  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 \lesssim 1% will be
realistically obtainable. A major source of systematic error is the
mismodelling \delta J_L in the static part of the even zonal harmonic
coefficients J_L, L=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 \delta J_L the difference between
the best estimates of different Earth's gravity solutions from the dedicated
GRACE mission 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\lesssim 7600 km), the bias due to the geopotential
may be up to ten times larger than what claimed, according to a calculation up
to degree L=20. Taking into account also the even zonal harmonics with L>20, as
required by the relatively low altitude of LARES, may further degrade the total
accuracy. Should a nearly polar configuration (inclination to the Earth's
equator i\approx 90 deg) be finally implemented, also other perturbations would
come into play, further corrupting the measurement of the Lense-Thirring
effect. The orbital configuration of LARES may also have some consequences in
terms of non-gravitational perturbations and measurement errors.
