[en] A relative accuracy and frequency stability of 2*10^-15 has been obtained with the atomic fountain FO1: an atomic frequency standard based on a fountain of cold cesium atoms. A ten fold improvement over those performances is problematic. The accuracy is presently limited by the 1*10^-15 uncertainty on the evaluation of the frequency shift induced by the black body radiation. A theoretical and experimental study of the Stark effect for the clock transition enables to improve the evaluation of the black body radiation shift. A cold atom clock operating in microgravity could be a solution for improving the stability. This is the concept of PHARAO project. The operation of a cold atom clock in a satellite requires stable and compact narrow linewidth lasers. We have developed a weak optical feedback on a DBR laser diode and we have explained the influence of the laser frequency noise on the stability of atomic clocks. This study specifies the detection lasers of cold atom cesium clocks. (author)