Construction, test and calibration of the GLAST silicon tracker

The Gamma-ray Large Area Space Telescope represents a great advance in space application of silicon detectors. With a surface of 80 m^2 and about 1 M readout channels it is the largest silicon tracker ever built for a space experiment. GLAST is an astro-particle mission that will study the mostly unexplored, high energy (20 MeV–300 GeV) spectrum coming from active sources or diffused in the Universe. The detector integration and test phase is complete. The full instrument underwent environmental testing and the spacecraft integration phase has just started: the launch is foreseen in late 2007. In the meanwhile the spare modules are being used for instrument calibration and performance verification employing the CERN accelerator complex. A Calibration Unit has been exposed to photon, electron and hadron beams from a few GeV up to 300 GeV. We report on the status of the instrument and on the calibration campaign.