Developments of the general relativity accuracy test (GReAT): a ground-based experiment to test the weak equivalence principle

Abstract. Some future tests of the weak equivalence principle (WEP) with laboratory-size proof masses are likely to be conducted in freefall conditions in order to improve the test accuracy substantially. Some years ago the authors of this paper proposed to test the WEP in a vertical free fall inside a capsule released from a high-altitude balloon. The estimated accuracy in testing the WEP, with a 95% confidence level, is a few parts in 10^15 in a 30 s free fall. When compared with other proposed orbital free fall experiments and ground-based tests, the vertical free fall retains some key advantages of the former without some of the disadvantages of the latter. Moreover, a two orders of magnitude increase in the accuracy of testing the WEP could be achieved with an affordable experiment that allows us to recover the detector and repeat the launches at short time intervals.