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Zond-4 mission: closing the loop!

The fifth mission within the L1 program launched on March 2, 1968, flew an unmanned prototype of the two-seat spacecraft on a giant egg-shaped trajectory extending as far as 330,000 kilometers away from Earth. Then, for the first time in the Soviet space program, the spacecraft headed toward Earth accelerating to the second cosmic speed to test the controlled reentry into the atmosphere from the lunar distance on March 9. However, a last-minute flight control failure left the capsule on an anomalous ballistic trajectory triggering the self-destruct mechanism.

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The Zond-4 (L1 No. 6L) spacecraft heads into deep space after separation from the Block-D upper stage on March 2, 1968.

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The Zond-4 mission at a glance:

Spacecraft designations 7K-L1 (11F91) No. 6
Launch vehicle 8K82K (UR-500K, Proton-K) No. Ya10723101 / Block D (11S824) (No. 14L)
Launch site Tyuratam, Site 81, "Left" pad
Crew Unmanned
Launch date and time 1968 March 2, 21:29:23 Moscow Time
Mission results The flight around a notional target 330,000 kilometers from Earth
End of mission 1968 March 9


Mission of Vehicle No. 6L

The primary mission objective for Vehicle 7K-L1 No. 6L was to climb from an initial low circular orbit around the Earth and enter a giant ellipse extending into deep space. The ship's trajectory would swing around an imaginary point located between 300,000 (52) and 330,000 kilometers away from Earth, which would be essentially a lunar distance. In the process, ground control could practice controlling the spacecraft in deep space, test long-range communications and try trajectory corrections using celestial navigation, giving engineers the overall experience for future missions to the vicinity of the Moon.

All systems during the 6L mission were expected to work as close as possible to a real flight with the crew onboard. (52) However, since the Moon itself was not targeted during the flight, the liftoff of Vehicle 6L had a relatively relaxed three-minute window. (820) Moreover, the short-term planning for the mission was also made easier by avoiding time restrictions of an actual Moon shot. Finally, the secrecy around the ultimate goal of the L1 project could still be maintained.

On its way back to Earth, the descent module was supposed to conduct a dual entry into the Earth's atmosphere allowing its landing on the Soviet territory. (202) Following the initial entry, the spacecraft would use its aerodynamic capabilities to "skip" itself back into space for the subsequent second entry and landing. The final descent trajectory was targeting a circle with a radius of 500 kilometers in the plains west of Karaganda in Kazakhstan.

Various contingency scenarios had the potential of shifting the landing of Vehicle No. 6 to the Indian Ocean, India, Iran, Africa and Turkey, but in all these cases, the capsule was programmed to self-destruct using the APO system.

Preparations for 6L launch

As before, Mishin's deputy Evgeny Shabarov oversaw the pre-launch processing of the L1 No. 6 vehicle, while Chelomei's associate Yuri Trufanov led the assembly and testing of the UR-500K rocket.

As usual, the preparation for the launch of Vehicle No. 6L was hampered by delays with the delivery of components, first of all the 100K star-tracking sensor. Critically important for the ship’s celestial navigation, this instrument gave many headaches to its developers at the TsKB Geofizika design bureau in Moscow led by Vladimir Khrustalev.

According to notes made at the beginning of May 1967 by the head of TsKBEM Vasily Mishin, the delivery of the 100K sensor was not expected before the end of June. Around the same time, Mishin also mentioned some issues with overweight solar panels on vehicles 6L and 7L. (It is possible, at that point that the decision was made to drop one of four sections of solar panels borrowed from the 7K-OK spacecraft to save mass, thus leaving L1 vehicles with three-section solar panels.)

At the time, the launch of the 6L vehicle was expected between July 12 and 17, 1967. By June 1967, the mission slipped to the August 24-30 period, but by mid August, the ship was expected to arrive at the Checkout and Test Station, KIS, at the TsKBEM design bureau on August 28, and its launch was now pushed to September 1967. (774)

On January 28, 1968, Mishin and his associates held a multi-hour meeting considering a multitude of issues facing TsKBEM. The event was chaired by Sergei Afanasiev, the Minister of General Machine-building, MOM, which oversaw the rocket industry. It took place just two days after an accident in Kapustin Yar with a prototype of the L1 capsule during an attempted test of its emergency escape system.

In addition to the discussion of technical problems, the meeting with Afanasiev turned into another round of soul-searching over the need for the L1 project, its continuous delays and the lack of assurance in its success, especially in the face of the impressive progress in the Apollo program in the US. (466)

Mishin told Afanasiev that the UR-500 rocket was not ready to carry the crew and, therefore, the L1 project required more test launches. However, the exact number of flights and the criteria for man-rating the vehicle were hotly debated. According to the head of the cosmonaut training Nikolai Kamanin, at least four or five (fully successful) unmanned flights would be required at that point before the UR-500K rocket and the L1 spacecraft could be trusted to carry a crew behind the Moon. Privately, Chertok and his closest colleagues expressed doubts whether L1 could or should been manned.

Moreover, Georgy Tyulin, who led the State Commission overseeing the project, Konstantin Bushuev (Mishin's deputy) and, apparently, even Afanasiev himself, raised the issue of canceling the L1 project altogether. Their argument was that in the course of its development, the L1 vehicle had evolved far from being a direct precursor to the L3 lunar orbiting spacecraft, as it was originally promised at the start of the program. In practice, the L1 ended up bearing little resemblance to the L3 and, as a result, turned into a distraction for the ultimate goal of landing a cosmonaut on the Moon within the L3 project. However Mishin’s first deputy Sergei Okhapkin argued that the L1 vehicle still had a chance to take cosmonauts behind the Moon in 1968, despite all the current problems. In this case, the USSR could still beat the Apollo program in a feat second only to the lunar landing itself.

In the end, Afanasiev instructed Mishin to throw all the energy of his design bureau to the L1 and the 7K-OK project, given their huge political significance.

At the time, Mishin planned monthly launches of the L1 spacecraft, with the next flight targeted at the beginning of March. It would be followed by a pair of 7K-OK ships scheduled for launch in April 1968. Such an ambitious schedule became possible because by that time, the serial production of the L1 vehicle finally overcame many of its growing pains with the help of the newly appointed project manager Yuri Semenov. At the very least, TsKBEM now had enough hardware in the pipeline for the entire 1968, making it remotely possible to send a pair of cosmonauts over the Far Side of the Moon in the second half of the year. However, the L1 project still faced many technical problems with the flight control and navigation systems.

Final countdown

On February 2, the Bezhitsa set sail from Odessa to the Atlantic Ocean on a six-month voyage to track the L1-6L mission and a number of subsequent launches. A second tracking ship – Ristna -- would be stationed on the opposite side of Africa.

On February 28, Kamanin boarded a Tu-124 aircraft for a flight to Tyuratam with a group of Soviet cosmonauts involved into the L1 project, including Yuri Gagarin, Valery Bykovsky, Anatoly Voronov and Vitaly Sevastyanov. The launch site met them with a bitter cold reaching minus 10C degrees and strong winds.

Because the frozen Aral Sea fell into the possible landing zone of the 6L mission, Kamanin ordered that one Mi-6 heavy helicopter be equipped with a 20-meter line, which could be used to extract the capsule from the icy waters and avoid an unlikely repeat of the situation at the end of the Kosmos-140 mission a year earlier.

Another group from the cosmonaut training center led by Aleksei Leonov flew directly to Crimea, where they were expected to participate in tracking of the 6L flight from the NIP-16 ground station near Yevpatoria on the Black Sea coast. At the time, NIP-16 was the primary control site for human space flight and deep-space missions.

March 2: Launch

On March 1, 1968, members of the State Commission overseeing the L1 launches, including Mishin, Chelomei, Barmin, Karas and Kazakov, flew to Tyuratam. (466) In the evening, the State Commission issued the final "go" to the liftoff the next day. Kamanin cited some minor technical issues with the 6L spacecraft, but because none of them were affecting this flight, the vehicle was declared to be ready.

On the day of the launch, it was minus 3C degrees and wind gusts were reaching 18 meters per second, but the final preparations for launch proceeded without a hitch.

The eight UR-500K rocket, carrying the 7K-L1 No. 6 spacecraft, lifted off from "Left" pad at Site 81 in Tyuratam exactly as scheduled on March 2, 1968, at 21:29:23 Moscow Time and quickly disappeared in the dark night clouds hanging just 150 meters above.

Two An-12 and one Tu-124 aircraft were tracking the rocket from 35 to 40 kilometers away from altitudes of 9, 10 and 11 kilometers. Their crews were trying to capture on film the critical period near the separation between the first and second stage around 126 seconds into the flight, where there had been a failure during the previous launch attempt. Kamanin was skeptical about the quality of the imagery from such a great distance but considered it to be a trial prior to upcoming launches of the N1 Moon rocket.

As reported by the pilots, after piercing through three layers of clouds, the rocket finally emerged from the top ceiling at an altitude of 8,300 meters. (820)

Fortunately, after the two previous failures, all three booster stages of the rocket finally worked as planned and the Block-D upper stage completed the insertion of the 6L spacecraft into an initial circular orbit around the Earth.

After making nearly one revolution around the Earth, Block D fired again at 22:41:19 Moscow Time. The 7-minute 39-second burn successfully stretched the circular orbit into an ellipse with an apogee of more than 300,000 kilometers away. In the Atlantic Ocean, the Bezhitsa tracking ship monitored the second firing of Block D.

Once the 6L mission proceeded into the deep-space trajectory, it was officially announced as Zond-4. Within the Soviet space industry, the term "zond" initially applied to flights heading into deep space without a particular destination such as Mars or Venus. However, this time, the Soviet officials decided to conflate the L1 mission with unrelated launches of three Zond unmanned probes to camouflage the connection of the project to the human missions.

The official Soviet announcement also said that the spacecraft had been inserted into its "predetermined trajectory" from an intermediate Earth's orbit. However, the communique gave no details on the flight program besides saying that "the aim of the flight is to explore deeper regions of near-Earth space, as well as to perfect new systems onboard." (50)

March 3

With Zond-4 on its way, Chertok, Ryzansky, Boguslavsky and Khitrik flew from Moscow for Crimea around noon on March 3 aboard an An-12 transport plane in order to monitor the mission from the NIP-16 ground station. Around the same time, more than 70 officials also landed at the same airfield in Saki near Yevpatoria aboard an Il-18, after watching the Zond-4 launch in Tyuratam. For many engineers, who were not directly involved in flight control operations, this trip was Mishin's way of thanking them for the successful liftoff. However, when Mishin bumped into Chertok and his associates from Moscow at the airfield, he got angry and demanded that the whole group to fly back to Moscow. Mishin was apparently upset because of recent complaints from his superiors at the Ministry or within the political leadership that too many mid-level managers had been involved in micro-managing the ongoing flights, instead of focusing on lagging development programs. They probably demanded that Mishin crack down on the practice.

Mikhail Ryazansky tried to reason with Mishin, but Chertok demonstratively turned around and started walking back to the plane, before being intercepted by a Navy officer who urged him to stay and offered a ride from the Saki airfield to NIP-16 along with his associates. During the ride, Chertok's colleague Evgeny Boguslavsky joked that despite Mishin's short temper, his management style should be considered a big progress for TsKBEM, because Mishin's predecessor Sergei Korolev during his own public outbursts famously threatened to make offenders "walk the rails" from Tyuratam to Moscow. "Compare that to Mishin, who provides an airplane," Boguslavsky laughed.

At NIP-16, newly arrived specialists learned that the systems aboard the 6L spacecraft had been operating well. On the recommendation from the ballistic calculations team, the officials made a decision to conduct a minor trajectory adjustment maneuver with the KD engine on the morning of March 4, when Zond-4 was expected to be 225,000 kilometers away from Earth.

March 4

The initial attempt to conduct the first maneuver of the L1 spacecraft at 07:35 Moscow Time had to be aborted because the 100K star tracker failed to lock onto Sirius just two seconds after the star came into its field of view. Without the continuous tracking of at least one bright star, such as Sirius or Canopus, ground control was unable to place the spacecraft into the proper orientation for the maneuver. After an initial failure to find the star, the 100K sensor apparently began reacting to bursts of peroxide thrusters, whose exhaust particles were sparkling in sunlight. A team of engineers from the TsKB Geofizika bureau in Moscow led by Vladimir Khrustalev tried to troubleshoot the issue but without much success.

Mishin, watching torturous efforts by the flight control team, wanted to consult with his top flight control experts Viktor Legostaev and Evgeny Bashkin but had to be reminded that he had ordered them to stay in Moscow, probably, as a part of the same crackdown on needless travel. Now, Mishin urgently summoned the specialists to Crimea. (466)

March 5

On March 5, Viktor Legostaev, Evgeny Bashkin, Oleg Babkov, Stanislav Savchenko, Vladlen Rastorguev, Aleksandr Sverchkov from TsKBEM and Anatoly Azarov from TsKB Geofizika flew to Crimea to troubleshoot the Zond-4 mission.

They first advised the flight control team to try resetting the sensitivity of the troubled 100K sensor to Venus, so that the ballistic calculations team could then try to use the brightest planet in the sky as a reference.

March 6

The first attempt to rely on Venus for navigation of the Zond-4 mission was made during the night from March 5 to March 6, 1968, but after long efforts to capture the planet into the field of view of the 100K sensor, it turned out that the instrument was not operating properly. Moreover, the angular distance between Sun and Venus was getting smaller threatening to blind the sensitive optics of the tracker. Engineers then attempted to re-calibrate the sensor for the brightness of Sirius but transmitting commands aboard the spacecraft flying nearly 300,000 kilometers from Earth required a prolonged effort of a large group of engineers.

After another failed attempt at stabilization, the 100K sensor was switched to a medium-density light filter, which worked. The spacecraft remained steady and in the proper orientation during the 15-second engine firing. The maneuver turned out to be very accurate, adding 9.129 meters per second compared to the planned 9.202 meters per second.

The Zond-4 then passed its apogee more than 300,000 kilometers away and headed back to Earth. For the first time, a Soviet space capsule was about to hit the Earth's atmosphere with nearly the second cosmic speed.

Mission control now considered another trajectory correction very early in the morning of March 9, 1968, on a "as needed" basis when the spacecraft would be 167,000 kilometers away from Earth. The maneuver would put the ship into a corridor for the dual atmospheric entry expected to begin just after 21:00 Moscow Time. (466)

March 7

Beginning on March 7, mission control faced another issue – concerns over the temperature of the hydrogen peroxide, which was used for the attitude control thrusters in the L1 spacecraft. It fell to minus 1 or 2 degrees, and at minus 4 or 5 degrees it could disable the attitude control thrusters, certainly leading to the loss of the spacecraft. At the same time, three ballistic calculations centers across the USSR were conducting non-stop estimates of the actual trajectory and their engineers debated between themselves whether another trajectory correction would be needed. (466) According to Kamanin, the latest reports from mission control indicated that the spacecraft was on the exact flight path. (820)

March 8

Around 3 a.m. in the morning, flight controllers began continuous measurements of the mission's trajectory trying to narrow down its expected Earth approach corridor. They were able to receive signal from the ship's high-gain antenna, but its signal-to-noise was considerably worse than expected. The radio team led by Boguslavsky was analyzing that issue but could not exactly pinpoint the culprit. In parallel, the main ballistic team still remained uncertain whether extra trajectory correction would be necessary.

In the meantime, tension and chaos were growing at NIP-16. By the middle of the day, the main control room was completely crowded with people. In addition to debating flight control problems, engineers simultaneously dealt with other most pressing technical issues, including finalizing paperwork for necessary upgrades on the follow-on vehicle 7L.

Tyulin, as the Head of the State Commission, finally demanded his subordinates to make a decision on whether the second trajectory correction would be necessary.

Colonel Pavel Elyasberg, who oversaw the ballistic forecasts at NII-4 in Bolshevo near Moscow explained to Chertok that his team had been continuously recalculating the trajectory based on the most current measurements, but his bulky and trouble-prone computers required their own time for maintenance and cooling off periods.

In the meantime, flight controllers were preparing to upload the algorithm to the timer-programmer, PVU, unit aboard the spacecraft for its upcoming descent sequence. It included a celestial navigation session, the activation of the onboard calculator, the spin up of gyroscopes of the three-axis stabilization system, which would be absolutely necessary for the aerodynamic control of the capsule during the first dip into the atmosphere. The spacecraft was also programmed to separate the instrument module and the high-gain antenna, before entering the atmosphere. The capsule would then reach deceleration of around 4 g and begin rotation around one axis, producing some aerodynamic lift, while descending into the stratosphere as low as 45.8 kilometers above the Earth’s surface. Around the time the capsule slowed down to a near orbital velocity, it would climb again, as high as 145 kilometers in the upper atmosphere, only to plunge back some 20 minutes later.

According to the latest calculations, the descent module was to begin its first atmospheric entry on March 9 at 21:19:18 Moscow Time. Its separation from the instrument module was expected around eight minutes earlier.

If everything went as planned, the descent module would land at 21:56 Moscow Time on March 9 or around 13 minutes behind the original schedule.

March 9: Landing

Beginning at 18:00 Moscow Time, General Agadzhanov, who was in charge of the mission control operations at NIP-16, began readiness review for all the ground and sea-based assets. The Ristna tracking ship called from the Southern Atlantic Ocean, where it was expected to hear from Zond-4 at 21:03 Moscow Time, before the descent and instrument modules were to separate. Then, at 21:20 Moscow Time, the descent module making its first reentry was expected to contact the Bezhitsa ship, stationed in the Gulf of Guinea of the eastern coast of Africa. Finally, NIP-16 in Crimea was expected to hear from the capsule at 21:33 Moscow Time.

When the actual time for reentry finally came, the Ristna did confirm via a communication post in Odessa that it had heard from the spacecraft as planned.

The separation was also confirmed to be as planned and on time. However, the Bezhitsa was not confirming its contact with the spacecraft, even after the vehicle was expected to have exited the ship's communications range.

In the meantime, the search and rescue aircraft entered the expected landing zone and, around the same time, a communications post in Tbilisi, Georgia, reported that it was hearing signals of the Zarya UHF transmitter aboard Zond-4. Then, the NIP-10 ground station, in Simferopol, in Crimea, also began receiving the signal.

Suddenly, word came from the Ristna that it was receiving signals from the spacecraft, which was unbelievably late, given its location, but its data indicated 20 g deceleration aboard the vehicle, which was a clear hint that the capsule was in a steep ballistic descent rather than on the planned aerodynamically controlled trajectory.

Moreover, the Soviet anti-aircraft services reported that they had not seen any radar signature from the capsule, which they should be able to track by the time the ship's Zarya radio could be heard in Tbilisi and Simferopol. The fact that neither NIP-16 nor the Bezhitsa heard the signals from the Zarya radio added to the suspicion that Tbilisi and Simferopol probably had picked some UHF signals from local TV stations reflected from the mountains.

After reviewing all the available data, it was increasingly clear that the spacecraft had not reached the Soviet Union. Also, if the data about 20 g deceleration was correct it would certainly trigger the APO self-destruct mechanism. The APO system was powered up in case the vehicle fell short of the Soviet territory, while crossing Africa and Turkey. The monitored deceleration rate seemed too high even for a ballistic descent in most contingency situations. Still, Aleksei Leonov, who was present at mission control and heard the number, said "we can endure that, only if you won't blow us up..."

Chertok then compiled a timeline of the actual radio contacts, which roughly coincided with the window forecasted by the ballistic team in the case of the uncontrolled ballistic descent. According to the actual data, the Ristna was in contact with the spacecraft from 21:11:39 until 21:18:58 Moscow Time. The communications ended during the first entry into the atmosphere, when the capsule was surrounded with plasma. However, the spacecraft never exited the atmosphere and continued ballistic descent. As the plasma around the capsule subsided, Bezhitsa picked its signals at 21:21 Moscow Time. However the signal was interrupted as the APO blew up the vehicle at an altitude of just 10 or 15 kilometers, and between 150 and 200 kilometers off the coast of Africa.

(One source claimed that the capsule had been destroyed over the Bay of Biscay.) (52)

While specialists were debating the likely landing scenario, more details emerged from the transmissions received by the Ristna. As it became apparent, during the orientation session aboard Zond-4 preceding the first atmospheric entry, star trackers recorded strong light exposure, followed by the blockage of the GSP gyroscope system and the failure of the Descent Control System, SUS. The attitude control system had never been able to lock onto the star and the autonomous flight control system was powered down.

Chertok and other specialists could only guess what had happened, but they immediately suspected that the 100K tracker had probably failed again, possibly confusing Sirius and Canopus and thus preventing all subsequent operations. For a more detailed analysis, the Ristna was urgently sent to the African coast and an Il-18 aircraft was dispatched to Somalia to pick up its telemetry tapes for the in-depth evaluation of the data received by the vessel. However, with all the logistical problems, the review process would require at least six days.

Before the end of the day on March 9, Chertok and Moisei Khitrik concluded that the 100K sensor had not been reliable and they had no other way to keep the L1 ships oriented in deep space.

By midnight, the specialists were finally ready to break up their discussions and catch a 9 a.m. flight to Moscow next morning.

Learning lessons from the Zond-4 mission

On March 11, Mishin called Chertok, who had fallen ill after the trip to Crimea, and expressed his satisfaction with the results of the Zond-4 mission. Besides the troubled 100K sensor, everything else had worked remarkably well. According to the latest report, the spacecraft had entered the descent corridor with a deviation of just two kilometers within the allowable 10-kilometer margin. Therefore, the Zond-4 mission was considered a success. (52)

While it was still necessary to figure out what was going on with the celestial navigation system, Mishin nevertheless proposed to go to the upcoming State Commission meeting on the L1 project, with a proposal to launch Vehicle L1 No. 7 no later than April 25. Moreover, the next L1 mission was to be preceded by another rendezvous flight of a pair of 7K-OK spacecraft.

The subsequent investigation of the star tracker problems found the contamination of its optical surfaces. (202) Engineers suspected that the black enamel on the protective tube-shaped blind of the sensor began flaking in the vacuum of space under the harsh impact of direct sunlight. Some particles from the baked paint could have gotten onto the lenses of the sensor. Simulations conducted at TsKB Geofizika had confirmed that hypothesis.

The continuous problems with the 100K sensors required the development of a special cover for the sensor, which itself would become a problem in the future.

Also, the problems with the powering the DRS long-range communications system required the introduction of special tests of the DRS via the ONA high-gain antenna at the processing complex of the launch site prior to all future missions of the L1 vehicles. (52)

Also, on March 12, Gagarin and Leonov reported on their experience from watching the Zond-4 mission to their boss General Kamanin. Leonov argued that a situation similar to the contingency during the reentry of Zond-4 would not be fatal for a hypothetical circumlunar mission with pilots onboard. However, Kamanin was outraged by the fact that TsKBEM continued flying vehicles rigged with APO explosives. "Why blow up the vehicle, even if it lands in Africa? We could test the parachute system, recover the capsule and learn much more!" Chertok remembered Kamanin as saying.

However, TsKBEM had strict instructions from the Communist Party bosses to destroy Soviet spacecraft landing beyond the USSR. The rational was two-fold -- to prevent "space secrets" from falling into the wrong hands, but also to deny any notion of failures in the Soviet space program. Still, Kamanin called Tyulin and Mishin and threatened that he would officially request that the APO explosives be disabled, no matter where the ship was landing, beginning with the next launch.

Chertok and Khitrik reported on their findings in the post-flight analysis of the Zond-4 flight during the meeting of the State Commission chaired by Georgy Tyulin on March 26, 1968. The event started at 15:00 that day, followed the morning review of the 7K-OK project.

According to the final report, during the first three days of the flight, the 100K sensor failed to capture Sirius in its sights, preventing trajectory corrections. The maneuver finally succeeded on the fourth day of the flight, putting the vehicle on the correct trajectory. Unfortunately, right before the first atmospheric entry, the 100K sensor failed again, preventing a controlled descent. As planned under such a contingency, the vehicle switched to a ballistic descent, followed by the activation of the APO self-destruct mechanism.

The post-flight analysis also revealed that the main beam and the umbrella of the High-Gain Antenna, ONA, had failed to deploy properly, compromising the main channel of communications with the Earth from lunar distances. During the communications through the botched antenna, the DRS deep-space communications system was apparently losing its power capacity.

At the conclusion, engineers, who were already exhausted by two back-to-back meetings, approved, without much debate, the target date for the next L1 flight -- Vehicle No. 7 -- on April 23, 1968. The April 23 launch date would allow a flight behind the Moon, while a backup window extending from April 25 to April 30, would require a flight around an imaginary point around 300,000 kilometers away.

Western view

Exactly as devised by Soviet secrecy officers, the Zond-4 mission generated a great deal of guessing in the West, first of all, because the timing of the launch indicated that the mission was headed in a nearly opposite direction from the Moon. Still, Western observers were eventually able to tie Zond-4 to the circumlunar flight program.

Also, because the USSR had never announced the return of Zond-4, there were disagreements in the West about its fate. Some speculated that the mission went into a heliocentric orbit, like the previous Zond flights. Other believed that the spacecraft had remained in a highly eccentric Earth's orbit. There were even speculations that the capsule had crashed in China. Still, there was at least one correct supposition that the recovery of the Zond-4 spacecraft had been planned but the landing had failed for an unknown reason. However, because during the following Zond-5 mission, the USSR was publishing periodic communiques on the progress of that flight, some suggested that the absence of such announcements during the Zond-4 mission could indicate a loss of communications with the spacecraft early into the flight. (50)

Next chapter: Mission of Vehicle 7K-L1 No. 7L

Read much more about the history of the Russian space program in a richly illustrated, large-format glossy edition:


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The article and illustration by Anatoly Zak; Last update: October 24, 2020

Page editor: Alain Chabot, Last edit: March 5, 2018

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Viktor Legostaev oversaw the development of the flight control system for the 7K spacecraft series.


Evgeny Bashkin from Department 312 at TsKBEM was responsible for troublesome attitude control system of the 7K -OK and 7K-L1 spacecraft. Credit: RKK Energia


Vladimir Khrustalev, Chief Designer at TsKB Geofizika (formerly TsKB-589), oversaw the development of the 100K star tracker.


Colonel Pavel Elyasberg led ballistic calculations at NII-4 research institute in support of the Zond-4 mission.


A Soviet mission control room in the 1960s.


A. L. Sudachenko, Boris Raushenbakh, D. A. Knyazev, Viktor Legostaev, V. S. Volodin, Evgeny Bashkin, S. A. Savchenko and O. I. Bobkov work on the flight control system of the L1 spacecraft. Credit: RKK Energia