HERMES Pathfinder and SpIRIT: From Technology Development to Operations, Data Analysis, and a Future Mission

The High Energy Rapid Modular Ensemble of Satellites Pathfinder (HERMES-PF) consists of a constellation of six CubeSats in low-Earth orbit (launched on 15 March 2025), each hosting a hybrid Silicon Drift Detector (SDD)/GAGG:Ce scintillator system for X-ray and γ-ray spectroscopy in the 3 keV to 2 MeV energy band. The Australian-Italian SpIRIT mission, launched on 1 December 2023, carries an HERMES-like detector. The main goals are to observe high-energy transient events such as the Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave events. An X-ray and γ-ray spectrometer, derived from that of HERMES-PF, was included also in TASTE (Terrain Analyzer and Sample Tester Explorer) mission study, aiming to perform spectroscopy of the surface of Deimos, one of the moons of Mars, to constrain its origin. The first part of the work describes the integration and the ground calibration activities of the last three HERMES-PF payloads, which were fully tested and calibrated at the FBK and INAF/IAPS facilities. Calibrations were performed at different operating temperatures between -20 °C and +20 °C with radioactive sources. The calibration data analysis and technical performance of all seven payloads (HERMES-PF + SpIRIT) were evaluated, and the results were consolidated into the calibration database (CALDB). The second part presents the in-orbit commissioning of SpIRIT, including functional verification, in-flight calibration, and first scientific observations confirming nominal payload performance. Finally, the last part focuses on defining the scientific requirements and trade-off studies to identify the modifications required to adapt the HERMES-PF payload for the TASTE mission.