The Tomorrow.io weather constellation leverages advances in small satellite technology and the emergence of affordable rideshare options to provide timely, global weather measurements using a constellation of precipitation radars and passive microwave sounders. The focus of this paper is on the design and deployment of Tomorrow.io's CubeSats carrying passive microwave radiometers known as Tomorrow.io Microwave Sounders (TMS). The TMS instrument design is based on technology transitioned from the MIT Lincoln Laboratory (MIT LL) with technology insertions to improve performance. TMS will achieve full operating capability (FOC) with 12 satellites in a hybrid mix of sun synchronous and mid inclination orbits. This paper will report on the development of the TMS constellation and provide an overview of the mission performance and lessons learned.