  The Time-of-Flight (TOF) system of the AMS detector gives the fast trigger to
the read out electronics and measures velocity, direction and charge of the
crossing particles. The first version of the detector (called AMS-01) has flown
in 1998 aboard of the shuttle Discovery for a 10 days test mission, and
collected about $10^8$ events. The new version (called AMS-02) will be
installed on the International Space Station on March 2004 and will operate for
at least three years, collecting roughly $10^{10}$ Cosmic Rays (CR) particles.
The TOF system of AMS-01 successfully operated during the test mission,
obtaining a trigger efficiency better than 99.9% and a time resolution of 120
ps for protons and better for other CR ions. In addition, the TOF system was
able to separate protons from all the other CR nuclei within 1% and to
distinguish between downward and upward crossing particles within at most
$10^{-8}$.
