Microscope mission and performance

Scheduled for a launch in 2005, the MICROSCOPE mission aims at testing the universality of free-fall, one of the most known manifestations of the equivalence principle (EP). To increase by a few orders of magnitude the experimental accuracy of the EP test up to an accuracy of 10-15, the MICROSCOPE mission will mainly take advantage of the calm in-orbit environment and the very long free-fall duration for the integration of the measurement. The instrument is composed of two differential electrostatic accelerometers, each of which is composed of two cylindrical and concentric test-masses. The masses of one accelerometer will both be made of the same material, Platinum, in order to demonstrate the accuracy of the experiment. In the second one, one mass will be made of Platinum, the other of Titanium. The EP test will be performed by measuring the force necessary to equalize the rate of fall of these two materials. This document presents the concept and design, presently developed at ONERA, of such a space payload. The most critical elements of the instruments are detailed to point out what mainly sets the test accuracy. Last experimental investigations concerning the main performance limitation are also mentioned