CGRO

The Compton Gamma Ray Observatory (CGRO) was NASA's second of the Great Observatories program, launched in 1991 into low Earth orbit and operated for nearly nine years before reentering Earth's atmosphere on June 4, 2000. It was designed to study gamma rays from cosmic sources, advancing the field of high-energy astrophysics and gamma-ray astronomy.

CGRO carried four major scientific instruments: BATSE (Burst and Transient Source Experiment), OSSE (Oriented Scintillation Spectrometer Experiment), COMPTEL (Imaging Compton Telescope), and EGRET (Energetic Gamma Ray Experiment Telescope). BATSE was optimized for detecting and localizing gamma-ray bursts across the sky. OSSE performed spectroscopy in the 0.05 to 10 MeV range. COMPTEL produced imaging in the 0.75 to 30 MeV band, and EGRET mapped the sky above roughly 20 MeV, identifying and cataloging hundreds of gamma-ray sources.

Scientific impact from CGRO was broad. BATSE observations established the isotropic distribution of gamma-ray bursts, supporting a cosmological origin. EGRET and COMPTEL contributed to the study of pulsars and active galactic nuclei, and to the understanding of diffuse galactic and extragalactic gamma-ray emission. The mission produced all-sky surveys in multiple gamma-ray bands and enabled numerous multi-wavelength studies that shaped subsequent high-energy astronomy.

Legacy of CGRO includes extensive data archives and engineering lessons that informed later gamma-ray missions and reinforced the overall success of NASA's Great Observatories program.