Lagrange: A proposal for fundamental physics in space

The paper presents some opportunities offered by the set of Lagrange points of the Sun-Earth pair, for scientific purposes. The relevant feature of the Lagrange points is that they move around the center of mass of the pair at the same orbital velocity as the Earth, thus keeping their relative positions and the global configuration. Spacecraft located at the Lagrange points may exchange electromagnetic signals or make them circulate along stable closed loops corresponding to the perimeter of polygons. It is then possible to exploit the general relativistic Sagnac effect, evidencing the presence of a gravito-magnetic field due either to the angular momentum of the Sun or to the presence of a galactic rotating halo of dark matter. Besides these fundamental physics measurements, the presence in the Lagrange points of devices emitting regular electromagnetic pulses can be the basis of a relativistic positioning and navigation system at the scale of the solar system. In this sense the Lagrangian emitters would act as artificial pulsars, much brighter than the real ones and keeping positions fixed with respect to the Earth rather than the sky.