  LETSGO (LEnse-Thirring Sun-Geo Orbiter) is a proposed space-based mission
involving the use of a spacecraft moving along a highly eccentric heliocentric
orbit perpendicular to the ecliptic. It aims to accurately measure some
important physical properties of the Sun and to test some post-Newtonian
features of its gravitational field by continuously monitoring the Earth-probe
range. Preliminary sensitivity analyses show that, by assuming a cm-level
accuracy in ranging to the spacecraft, it would be possible to detect, in
principle, the Lense-Thirring effect on it at a 10^-3-10^-4 level over a
timescale of 2 yr, while the larger Schwarzschild component of the solar
gravitational field may be sensed with a relative accuracy of about 10^-8-10^-9
during the same temporal interval. The competing range perturbation due to the
non-sphericity of the Sun would be a source of systematic error, but it turns
out that all the three dynamical features of motion examined affect the
Earth-probe range in different ways, allowing for a separation in data
analyses. The high eccentricity would help in reducing the impact of the
non-gravitational perturbations whose impact would certainly be severe when
LETSGO would approach the Sun at just a few solar radii. Further studies should
be devoted to investigate both the consequences of the non-conservative forces
and the actual measurability of the effects of interest by means of extensive
numerical data simulations, parameter estimations and covariance analyses. Also
an alternative, fly-by configuration is worth of consideration.
