  We present a new measurement of the Lense-Thirring effect on the orbits of
the geodetic satellites LAGEOS, LAGEOS II and LARES. This secular precession is
a general relativity effect produced by the gravitomagnetic field of the Earth
generated by its rotation. The effect is a manifestation of spacetime curvature
generated by mass-currents, a peculiarity of Einstein's theory of gravitation.
This measurement stands out, compared to previous measurements in the same
context, for its precision ($\simeq7.4\times10^{-3}$) and accuracy
($\simeq16\times10^{-3}$), i.e. for a reliable and robust evaluation of the
systematic sources of error due to both gravitational and non-gravitational
perturbations. For this new measurement, we have largely exploited the results
of GRACE mission to significantly improve the description of the gravitational
field of the Earth, by also modeling its time dependence. In this way, we
strongly reduced the systematic errors due to the uncertainty in the knowledge
of the Earth even zonal harmonics and, at the same time, avoided a possible
bias of the final result and, consequently, of the precision of the
measurement, linked to a non-reliable handling of the unmodeled and mismodeled
periodic effects.
