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Pioneer 5



Pioneer 5 (1960 Alpha 1), also known as the "Paddlewheel Probe", was a spin-stabilized space probe used to investigate interplanetary space between the orbits of Earth and Venus. The spacecraft measured magnetic field phenomena, solar flare particles, and ionization in the interplanetary region. Pioneer 5 had the mission objectives of accomplishing a precise injection of an instrumented space probe into heliocentric orbit between Earth and Venus and to test communications at interplanetary distances. The science objectives involved exploring interplanetary space between Earth and Venus, specifically measuring radiation, cosmic rays, magnetic field, and the number and momentum of meteoritic dust particles. It also studied methods to measure the astronomical unit and other astronomical distances.

Spacecraft and Subsystems

The spacecraft bus was a 66 cm (26 in.) diameter sphere with solar cell paddle arrays expending on arms from the spacecraft equator, spaced by 90 degrees. The tip-to-tip distance of the arrays was 244 cm (96 in.). The sphere was an aluminum alloy shell. The solar arrays held 4800 boron-diffused silicon solar cells mounted on 48 aluminum modules, twelve were mounted on each solar array. The cells charged two packs of 14 nickelcadmium batteries in series, producing 18 volts. A 5-Watt transmitter handled communication for the telebit telemetry system. It could transmit at 64, 8, or 1 bits per second, depending on the distance from the Earth and the size of the receiving antenna, and the power could be increased to 150 W by ground command. Transmissions were at 378 MHz. Telemetry used a diplexer, it was digital and biphase modulated onto the carrier. The receiver could operate on command in either a wide-band or narrow-band search mode. Communications were via quarter-wave dipole antennas. Total mass was 43 kg.

The instrument payload had a total mass of 19.5 kg. It had a number of instruments to study the interplanetary environment. A search-coil magnetometer could measure components of the magnetic field perpendicular to the spin-axis of the spacecraft. Total radiation flux, particularly medium-energy radiation, was measured by a Geiger-Mueller tube and an ionization chamber. A proportional counter telescope was designed to detect very-high energy radiation, above 75 MeV protons and 13 MeV electrons, and bremstrahling from lower energy electrons and gamma-rays. A micrometeorite counter was also mounted on the spacecraft. A photoelectric aspect indicator, which recorded any direct looks at the Sun, was used to establish the orientation of the spacecraft.

Mission Profile

Pioneer 5 was launched on 11 March 1960 at 13:00:07 UT from Cape Canaveral on a three-stage Thor-Able booster into a 0.9931 x 0.8061 AU heliocentric orbit between Earth and Venus, with an inclination of 3.35 degrees to the ecliptic and a period of 311.64 days. The micrometeorite counter and aspect indicator ceased operating at launch. 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 million binary bits 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 the earth from a record distance of 22.5 million miles on June 26, 1960, which was the last day of transmission.

Alternate Names

  • 1960 Alpha 1
  • 00027
  • Pioneer5

Facts in Brief

Launch Date: 1960-03-11
Launch Vehicle: Thor-Able
Launch Site: Cape Canaveral, United States
Mass: 43 kg

Funding Agencies

  • NASA-Office of Space Science Applications (United States)
  • Department of Defense-Department of the Air Force (United States)


  • Planetary Science
  • Space Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Mr. Charles F. HallProject ManagerNASA Ames Research Center

Selected References

  • Fan, C. Y., et al., Preliminary results from the space probe Pioneer 5, J. Geophys. Res., 65, No. 6, 1862-1863, doi:10.1029/JZ065i006p01862, June 1960.
  • NASA cites data gained by Pioneer V, Space Technol., 3, No. 4, 9, Oct. 1960.
  • Clark, E., Pioneer V transmits deep space data, Space Technol., 3, No. 2, 8-10, Apr. 1960.
Pioneer 5 model at the Smithsonian Air and Space Udvar-Hazy Center.

Pioneer 5 during ground testing

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