The scintillating FIber Tracker (FIT) has been designed as a tracking detector for the upcoming
High Energy cosmic-Radiation Detection (HERD) facility. The FIT combines excellent angular
resolution with precise charge reconstruction measurements for cosmic-ray detection. The tracker
consists of multiple tracking planes made of fiber mats, arranged in two orthogonal directions, and
read out with Hamamatsu S13552-10 SiPM arrays. A custom-made ASIC, the BETA ASIC, has
been developed to fulfill the stringent requirements for noise, linearity, dynamic range, and power
consumption of space applications. This work reports the performance of the SiPMs and the
BETA read-out system used in FIT. Our setup has been optimized, characterized, and calibrated
using an LED light source. Additionally, we discuss the system’s performance in generating
efficient triggers for the identification of ionizing particles.

