Nuclear Instruments and Methods in Physics Research A 512 (2003) 136–142 The silicon-strip tracker of the Gamma ray Large Area Space Telescope R. Bellazzini*, F. Angelini, R. Bagagli, L. Baldini, A. Brez, M. Ceccanti, J. Cohen Tanugi, M. Kuss, L. Latronico, M.M. Massai, M. Minuti, N. Omodei, G. Spandre, L. Vigiani, F. Zetti Istituto Nazionale di Fisica Nucleare, University the Pisa, Sezione di Pisa, via Livornese 1291, I-56010 San Piero a Grado (PI), Italy Abstract The Gamma ray Large Area Space Telescope (GLAST) is an astro-particle mission that will study the mostly unexplored, high energy (20 MeV–1 TeV) spectrum of photons coming from active sources in the universe. ConstructionoftheGLASTsilicontracker,byfarthelargesteverbuiltforaspacemission,isnowwellontheway,asit is scheduled for launch by NASA in autumn 2006. We report on the basic technology adopted for the silicon detectors, particularly in connection to their use in space, on the first results of sensors testing and on the status of tracker assembly. r 2003 Elsevier B.V. All rights reserved. Keywords: High-energy astrophysics; Silicon-strip tracker; Gamma ray 1. Introduction Gamma rays are one of the deeper probes into nature’s highest-energy processes. Due to their small interaction cross-section, they potentially offer a direct view into the most distant energetic sources;moreover,unlikecosmicrays,theyarenot affected from intergalactic magnetic fields. Un- fortunately technological difficulties have pre- vented for a long time the effective exploitation of astronomy within this energy band. After some pioneering missions (OSO III, SAS-2, COS-B), the Energetic Gamma Ray Experiment Telescope (EGRET), launched in 1991, has performed the first complete survey of the gamma ray sky above 30 MeV; finding it surprisingly dynamic and various. The most recent EGRET catalog includes 271 point sources. Among them 170 remain unidentified (no counterparts are known at other wavelengths). The others are incredibly diverse, ranging from Active Galactic Nuclei to Pulsars and Supernova Remnants. GLAST capabilities will greatly exceed those of previously flown instruments, providing an un- precedented advance in sensitivity. GLAST will presumably discover thousands of AGN and hundreds of gamma ray pulsars. Precise time- resolved spectral measurements will likely allow to ARTICLE IN PRESS *Corresponding author. E-mail address: ronaldo.bellazzini@pi.infn.it (R. Bellazzini). 0168-9002/03/$-see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-9002(03)01887-4