The AMS Time of Flight System

The Time of Flight (TOF) system of the AMS experiment provides the fast trigger to the detector and mea- sures the crossing particle direction, velocity and charge . AMS was operated aboard of the shuttle Discovery on June 1998 (NASA STS-91 mission) and will be upgraded and installed on the International Space Station at the end of 2003, for 3 years of data taking. The performances of the TOF during the precursor flight and modifications needed in the final ver- sion of the detector are presented.