The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS)

TIGERISS is a future space-based ultra-heavy galactic cosmic ray (UHGCR) mission to be proposed to the NASA Astrophysics Pioneers program with heritage from the long-duration balloon-borne TIGER and SuperTIGER experiments.  TIGERISS incorporates silicon detector technology in place of scintillators, increasing the dynamic range for charge measurement without saturation.  From a vantage point on the ISS and a geometrical factor between 1.1 and 1.7 m2sr depending on attachment point, TIGERISS will accumulate in one year statistics up to 56Ba with significance comparable to current SuperTIGER results without the need for atmospheric propagation corrections.

SuperTIGER results up to 40Zr support a model of CR origins in OB Associations, selective acceleration of refractory elements in dust grains, and the expected charge dependence from grain sputtering injection of CRs into SN shocks.  Above 40Zr this model breaks down, and a change in acceleration mechanism and/or an additional r-process source (potentially neutron star mergers, now known sites of r-process nucleosynthesis) is needed.  TIGERISS will measure CR abundances from 5B to 82Pb, probing the relative contributions of r-process sites to the CR reservoir and searching for further evidence of a change in CR sources at high Z.