Pioneer 11 was launched on 5 April 1973, like Pioneer 10, on top of an Atlas/Centaur/TE364-4 launch vehicle. After safe passage through the Asteroid belt on 19 April 1974, it made a fly-by of Jupiter on 2 December 1974, and obtained dramatic images of the Great Red Spot.

It made the first observation of the immense polar regions, and determined the mass of Jupiter's moon, Callisto. Looping high above the ecliptic plane and across the Solar System, Pioneer 11 then raced toward its appointment with Saturn on 1 September 1979.

Pioneer 11 flew to within 13,000 miles of Saturn and took the first close-up pictures of the planet. Instruments located two previously undiscovered small moons and an additional ring, charted Saturn's magnetosphere and magnetic field and found its planet-size moon, Titan, to be too cold for life.

Hurtling underneath the ring plane, Pioneer 11 sent back amazing pictures of Saturn's rings. The rings, which normally seem bright when observed from Earth, appeared dark in the Pioneer pictures, and the dark gaps in the rings seen from Earth appeared as bright rings.