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3MV (Zond)

Missions to Venus

Venera-72 (Kosmos-482)

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Zond finally goes public

Previous chapter: Mission of Kosmos-27 (3MV-1 No. 5)

Above: Zond-1 (3MV-1 No. 4) spacecraft. (52)

The 3MV-1 No. 4 spacecraft arrived to Tyuratam on March 11, 1964. After learning the cause of the previous failure on March 27, technicians needed just a soldering tool and some 20 minutes of work inside the avionics box of the BOZ unit to fix the problem, which had doomed at least three planetary missions! (52)

The 3MV-1 No. 4 spacecraft equipped with a lander designed to land on Venus lifted off from Site 1 in Tyuratam on April 2, 1964, at 05:42:40 Moscow Time. This time, the 8K78 (Molniya) rocket performed flawlessly, with its third stage (Block I) inserting the payload into the initial parking orbit around the Earth and separating. Block L fourth stage then fired successfully, propelling the spacecraft into an orbit around the Sun with a period of 290 days and heading to Venus. (227) The probe then successfully separated from Block L, however a leak was detected in the pressurized compartment of the spacecraft. In just a week, the pressure inside dropped to just 1 millimeter of the mercury table.

Immediately, it was clear that with such a major problem, the spacecraft would not be able to fulfill its mission, because sensitive electronics inside the orbital module, such as radio-transmitters, were not designed to function in vacuum. Therefore, it was not politically acceptable to announce the mission as Venera-2. At the same time, the spacecraft had left the Earth orbit and was heading into deep space, which would not fit very well into the profile of faceless Kosmos missions. As a result, it was decided to announce this launch as Zond-1. After all, it had become an endurance test vehicle, as it had been originally envisioned in the Zond project.

Ironically, on April 15, Korolev received a response to his March 23 letter to Sergei Vekshinsky, a top Soviet specialist in vacuum electronics, who agreed to consult OKB-1 on reliable pressurization of spacecraft during long-duration missions. (84) However it was too late for Zond-1. As expected, the probe's main transmitters fell silent.

Until May 25, 1964, ground control was able to communicate with the spacecraft thanks to functioning transmitters and batteries onboard the lander. (52) The spacecraft was also able to orient itself in space using star trackers. As a result, ground control conducted two trajectory correction maneuvers, one at a distance of 560,000 kilometers from Earth and another 14 million kilometers away. (2) The second firing was off by 20 meters per second, possibly due to a malfunction in the propulsion system. (202)

Ultimately, at least one of the star trackers was apparently lost, making accurate orientation impossible. (202) The spacecraft was then commanded to enter into gyroscopic stabilization, which still enabled to conduct communications until around mid-June, or about a month before its rendezvous with Venus. The dead spacecraft then drifted as close as 110,000 kilometers from Venus around July 19, 1964. (52)

Western public sources identified this mission as a Venus flyby, again, with no way of knowing that it was carrying a lander. (185)

Taking a lesson from the failure, the OKB-1 design bureau introduced low-frequency vibration tests for all future pressurized spacecraft compartments and x-ray inspection of all welding lines. Korolev was still upset enough about the depressurization of the Zond vehicle in November 1964, when during a conference of his bureau's Communist Party members, he mentioned the incident as an example of poor performance by his employees. (84)

In 1994, a drawing of the 3MV-1 No. 4 (Zond-1) spacecraft was published for the first time, but no photos of this historic vehicle are apparently available.

Next chapter: Venera-72

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APPENDIX

Zond-1 mission at a glance (202):

Article by Anatoly Zak; last update: April 1, 2014

Page editor: Alain Chabot; last edit: March 31, 2014

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A 8K78 (Molniya) rocket lifts off from Site 1 in Tyuratam. Credit: RKK Energia