The PolSIR instrument – short for Polarized Submillimeter Ice-cloud Radiometer – will study high-altitude ice clouds to determine how and why they change throughout the day. This will provide crucial information about how to accurately simulate these high-altitude clouds in global climate models.The investigation consists of two identical CubeSats – each small satellite is just a little over a foot tall – flying in orbits separated by three to nine hours. Over time, these two instruments will observe the clouds’ daily cycle of ice content.