Pioneer 10 was the first U.S. spacecraft sent to one of the solar system's large outer planets. It was launched March 2, 1973. Unlike previous probes in the Pioneer series, Pioneer 10 was powered by nuclear generators rather than solar cells because its path took it away from the sun. En route to Jupiter, Pioneer 10 became the first spacecraft to pass through the asteroid belt between Mars and Jupiter. It not only made it safely through the region, but reported hardly any detectable change in the concentration of micro -meteoroids. The craft flew by Jupiter on December 3,1973, providing scientists with a considerable amount of useful data.