LETSGO: A spacecraft-based mission to accurately measure the solar angular momentum with frame-dragging

Abstract

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 test, in principle, the Lense-Thirring effect at a ∼10−2 level over a timescale of 2 years, 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 separating them in real data analyses. The high eccentricity would help in reducing the impact of the non-gravitational perturbations whose disturb would certainly be severe when LETSGO would approach the Sun at just a few solar radii. It can be preliminarily argued that a drag-free apparatus should perform at a 10−8−10−9ms−2Hz−1/2 level for frequencies of about 10−7Hz. 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.