Measurements from constellations of low Earth orbiting (LEO) satellites are proving extremely useful for ionospheric science and space weather studies. The Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC), a joint US/Taiwan mission launched in April 2006, is a six micro-satellite constellation that is flying three scientific payloads on each spacecraft: 1) a Global Positioning System (GPS) radio occultation (RO) receiver, 2) a nadir-viewing Tiny Ionospheric Photometer (TIP), and 3) a Coherent Electromagnetic Radio Tomography (CERTO) tri-band beacon transmitter. COSMIC has collected a large amount of useful data from these scientific payloads and is still currently collecting between 1,000 and 1,500 RO measurement events per day on average. The GPS RO dual-frequency L-band phase and amplitude measurements can be used to observe absolute Total Electron Content (TEC) and scintillation on all lines of sight between the LEO and GPS satellites, and electron density profiles (EDP) via the radio occultation (RO) method when GPS satellites are occulted by Earth's ionosphere. The large number and complete global and local time coverage of COSMIC data are allowing scientists to observe ionospheric and plasmaspheric phenomena that are difficult to see with other instruments. The success of COSMIC has prompted the U.S. NOAA to initiate plans for a COSMIC follow-on mission (called COSMIC-2) with Taiwan that will put twelve satellites with GNSS (Global Navigation Satellite System) RO payloads into orbit on two launches in the 2015-17 time frame. The US Air Force is also partnering on COSMIC-2 and will provide twelve space weather payloads that will fly on the first launch of six satellites into low inclination orbits: six RF Beacon transmitters, and six Velocity, Ion Density and Irregularities (VIDI) instruments. This presentation will give a short overview of the COSMIC mission, and then discuss advances in RO data processing techniques, quality of data products, and main science results from COSMIC. Then a summary of the NOAA COSMIC-2 mission will be presented in terms of expected data quality, quantity, sampling coverage, latency and potential science applications.