Before 1972, no man-made object had made it to an outer planet. No one had even tried it. Pioneer 10 changed all that with a mission that paved the way for some of the most daring goals of the space program.
Pioneer 10 left Kennedy Space Center in 1972, bound for Jupiter. Since there is a known asteroid belt between Earth and Jupiter, astronomers had long believed it to be impassable. This asteroid belt was blocking the path to the universe beyond the outer planets. Pioneer 10 made it through the asteroid belt.
The probe travelled onboard the Atlas launch vehicle, equipped with more than 400,000 pounds of thrust. When it made it to Jupiter, it delivered the first-ever direct observations of an outer planet. And then it moved on. Pioneer 10 travelled farther in space than any other man-made object when it left our solar system and entered interstellar space in 1983. When it sent its last transmission in 2003, it was 7.6 billion miles (12.2 billion km) from Earth [source: NASA].
Another spacecraft, launched two years before Pioneer 10, also achieved the seemingly impossible. This time, it wasn't the successful navigation of an impenetrable asteroid belt; it was the recovery of a crew that by all logical reasoning should have been forever lost in space.