During the opening years of the Space Age, the Soviet Union took an early lead with an impressive series of space firsts: the first satellite, the first animal in orbit, the first lunar probe, the first lunar impact and the first human in orbit to name a few. And because of their early lead in rocket lift capability afforded by launch vehicles based on the R-7 ICBM (also known as the 8K71), the Soviet Union’s spacecraft were much more massive than their miniaturized American counterparts of the time (see “The Largest launch Vehicles Through History“).

Soviet space ambitions were no confined to the Earth’s neighborhood. Shortly after the launch of the first Sputnik satellites, the engineers and scientists at the Soviet’s premier aerospace design bureau, OKB-1 (the Russian acronym for Experimental Design Bureau 1, the forerunner of today’s Russian aerospace giant, RKK Energia) run by the legendary Soviet space engineer, Sergei Korolev, was already developing automated planetary probes and the launch vehicle needed to send them to Venus and Mars. Unfortunately the pair of 1M Mars probes launched in October 1960 failed during ascent due to issues the new four-stage 8K78 Molniya rocket (see “The First Mars Mission Attempts”). A pair of 1VA probes launched in February 1961 and destined for Venus fared slightly better. The first one became stranded in its Earth parking orbit after its Blok-L escape stage failed to ignite. And while the second probe, known today as Venera 1, was successfully launched towards our sister planet, the spacecraft succumb to a series of system failures only days after launch (see “Venera 1: The First Venus Mission Attempt”).

In order to meet the demanding schedule of back-to-back launch windows to Venus and Mars in the fall of 1962, as well as incorporate the lessons learned from the development and flight problems of his first quartet of Soviet planetary probes, Korolev envisioned a common multipurpose interplanetary spacecraft design to be used for both the Mars and Venus missions, designated Object 2MV. While sharing a common configuration and most key systems, slight variations would exist in this basic design to better tailor the spacecraft for their specific targets and missions – a photographic flyby and landers. With a launch mass of around a metric ton, these spacecraft would be far larger and more capable than the American Mariner spacecraft also under development at that time. Out of a fleet of a half dozen 2MV spacecraft dispatched in late 1962, just Mars 1 survived launch on November 4, 1962 only to fail en route to its target due to attitude control issues (see “You Can’t Fail Unless You Try: The Soviet Venus & Mars Missions of 1962”).

The New 3MV

By the beginning of 1963 as the crippled Mars 1 was making its way towards the Red Planet, Chief Designer Sergei Korolev and his team at OKB-1 were already making plans for an improved family of interplanetary spacecraft designated Object 3MV that would be sent to Venus and Mars during the next launch opportunities in 1964. These new spacecraft would incorporate a laundry list of improvements and design changes based on the experience with the earlier 2MV series of spacecraft.

Problems with the 8K78 Molniya, which had doomed eight out of ten planetary probes launched between 1960 and 1962, not to mention the first two out of three E-6 unmanned lunar landers launched during the first quarter of 1963, were also to be addressed with a new version called the 8K78M under development at OKB-1’s Branch No. 3 in Samara under the direction of Dmitri Kozlov (which became an independent organization in 1974 and is today known as RKTs Progress and is responsible for the Soyuz family of launch vehicles). The upgraded 8K78M incorporated its own list of improvements, including upgraded engines and significant modifications to the Blok L escape stage, whose poor performance had stranded a half dozen planetary probes in their temporary parking orbits around the Earth.

Externally, the 3MV series of spacecraft resembled the earlier 2MV series. The 3.6-meter tall 3MV would was built around a cylindrical orbital compartment with a diameter of 1.1 meters that was about as tall. This compartment contained control systems, power supplies, and communications gear, as well as some instrument electronics with a planetary compartment mounted beneath that was geared towards specific investigations of the target planet. Like the earlier 2MV design, mounted on top of the orbital compartment was a course correction system that employed a KDU-414 engine designed and built at the OKB-2 design bureau led by Aleksei Isayev. The pressure-fed KDU-414 had a 35-kilogram supply of UMDH (unsymmetrical dimethylhydrazine) and nitric acid to generate two kilonewtons of thrust. Depending on the actual mass of the spacecraft, this was sufficient propellant for a delta-v of 80 to 100 meters per second. Normally this engine would be employed twice during a typical mission: once a few days after leaving the Earth to correct the 3MV trajectory for launch errors, and a second time a few days before encountering its target to refine its approach trajectory to meet the mission’s objectives. Also located here was the attitude control system, which used pressurized nitrogen stored in a pair of tanks mounted on the orbital compartment. An experimental ion thruster-based attitude control system was also carried for evaluation.

Mounted either side of the orbital compartment were a pair of solar panels with a total span of about 4 meters that provided power for the spacecraft. Attached to the ends of the solar panels were hemispherical radiators designed to provide thermal control for the spacecraft’s interior systems. Water pumped through heat exchangers in the interior would circulated out through black- or white-painted sections of the radiators to heat or cool the spacecraft systems as needed to maintain the interior’s temperature between 20°C and 30°C. A two-meter in diameter high-gain directional antenna mounted on the anti-sun side of the orbital compartment was used for long distance communications. Various low gain antennae were also mounted on the exterior of the orbital compartment to provide an omni-directional communications capability. Instrument sensors to measure magnetic fields, various types of radiation and micrometeoroids that were mounted on the exterior rounded out the orbital compartment.

Both the orbital and planetary compartments were pressurized to provide a laboratory-like environment for the internal equipment in order to simplify the design and testing of various systems as well as ease thermal control. As before, the planetary compartment of the 3MV came in two varieties. The first was a one meter tall compartment with a film camera system, a set of ultraviolet and infrared instruments designed to study the target planet during a close flyby as well as its own transmitter which fed through the orbital compartment’s high gain antenna. The other version was a roughly spherical lander with a diameter of about 0.9 meters designed to detach from the orbital compartment before encounter and touchdown on the target planet. As with the 2MV, the 3MV design had four design variants. The 3MV-1 would have a launch mass of 948 kilograms and carry a planetary compartment designed to land on Venus. Its sister craft, the 3MV-2, would have a launch mass of 935 kilograms and sport a planetary compartment designed to study Venus during a flyby. The other variants were the 3MV-3 and 3MV-4 which were designed to land and flyby Mars, respectively.

Both the Venus and Mars landers carried instruments to measure the temperature, pressure, density and composition of the atmosphere during descent and on the surface. Also carried was an instrument to measure gamma rays so that the quantities of radioactive elements like potassium-40, thorium, and uranium present in the surface could be measured, allowing geologists to roughly characterize the types of rocks present. The landers carried no cameras since their data volume requirements far exceeded the limited capacity of the direct radio communications link from the lander to the Earth.

Influenced by Soviet astronomers like Gavril Tikov (1875-1960) who believed in more Earth-like (albeit hotter) conditions on Venus, engineers at OKB-1 tailored the design of the 3MV-1 lander for a dense atmosphere of nitrogen and carbon dioxide with a surface pressure of 1.5 to 5 bars and temperatures up to 77°C. Some in the scientific community believed that the actual surface pressure could be as high as 300 bars with temperatures soaring to 480° C or more. Unfortunately, the true values were not known with any certainty despite observations from increasingly sophisticated ground-based instruments and a distant flyby performed by the American Mariner 2 in December 1962.

The nominal launch window to Venus extended from late March to early April 1964. The 3MV probes would follow fast Type I trajectories to arrive at Venus in the second half of July. Because of the success of NASA’s Mariner 2 mission, in January 1963 the United States cancelled plans to launch a follow on mission using Mariner R-3 (to have been assembled from spare flight hardware) during this window, so these Soviet Venera spacecraft would be flying without competition.

Engineering Test Flights

Korolev understood that there was a need to flight test the new 3MV design in order to iron out the problems that would inevitably crop up. To this end, Korolev envisioned flying two or three dedicated 3MV engineering missions to be launched into interplanetary space starting in the summer of 1963. It was hoped that any problems uncovered during these test flights could be resolved in time for the 1964 planetary missions thus increasing their chances for success. Since these test flights would not be directed towards Venus or Mars, after launch they would receive the generic name of “Zond,” which means “probe” in Russian.

The first Zond version would be a stripped down model of the Venus lander craft designated 3MV-1A. Originally envisioned to have a launch mass of about 800 kilograms, this spacecraft would carry little scientific instrumentation and a lightweight 275-kilogram entry probe. The 8K78 rocket would be used to launch the 3MV-1A into a nearly circular solar orbit inclined about 5° to the ecliptic. About nine days after launch, a course correction maneuver using the propulsion system employing the KDU-414 engine would be performed. In this solar orbit, the probe would recede to a maximum distance of 12 to 16 million kilometers before returning back to the vicinity of the Earth five to six months after launch.

About 10 to 15 days before reaching Earth, the 3MV-1A would make one more course correction to refine its final approach trajectory. Before reaching the Earth, the entry probe would detach from the orbital compartment and reenter the atmosphere at a speed in excess of 11.5 kilometers per second to simulate the conditions of an entry into the Venusian atmosphere. After reentry, the parachute system would be tested and, presumably, the lander would be recovered. In addition to giving Korolev’s engineers a chance to test the 3MV-1 design on a long mission, it would be the first spacecraft ever to return to the Earth from interplanetary space, giving the Soviet Union yet another space first. The second Zond variant would be a stripped down version of the Mars flyby spacecraft designated 3MV-4A. It would be launched into solar orbit in the direction of the orbit of Mars and take images of the receding Earth to test the new photo-television imaging system.

On March 21, 1963, the Soviet government officially approved the 3MV program. It would consist of one or two 3MV-1A flights and a single 3MV-4A flight to be launched in 1963 as well as a total of six operational 3MV spacecraft to be launched to Venus and Mars in 1964. As had happened all too frequently in the past with other projects, however, design and construction of the new 3MV took longer than expected. However, by July of 1963 Korolev had set the launch schedule for the Zond tests. A 3MV-1A would launch sometime between September 1 and October 15 (with the optimum launch date being October 12) on an Earth-return mission. This launch date would allow the 3MV-1A to be visible high in the sky as viewed from Soviet tracking stations during most of its mission and would result in a return just as the launch window to Venus was opening. While this would be too late to make any major changes to the design of the 3MV-1 Venus lander, it would still allow any problems with the basic 3MV design to be uncovered early enough to make changes a few months before the Venus launches. The 3MV-4A Zond mission was scheduled for launch in March 1964 with sufficient time to make any needed changes to the Mars-bound 3MV design to be launched eight months later.

The Zond Missions

Continued delays in the preparation of the first 3MV-1A ended up pushing its launch date out by several weeks, but by early November 1963 it was finally ready. Less time would be available to correct any problems uncovered by this flight, but it was felt to be vitally important. On November 4, the Central Committee officially approved two TASS press releases for the upcoming mission. If the test craft was successfully placed on its interplanetary trajectory, it would be called “Zond 1”. But if it got stranded in its short-lived parking orbit by another launch vehicle failure, it would receive a generic “Kosmos” designation to avoid the international treaty and public relations issues that had arisen as a result of the unannounced 2MV launch failures towards Venus and Mars a year earlier.

At 06:23:35 GMT on November 11, 1963, 8K78 serial number G103-18 lifted off from Site 1/5 at the Baikonur Cosmodrome in Soviet Kazakhstan carrying the 800-kilogram 3MV-1A No. 2 on an Earth-return mission. The first three stages of the launch vehicle successfully placed the Blok L escape stage and its payload into a 195 by 229 kilometer parking orbit with an inclination of 64.8°. But as had happened eight times before, the Blok L stage failed to function as intended. During its coast in parking orbit, all telemetry stopped at about 06:45:45 GMT as attitude control was lost. When the time came to make its burn to escape its parking orbit, the Blok L ended up firing its engine in the wrong direction stranding the rocket and its payload in Earth orbit. The orbit of what was now called Kosmos 21 decayed three days later. This would be the first of many failed lunar and planetary missions to be hidden (rather poorly, I might add) by the Kosmos designation.

With the launch failure of the first Zond engineering test mission and the continued unsatisfactory condition of the 3MV spacecraft under final assembly and test, by the end of December 1963 a second 3MV-1A mission was officially approved for launch in January 1964 on the first improved 8K78M, with the 3MV-4A test flight to follow in the April-May time frame after the launch of the Venus missions. While a longer test flight would have been preferred, at least the new 8K78M could be tested and a few weeks of flight experience could be gained before the launch of the Venus missions in two months. Since the problems with Venera 1 and Mars 1 occurred during the first few days of their missions, it was hoped that any hidden problems with the 3MV design would become apparent early enough – and be minor enough – so that the operational 3MV craft could be modified before launch. Eventually it was decided that no 3MV-2 flyby probes would be launched towards Venus during the 1964 window and that all resources instead would be concentrated on preparing the pair of 3MV-1 landers.

Still more delays pushed the launch of the 3MV-1A test flight out further, towards the very beginning of the 1964 Venus window. Additional issues with the scheduling of E-6 lunar landing missions, also being developed at OKB-1 at the same time, complicated matters further. Officials finally decided that the 3MV-1A test flight would now take place in late February 1964 – at the very beginning of the Venus launch window. Some Russian sources now claim the a Venus flyby was the intended objective of this mission (which raises questions about the type of planetary compartment actually carried). An analysis of the trajectory options at this time suggests that the 8K78M did indeed have sufficient payload capability to launch the lightweight 3MV-1A on a longer Type II trajectory towards Venus that could reach the planet sometime around the end of August (see “Trajectory Analysis of the 1964 Soviet Venus Missions”). Although it is likely that there was little expectation that this test mission would actually survive the six-plus months needed to reach Venus, it would still provide a vital test of the new 8K78M launch vehicle and a month’s worth of in-flight engineering data that could help improve the chances of success for the pair of operational 3MV-1 landers. After the next E-6 lunar lander was launched during its narrow window around March 21, launch opportunities to Venus on the faster Type I trajectories that would get the landers to Venus in the last half of July became available over the course of the following couple of weeks.

The Venus Missions

On February 11, 1964, the first completed 3MV-1 spacecraft arrived at Baikonur for prelaunch processing. In the mean time, at 05:45:40 GMT on February 19, 1964, the first of the improved 8K78M rockets, serial number T15000-19, lifted off carrying 3MV-1A No. 4A on the last chance at a test flight of the Venus probe design. But just as the Blok I third stage was supposed to ignite, failure occurred once again. Liquid oxygen leaking from a bad valve seal froze a kerosene fuel line, causing it to break. This resulted in an explosion and the loss of the launch vehicle with the debris falling to Earth 85 kilometers north of Barabinsk in Siberia.

With the loss of the last available 3MV-1A test craft, it appears that a rather drastic decision was made. Apparently desperate to get some test flight data to improve the chances of reaching Venus, it seems that officials decided to launch one of the pair of operational 3MV-1 spacecraft early at the beginning of March on a slower Type II trajectory towards Venus that would provide three weeks of flight data before the opening of the faster Type I launch window later in the month. While the longer, six-month trip time increased the chances that the 3MV-1 would fail before reaching Venus in early September, it would seem that it was felt to be less risky than launching a pair of untried spacecraft with absolutely no flight testing. But the launch of 8K78M serial number T15000-22 for March 1, 1964 was ultimately scrubbed because of problems encountered during prelaunch integration of the 3MV-1 with the 8K78M. In order to resolve the problem, the launch was postponed to the opening of the Type I launch window at the end of the month. The 3MV-1 would now have to fly untested.

As the final preparations for the pair of 3MV-1 landers were being made, the focus shifted to the launch of the unmanned lunar lander, E-6 No. 6. The E-6 Luna program was coming out of a self-imposed year-long stand down as major problems with the E-6 uncovered during the first three attempts in early 1963 were fixed. It was hoped that the E-6 problems were resolved and that this flight would beat America’s delayed Surveyor lunar lander by a year or more (see “Surveyor 1: America’s First Lunar Landing”). At 08:15:35 GMT on March 21, 1963, 8K78M serial number T15000-20 lifted off carrying the new E-6. But a series of problems with the 8D715P engine on the Blok I third stage culminated in its premature shutdown 487 seconds into the flight. The rocket and its payload were destroyed during reentry (for more details on this and other early E-6 failures, see “The Mission of Luna 5”).

With two successive failures of the new 8K78M, it was now the turn of the 950-kilogram 3MV-1 Venus landers. With its earlier problems now resolved, 3MV-1 No. 5 was launched at 03:24:42 GMT on March 27, 1964, on 8K78M serial number T15000-22. This time the first three stages of the new 8K78M worked as intended to place the Blok L escape stage and its Venus-bound payload into a 191 by 237 kilometer parking orbit with an inclination of 64.8°. But during the unpowered coast, an electrical fault caused attitude control to be lost and the Blok L never ignited its 11D33 engine. Stranded in Earth orbit, the rocket and its payload were designated Kosmos 27. Despite the failure, one of the many improvements made to the new Blok L paid off this time. Data from the various systems gathered by the new telemetry system were recorded and radioed back to ground controllers on the next orbit allowing engineers to diagnose the failure like never before. This failure (and probably a couple of earlier failures) were found to be the result of a fault in the design of the wiring of a key control system in the Blok L. Fortunately, the fix involved only 20 minutes of a technician’s time with a soldering iron to resolve for the next launch attempt.

With its wiring fault fixed just in time for the end of the Venus launch window, 8K78M serial number T15000-23 lifted off the morning of April 2, 1964, at 02:42:40 GMT carrying 3MV-1 No. 4 and its escape stage into a 187 by 213 kilometer parking orbit with an inclination of 64.8°. This time all four stages of the 8K78M worked sending the spacecraft out of Earth orbit and into a 0.65 by 1.06 AU solar orbit with an inclination of 3.92° to the ecliptic and a period of 290 days. What was to be called “Venera 2” was now on its way to Venus and the first attempted landing on another planet. However, before the triumphant launch announcement could be made, ground controllers discovered a major problem during the first communication session with the receding probe. The pressurized orbital compartment was leaking and all its gas would be lost within a week severely compromising the ability of its equipment to operate. With bleak prospects for success, the Soviets announced the probe simply as “Zond 1” making no mention of its mission to Venus.

Diagnosing the Failure of Zond 1

Because of the torque from the leak in the orbital compartment, Soviet engineers were able to pin down the problem quickly as a bad weld near the quartz window for the probe’s star and Sun sensors. Although it would not help Zond 1, future 3MV craft would have their welds X-rayed as a new quality control check. While the probe was still fully functional and engineers formulated a contingency plan to keep the spacecraft operating as long as possible, Zond 1 made a course correction maneuver the day after launch at a distance of 563,780 kilometers to refine its trajectory. This was the first time the KDU-414-based propulsion system had been used on a Soviet planetary mission.

By April 9 the pressure in the orbital compartment had dropped to the point where it became unreadable by the onboard sensors. Since the Zond’s main transmitter required a pressurized compartment to maintain thermal control and suppress arcing in its high voltage circuitry, ground controllers routed communications through one of the redundant pair of transmitters in its 290-kilogram lander. Obviously Soviet engineers had learned the same hard lessons of redundancy that their American counterparts had during the failures in NASA’s early Ranger missions (see “NASA’s First Lunar Lander”). With some measure of command, control and communications, Zond 1 proceeded to gather limited data from its instruments about the interplanetary environment. Its new ion thrusters were also tested but were found to operate erratically, possibly due to the loss of pressure in the orbital compartment where the thrusters’ control systems were located.

Continued tracking of Zond 1 showed that it would still miss Venus by a large margin, so on May 14, a second course correction was attempted. At a range of 14 million kilometers from Earth, the KDU-414 engine ignited for a second time changing the velocity of Zond 1 by 50 meters per second before the engine apparently cut off early. Still 20 meters per second shy of the required velocity change, Zond 1 would still miss Venus by about 100,000 kilometers.

As the cruise to Venus continued, more problems cropped up including the apparent loss of one of its star sensors required for attitude control. Zond 1 was placed into a flat spin to stabilize its orientation and keep the solar panels pointing towards the Sun. Unfortunately, the high gain antenna could no longer be used so contact via the lander’s communication systems could only be maintained until about the middle of June before it was too far away – a full month before reaching Venus. As luck would have it, though, Zond 1 would not last that long. The last public announcement about Zond 1 came on May 19 and all communications were lost on May 24. The now silent Zond 1 flew by Venus on July 19. But even if Zond 1 had successfully deployed its lander, it would have been crushed at an altitude of 35 kilometers or more and never would have reached the surface intact because the conditions were far more sever than expected (see “Venera 4: Probing the Atmosphere of Venus“).

With this latest failure, plans for future Zond test flights were reassessed as were those for the upcoming Mars launch window (see “The Soviet Zond Missions of 1963-65: Planetary Probe Test Flights”). It would be November 1965 before improved 3MV spacecraft would have another chance to reach Venus (see “Venera 2 & 3: Touching the Face of Venus”).

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Related Reading

“You Can’t Fail Unless You Try: The Soviet Venus & Mars Missions of 1962”, Drew Ex Machina, November 1, 2017 [Post]

“Trajectory Analysis of Soviet 1964 Venus Missions”, Drew Ex Machina, April 2, 2014 [Post]

“The Soviet Zond Missions of 1963-65: Planetary Probe Test Flights”, Drew Ex Machina, April 18, 2019 [Post]

General References

Boris Chertok, Rockets and People Volume III: Hot Days of the Cold War (ed. Asif Siddiqi), SP-2009-4110, NASA History Division, 2009

Brian Harvey, Race Into Space: The Soviet Space Programme, Halsted Press, 1988

Brian Harvey, Russian Planetary Exploration: History, Development, Legacy and Prospects, Springer-Praxis, 2007

Bart Hendrickx, “Managing the News: Analyzing TASS Announcements on the Soviet Space Program (1957-1964)”, Quest, Vol. 19, No. 3. pp. 44–58, 2012

Wesley T. Huntress and Mikhail Ya. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer-Praxis, 2011

Nicholas L. Johnson, Handbook of Soviet Lunar and Planetary Exploration, Univelt, 1979

Timothy Varfolomeyev, “The Soviet Venus Programme”, Spaceflight, Vol. 35, No. 2, pp. 42–43, February 1993

Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 5: The First Planetary Probe Attempts, 1960–1964”, Spaceflight, Vol. 40, No. 3, pp. 85–88, March 1998

Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 6: The Improved Four-Stage Launch Vehicle, 1964–1972”, Spaceflight, Vol. 40, No. 5, pp. 181–184, May 1998