Pioneer 5 (1960 Alpha 1) was a spin-stabilized space probe in the Pioneer program. Pioneer 5 was used to investigate interplanetary space between the orbits of Earth and Venus. Pioneer 5 was launched on March 11, 1960 13:00:00 UTC with an on-orbit dry mass of 43 kg. Pioneer 5 is a 0.66 m diameter sphere with 1.4 m span across its four solar panels and achieved a solar orbit of 0.806 × 0.995 AU (121,000,000 by 149,000,000 km). Pioneer 5 was the only completely successful probe in the Pioneer/Able missions, the rest of which attempted to rendezvous with the Moon.
The spacecraft measured magnetic field phenomena, Solar flare particles, and cosmic radiation in the interplanetary region. A micrometeorite counter failed to operate. The digital data were transmitted at 1, 8, and 64 bit/s, depending on the distance of the spacecraft from Earth and the size of the receiving antenna. Weight limitations on the solar cells prevented continuous operation of the telemetry transmitters. About four operations of 25 min duration were scheduled per day with occasional increases during times of special interest. A total of 138.9 h of operation was completed, and over 3 megabits of data were received. The major portion of the data was received by the radio telescope at Jodrell Bank and the Hawaii tracking station because their antennas provided grid reception. Data was received until April 30, 1960, after which telemetry noise and weak signal strength made data reception impossible. The spacecraft's signal was detected by Jodrell Bank from a record distance of 22.5 million miles (36.2 million km) on June 26, 1960, although it was much too weak by then to acquire data.