoted to the measurement of the general relativistic Lense–Thirring effect in the gravitational field of the Earth with Satellite Laser Ranging, it seems that the LARES satellite might be finally launched in a polar, low– altitude orbit by means of a relatively low–cost rocket. The observable would be the node only. The Lense–Thirring effect on it would consist of a secular linear trend. The biasing classical secular nodal precessions due to the even zonal harmonics of the geopotential, which represent the major source of uncertainty, exactly vanished if and only if the orbit would be exactly polar. Due to the small altitude, even small possible deviations from the projected inclination, which might be induced by the orbital injection errors, would yield a rather large systematic error due to the even zonal harmonics of geopotential in the measurement of the relativistic nodal shift. So, in this paper we show how such a configuration, in fact, to the present level of knowledge of the terrestrial gravitational field according to the EGM96 gravity model, should be of relatively little utility in increasing the obtainable accuracy in measuring the Lense–Thirring effect with respect not only to the originally proposed supplementary LARES–LAGEOS configuration, but also to the present LAGEOS–LAGEOS II experiment which has a total accuracy of the order of 20% − 30%. Maybe the situation might be improved, at least to a certain extent, when the new, more accurate Earth gravity models from the CHAMP and GRACE missions will be available.