Pioneer spacecraft were the first to investigate Jupiter and Saturn. The missions were managed by NASA's Ames Research Center in Mountain View, California, for the agency's Office of Space Science. The two spacecraft involved were called Pioneer 10 and Pioneer 11. The total cost of their mission was approximately $350 million.
On each spacecraft was mounted a 6-inch by 9-inch metal plaque with greetings from Earth. The plaque included illustrations of a human man and woman, the spacecraft's silhouette, and some mathematical, chemical, and astronomical data represented in binary code symbols. An image of the solar system at the bottom of the plaque shows a Pioneer spacecraft leaving Earth and passing between Jupiter and Saturn on its way out of the solar system. The scientists who designed the plaque hoped that the images and symbols would serve as a viable means of communication, should any intelligent life form happen to encounter the spacecraft.
Pioneer 10
On March 3, 1972, Pioneer 10 was launched atop an Atlas-Centaur rocket from Cape Kennedy in Florida. It was the first mission ever sent to the outer solar system. Ultimately it became the first human-made object to leave the solar system for interstellar space.
Pioneer 10 was the first spacecraft to travel through the asteroid belt between Mars and Jupiter. Scientists had feared that this would be a dangerous area of space. They learned that the asteroids in the belt are spread far apart and do not pose a significant hazard to spacecraft flying through.
In December 1973 Pioneer 10 was the first spacecraft to investigate Jupiter. Its closest approach came within 124,000 miles of the planet. Pioneer 10 carried various instruments to study the solar wind, magnetic fields, cosmic radiation and dust, and hydrogen concentrations in space. Its Jupiter studies focused on the planet's magnetic effects, radio waves, and atmosphere. The atmospheres of Jupiter's satellites (particularly Io) were also investigated.
On June 13, 1983, Pioneer 10 became the first human-made object to leave the solar system. Over the years the instruments aboard the spacecraft began to fail or were turned off by NASA to conserve power. In 1997 NASA ceased routine tracking of the spacecraft due to budget reasons. The spacecraft was the most distant human-made object in space until February 1998, when it was passed by an even faster spacecraft called Voyager 1. NASA last detected a signal from Pioneer 10 in January 2003. It was approximately 7.6 billion miles away from Earth.
As of March 2004 Pioneer 10 is on its way out of the solar system. It is headed in the general direction of a star called Aldebaran that forms the eye of the constellation Taurus (The Bull). It will take the spacecraft nearly 2 million years to reach the star.
Pioneer 11
On April 5, 1973, the Pioneer 11 spacecraft was launched into space by an Atlas-Centaur rocket. A year and a half later it flew by Jupiter on its way to Saturn. The spacecraft approached within 21,000 miles of Jupiter. It was the first spacecraft to observe the planet's polar regions. It also returned detailed images of the Great Red Spot. Like its sister spacecraft, Pioneer 11 investigated solar and cosmic phenomena and interplanetary and planetary magnetic fields during its journey.
In September 1979 Pioneer 11 flew within 13,000 miles of Saturn and returned the first close-up pictures of the planet and its rings. It continued past the planet toward the edge of the solar system. In 1995 routine missions operations were ended and NASA received its last transmission from the spacecraft. By the end of that year, Pioneer 11 was approximately 4 billion miles from Earth.
Pioneer and Plutonium
The Pioneer spacecraft were built with special power systems based on radioisotope thermoelectric generators (RTGs). RTGs generate electricity from the heat released during the natural radioactive decay of a plutonium pellet. Although sending plutonium into space is controversial, NASA has used the power source on all of its missions to the far planets. The planets are too far from the sun to make solar power a feasible and reliable choice for these spacecraft.
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