The TIGERISS Galactic Cosmic Ray Detector

The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS) is a Galactic Cosmic Ray (GCR) detector being developed as a NASA Astrophysics Pioneers mission to launch to the ISS in 2027. TIGERISS has been assigned the Starboard Overhead X-Direction (SOX) location on the Columbus External Payload Facility (EPF) of the ISS. It will be the first instrument to measure the GCR elemental abundances from ₅B to ₈₂Pb over ∼400 MeV/nucleon to ∼10 GeV/nucleon with single element resolution. TIGERISS builds on the heritage of the TIGER and SuperTIGER stratospheric balloon-borne experiments flown from Antarctica and uses the proven combination of ionization (dE/dx) detectors with acrylic and silica aerogel Cherenkov-light-radiator (∝β) detectors for charge and energy measurements. It improves on the predecessor instruments by using silicon strip detectors (SSDs) in place of both scintillating fiber hodoscopes for track reconstruction and large area scintillator detectors for dE/dx measurement and the instrument trigger. The superior charge resolution (σ_Z < 0.25) and signal linearity over the full dynamic range of the TIGERISS SSDs have been demonstrated in CERN beam tests. TIGERISS will also use silicon photomultipliers (SiPMs) instead of photomultiplier tubes (PMTs) to forego the need for high voltage (HV) and for the more compact Cherenkov detector readout needed to maximize the instrument geometry within the payload envelope. This enables an instrument geometry factor of 1.21 m²sr that will allow TIGERISS in one year to observe GCR statistics comparable to those observed in the first 55-day SuperTIGER flight over their common measurement range without the systematics from atmospheric propagation corrections. With the possibility of extended observations, TIGERISS will test models of GCR origins, including their source environments and acceleration mechanisms. In measuring GCRs over nearly the entirety of the s-process and r-process (slow and rapid) neutron capture processes and the rp-process rapid-proton capture process of heavy-element nucleosynthesis, TIGERISS will make a significant contribution to the wider multi-messenger effort to determine the relative contributions of supernovae (SNe) and Neutron Star Merger (NSM) events.