NASA has launched over 500 missions in its 50-year history. Over 150 missions had humans on board. Such "manned" missions are the most expensive and make the most news but the majority of launches are for space exploration, science, and other purposes that do not need people. NASA spacecraft such as Cassini-Huygens and the Voyager program have visited every planet in the Solar System. Four NASA spacecraft have left the Solar System, Voyager 1, Voyager 2, Pioneer 10 and Pioneer 11. As of 2013 Voyager 1 is around 18,800,000,000 (18.8 billion) kilometers away from Earth.