The PolSIR instrument – short for Polarized Submillimeter Ice-cloud Radiometer – will help humanity better understand Earth’s dynamic atmosphere and its impact on climate by studying ice clouds that form at high altitudes throughout tropical and sub-tropical regions. The PolSIR mission consists of two 12U CubeSats, each equipped with a cross-track scanning polarized submillimeter radiometer in two spectral bands with center frequencies at 325 and 684 GHz.