The Compton Spectrometer and Imager (COSI) 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. COSI’s compact Compton telescope combines improvements in sensitivity, spectral resolution, angular resolution, and sky coverage to facilitate groundbreaking science.  Learn more by reading about the Science COSI will explore and its Instrument Design.

The COSI mission has matured over decades through technology development with scientific balloon campaigns in 2005, 2009, 2010, 2014, 2016, and 2020.

The COSI Small Explorer NASA satellite is currently planned for launch in 2027. See NASA’s Explorers website for more on the Explorers program and COSI.

Also, see NASA’s COSI website.

Announcements

  • The third COSI data challenge is publicly available and can be found here: https://github.com/cositools/cosi-data-challenges. This is a great opportunity to try out the COSI software and provide feedback to the team.
  • COSI reached a significant milestone by assembling the engineering model cryostat and doing a successful cold vacuum test. Videos including views of the work along with explanations of how COSI works and its science can be found here: https://www.ssl.berkeley.edu/watch-cosi-will-explore-the-gamma-ray-sky/
  • COSI’s student-led instrument is called the Background and Transient Observer (BTO). A review of the BTO design was held on January 22, 2025. The students did a great job presenting!
  • The COSI Critical Design Review (CDR) occurred at Northrop Grumman (Dulles) on December 4-6, 2024. The review was successful, and COSI is on-track to continue into the build phase.
  • NASA has selected SpaceX to provide launch services for COSI. The launch is planned for 2027 on a Falcon 9 rocket from Cape Canaveral. The press release is here: https://www.nasa.gov/news-release/NASA-Awards-Launch-Services-Contract-for-Space-Telescope-Mission/
  • COSI has been confirmed and is proceeding to Phase C! The Key Decision Point (KDP) review occurred on April 16, 2024, and the KDP-C Decision Memo was signed on April 16-17. This marks the end of the mission formulation phase and the start of implementation.
  • The COSI Preliminary Design Review (PDR) occurred at Northrop Grumman (Dulles) on February 27-29, 2024. Congratulations to the team for an excellent review.
  • Members of the COSI team attended the 38th International Cosmic Ray Conference (ICRC) in July/August 2023, and conference proceedings papers are available:
  • See also COSI in the news.