TIGERISS Instrument Science and Status*

The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS) is a NASA Astrophysics Pioneers mission planned for launch to the ISS in 2026 to measure the Galactic cosmic rays (GCRs) from ₅B to ₈₂Pb. TIGERISS is past the formulation stage of Phase A and working toward its preliminary design review (PDR) in July/August of this year. An ISS accommodation location was not assigned in Phase A and payload designs were being developed for both ESA Columbus and JAXA Japanese Experiment Module-Exposed Facility (JEM-EF) locations, and we hope to have a site selection in advance of the PDR to report as well as the selected flight instrument performance. TIGERISS advances on the TIGER and SuperTIGER long-duration balloon instruments by incorporating pairs of crossed silicon strip detectors (SSDs) in place of both scintillating fiber hodoscopes and scintiallator detectors for trajectory, energy and charge measurement. Cherenkov light-collection boxes with silica aerogel and acrylic radiators will still provide velocity and charge measurement, but they will have the radiators at the tops of the boxes for improved light collection and be read out with silicon photomultipliers (SiPMs) instead of photomultiplier tubes (PMTs) to maximize detector size within the payload envelope and eliminate high voltage. The SSDs and SiPMs have been tested at CERN/SPS beam runs that demonstrated they will provide TIGERISS with high fidelity charge assignment and resolution σ_Z <0.25. In one-year TIGERISS is expected to measure with superior resolution statistics that match those of SuperTIGER from ₁₆S to ₅₆Ba. Observations that could be extended to the end of the ISS will allow TIGERISS to make the best single-element resolution measurements through ₈₂Pb to probe GCR origins and acceleration. TIGERISS measurements of s- and r-process neutron capture nucleosynthesis production will contribute to the multi-messenger effort to determine the relative contributions of supernova (SN) and Neutron Star Merger (NSM) events to GCRs and galactic nucleosynthesis.