The Space-Time Explorer and Quantum Test of the Equivalence Principle mission (STE-QUEST) is devoted to a precise measurement of the effect of gravity on time and matter using an atomic clock and an atom interferometer. The mission was selected by ESA as one of four candidates for the M3 mission within the Cosmic Vision Program (launch in 2022).

It is aiming to test a fundamental prediction and one of the most fundamental assumptions of Einstein’s Theory of General Relativity (the Universality of Gravitational Redshift and the Universality of Free Fall. The first primary goal of the mission will be to measure space-time curvature via the precise determination of gravitational time dilation, i.e. the difference in the tick rate of the satellite’s clock when it is compared with a ground-based clock. Making use of a highly elliptic orbit and advanced atomic clocks STE-QUEST aims to achieve an improvement by a factor 450, compared to the most precise gravitational time dilation measurement of ~10^-4. The second primary goal is a quantum test of the Universality of Free Fall (UFF). STE-QUEST will test UFF by measuring the free propagation of coherent matter waves of ⁸⁵Rb and ⁸⁷Rb under the influence of the Earth’s gravity with precision cold atom interferometry, striving for an accuracy better than one part in 10^-15. The use of ultra-cold matter at quantum degeneracy will go far beyond the current accuracy of tests and permit to search for hints of quantum effects in gravity, contributing to the exploration of one of the current frontiers in fundamental physics. The dual atom interferometer, which is the focus of this presentation, is based on the strong European developments in this field, including the pre-phase A studies in the ELIPS-3 program SAI (Space Atom Interferometer), SpaceBEC (Quantum gases in microgravity), the DLR project QUANTUS (QUANTengase Unter Schwerelosigkeit) and the CNES project I.C.E. (Interfrometrie Cohrente pour l’Espace).