  HERMES (High Energy Rapid Modular Ensemble of Satellites) is a space-borne
mission based on a constellation of six 3U CubeSats flying in a low-Earth
orbit, hosting new miniaturized instruments based on a hybrid Silicon Drift
Detector/GAGG:Ce scintillator photodetector system sensitive to X-rays and
gamma-rays. Moreover, the HERMES constellation will operate in conjunction with
the Australian-Italian Space Industry Responsive Intelligent Thermal (SpIRIT)
6U CubeSat, that will carry in a Sun-synchronous orbit (SSO) an actively cooled
HERMES detector system payload. In this paper we provide an overview of the
ground calibrations of the first HERMES and SpIRIT flight detectors, outlining
the calibration plan, detector performance and characterization.
