The TIGERISS Galactic Cosmic Ray Detector

TIGERISS is an ultra-heavy Galactic cosmic ray (UHGCR) detector awarded under the second round of the NASA Astrophysics Pioneers Program, planned to launch in 2026 and which will measure the abundances of every element from $_{5}$B to $_{82}$Pb relative to $_{26}$Fe with kinetic energies over 350 MeV/nucleon. TIGERISS is the successor to the TIGER and SuperTIGER long-duration balloon instruments incorporating silicon strip detectors in place of scintillation detectors and scintillating fibers and using silicon photomultipliers (SiPM) instead of photomultiplier tubes (PMT). These new detector components have been tested at CERN/SPS beam runs and will provide TIGERISS with high fidelity charge assignment with $\sigma_{Z}$ $\leq$ 0.25. Instrument configurations for available ISS external attachment accommodations on the JAXA JEM-EF and the ESA Columbus Laboratory are being studied for site selection at the end of the formulation phase. The TIGERISS geometry factor depends on attachment location ($\sim$1 to 1.6 m$^{2}$sr), but in one year the threshold instrument would obtain statistics comparable to the current SuperTIGER UHGCR data set while expanding measurements to higher and lower atomic numbers. These measurements will be cleaner than SuperTIGER’s, as they will not require corrections for atmospheric interactions and scintillator saturation effects, and will give the first single-element resolution measurements of elements above $_{56}$Ba. Extended observations will test models of UHGCR origins and cover elements produced in s-process and r-process neutron capture nucleosynthesis, adding to the multi-messenger effort to determine the relative contributions of supernova (SN) and Neutron Star Merger (NSM) events to r-process nucleosynthesis.