Mariner V

Mission to Venus

 
 Mariner V spacecraft. Credit: NASA
 
Following Mariner II’s successful flyby of Venus in December 1962, and Mariner IV’s successful flyby of Mars in July 1965, in December 1965, NASA approved the Mariner-Venus 1967 project to modify the Mariner IV backup spacecraft for a mission to flyby Venus in 1967. The primary scientific objective of the Mariner V mission was to investigate the atmosphere, the ionosphere, and the magnetosphere of Venus. Secondary objectives were to acquire engineering experience by converting and operating a spacecraft designed for a flight to Mars into one to be flown to Venus and to obtain information on the interplanetary environment during a period of increasing solar activity. Major modifications to the spacecraft to operate closer to the Sun included the addition of a Sun shield and reversing the orientation and reducing the size of the solar arrays. Engineers removed the imaging system, since scientists expected the planet’s thick atmosphere to prevent photography of any surface features.

   The Mariner V spacecraft consisted of an octagonal magnesium frame, 127 cm across a diagonal and 45.7 cm high. Four solar panels were attached to the top of the frame. A 116.8 cm diameter high gain parabolic antenna was mounted at the top of the frame as well. An omnidirectional low gain antenna and the magnetometer were mounted on a 223.5 cm tall mast next to the high gain antenna. The overall height of the spacecraft was 289 cm. The octagonal frame housed the electronic equipment, cabling, midcourse propulsion system, and attitude control gas supplies and regulators. Most of the science experiments were mounted on the outside of the frame.

   Power was supplied by 17,640 n/p solar cells contained in the four solar panels with an end-to-end span of 550 cm, which could provide 555 W at Venus. A rechargeable 1200 W-hr silver-zinc battery was also used for maneuvers and backup. Monopropellant hydrazine was used for propulsion, via a 4-jet vane vector control 222-N motor installed on one of the sides of the octagonal structure. Attitude control was provided by 12 cold nitrogen gas jets mounted on the ends of the solar panels and three gyros. Positional information was provided by two primary Sun sensors, secondary Sun sensors, an Earth sensor, a planet sensor, a Venus terminator sensor, and Canopus star tracker.

   Telecommunications equipment consisted of a dual, S-band 6.5-W triode cavity amp/10.5-W TWTA transmitter and a single receiver which could send and receive data via the low- and high-gain antennas at 8 1/3 or 33 1/3 bps. Data could also be stored on a tape recorder for later transmission. All operations were controlled by a command subsystem. The central computer and sequencer operated stored time-sequence commands. Temperature control was maintained through the use of adjustable louvers, deployable sunshade, multilayer insulating blankets, polished aluminum shields, surface treatments, and reference units mounted on three solar panels. The mass of the spacecraft was 244.8 kg.
 
A view of the Sun-facing underside of Mariner V. Credit: NASA

The spacecraft carried seven scientific experiments:

  • The solar plasma probe to monitor the properties of the solar wind.
  • The helium magnetometer to measure the direction and strength of the magnetic field.
  • The trapped-radiation detector to measure the flux of energetic particles.
  • The ultraviolet photometer to detect atomic hydrogen and oxygen in Venus’ upper atmosphere.
  • The celestial mechanics investigation to help refine the orbits of Earth and Venus.
  • The S-band radio occultation experiment to measure the density of Venus’ atmosphere as the spacecraft passed behind the planet.
  • The dual-frequency propagation experiment to provide information on Venus’ ionosphere. 
Mariner V spacecraft being weighed on May 15, 1967 at Cape Kennedy Air Force Station. Credit: NASA


   Mariner V was launched from the Eastern Test Range of Cape Kennedy on 14 June 1967 at 06:01:00 UT. The Atlas Agena D launch vehicle successfully placed Mariner on a direct-ascent trajectory to Venus. The nominal aiming point was designed to place the spacecraft 8165 km from the center of Venus on October 19, 1967. At injection, however, this aiming point was deliberately biased to 75,000 km to avoid any chance of the spacecraft and Agena impacting the planet. As a result, a midcourse maneuver was planned to achieve the nominal aiming point. A mid-course correction (a 17.66 second burn) was made on 19 June, placing the spacecraft at a closest approach distance of about 10,000 km from the planet's center.

 
Liftoff of Mariner V from Launch Pad 12 on June 14, 1967. Credit: NASA

   The spacecraft flew by Venus on October 19, 1967. The closest approach occurred at 17:34:56 UT at a range of 4,094 kilometers above the surface of the planet. At this time Venus was approximately 79.5 million km from Earth. Mariner V passed in front of Venus' orbit and was occulted from Earth for approximately 26 minutes. The spacecraft conducted a radio-occultation experiment to determine the atmospheric properties of Venus, and measured its radiation and magnetic field environment. Data transmissions occurred after the encounter.

   Mariner V found no trapped radiation belts around Venus, and that although Venus does not have a magnetic field, the dense daylight ionosphere produces a bow shock that deflects the solar wind around the planet. The ultraviolet photometer detected a hydrogen corona (as found by the Soviet Venera 4) but no oxygen emission. Mariner V’s instruments indicated that the planet’s surface temperature and pressure were 527o Celsius and 75 to 100 atmospheres, respectively — which countered the Soviet claim that its Venera 4 spacecraft had managed to transmit from the planet’s surface.

   The encounter with Venus deflected the spacecraft toward the Sun, and Mariner 5 entered solar orbit with parameters ranging from 0.579 au and 0.735 au. On December 4, 1967, NASA lost contact with the spacecraft, although controllers briefly regained contact on October 14, 1968. The spacecraft did not transmit any additional telemetry and NASA stopped trying to contact the spacecraft on November 5, 1968. 

Schematic of Mariner 5’s trajectory during its flyby of Venus. Credit: NASA

   On the day before the Mariner V encounter with Venus, the Soviet probe, Venera 4, dropped through the atmosphere on its parachute. Planetary scientists reviewed data from both Mariner V and Venera 4 at a conference at Kitt Peak National Observatory in Tucson, Arizona, in March 1968, one of the first major international meetings to discuss the results of planetary exploration. Scientists concluded that neither Mariner V nor Venera 4 had been entirely successful in communicating data about conditions at the planet’s surface.


References:

Andrew LePage. The Return to Venus: The Mission of Mariner 5. Drew Ex Machina, June 15, 2017
Asif A. Siddiqi. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. Washington, DC: NASA History Program Office, 2018. ISBN 978-1-62683-042-4
John Uri. 55 Years Ago: Mariner 5 Launches to Explore Venus. NASA Johnson Space Center
NASA. Mariner-Venus 1967 Final Project Report, NASA SP-190, 1971
NASA. NSSDCA:  Mariner 5
NASA Solar System Exploration: Mariner 5


© 2025, Andrew Mirecki

 

 

 

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