# COSMIC-2 Mission Summary at Three Years in Orbit
## 1 Introduction  
The six-satellite FORMOSAT-7/COSMIC-2 (COSMIC-2) mission, a Taiwan-U.S. partnership, launched in June 2019 and has now completed nearly 3 years in orbit [1]. The constellation is deployed into six evenly spaced circular orbital planes with 24 deg inclination at an altitude of approximately 550 km. Each satellite carries as its primary payload a Tri-GNSS (Global Navigation Satellite System) Radio-occultation (RO) System (TGRS) instrument developed by NASA's Jet Propulsion Laboratory (JPL), which observes atmospheric bending, refractivity in the troposphere and stratosphere and absolute total electron content (TEC), and electron density and scintillation in the ionosphere [2]. Secondary payloads are the Ion Velocity Meter (IVM) developed by the University of Texas at Dallas and tri-band Radio Frequency Beacon (RFB) developed by SRI International [3, 4]. The IVM measures in-situ ion plasma density, composition, temperature, and velocity. The RFB is a transmitter enabling measurements of TEC and scintillation by terrestrial receivers. The COSMIC-2 instruments are currently producing upwards of 5000 daily high signal-to-noise ratio (SNR) and high-vertical-resolution profiles of neutral atmosphere bending angle, refractivity, and temperature in the tropics and subtropics; ionosphere products including typically more than 10,000 slant TEC tracks, \(\sim\)4000 electron density profiles, and scintillation indices; in situ plasma density, composition, temperature, and drift. Neutral atmosphere bending angle and refractivity are assimilated by operational and research numerical weather prediction models [5, 6, 7]. Ionospheric data products are utilized by operations and research centers for space weather specification and prediction [8, 9].  
Multiple detailed scientific studies on the accuracy and utility of COSMIC-2 data products for neutral atmosphere and ionosphere applications have been published since launch, e.g., [1; 10; 11; 12; 13; 14; 15; 16].  
COSMIC-2 follows upon the successful FORMOSAT-3/COSMIC (COSMIC) mission that operated from 2006-2020. Some key differences between COSMIC-2 and COSMIC are: COSMIC had global coverage, whereas COSMIC-2\({}^{\prime}\)s low-inclination orbit configuration provides dense sampling between approximately \(\pm\)40 deg latitude and no coverage outside this range; the COSMIC-2 spacecraft are larger and heavier, providing better attitude stability and room for larger payload packages; COSMIC-2\({}^{\prime}\)s precise orbit determination (POD) antennas have choke-rings to reduce local multipath effects; the COSMIC-2 RO antennas are phased arrays that steer gain in the direction of neutral atmosphere occultations in order to increase the SNR and enable tracking deeper into the troposphere; COSMIC tracked the Global Positioning System (GPS) only, while the COSMIC-2 TGRS tracks both GPS and Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) navigation signals; the TGRS collects high-rate POD antenna measurement if scintillation is detected along a link; COSMIC-2 data products are available with significantly lower latency due to an extensive downlink station network. Also, the IVM and RFB payloads are new to COSMIC-2.  
At this point the COSMIC-2 mission has completed several important programmatic and scientific milestones and is making significant contributions to neutral atmosphere and space weather operations and science applications. To summarize the mission's achievements and plans, this paper surveys the COSMIC-2 mission from several vantage points. We begin with current mission status, operations, and major milestones since launch. Next, we cover the verification of select mission requirements, available data and products generated in near real-time and post-processing modes. We also describe plans for future data products.