Pioneer 5 (1960 Alpha 1) was a spin-stabilized space probe in the Pioneer program used to investigate interplanetary space between the orbits of Earth and Venus. It was launched on March 11, 1960 13:00:00 UTC with an on-orbit dry mass of 43 kg. It 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).
The spacecraft measured magnetic field phenomena, solar flare particles, and ionization in the interplanetary region. 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 at the Manchester and Hawaii tracking stations because their antennas provided grid reception. Pioneer 5 performed normally until April 30, 1960, after which telemetry transmission became too infrequent for any significant addition to the data. The spacecraft established a communications link with Earth from a record distance of 22.5 million miles (36.2 million km) on June 26, 1960, which was the last day of transmission.
PioneerV, launched as a probe of the space between Earth and Venus, began to provide invaluable information on solar flare effects, particle energies and distributions and magnetic phenomena.
PioneerV continued to transmit such data until on June 26, 1960, when at a distance of 22.5 million miles from Earth, it established a new communications record.
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