Zond-6: Racing Apollo-8
On Nov. 10, 1968, the USSR launched the eighth prototype of the L1 spacecraft, publicly announced as Zond-6. The spacecraft looped around the Moon and returned to Earth a week later. The official Soviet press was now making no secret that the Zond flights aimed to rehearse a piloted mission around the Moon, which could be imminent. The seemingly successful landing of Zond-6 on Nov. 17, 1968, added even more anxiety to NASA's hectic preparations for the super-risky Apollo-8 mission assigned to orbit the Moon with a crew following December.
An artist rendering of the Zond-6 spacecraft during its flyby of the Moon.
The Zond-6 mission at a glance:
Vehicle No. 12L flight program
If everything worked as planned, Vehicle 7K-L1 No. 12L (or simply 12L), which would become Zond-6, could be one of two dress rehearsal missions before the launch of a Soviet crew around the Moon. However, it would be possible on the condition that these two robotic flights perform without major technical problems, giving the political leaders in the Kremlin enough confidence in the safety of the cosmonauts. (820)
Following the flight of Vehicle No. 9L in September 1968 (announced as Zond-5), the successive ship -- No. 10 -- was being converted into a payload for the first test launch of the N1 Moon rocket scheduled for the beginning of 1969. (231) In the meantime, Vehicle No. 12L was picked for the next test launch in the L1 program planned for November 1968.
The main goal of the Zond-6 mission was to land the circumlunar vehicle in the Soviet territory, rather than in the Indian Ocean, where it had ended up following a ballistic return in the previous mission. To reach the USSR from its lunar-return trajectory, the Descent Module would have to use a so-called skip reentry. Moving with the second cosmic velocity of around 11.2 kilometers per second, the capsule would hit the dense atmosphere and use its aerodynamics to bounce back into space. (52) The capsule would emerge from the atmosphere with a considerably reduced speed and then plunge back again for the final descent. (50)
In addition to shifting search and rescue operations from the Indian Ocean to routine Soviet landing zones in Kazakhstan, the skip reentry would also dramatically reduce g-forces affecting the crew from 10-15 times to just 4-7 times. (50)
The assembly of Vehicle No. 12L was completed at the experimental plant of the TsKBEM design bureau in Podlipki near Moscow in the middle of August 1968. The spacecraft was then transferred to the organization's Control and Checkout Facility, KIS, for tests before its shipment to the launch site in Tyuratam, planned for Aug. 25, 1968. (774)
After the successful landing of Georgy Beregovoi on Oct. 30, 1968, Soviet space officials had slightly more than a week for celebrations in Moscow, before returning to the Tyuratam launch site in Kazakhstan for the launch of Vehicle No. 12L.
On Nov. 9, 1968, key managers at TsKBEM, including its Designer General Vasily Mishin and the Head of cosmonaut training Nikolai Kamanin flew to Tyuratam, along with the cosmonauts training for the L1 missions. The group led by Aleksei Leonov also included Valery Bykovsky, Pavel Popovich, Oleg Makarov, Nikolai Rukavishnikov and Vitaly Sevastyanov.
On the same day, at 19:00 local time, the State Commission met at Site 81, where the UR-500K rocket was standing ready for launch. The officials approved the liftoff time on Nov. 10, 1968, at 22:11:30 Moscow Time. (820)
Launch and trip to the Moon
The UR-500K/Block D rocket carrying the L1 No. 12L spacecraft lifted off from Site 81 in Tyuratam right after midnight local time on Nov. 10, 1968, with a delay of just 0.08 seconds. Thanks to a cold clear night sky, eyewitnesses at the launch site could see the rocket for more than six minutes after its liftoff.
Following normal operation of the first three stages, the Block D/L1 stack was reported entering a close-to-planned initial orbit:
Around 67 minutes after the liftoff, the Block D upper stage restarted, successfully boosting the spacecraft from the Earth's orbit into the trans-lunar trajectory. (50)
The initial measurements of the trajectory showed that Vehicle No. 12L was on track to swing behind the Moon at a distance of around 3,000 kilometers without any additional corrections. However, the telemetry also showed that the main boom of the umbrella-shaped high-gain antenna on the spacecraft had failed to deploy, which could hamper the trajectory corrections necessary for the atmospheric reentry. Without the trajectory corrections, the spacecraft would fly 1,050 kilometers from Earth without hitting the atmosphere. Fortunately, the additional omni-directional antenna provided good contact between the mission control and the spacecraft.
The Soviet press announced the flight under the name Zond-6.
In the first half of the day on November 11, the most of the officials left Tyuratam for the main control center of the L1 project at the NIP-16 ground station in Crimea. There, an engineering meeting on the status of the flight was held, concluding at 22:00 Moscow Time. Specialists confirmed that despite the folded antenna, the quality of communications was excellent, all other systems aboard the spacecraft were also functioning well and engineers responsible for the celestial navigation system were positive that the 100K and 101K star trackers would work well to ensure reliable attitude control of the spacecraft for the upcoming engine firing. (820)
November 12: First orbit correction
At 4.a.m. in the morning on November 12, Kamanin, Mishin and Georgy Tyulin, who chaired the State Commission, reported to mission control. Aleksei Leonov, who had spent the night monitoring systems, said that he had heard his own voice reaching the spacecraft and then being transmitted back with a 2-second delay.
Unfortunately, the 101K sensor, located at the tip of the folded high-gain antenna refused to work, because the antenna boom was too close to the body of the spacecraft. As a result, specialists had to resort to the 100K sensors, which had often misbehaved in the past. Fortunately, this time, the tracker quickly homed in on the star Sirius and kept it in its sight, giving mission control a reliable reference point for navigation. The spacecraft was successfully put in the right attitude 40 minutes before the planned maneuver and the main engine was ignited at 08:40:39 Moscow Time, firing for 8.5 seconds. (820) At the time, the spacecraft was 246,000 kilometers from Earth. (2)
Following the maneuver, mission control conducted as many as four sessions measuring the resulting trajectory and it appeared to be very accurate. However at that point, engineers still could not ensure the altitude of the perigee (lowest) point from Earth on the return leg of the trip, which would determine, the ship's reentry corridor. Some estimates showed that the spacecraft would pass farther than 200 kilometers from Earth, which would be too high for reentry and result in a flyby of the planet. Therefore at least one or possibly two more corrections were planned after the flyby of the Moon. (820)
November 13: Challenge from Apollo-8
On November 13, the powerful Secretary of the Central Committee of the Communist Party Dmitry Ustinov, who oversaw the rocket industry, called mission control and said that NASA had publicly announced that the Apollo-8 mission scheduled for launch on Dec. 21, 1968, would be prepared for entering lunar orbit. If successful, it would upstage the yet-to-be achieved goal of the L1 project.
Ustinov asked how the USSR could respond to that. Tyulin, Mishin and Kamanin discussed the situation and sent Ustinov a list of their talking points:
The officials also reported to Ustinov their plans for the next two months. In December, another L1 mission and the first N1 Moon rocket with a prototype of the L3 spacecraft were scheduled for launch. By January 1969, there were plans to fly the L1 spacecraft around the Moon with two cosmonauts onboard and land a robotic rover on the lunar surface. Also, in January, two piloted Soyuz spacecraft would dock in space and two of their crew members were to transfer from one ship to another.
Kamanin admitted that this program was very challenging for both the industry and the cosmonauts training for the L1 project. He blamed the high automation of the Soviet spacecraft for pushing the program a minimum three or four years behind the Apollo project, where pilots played a critical role in controlling the spacecraft.
On the same day, Kamanin, Mishin, Tregub and Shabarov met with L1 cosmonauts, including Leonov, Bykovsky, Popovich and Makarov, where they debated the contents of the onboard documentation for the circumlunar flights. Mishin tried to convince Kamanin to merge the flight journal and instructions into a single document, but Kamanin fiercely resisted seeing in it as a ploy to strip cosmonauts of their ability to control automated systems aboard the spacecraft. (820)
November 14: Imaging the Moon, flyaround
On November 14, as Zond-6 was approaching the Moon, mission control prepared for imaging of the lunar surface. (820) The first photo session was conducted from a distance between 11,000 and 8,000 kilometers from the Moon. It had the goal of imaging the entire surface of the Earth's natural satellite to enable photometric measurements and the calculation of its exact size and shape. (2, 52)
The second photo session was conducted from a distance of around 3,300 and 2,600 kilometers, aiming to produce high-resolution images for mapping the Far Side of the Moon. The camera used a focus length of 400 millimeters and exposed images on 13 by 18-centimeter frames. The aperture was automatically setup by the camera. (2, 52)
According to Kamanin both photo sessions were conducted between three and six in the morning Moscow Time on November 14, during the flyby of the lunar surface.
After the ship had disappeared behind the lunar horizon, communications were interrupted at 05:49:37 Moscow Time. Slightly more than half an hour later, Zond-6 reappeared on the opposite side of the Moon and radio contact was restored at 06:21:11 Moscow Time. (820) During that period, the spacecraft flew at a minimum distance from the Moon of about 2,420 kilometers. (2, 50) At the same time, Zond-6 was around 390,000 kilometers away from Earth.
By that time, mission control had conducted a total five successful attitude control sessions using celestial orientation. To the satisfaction of flight controllers, the 100K sensor was now reliably locking in on Sirius. (820)
However, Kamanin also claimed that Mishin had gotten heavily drunk and had to go to bed. He also characterized Mishin as capricious, disorganized and not a very deep person (despite being Korolev's right hand man since their work in Germany at the end of World War II.) Kamanin also quoted Tyulin as talking about replacing Mishin, but concluding that it would be impossible at the culmination of the 7K-OK, L1 and L3 projects. (820)
On November 14, Kamanin again discussed the timeline of the L1 project with the cosmonauts. According to Kamanin, everybody understood that a piloted circumlunar flight would not be possible before April 1969, at the earliest. However, under pressure from the Apollo-8, it might be realistic to advance the flight without much risk to January 1969. (820)
The cosmonauts expressed readiness to fly as early as December (in an effort to upstage Apollo-8), but Kamanin knew that it would not possible to prepare the spacecraft by that time, taking into account the fact that one more fully successful unpiloted mission would be required after Zond-6. Kamanin informed the group, that flight of the crew would be aimed for January 1969, however, if Apollo-8 succeeded with its mission in December 1968, the piloted launch would default back to April 1969. (820)
November 15: Thermal control issue
During the night from November 14 to November 15, mission control began worrying about the thermal conditioning of the hydrogen peroxide, which served as a propellant in the Descent Control System, SUS, of the Descent Module. The initial temperature of the peroxide was +20, but in the first two or three days of the flight, it slowly fell to -2 degrees. The temperature then continued its downward trend and finally reached a dangerous level of -5 degrees. Flight controllers were now worrying that any further cooling of the fluid could lead to the separation of oxygen and freezing of the remaining water. Without the attitude control thrusters, the SUS system would not be able to control the aerodynamic descent of the capsule in the atmosphere. As a result, the ship would end up on a ballistic trajectory, precluding a landing on the Soviet territory -- the main goal of the mission.
The cooling of peroxide to between -2 and -3 degrees had already been observed during Zond-4 and Zond-5 missions, but flight controllers had tackled the problem by activating TV monitors inside the capsule, which had radiated enough heat to keep the temperature of the peroxide tanks also located inside the capsule at an acceptable level. However, according to Kamanin, TV monitors had been removed from Vehicle No. 12 under orders from Mishin, who had not bothered informing the State Commission about this move.
This time, flight controllers had to resort to heating peroxide tanks by changing the orientation of the spacecraft relative to the sun, but that move risked blinding and overheating critically important 100K star tracker, which was located on the same side of the spacecraft as the peroxide tanks. (820)
November 16: Loss of pressure
Around 4 a.m. in the morning on November 16, mission control successfully re-oriented the Zond-6 spacecraft relative to the sun, to allow the peroxide tanks aboard the Descent Module to warm up. The controllers kept the ship in the required position for about an hour. The measure had the desired effect, bringing the peroxide temperature up to satisfactory -1 degrees. However, at the same time, mission control detected a more serious problem -- an air leak inside the Descent Module. From 05:13 to 05:20 Moscow Time (when the orientation of the spacecraft toward the sun had already discontinued), the pressure inside the capsule dropped from from 718 to 610 millimeters of mercury. The pressure then continued falling and by 08:30 Moscow Time it had dropped to 380 millimeters, where it had finally stabilized for the time being. (820, 52)
Adding to the tense atmosphere at the NIP-16 ground station in Crimea was the health of Mishin, who after another sleepless night and heavy drinking, experienced high blood pressure upon hearing the news of the depressurization of Zond-6. Fortunately, Air Force physician Colonel Lebedev was on hand to help the Designer General. Kamanin told Lebedev to escort Mishin to bed in his hotel, and after around 15 minutes trying to stay at his post, Mishin finally relented and left.
The specialists at mission control were also distracted by phone calls from Ustinov, Smirnov and other high officials in Moscow, who were now also worrying about the fate of Zond-6.
Fortunately, in the following 12 hours, the pressure inside Descent Module and the temperature of the peroxide propellant remained stable. Mission control also successfully conducted a seventh session of celestial orientation using the 100K sensor, boosting confidence in a successful landing. (820) Around 06:40 GMT, Zond-6 successfully conducted the second trajectory correction at a distance of 236,000 kilometers from the home planet. (2, 50)
Kamanin then called General Kutasin, who was in charge of search operations, and told him that the landing of Zond-6 in Kazakhstan was expected at 17:02 Moscow Time, the next day. For Kutasin, it meant search operations in night-time conditions, further complicated by the less-than-ideal weather forecast.
In the meantime, Mishin was absent from the ground control center for the entire day. According to Kamanin, he stayed at his hotel room "sick" and indifferent to all the activities. In fact, Mishin's own notes on the Zond-6 mission appear rather scarce.
November 17: Return to Earth
On November 17, the latest radio contact with Zond-6 showed that the internal pressure remained at 380 millimeters and that the temperature of the peroxide had increased to a comfortable +1 degrees. However, the trajectory measurements showed that the previous correction on November 16 had "depressed" the trajectory too much, pushing the lowest point of the ship's Earth flyby to just 25 kilometers above the surface, while the required perigee was supposed to be 49 kilometers with an allowable deviation not exceeding seven kilometers. (820)
To adjust the flight path, the third and final adjustment was conducted on November 17, at 05:36 GMT, some 8.5 hours before reentry. (2, 50) The 100K sensors worked perfectly again and the 3.3-second engine firing ensured that the spacecraft was within the 10-13-kilometer wide corridor with a minimum altitude of 45 kilometers above the Earth's surface. (2)
Kamanin then chaired a meeting on the recovery operations at the primary landing zone, where the touchdown seemed increasingly likely. However due to concerns about the effects of the still folded high-gain antenna and the low air pressure on the reentry of the capsule, mission management made a decision to arm the self-destruct mechanism aboard the spacecraft. According to Kamanin, he spoke against such a "barbarism," but was overruled by the majority.
By 16:00 Moscow Time on November 17, Zond-6 had received all the commands for the descent, and around 20 minutes earlier, the spacecraft had oriented itself for landing. The descent sequence was initiated shortly thereafter.
Up to the moment of separation between the Descent Module and the Instrument Compartment, telemetry from the spacecraft was being received by the Kosmonavt Vladimir Komarov vessel, and after the separation, three other ships in the Indian Ocean, followed by ground stations on the Soviet territory and by specially equipped tracking aircraft. However, none of these assets managed to receive confirmations about the separation itself, the first entry into the atmosphere, the exit or the second entry. (820)
Fortunately, as Zond-6 began its final descent, the Soviet Krug (circle) anti-aircraft radar detected the capsule over Afghanistan, around 300 kilometers south of the Soviet border.
Mission control in Crimea received the first confirmation that the capsule was being tracked from General Kutasin at the Air Force headquarters. "Distance for the projected landing point is 1,800 kilometers," Kutasin announced.
Kutasin continued reports every 200 kilometers of the ship's progress toward the landing area located between 100 and 150 kilometers north of its launch site near Tyuratam.
However, at a distance of 300 kilometers from the landing zone, Kutasin's reports stopped. Not only the spacecraft disappeared from the radar screens, but neither aircraft nor ground stations picked any radio signals either in short waves or UHF.
The officials expected that the ship would send signals after the deployment of the parachute system, which contained its own antenna in the parachute lines. The parachute opening was scheduled at 17:19 Moscow Time, but again there was no signal then, or 15 minutes thereafter, when the capsule was supposed to touch down.
There were reports from Baku, in Azerbaijan, and from Kiev, in Ukraine, about signals from the parachute antenna lasting just one or two seconds. A few minutes later, there was a report from a group of officers at Tyuratam, who apparently saw a fireball, heading from south to north (along the expected path of the capsule).
However in the following two hours, mission control had no news on the fate of the spacecraft.
By around 20:00 on November 17, based on the available telemetry, it was established that soon after the separation of the descent and instrument modules, the pressure inside cabin had suddenly dropped from 380 to 180 millimeters and the very last measurements showed that the pressure was just 25 millimeters or near vacuum. It now became clear that the Descent Module had almost completely depressurized, which would most certainly lead to the failure of all transmitters, which had not been designed to function in vacuum. The same problem could affect the operation of the parachute system.
November 18: Search operations
In the meantime, planes and helicopters continued searching for the capsule throughout the night from November 17 to November 18, but without results. As Kamanin and Mishin returned from Crimea to Moscow around 15:30 on November 18, there was still no word on the fate of Zond-6. A total of 50 plane and 20 helicopter flights were made during the daylight hours of November 18, but again without results. (820)
Still, it was apparent that at the very least, the descent module had gotten into the target landing circle with a diameter of 500 kilometers, which could be considered a success given the complexity of the skip reentry trajectory.
That fact apparently gave the Soviet authorities enough confidence to issue an official announcement on the successful completion of the Zond-6 flight.
November 19: Spacecraft found
At 06:35 on November 19, the commander of a Mi-4 helicopter spotted the white and orange stripes of the main parachute from the Zond-6 mission in Kazakh grasslands. Shortly thereafter, another helicopter landed nearby and deployed guards at the spot. According to eyewitnesses, the parachute was stretched along the steppe, but, mysteriously, there was no capsule anywhere in sight. The location of the parachute was determined to be 38 kilometers northeast of Novokazalinks and 70 kilometers from Tyuratam, (820) not far from Zhemchug airfield. The parachute was 70 kilometers south of the projected landing spot, which was determined based on the radar data and which was used for search operations on November 18.
Now, based on the parachute location, it was decided to focus on an area with a radius of 12-15 kilometers from the parachute. All search operations with fixed-wing aircraft were discontinued. Instead, helicopters would be used to scan the area and to deploy a 100-person-strong team assembled in Tyuratam. The State Commission also formed a nine-member group of recovery specialists led by Timchenko, which was to be delivered to the parachute for a detailed inspection.
At 12:00 on November 19, General Gaidaenko, Deputy Commander of the 73rd Air Army, who led the helicopter search operations, reported that the Zond-6 had finally been located three kilometers from its parachute. Gaidaenko dropped Timchenko's brigade by the capsule and returned to Tyuratam. Gaidaenko described the capsule as crashed, but he also noted that the damaged vehicle was largely in one piece, without any signs of fire or explosion. (820) It was a clear indication that the APO self-destruct mechanism had remained intact.
Despite this news, on the same day, Kamanin had a meeting with the cosmonauts training for the L1 project, where he discussed the possibility of launching the spacecraft with a crew around the Moon in January or February 1969, even though there was talk about yet another unpiloted test flight of the L1 spacecraft, in addition to an already planned robotic mission to precede the piloted circumlunar mission. (820)
Recovery operations: De-mining Zond-6
The recovery specialists knew that the crashed Zond-6 capsule contained a black box with information which would be critical for the investigation into the failure. Also inside was supposed to be a film with photos of the Earth and the Moon taken during the flight. However, at the same time, the capsule contained a self-destruct mechanism with 10 kilograms of explosive. The state of the device after the impact was unknown, besides that it had not been triggered. Therefore, any recovery operations at the crash site had to start with the de-mining of the wreckage. (52)
The team of specialists had the task of inspecting the surviving hardware and preparing a scenario to deactivate the self-destruct mechanism. The next day, Konstantin Bushuev, Deputy to Designer General Vasily Mishin, also arrived at the site at the insistence of the State Commission. (52)
At the site, specialists discovered that the spacecraft was heavily smashed and breached, protruding from the surface by no more than one meter.
It was agreed to use only manual tools and avoid any strikes. Just two people were to directly access the dangerous wreckage: V. L. Zemskov, an expert from TsKBEM design bureau, and V.P. Petrov, the machinist from Shop No. 439. at the experimental plant where the spacecraft was assembled. (52)
After careful inspection of the wreckage, specialists began a very slow, piece-by-piece dismantling of the debris of the exterior, followed by internal components, aiming to access the location of the self-destruct mechanism. Eventually, they located the dangerous device, and after another inspection, removed it without accident. Engineers then transferred the mechanism to the officers of the operational technical team of the Air Force, who safely detonated it far in the steppe. (52)
Specialists also recovered the film with color and black and white photos of the Moon and the Earth. (52, 774) The fortified metal cassettes containing the film were deformed by the crash and the film itself was partially torn and overexposed, but at least some photos could still be produced. (231)
The spacecraft was also reported delivering scientific data on multi-charged component of the space rays and meteoroid particles. (2)
Preliminary results of the investigation were discussed on November 19, but specialists apparently continued sorting out problems of the Zond-6 mission until the end of December 1968.
The inspection of the Descent Module showed that the parachute was separated from the capsule on the command of the flight control system and that the spacecraft had reentered the atmosphere with its high-gain antenna still attached to the top bulkhead of the capsule. Fortunately, most of the antenna's structure burned up during the reentry without causing major interference in the descent process.
The investigation apparently showed that the initial depressurization of the spacecraft in flight to 380 millimeters took place along the resin insulator of the hatch. However, during the descent itself, the parachute container lost pressure as well and this led to a complete depressurization of the cabin. (231)
On December 27, Mishin's Deputy Konstantin Bushuev, who led the recovery operations, reported the results of the probe to the members of the State Commission.
The probe into the accident showed that at a height of 7.5 kilometers above the Earth's surface when the capsule was hurtling down with a speed of 200 meters per second, the parachute had successfully opened. (50) However, the near-vacuum internal conditions apparently led to the formation of a "coronal charge" in the avionics, as soon as the SUS descent system was powered up. It triggered the onboard gamma-ray altimeter, GLV, to generate a faulty two-step command to jettison the lines of the parachute system, when the capsule was still at an altitude of 5,300 meters. Soft-landing engines, which were supposed to fire at touchdown, were also activated high in the air. (466, 774) As a result, the spacecraft crashed in Tyuratam just 16 kilometers from the site where it had lifted off just a week earlier. (52)
Bushuev also reported the following problems during the Zond-6 mission:
Bushuev also reported that the depressurization was caused by inadequate sealing on the edges of the hatch and coincided with the cooling of the peroxide tanks.
Obviously, there was no word in the Soviet press about the serious failures aboard Zond-6. In fact, the post-landing TASS announcement hinted at the upcoming piloted circumlunar mission:
However, given all the technical problems uncovered by Zond-6, the flight of a crew aboard L1 spacecraft was out of the question at the time.
A night launch of an UR-500K rocket with a 7K-L1 spacecraft. Credit: RKK Energia
Specialists working on the L1 flight scenario, among them: V. S. Volodin, A. L. Sudachenko, Yu. V. Sparzhin, S. N. Maksimov, O. I. Babkov and S. A. Savhecnko. Credit: RKK Energia
An AFA-BAF camera. Credit: Roskosmos
Photos of the Earth and the Moon attributed to the Zond-6 mission.
A Soviet-era poster dedicated to the Zond-6 mission.