STS-37, the 39th NASA Space Shuttle launch and landing April 1991

STS-37, the thirty-ninth NASA Space Shuttle mission and the eighth flight of the Space Shuttle Atlantis, was a six-day mission with the primary objective of launching the Compton Gamma Ray Observatory (CGRO), the second of the Great Observatories program which included the visible-spectrum Hubble Space Telescope (HST), the Chandra X-ray Observatory (CXO) and the infrared Spitzer Space Telescope
4-5-91