The Pioneer 10/11 Program: From 1969 to 1994

The Pioneer 10/11 program began in the summer of 1969 and had as its objective the exploration of the Asteroid Belt-that region between Mars and Jupiter-and the exploration of Jupiter. Two flight spacecraft were built-Pioneer 10 and Pioneer 11. Pioneer 10 was launched in 1972 March, passed by Jupiter in 1973 December, and continued on a trajectory that will allow it to escape the solar system. Thus Pioneer 10 became the first man-made object to pass successfully through the Asteroid Belt, to encounter Jupiter, and to escape from the solar system. Pioneer 11 was launched in 1973 April and passed by Jupiter in 1974 December. As a result of Jupiter's influence on its trajectory, it turned around at Jupiter, crossed back through the solar system, then beyond the orbits of Mars and Jupiter, and then encountered Saturn in 1979 September. This encounter was beyond the original objectives and was made possible by the long life and reliability of the spacecraft. Pioneer 11 became the first man-made object to encounter Saturn. At present, Pioneer 11 is also on a solar-escape trajectory although in the opposite direction from Pioneer 10.