COSI: overview of mission concept, profile, and data operations

The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission scheduled to launch in 2027 into a low-Earth equatorial orbit. COSI is a Compton telescope composed of 16 high-purity germanium cross-strip detectors, which are surrounded on the bottom and sides by a BGO anti-coincidence system to veto radiation from Earth’s atmosphere. COSI will operate in the energy band from 0.2 to 5.0 MeV. Its germanium detectors enable excellent energy resolution, all-sky imaging due to its instantaneous field of view covering 25% of the sky, and the observation of polarization. COSI’s main science goals include uncovering the origins of Galactic positrons, revealing sites of Galactic nucleosynthesis, gaining insights into extreme environments such as those near black holes and pulsars through polarization, and probing the physics of multi-messenger events such as merger events.