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COSI (Compton Spectrometer and Imager) is a soft gamma-ray survey telescope (0.2-5 MeV) designed to probe the origins of Galactic positrons, uncover the sites of nucleosynthesis in the Galaxy, perform pioneering studies of gamma-ray polarization, and find counterparts to multi-messenger sources. The mission is conducted by the University of California, Berkeley, Space Sciences Laboratory.

COSI’s compact Compton telescope combines improvement in sensitivity, spectral resolution, angular resolution, and sky coverage to facilitate groundbreaking science. COSI will study gamma rays from radioactive atoms produced when massive stars exploded to map where chemical elements were formed in the Milky Way. The mission will also probe the mysterious origin of our galaxy’s positrons, also known as antielectrons – subatomic particles that have the same mass as an electron but a positive charge. COSI employs a novel Compton telescope design, utilizing sixteen 3-D imaging, high spectral resolution germanium detectors (GeDs). The Compton imaging serves three purposes: imaging the sky, measuring polarization, and very effectively reducing background.

Nation: USA
Type / Application: Astronomy, Gamma-ray
Operator: University of California, Berkeley, Space Sciences Laboratory, NASA
Equipment: Compton telescope
Propulsion: None
Power: Deployable solar array, batteries
Satellite COSPAR Date LS Launch Vehicle Remarks
COSI (SMEX 17) - 2025


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