The PHARAO project has been initiated in the frame of the Fundamental Physics scientific programme at CNES in order to test the principle of the atomic fountain in space. In October 1993, one of the main recommendations of the Seminar of Scientific Prospective, held in Saint-Malo, was to support the development of the cold atom clock, PHARAO.

The main elements at the origin of the PHARAO project are:

the successful method of cooling and trapping caesium atoms by laser at the Laboratoire Kastler-Brossel (LKB) of the Ecole Normale Supérieure in Paris (ENS), supported by CNES in the frame of the scientific programme since 1990;
the application of this method to a new type of clock called atomic fountain;
the advantage of the microgravity environment in increasing the performances of the clock;
the usefulness of ultra-accurate and ultra-stable atomic clocks in space for fundamental physics and particularly for testing the effects predicted by General Relativity.

PHARAO is a major step in research and applications linked to the fundamental physics:

Metrology by improving the accuracy of atomic clocks,
Fundamental Science by testing in space, taking advantage of microgravity, the laws of physics in a domain not accessible on ground,
Technology by developing a new generation of space clocks and opening technologies for experiments in other fields impacted by atom cooling and manipulation.

Nevertheless flying PHARAO is a real challenge due to the complexity of the various technologies freshly out from their laboratories of origin. Today, the PHARAO instrument is completing its qualification. All the subassemblies are delivered and integrated in the complete Engineering Model (EM) since end of 2006. Every day at CNES PHARAO team operates cold atoms to assess EM performances and prepare the Flight Model (FM).