 Artistic rendering of COSI | |
| Names | COSI SMEX-17 |
|---|---|
| Mission type | Gamma-ray astronomy |
| Operator | University of California, Berkeley NASA |
| Website | https://cosi.ssl.berkeley.edu/ |
| Spacecraft properties | |
| Spacecraft | COSI |
| Payload mass | < 400 kg |
| Start of mission | |
| Launch date | August 2027 (planned)[1] |
| Rocket | Falcon 9[1] |
| Launch site | Cape Canaveral Space Force Station[1] |
| Contractor | SpaceX[1] |
| Orbital parameters | |
| Reference system | Geocentric orbit |
| Regime | Low Earth orbit |
| Main Germanium detectors | |
| Name | Compton telescope |
| Collecting area | 25% field of view of the sky |
| Transponders | |
| Band | Gamma Rays |
| Bandwidth | 0.2–5 MeV |
 Logo of COSI with all the participating institutions. | |
TheCompton Spectrometer and Imager (COSI) is aNASASMEX astrophysics mission that will launch a softgamma-ray telescope (0.2–5 MeV) in 2027.[2][3] It is a wide-field compactCompton telescope (CCT) that is uniquely suited to investigate the "MeV gap" (0.1–10 MeV).[4] It provides imaging, spectroscopy, and polarimetry of astrophysical sources, and its germanium detectors provide excellent energy resolution for emission line measurements.[5]
The germanium detectors have an instantaneous field of view of more than 25% of the sky, and they are surrounded on the sides and bottom by active shields, which provide background rejection while also allowing for detection of gamma-ray bursts and other gamma-ray flares across the majority of the sky.[5]
COSI has its origins in theNuclear Compton Telescope (NCT),[6] which was a prototype designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. The NCT was a balloon-borne soft gamma-ray telescope, flying on several high-altitude balloon missions to test and refine its technology. Flights included launches from locations such as New Zealand and Antarctica.[6][7]
COSI evolved from the advancements and lessons learned from the NCT missions. The improved design incorporated germanium cross-strip detectors to enhance sensitivity and resolution. This progression culminated in the development of a more sophisticated instrument capable of high-resolution spectroscopy, wide-field imaging, and gamma-ray polarization measurements. The successful demonstration of NCT's technology in balloon missions laid the groundwork for COSI to be selected as a NASA Small Explorer (SMEX) mission.[3][8]
"For more than 60 years, NASA has provided opportunities for inventive, smaller-scale missions to fill knowledge gaps where we still seek answers", saidThomas Zurbuchen, associate administrator for the agency'sScience Mission Directorate inWashington, D.C. "COSI will answer questions about the origin of thechemical elements in our own Milky Waygalaxy, the very ingredients critical to the formation ofEarth itself".[3]
Theprincipal investigator is John Tomsick at theUniversity of California, Berkeley. The mission will cost approximately US$145 million, with an additional launch cost of approximately US$69 million.[1] The spacecraft is targeted to launch August 2027 on aSpaceXFalcon 9 rocket fromCape Canaveral Space Force Station.[1] The COSI team spent decades developing their technology through flights on scientific balloons. In 2016, they sent a version of the gamma-ray instrument aboard NASA's super pressure balloon, which is designed for long flights and heavy lifts.[3]
NASA'sExplorers Program is the agency's oldest continuous program. It provides frequent, low-cost access to space using principal investigator-led space research relevant to the astrophysics and heliophysics programs. Since the 1958 launch ofExplorer 1, which discoveredEarth's radiation belts, the program has launched more than 90 missions. TheCosmic Background Explorer (COBE), another NASA Explorer mission, led to aNobel Prize in 2006 for its principal investigators. NASA'sGoddard Space Flight Center inGreenbelt, Maryland, manages the program for NASA.[3]
COSI is a collaboration between High Energy Astrophysics Group,Space Sciences Laboratory at UC Berkeley; Center for Astrophysics and Space Sciences,UCSD; Institute of Astronomy atNational Tsing Hua University, Taiwan;Lawrence Berkeley National Laboratory;NASA Goddard Space Flight Center;U.S. Naval Research Laboratory;NASA Columbia Scientific Balloon Facility andNASA Super Pressure Balloon Blog.[9]
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