Pioneer 1 (also known as Able 2) was an American space probe, the first under the auspices of NASA, which was launched by a Thor-Able rocket on 11 October 1958. It was intended to orbit the Moon and make scientific measurements, but due to a guidance error failed to achieve lunar orbit and was ultimately destroyed upon reentering Earth's atmosphere. The flight, which lasted 43 hours and reached an apogee of 113,800 km (70,700 miles), was the second and most successful of the three Thor-Able space probes.

The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to fly by the Moon, and successfully sent one spacecraft to investigate interplanetary space between the orbits of Earth and Venus. The second program, which ran from 1965 to 1992, sent four spacecraft to measure interplanetary space weather, two to explore Jupiter and Saturn, and two to explore Venus. The two outer planet probes, Pioneer 10 and Pioneer 11, became the first of five artificial objects to achieve the escape velocity that will allow them to leave the Solar System, and carried a golden plaque each depicting a man and a woman and information about the origin and the creators of the probes, in case any extraterrestrials find them someday.