The Microscope satellite, a CNES mission with ESA cooperation to test the universality of freefall.
The equivalence principle states that all objects should fall freely under gravity at the same rate, independent of their mass and composition, and is the founding principle of General Relativity, Albert Einstein’s theory of gravity.
This principle has been tested by experiments on the ground, confirming with an accuracy of 10–13 that objects with different characteristics experience the same acceleration from Earth’s gravity.
By taking the experiment into space, Microscope will extend the range of measurements to an accuracy of 10–15, enabling scientists to make a much more stringent test of General Relativity and possible extensions of this theory.
Microscope was launched at 21:02 GMT (23:02 CEST) on 25 April 2016 from Europe’s Spaceport in Kourou, French Guiana, taking advantage of the Soyuz launch that took ESA’s Sentinel-1B satellite into orbit.