This work reports on the Microwave Sounder Mission Pathfinder (MSM-PF) Pre-Phase A Study and subsequent work completed at the Australian National Concurrent Design Facility (ANCDF) by UNSW Canberra Space on the 11 – 14th October 2022 in Canberra, Australia, on behalf of and for the Bureau of Meteorology. From October 2022 to February 2023, 28 experts from 8 organisations contributed to this study. The MSM-PF mission described in this report proposes to develop in Australia and fly a novel passive hyperspectral microwave sounder, enabling excellent noise performance, with a large number of channels (> 1000), over a wide spectral range. This mission is a fully capable precursor to an envisioned MSM constellation that would enable a high temporal resolution and low latency data provision, greatly benefiting the accuracy of global and local numerical weather prediction.