High Energy Astronomy Observatory (HEAO 3) satellite, 1979.
© National Aeronautics & Space Administration / Science & Society
This satellite, seen here undergoing pre-flight check out, was launched on 14th September 1979. It mapped the sky at X-ray wavelengths, increasing the number of known X-ray sources from 500 to 1500. HEAO 3 was the third and last in the series of HEAO satellites launched between August 1977 and September 1979.