GALILEO GALILEI (GG) SPACE TEST OF THE WEAK EQUIVALENCE PRINCIPLE TO 10~(-17): THE KEY FEATURES

摘要

Galileo Galilei (GG) is a small satellite to fly in a low altitude, near circular, Sun-synchronous orbit around the Earth with the goal of testing in its field the weak equivalence principle to 10~(-17). It would improve the best tests with slowly rotating torsion balances by four orders of magnitude. The sensor is a differential accelerometer with two concentric coaxial test cylinders of different composition rotating together with the whole satellite around the symmetry axis, and weakly coupled in the plane perpendicular to it as a 2D mechanical oscillator. One axis rotation at 1 Hz, to be provided once and for all at launch, stabilizes the satellite and up-converts the signal from the low orbital frequency of ≈ 1.7 ? 10~(-4) Hz to the much higher 1 Hz rotation frequency, needing neither motor nor bearings (passive rotation). For test masses suspended in orbit the major gain is a signal from Earth almost 500 times stronger than for the same masses suspended on ground. In GG both the sensor and the spacecraft are designed to fully exploit the properties of space in order to push the test four orders of magnitude better than slowly rotating torsion balances on ground.