Towards a 1% measurement of frame drag- ging with LARES?

After the recent approval by the Italian Space Agency (ASI) of the LARES mission, which will be launched at the end of 2008 by a VEGA rocket to measure the general relativistic gravitomagnetic Lense-Thirring effect by combining LARES data with those of the existing LAGEOS and LAGEOS II satellites, it is of the utmost importance to assess if the claimed accuracy . 1% will be realistically obtainable. A major source of systematic error is the mismodelling δJ` in the static part of the even zonal harmonic coefficients J`, ` = 2, 4, 6, .. of the multipolar expansion of the classical part of the terrestrial gravitational potential; such a bias crucially depends on the orbital configuration of LARES. If for δJ` the difference between the best estimates of different Earth’s gravity solutions from the dedicated CHAMP and GRACE missions is conservatively taken instead of optimistically considering the statistical covariance sigmas of each model separately, as done so far in literature, it turns out that, since LARES will be likely launched in a low-orbit (semimajor axis a . 7600 km), the bias due to the geopotential is up to 1 order of magnitude larger than what claimed, according to a calculation up to degree ` = 20. Should a nearly polar configuration (inclination to the Earth’s equator i ≈ 90 deg) be finally implemented, also other perturbations would come into play, further corrupting the measurement of the Lense-Thirring effect.