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A secret path into deep space

Enduring mystery of the Zond project

50 years ago, the USSR introduced a new series of deep-space probes with the launch of the Zond-1 mission on April 2, 1964. Unlike the Venus-bound Venera spacecraft and Mars probes heading to the Red Planet, Zonds had vaguely defined missions and their destinations varied strangely. Even all the revelations of the 1990s did not shed much light on the origin of the Zond project. Only recently, it was disclosed that Zond-1's predecessor was sent on a unique deep-space mission, unlike any other in the history of the Soviet space flight. Yet, it added just another piece of the puzzle into the yet-to-be complete picture of the Zond project.

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1 Thermal control system radiators
2 Low-gain antennas
3 Earth orientation sensor (29K)
4 High-precision solar orientation sensor (25K)
5 Parabolic antenna
6 Attitude control sensors
7 Scientific instruments sensors
8 Pneumatic attitude control system
9 Descent capsule
10 Orbital manuevering system, KDU
11 Permanent solar orientation sensor, (21K)
12 Orbital module
13 Solar panels
14 Magnetometer boom with descent capsule testing antenna

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


The origin of the 3MV and Zond project

The name "Zond" (or "probe" in Russian) as applied to a spacecraft appeared in a letter sent by the leader of the Soviet space program Sergei Korolev to the government on April 7, 1960. Among other space missions Korolev proposed for launch in 1961 was a Zond rocket, which would derive from the 1M Mars probe. (84) However, the mission was not approved at the time. Then, in 1962, six Soviet 2MV probes heading to Venus and Mars failed to reach their destinations. These costly loses prompted leaders of the project to reexamine their quality control procedures and consider pathfinder missions before embarking on another ambitious planetary launch campaign.

On Jan. 31, 1963, Dmitry Ustinov, the top official overseeing the rocket industry, proposed to the Soviet government to repeat launches of MV vehicles in 1964. According to his proposal, the planetary missions would be preceded by two or three test launches beyond the Earth's orbital plane, following by the return of experimental landers back to Earth! Another experimental probe would be sent away from Earth as far as 200-300 million kilometers to test deep-space communications. (509)

On February 7, Korolev, who was at the Tyuratam launch site at the time, sent a letter to his deputy Konstantin Bushuev back in Moscow. From the letter it is clear that engineers at Korolev's OKB-1 design bureau had already completed initial specifications, or IDs, on the third generation of a standard planetary probe designated 3MV, which stood for 3rd-generation Mars-Venus probe. In the same letter, Korolev discussed ongoing work on the precursor space probe called "Zond," which had also been described in the initial specification documents. Korolev proposed to increase the number of Zonds from two to four. He expressed hope that the first and simplest of these Zond probes could be launched as early as the summer. It would carry deep-space communications gear and a minimum of scientific instruments.

Korolev emphasized the importance of backup capability for the new spacecraft but warned against too many departures from the design of the previous generation 2MV standard bus. He urged his associates to keep the standardization of all complex systems as high as possible. The main goal of the effort should be increased survivability of the spacecraft, Korolev wrote. (84)

Zond program formulated

By March 1963, the Soviet planetary exploration program envisioned the development of nine spacecraft designated 3MV. The first vehicle would be launched to a distance of 200 million kilometers to test deep-space communications. The two following spacecraft would be launched on five- or six-month-missions into deep space, concluding with a landing on Earth. All of them were scheduled to fly before the end of 1963. The remaining six probes would fly in 1964, with two landers heading to Venus in March and four dispatched to Mars in November. The Soviet government approved the plan with a formal decree on March 21, designating the initial test launches as "obyekt-zond" or probe-vehicles. (509) As of mid-April 1963, the launch of the first Zond spacecraft was expected during the year, while 3MV spacecraft were expected to follow in 1964. (84)

Comparison of post-Cold War information with Soviet-era documents allows to suggest that the Zond vehicles would be equipped with the 78-kilogram propulsion unit designated S5.19, rather than the more powerful 90-kilogram S5.45 engine developed for the follow-on 3MV probes. (697)

3MV plan approved

At the end of July 1963, Korolev and Keldysh approved the flight program for 3MV probes. The first pathfinder spacecraft, 3MV-1 No. 2, was expected to lift off around October 12, 1963. Then, 3MV-4 Zond-2 would be launched in March 1964, followed by a pair of probes to Venus in April and to Mars in December 1964.

3MV flight program as of July 21, 1963:



Planned launch window*

Optimal launch date

Mission details


3MV-1A (3MV-1 No. 2) Zond

1963 Sept. 1 - Oct. 15

October 12

Flight beyond the ecliptic and return to Earth


3MV-4A (3MV-4 No. 2) Zond

1964 March


Deep-space test mission similar to 3MV-3 and 3MV-4


3MV-1 (3MV No. 3, No. 4)

1964 March 21 - April 4

March 28

Venus landing


3MV-2 (No. 1)

1964 March 21 - April 4

March 29

Venus flyby from 2,000 to 14,000 kilometers


3MV-3 (No. 1, No. 2)

1964 Nov. 17 - Dec. 3

November 29

Mars landing


3MV-4 (No. 3, No. 4)

1964 Nov. 17 - Dec. 3

November 21

Mars flyby from 6,000 to 40,000 kilometers

*Exact launch date would depend on final mass of spacecraft and the Block L stage

Next chapter: Mission of Kosmos-21 (3MV-1A No. 2)


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Key dates in the 3MV program:

1963 Jan. 31: Dmitry Ustinov sends a memo No. VP-13/169 to TsK KPSS proposing to repeat MV launches in 1964, preceded by test launches in 1963.

1963 March 19: Ivan Serbin sends a memo No. 105op to TsK KPSS proposing to build nine 3MV vehicles for launches in 1963 and 1964.

1963 March 21: The Soviet government issues a decree No. 370-128, approving the launches of 2-3 "probes" (zonds) in 1963 and six 3MV spacecraft in 1964.

1963 July 21: Korolev approves the 3MV flight program.

1963 July 29: Keldysh approves the 3MV flight program.

1963 Nov. 4: The Presidium of the TsK KPSS issues a decree No. P122/27, approving the flight program for "obyekt-zond" and a public announcement about its launch scheduled in November 1963.


Article by Anatoly Zak; last update: November 3, 2014

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

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A 3MV-1 (Mars-Venus) spacecraft configured for the mission to Venus. 3MV-4 No. 4 spacecraft was officially announced as Venera-2, 3MV-3 No. 1 as Venera-3. Copyright © 2011 Anatoly Zak

Venus lander


A replica of an early Venera lander. Copyright © 2000, 2009 Anatoly Zak


A dissected Venus lander and a propulsion system (background, left) for a planetary spacecraft. Copyright © 2000 Anatoly Zak


The engine which propelled 2MV spacecraft toward Mars and Venus. Its variation was probably used onboard Zond probes. Copyright © 2000 Anatoly Zak










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