NASA’s Great Observatories – the Hubble Space Telescope, the Compton Gamma Ray Observatory (CGRO), the Chandra X-ray Observatory, and the Spitzer Space Telescope – were launched between 1990 and 2003, each intended to observe the universe in a different wavelength. Hubble, launched in 1990 and still operational today, observes primarily in visible light and near-ultraviolet. Chandra, launched in 1999 and also still operational, observes in X-ray. Spitzer, which launched in 2003 and was deactivated in 2020 after its coolant was depleted, observed in infrared. And CGRO, launched in 1991, observed in gamma ray.
CGRO set off for space aboard Space Shuttle Atlantis on April 5, 1991, with an April 7 deployment. Plagued by budget cuts and technical problems before its launch, even CGRO’s deployment encountered a snag: A thermal blanket caught on a bolt and the spacecraft’s high-gain antenna couldn’t open. An unscheduled spacewalk by astronauts Jerry Ross and Jay Apt was required to manually correct the problem so that CGRO could finally be sent on its way.
CGRO carried four instruments that could observe at a sensitivity 10 times higher than previous missions had, and went on to make groundbreaking discoveries about gamma-ray bursts, blazars, antimatter fountains, and more. In 1999, after a gyroscope failed, NASA decided to deorbit the observatory for safety; it reentered Earth’s atmosphere and sank in the Pacific Ocean in June of 2000.
