Country: USA
Mission: Jupiter & Saturn Flyby
Launched: 0211 GMT April 6, 1973
Launch Vehicle: Atlas-Centaur
Spacecraft Mass: 258.5 kg at launch
Launched in 1973, Pioneer 11 provided scientists with their closest view of Jupiter, passing within 26,600 miles of the cloud tops in December 1974. The close approach and the spacecraft's speed of 107,373 mph, hurled Pioneer 1.5-billion miles across the solar system toward Saturn.
Before reaching Saturn in 1979, Pioneer 11 reached an inclination of 17 degrees above the solar equatorial plane, high enough to illuminate the true character of the sun's magnetic field. Now 780 million miles above the ecliptic plane where most of the planets orbit the sun, the spacecraft recently showed that many of the solar cosmic rays in the heliosphere originate outside the Sun's atmosphere in the interstellar gas, the space between the stars.
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.
Pioneer 11 crossed the orbit of Neptune in 1990 and become the fourth spacecraft to leave the solar system, providing a coda to humanity's first major planetary explorations. Pioneer 11 will join Pioneer 10 and Voyagers 1 and 2 in searching for the heliopause, the point at which the Sun's electromagnetic influence gives way to the galaxy's influence.
When it crossed Neptune's orbit, Pioneer 11 was 2.8 billion miles from the Earth. Neptune's orbit currently marks one measure of the expanse of the solar system because, for the next 12 years, Pluto's eccentric orbit carries it inside Neptune's path. Some scientists refer to the heliopause as the edge of the solar system. By that definition, all four spacecraft are still within the solar system.
Pioneer 11, which will traverse interstellar space in the same direction as the Sun moves, continues to return good data, but operating the radio transmitter and scientific instruments simultaneously will be difficult. Technical adjustments may extend the spacecraft's life through 1997. Pioneer 11 continues to search for the heliopause for very long-wavelength gravity waves that would further understanding of Einstein's Theory of Relativity and for evidence of a 10th planet.
Pioneer 10 and 11 are managed by the Ames Research Center, Mountain View, Calif., for NASA's Office of Space Science and Applications. The spacecraft were built by TRW Space & Technology Group, Redondo Beach, Calif.
