Pioneer program
Approved by NASA in February 1969, the twin spacecraft were designated Pioneer F and Pioneer G before launch; later they were named "Pioneer 10" and "Pioneer 11". They formed part of the Pioneer program, a series of United States unmanned space missions launched between 1958 and 1978. This model was the first in the series to be designed for exploring the outer Solar System. Based on multiple proposals issued throughout the 1960s, the early mission objectives were to explore the interplanetary medium past the orbit of Mars, study the asteroid belt and assess the possible hazard to spacecraft traveling through the belt, and explore Jupiter and its environment. Later development-stage objectives included the probe closely approaching Jupiter to provide data on the effect the environmental radiation surrounding Jupiter would have on the spacecraft instruments.