Ultra-Heavy Galactic Cosmic Ray Measurements with TIGERISS

The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS) is a Galactic Cosmic Ray (GCR) detector developed under NASA’s Astrophysics Pioneers Program. It will be the first instrument to measure single-element GCR abundances from ₅B to ₈₂Pb between ~400 MeV/nucleon and ~10 GeV/nucleon. TIGERISS is slated to launch in September 2027 on JAXA’s HTV-X3 to the ESA Columbus External Payload Facility (EPF) aboard the ISS. Building on TIGER and SuperTIGER balloon-borne missions, it combines ionization (dE/dx) detectors with acrylic and silica aerogel Cherenkov-light-radiator (∝β) Detectors for change and energy measurements. Silicon Strip Detectors (SSDs) replace scintillator detectors, improving charge resolution (σ_Z<0.25) and linearity while reducing signal saturation, as demonstrated in CERN beam tests. Silicon photomultipliers (SiPMs) replace photomultiplier tubes, eliminating high voltage and allowing compact Cherenkov readout. To meet ISS and launch constraints, the active area was reduced from a 9x10 to a 9x9 SSD array, lowering the geometry factor from 1.21 m²sr to 1.06 m²sr. In one year, TIGERISS will match the GCR statistics of SuperTIGER’s 55-day flight over their common range. Its measurements will test GCR origin models and advance understanding of heavy-element nucleosynthesis via s-, r-, and rp-processes, contributing to the multi-messenger effort to distinguish supernova and r-process source contributions.