Innovative Methods for LEO Particle Experiments]{Innovative Methods and Instrumentation for Low-Energy Particle Experiments in Low-Earth Orbit Space Mission Analysis and Hardware R&D across the NUSES, CSES-Limadou and SPaRKLE Projects

This thesis summarizes the research activity conducted during my Ph.D. at the University of Trento, covering the entire scientific process of space-based astroparticle physics experiments, from initial design and concepts to the detailed modeling of instrument response and calibration strategies, followed by the analysis of flight data. This comprehensive perspective, spanning the full spectrum of activities from hardware development to data analysis, is rarely achievable in a single research program and represents a unique opportunity to gain an in-depth understanding of the challenges and solutions in this field. The leitmotif throughout is that accurate scientific results in space physics are inseparable from a deep understanding of the hardware and its operative environment. From the measurement of galactic cosmic-ray flux spectra to the reconstruction of a light curve from a primordial gamma-ray burst, every systematic uncertainty in the measurement chain, from radiation–matter interactions, through digitisation strategies, to onboard algorithmic processing, must be understood and controlled. Space imposes an additional layer of complexity: the Low-Earth Orbit (LEO) environment subjects instruments to severe radiation loads, thermal cycling, launch mechanical stresses, and strict constraints on mass, power, and telemetry budget. These engineering boundaries do not merely limit the design space, they define it, challenging the experimenter to extract maximum scientific return from minimum resources. The methods developed to navigate this challenge, accurate virtual detector models built with the Geant4 Monte Carlo toolkit, trigger strategy simulations, and figure-of-merit frameworks for cross-instrument comparison, have been applied to three missions, which form the core case studies of this thesis. The Low Energy Module (LEM) onboard the NUSES Mission. The NUSES mission is a scientific pathfinder flying a Sun-synchronous orbit at 550 km altitude with a nominal duration of three years. The LEM is a compact (10×10×10 cm³) spectrometer designed for event-by-event identification of electrons in the 0.1–7 MeV range and protons in the 3–50 MeV range. Its primary scientific objectives are the monitoring of radiation-belt dynamics, space-weather transients driven by solar energetic particle events, and the study of the MILC framework, which postulates a correlation between particle precipitation and seismic activity. Operating at LEO altitudes, the instrument must sustain omnidirectional particle rates up to 10⁷–10⁸ cm⁻²s⁻¹ in the South Atlantic Anomaly (SAA) while maintaining particle identification and manageable data rates. My contributions covered the full design cycle: detector concept and active-collimation technique, Geant4 simulation framework, sensor procurement and ground characterisation, and calibration strategy. The High Energy Particle Detector (HEPD-02) onboard CSES-02. As part of the Italian Limadou collaboration, I worked on the HEPD-02 instrument aboard the China Seismo-Electromagnetic Satellite (CSES-02), a China–Italy joint mission dedicated to the monitoring of the near-Earth electromagnetic and particle environment. HEPD-02 is designed to measure electrons in the 3–100 MeV range and protons in the 30–300 MeV range with a silicon-pixel tracker and calorimeter architecture, targeting the measurement of radiation-belt particle precipitation, solar energetic particle (SEP) events, and galactic cosmic-ray modulation over the solar cycle. My contributions included debugging and maintaining the data acquisition software and firmware of the tracker system, extending the Monte Carlo simulation to incorporate the satellite geometry to evaluate systematic effects on the detector response, characterising the instrument response to gamma-ray photons, and conducting preliminary flight-data analyses demonstrating species discrimination among protons, electrons, and alpha particles. The SPaRKLE payload onboard Space Rider. Space Rider is an uncrewed reusable orbital spaceplane developed by ESA, offering a low-cost platform for in-orbit experimentation in LEO. SPaRKLE is a compact payload conceived for the simultaneous detection of charged particles and photons in the 10 keV – few MeV range, with scientific objectives including the detection of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs) as well as the characterisation of the LEO charged-particle environment. I proposed the initial detector concept by submitting the project to the ESA Academy Experiment Programme call, conducted scientific performance analyses using Monte Carlo simulations, and performed initial characterisations of scintillator crystals coupled with silicon photomultipliers (SiPMs). The thesis is organised to guide the reader from the physical and methodological foundations to the experimental results achieved across the three missions. Chapter 2 introduces the LEO particle environment, the Van Allen radiation belts, space-weather phenomena, and astrophysical transients, that motivates the measurement requirements of all three instruments and space missions (introduced in Chapter 3). Chapter 4 details the fundamental principles of particle interactions with matter and the simulation and reconstruction techniques developed during this work. Chapters 5, 6, and 7 present the specific design, simulation, and results obtained for the LEM, SPaRKLE, and HEPD-02 instruments, respectively.