The FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) mission consisting of six low-Earth-orbit satellites is the world's first demonstration of Global Positioning System radio occultation in a near real-time operational constellation for global weather monitoring and research. The mission has produced over 1800-2200 high-quality good atmospheric sounding profiles per day. Currently, the atmospheric soundings data are assimilated into operational numerical weather prediction models for global weather prediction, including typhoon/hurricane forecasts. The radio occultation data have been shown to have a positive impact on weather predictions at many national weather forecast centers. The goal of a proposed follow-on mission is to transfer from the current experimental research mission to a significantly improved real-time operational mission, which will reliably provide no less than 8000 soundings per day. We envision a new and improved mission to be a constellation of 12 satellites with data latency less than 1.5 h, which will provide greatly enhanced opportunities for operational forecasts and scientific research. In this paper, we describe highlights of the results of the current mission, the follow-on mission definition trade analysis results, and the new spacecraft constellation system design with the next-generation radio occultation receiver onboard.