720 XTF Search Results (f1-subject=Observatory (space-based);f2-subject=Explorer 11);f2-subject%3DExplorer%2011 Results for your query: f1-subject=Observatory (space-based);f2-subject=Explorer 11 Thu, 01 Jan 1970 12:00:00 GMT Artist’s Impression of the Explorer 11 in Orbit. Explorer 11, the first gamma-ray detection satellite flown, was launched on April 27, 1961. The satellite could not be actively pointed, so it was put into a tumble in order to get a "rough" scan of the entire celestial sphere.. Thu, 01 Jan 1970 12:00:00 GMT