An unmanned American spacecraft. It was the first probe to pass by the planet Saturn.

Launched on April 5, 1973, Pioneer 11 was meant as an insurance policy for its identical twin Pioneer 10, in case it was destroyed in the asteroid belt, which many thought to be impenetrable. Both probes made it through without a scratch and Pioneer 11's flight path was modified in-flight to include an encounter with Saturn after its initial mission to Jupiter. There was some thought to thread the spacecraft through the Cassini Gap in Saturn's rings. Luckily, this was not done, as Pioneer found that there are rings inside the gap that we cannot see from Earth.

The spacecraft flew by Jupiter at a distance of only 43,000 km above the cloud tops on December 2, 1974 where it took closeup pictures of the Great Red Spot and the first pictures of Jupiter's polar regions. This accelerated the probe to 48 km/sec. It reached Saturn on December 1, 1979 returning many beautiful pictures of the planet and its rings, charted its magentosphere, found a new ring and two more small moons, and found that Titan was colder than many had hoped, and thus not a likely place to find life.

Scientific operations were halted on September 30, 1995 with the probe's radioactive power source nearly exhausted. Intermittant contact continued until November 1995 at which time the last communication took place with the spacecraft. Earth's motion has since carried it out of view of Pioneer's antenna which could not be moved due to lack of power, so it is not known if the spacecraft is still transmitting a signal or not. It is travelling in the general direction of the constellation Aquila, and may pass near one of its stars in about 4 million years.

Like Pioneer 10, the spacecraft carries a gold-plated aluminum plaque designed by Carl Sagan in the event that extraterrestrial intelligent life encounters the spacecraft in some future eon. It includes figures of a nude man and woman in scale next to a line drawing of the spacecraft. Also included is a map of the solar system and the path the probe took to escape it, as well as a radial pattern that maps the relative position of the Sun to 14 nearby pulsars and the center of the Milky Way.

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