The USSR launches first space station crew
Four days after the Salyut space station entered orbit on April 19, 1971, the first crew was also on its way. After one aborted launch attempt, the Soyuz-10 transport ship lifted off with three cosmonauts in early hours of April 23, 1971, and reached the station the following day, but then ran into a string of potentially dangerous problems just inches away from its destination.
Ground testing of the docking mechanism between the Soyuz and Salyut space station, probably at Hall No. 439 at TsKBEM in Podlipki.
Soyuz-10 mission at a glance:
Final preparations for the Soyuz-10 mission
With the largely successful launch of the DOS-1 space station, officials quickly approved the rollout of the Soyuz-10 crew vehicle to the launch pad with the liftoff scheduled for April 22, 1971, at 02:20 Moscow Time.
On the morning of April 20, General Leonid Goreglyad, who returned from a night shift at Tyuratam's tracking facility, informed Nikolai Kamanin, the head of cosmonaut training, that six out of eight fans in the Salyut's ventilation and thermal control system had stopped working for the unknown reasons. Because these devices had operated reliably in the past, there were only two spares onboard, which was considered enough for 90 days of combined crew stay aboard the lab. For more than two hours on April 20, specialists briefed cosmonauts slated to go to Salyut on the situation. There were indications that the fans had stopped working at different time, largely excluding power supply problems and pointing toward dust or other contamination issues. It was now up to the crew to sort out the problem.
On the same day at 17:00, the State Commission gathered at the sports hall of the hotel at Site 17 for a formal crew approval ceremony to be recorded by the official Soviet press. Nevertheless, during this largely symbolic event, Vasily Mishin, Head of TsKBEM design bureau, the prime developer of the DOS-7K complex, confirmed that there was an issue with the air fans, which he believed could be easily resolved by the crew. (142) (All reports of official Soviet press representatives were going through the Soviet censorship, so Mishin's disclosure had no chance of going public). According to tradition, Kamanin asked the State Commission to approve Vladimir Shatalov, Aleksei Yeliseev and Nikolai Rukavishnikov for the Soyuz-10 mission, even though this crew had been finalized back in January. (774) Commander Shatalov and flight engineer Yeliseev had previously participated in the dual flight of the Soyuz-4 and -5 spacecraft and in the triple mission of Soyuz-6, -7 and -8. Rukavishnikov, the second flight engineer on the crew, would be making his first flight.
April 22: Launch abort
In the late hours of April 21, fueling crews were ready to begin loading propellant components onboard the launch vehicle. However, as relentless rains unseen by veterans of the range continued over Tyuratam, specialists detected stray current on the hull of the rocket. Still, preparations were allowed to proceed and the crew took their seats inside Soyuz-10 around 3:10 a.m. local time (01:10 Moscow Time) on April 22.
Just one minute before the scheduled ignition command, the umbilical cable mast connected to the third stage of the rocket failed to retract. Given the short launch window, dictated by the passage of the space station over the launch site, mission managers had no choice but to call a 24-hour delay, while the rocket remained fueled on the pad.
Kamanin claimed that a launch abort that close to the liftoff time created potentially dangerous conditions, threatening the inadvertent activation of the Emergency Escape System, SAS, and a subsequent fire, reminiscent of a catastrophe with the first Soyuz in 1966, even though a number of modifications had been made to the system to avert a repeat of that type of tragedy. Kamanin credited Mishin and Colonel Patrushev, at the controls in the firing bunker, who quickly realized the seriousness of the moment and immediately called off the launch. Within seconds, the SAS system was commanded to stand off, while two arms of access gantry were lifted back to the rocket. The emergency team headed to the pad, followed (perhaps not very wisely) by Mishin, Patrushev, Voitenko, Nikolaev, Leonov and Kamanin.
Kamanin was concerned that an evacuation of the crew from the +28C degrees interior temperature via an open gantry through blistering wind and pouring rain could result in his cosmonauts catching cold, so he demanded that jackets, pants, hats and shoes be brought to the entrance hatch. Around 40 minutes later, the cosmonauts were met at the base (of the still fueled) rocket by basically the entire leadership of the Soviet space program, including Kerim Kerimov (the chairman of the State Commission), Sergei Afanasiev (Minister of General Machine-building), Vasily Mishin, Vladimir Barmin (head of launch complex development), Valentin Glushko (top propulsion expert). Clearly, the lessons of the Nedelin disaster 11 years earlier had been largely forgotten.
The problem with the umbilical retraction was not immediately understood, but as the day progressed, Barmin's engineers made three test runs of the mast operation without any issues. They concluded that a pull-off plug of the umbilical cable might have stuck the previous night due to freezing raindrops in its control mechanism.
In the anticipation of another launch attempt the following morning, the cosmonauts were sent to bed at 15:30 and the doctors had to give the members of the primary crew sleeping pills to fight their shifted sleep pattern and the excitement of all the recent events.
The members of the State Commission reconvened in Tyuratam around 1 a.m. local time on April 23 (11:00 Moscow on April 22) and cleared the mission for the second launch attempt. Fortunately, rain had finally stopped and cold subsided, even though the skies remained gray. (142)
Soyuz-10 lifts off
In wee hours of April 23, 1971, personnel in Tyuratam ran through the pre-launch routine of the Soyuz-10 mission, but the problem with the stubborn umbilical mast, that had prevented the previous night's attempt, reappeared. However, this time, knowing the probable cause, Mishin directed the engineers to press ahead and, after three failed commands, the mast finally moved out of the way.
Soyuz-10 lifted off from Site 1 on April 23, 1971, at 02:54:06 Moscow Time and successfully entered its planned orbit. Its solar panels and antennas deployed and the crew began preparing for chasing the unpiloted Salyut station.
According to the flight scenario, during Salyut's 80th orbit (5th day after the station's launch), mission control at NIP-16 facility in Yevpatoria, on the Crimean Peninsula, had to send sequence commands to the crew vehicle and the station for their respective trajectory corrections during the following revolution based on the latest measurements of their mutual positions. In case of Soyuz-10, controllers simply radioed the necessary settings to the cosmonauts who would then input the numbers into the ship's control system from their console. (Pavel Popovich, the veteran of the Vostok-4 mission, was on the radio with the crew at NIP-16 station.) In the case of Salyut, all the data had to be uplinked from ground stations via dedicated radio command channels. If successful, the long-range rendezvous process would start during the station's 82nd orbit. At 04:00 on April 24, 1971, the two spacecraft were expected to be within 11 or 12 kilometers from each other, close enough for the Igla system to initiate a fully automated rendezvous. The docking was expected between 05:36 and 05:52 Moscow Time. The transfer of the crew into the station was planned during its 84th orbit, the following two orbits were allocated for the activation of the systems aboard the lab and the crew sleep period was planned during Orbit 87. (78)
Rendezvous and docking
As General Pavel Agadzhanov, the head of the flight control operations, GOGU, and the top rendezvous expert Mikhail Raushenbakh were finalizing the details of the rendezvous operations in Yevpatoria, their well-choreographed plan started unraveling. First, they received instructions from Moscow to prepare the crew for a conversation with Soviet leader Leonid Brezhnev and to transmit onboard the ship greetings from the Bulgarian Communist Party, whose delegation was visiting Moscow. Soon thereafter, the Soyuz-10 crew reported that the pre-programmed engine firings, designed to intercept the station during Orbit 5 and 6 of the mission, had failed. (78, 774) Kamanin remembered that during the fourth orbit, the crew encountered problems with the gyroscopic system which was required to maintain the correct attitude of the ship during engine firings. (142)
Fortunately, Minister Afanasiev, who was relaying the news from NIP-16 to his boss Dmitry Ustinov in Moscow, suggested to hold off on the conversation with Brezhnev and the Bulgarian ceremony, so that the cosmonauts and ground specialists could focus on the problems at hand. But, as if there were not enough distractions, Mishin started demanding that Raushenbakh explained the reason for the failed orbit correction. (78)
In the meantime, the crew was instructed to switch to manual attitude control, while tShe top officials who had watched the launch in Tyuratam rushed to the Krainy airport to fly to the Saki navy airfield in Crimea, so they could be at the next center of action at NIP-16 in Yevpatoria.
By the time of Kamanin's arrival at the Crimean center on the evening of April 23, the Soyuz-10 crew had manually fired the engine, putting the spacecraft back on track for a rendezvous with Salyut. (142) Another 17-second maneuver was apparently initiated at 01:34 Moscow Time on April 24. Around the same time, the NIP-15 ground station near Ussuriisk in the Soviet Far East confirmed that the sequence for the Salyut's acceleration maneuver starting at 02:54 Moscow Time (on April 24) had been successfully uplinked into the station's flight control system.
However, by then, the influx of high officials and their entourages into the main operations room in Crimea threatened to turn the already tense process into complete chaos. The place, not designed to accommodate a large number of dignitaries or to clearly display information, was now packed with officials, while the specialists and managers had to switch their attention to the fact that their high-profile bosses had nowhere to sit and constantly demanded updates.
According to Chertok, as Soyuz-10 flew within range of the Soviet ground stations in the midst of the rendezvous process, flight controllers could not normally talk to the crew, because Mishin and Kerimov repeatedly barged into the conversations. When the announcement came over the intercom that the crew ship was two (angular) seconds ahead of the station, the enraged bosses demanded a conversion of those numbers into kilometers. Mishin and Kerimov also went into a rage when controllers unwisely mentioned a glitch in the Saturn long-range communications system, clearly not a kind of problem to be focused on at the time.
Frustrated with all the interruptions, General Agadzhanov yelled into the intercom line open to the crew: "I confirm – range 10 kilometers. Don't disrupt my work!" Unaware of the situation on the ground, the confused cosmonauts responded: "we are reporting on the rendezvous progress according to the readings on the console."
Still, Kerimov had more meaningless complaints: "Why aren't you reporting about the completion of the orbit," he asked Agadzhanov. Barely able to contain himself, Agadzhanov announced into the intercom: "Igla is operating, I confirm – this is for Granit (Shatalov). Range is 11 kilometers – this is for the guests."
Now, it was Mishin's turn: "What is wrong with you? Before it was 10 kilometers and now it is 11? Whose fault is that?" "What a mad house," Chertok remembered Raushenbakh saying to himself, "I hope Igla will not go crazy." (78)
Despite the circus at the nerve center of the mission, the Igla rendezvous system aboard Soyuz-10 homed in on Salyut, after it had completed a 60-second engine firing during its 81st orbit. The orbit corrections brought the crew ship within around 16 kilometers from the station in the early hours of April 24, 1971. At a range of around 15 kilometers between the two spacecraft and a rate of approach of 24 meters per second, the cosmonauts reported seeing a bright dot through the Soyuz periscope.
As the ship was approaching its destination, the relative velocity between the two spacecraft was gradually reduced from 27 meters per second to just two meters per second at a distance of half a kilometer. (142)
The cosmonauts and ground controllers monitored as the spacecraft actively maneuvered, making several "U-turns" to fire its main SKD engine against the direction of flight in order to slow down a sometimes dangerously high rate of closure, to the further consternation from Mishin. At the time, Shatalov and Yeliseev had a pulse of over 100 and Rukavishnikov was at 90.
Falling behind schedule on rendezvous, the spacecraft left the communications range, as Shatalov reported the station well in sight but still out of reach despite the original plan to dock within view of ground control.
As communications ceased for half an hour, Mishin noticed Raushenbakh whispering something to orbital mechanics expert Bashkin. "Don't keep secrets... tell us why the rendezvous is going so slowly," Chertok remembered Mishin saying.
Raushenbakh replied that the latest checks of propellant reserves had shown that the SKD main engine had fuel worth for 13 meters per second in velocity change, while the DPO thrusters had 20 kilograms of propellant. It meant that if the ships would not complete docking before reentering the communications range, further attempts would have to be called off. Otherwise, the ship risked starting burning its landing reserves. Chertok assured Minister Afanasiev that the cosmonauts were well aware of their propellant balance and would not endanger their return trip. (78)
Docking completed... almost!
As it transpired, at a range of 200 meters (142) (140 meters according to Chertok (78), Shatalov switched to manual control and steered the ship to its final approach. The berthing took place at a relative speed of between 20 and 30 centimeters per second.
According to Shatalov, the mechanical capture between the two spacecraft was registered on April 24, 1971, at 04:47 Moscow Time, but around nine minutes after the first contact, the docking process stopped before the completion. Around 15 minutes after the first contact, Shatalov radioed to the ground that the "Yest' stykovka" (there is docking) light on his control panel in Soyuz had never lit up.
For some reason, the electric motors failed to drive the two ships together, making it impossible to form a pressurized tunnel in the docking port or to connect electrical interfaces between the two vehicles.
Mission control told Shatalov to wait while specialists tried to figure out what to do. According to some accounts, after another orbit around the planet, the controllers advised Shatalov to try firing the ship's maneuvering thrusters to press it into the docking, however these attempts were also futile.
In any case, Shatalov asked ground control to check the telemetry and suggest further course of action.
The telemetry from the spacecraft showed that the Soyuz and Salyut remained separated by just 90 millimeters (around three inches), out of 390-millimeter length of the probe mechanism.
The specialists tried several potential explanations for the failure of the mechanism to fully retract:
That last theory was quickly backed up by the data indicating some unusual motion of the spacecraft. Mishin quickly zeroed in on the supporting evidence and peppered specialists with questions: "Why could there be the shaking? Where are the dynamics (experts)? Raushenbakh? Why were there oscillations?"
With a sinking feeling, Chertok turned to Popovich, who was on the radio with the crew: "Ask Granit (Shatalov's call sign) what kind of oscillations there were during docking."
"There is no need for asking," Popovich responded gloomily, "Yeliseev (had already) reported that the "DPO (thruster) nozzles" signal was lighting up (on the control panel after capture) and kept blinking for around 30 seconds. During that time, the ship was shaking a lot!"
Chertok immediately realized that no other inquiries to docking experts would be needed.
After a short consultation with Raushenbakh and Tregub, he went to Mishin and Kerimov with a probable scenario — a mechanical failure of the docking mechanism as a result of major side movements of the spacecraft. "We failed to turn off the motion control system (aboard Soyuz after the mechanical capture), Chertok wrote, "Right after capture, there was motion of the spacecraft" (probably resulting from the docking mechanism pulling in and rotating the vehicle to align it with the opposite port on the station's side.) However, the angular velocity sensors of the (still active) flight control system detected that motion and commanded the thrusters to counteract it (in order to keep the ship in a "stable" position). Instead, it produced a wild motion of the spacecraft from side to side, (because it was already held by the probe mechanism locked in the receptacle of the station's docking cone.) "We broke something," Chertok concluded, "There is no point in continuing docking attempts. We have to make the decision to undock." (78)
The move to abandon the station immediately posed another potential problem for mission control, this time with undocking. Engineers warned Chertok and others that the electric design of the mechanism had no way of initiating the undocking sequence without first completing the docking process and connecting the electric interfaces of the opposing docking ports. A nominal docking process would normally conclude with the opening of latches holding the central probe and its retraction back into the active port. At the same time, all the mechanical and electric interfaces would be made on the circumference of the port. As a result, there was no command in the undocking sequence to unlatch the central probe from the passive cone, since it was a part of docking. Now, mission control had to figure out how to reverse the process halfway in the docking sequence!
In Kamanin's interpretation of events, Soyuz-10 actually had initiated the undocking process, but it had failed. Countless books then repeated that version of the story. Kamanin further dramatized the scene by the fact that the unreachable station had supplies for three months, while the cosmonauts aboard the "stranded" Soyuz had oxygen for only 40 hours.
There is also discrepancy as to whether in a last resort scenario to free itself from the station, the crew could jettison the docking mechanism and/or the entire Habitation Module (according to Kamanin) or just the probe component of the docking mechanism as described by Chertok. The latter method seems more likely as it appears to be Chertok's version of subsequent events which he had directly participated in rather than simply witnessed.
In any case, the severing of the stuck docking mechanism would leave Soyuz hardware blocking the only docking port on the Salyut, thus rendering the station inaccessible by any future crew and was thus to be avoided at all costs but the lives of the crew.
According to Chertok, after spending some time peering at the electrical design schematics of the docking mechanism, his colleagues came up with a couple of options.
Docking specialist Vsevolod Zhivoglotov proposed opening an electric box containing the docking wiring in the Habitation Module, finding the Sh28/201 connector and installing a jumper on pins No. 30 and 34 of the plug facing the instrument. Next, the cosmonauts would send the undocking command from their console and then remove the jumper. The resulting command running through the circuitry would trigger the retraction of the latches holding the probe in the receptacle of the passive docking cone. "It is like unlocking the door from the inside," Chertok wrote, saying that during his career as an electronics engineer, Rukavishnikov, now aboard Soyuz-10, had performed much more complicated manipulations. Chertok estimated that around hour and a half was spent on writing the instruction for the operation which was then transmitted to Soyuz-10. "We got it," Chertok remembered cosmonauts saying without much enthusiasm. (78)
In Kamanin's interpretation of that episode, then copied in various subsequent accounts, Rukavishnikov actually implemented that plan which finally freed Soyuz-10. (142) However, Chertok explained that a much simpler solution was found for sending a command to open the latches of the passive docking port to the station rather than to the Soyuz. The only uncertainty with that method was the fact that with the incomplete docking, the entire mass of the ship hung on the probe, which in turn could be pressing on the latches so hard that their motors would not be able to move them. Nevertheless, that plan was put into action during the 84th orbit of the station's flight and during the 85th orbit, at 08:44 Moscow Time on April 24, 1971, the undocking command went through.
Both the crew and the ground controllers confirmed that the decoupling of the spacecraft had taken place and the DPO thrusters on Soyuz fired, pushing the crew vehicle away from the station. According to Chertok, the confirmation of the undocking of the two spacecraft caused more celebration than the docking. A group of docking mechanisms experts then approached Chertok and said "in secret" that the undocking should not have worked by their estimates. (78)
Return to Earth
According to one source, the freed Soyuz-10 then performed a flyaround of Salyut-1 for detailed photography of the station and its troublesome docking port. (134) However, other key witnesses of the events make no mention of such maneuvers and no visuals documenting the docking port in flight has seemingly appeared. Chertok in his memoirs did cite the crew recalling the visual appearance of the station as good in context of the undocking events. (78)
Kamanin wrote that after the spacecraft had finally parted with the station, mission control considered making another docking attempt (142), also mentioned without context in Mishin's notes. (774) However, according to Kamanin, specialists had concerns about preserving a 45-kilogram propellant cache for the return to Earth. As it transpired, Soyuz-10 had spent 80 kilograms of propellant for the first attempt, which was the twice of the allocated amount. After some discussions, mission control finally radioed the crew the permission to enter "station-keeping" mode with the Salyut (in preparation for re-docking), but, by that time, the cosmonauts had already lost view of the station after several minutes of drifting away.
With the two vehicles too far apart, there was no other options left but to wrap up the flight. Now, mission control faced another dilemma. Because the original flight program called for a 30-day flight, Soyuz-10 had been launched at night to time its landing a month later in daylight at the primary sites on Soviet territory. However, a return after a two-day flight meant nighttime conditions in the designated areas and no possibility for the crew to manually orient the ship for a braking maneuver using Earth's surface as a reference. If the automated landing sequence failed, Soyuz-10 would not be able to land in the USSR using manual control. For that contingency, specialists started looking at potential landing locations in South America, Africa and Australia. In the meantime, mission control instructed Shatalov to perform manual orientation and then leave it to the gyroscopic system to keep the ship in the correct attitude for an automated braking maneuver. The crew reported that the flight control system performed as required, giving officials some confidence in the first night landing in Soviet space flight history.
The landing team reviewed orbital mechanics during the first three orbits passes over Baikonur on April 25, 1971, and scheduled the reentry during the first orbit, which would bring the ship to landing between 80 and 100 kilometers northwest of Karaganda in Kazakhstan, around four or five minutes before local sunrise.
Several minutes after the TDU engine completed the braking maneuver, Shatalov reported "Controlled descent" and "growing g-forces," "very bright behind the window... "flames lick the vehicle" -- all as expected.
Soviet anti-aircraft radar then detected the capsule over the Caspian Sea and the main control room at the Crimean ground station began receiving continuous radio reports on the distance of the ship from the landing point. Soon thereafter, a report from the Air Force command center said, "Crew of Mi-4 helicopter observing the descent of the Soyuz-10 under a parachute." After a few more minutes, another report said that the spacecraft "has landed, ...stands vertically, ...a helicopter is landing next to the spacecraft..." and after another pause came long awaited: "Shatalov, Yeliseev and Rukavishnikov exited the vehicle... cosmonauts are feeling well." (142) However, in the post-landing briefing, the crew said that they rolled over the head after the touchdown. (78)
The landing was recorded as taking place on April 25, 1971, at 02:40 Moscow Time, 120 kilometers northeast of Karaganda. (231)
According to Kamanin, despite Soyuz-10 essentially failing to achieve its main mission objective, everybody was happy with the outcome.
Post-flight analysis of the Soyuz-10 mission
Before the officials started departing mission control center in Crimea on the morning of April 25, 1971, the State Commission decided to set up a special team led by Chertok to investigate the root cause of the failed docking. (142)
Even before Soyuz-10 landed, Chertok and Raushenbakh called from Crimea to their colleagues at the TsKBEM bureau in Podlipki with instructions to immediately prepare simulations of the botched docking at a special stand at Hall No. 439.
On April 26, at Star City, members of the Soyuz-10 crew, who just had landed at Chkalovo airfield near Moscow after the flight from Karaganda, provided their accounts of the mission to the specialists. Shatalov said that despite the overall good piloting qualities of the Soyuz spacecraft, the crew felt uncomfortable with the frequent wild U-turns of the ship to fire its SKD engine for braking. The manual docking, according to Shatalov, was very soft, with no vibrations or squeaking (that he had experienced during the Soyuz-4 mission). Despite the spacecraft having practically no misalignment at berthing, right after capture, the Soyuz had swung to the right by 30 degrees, then to the left. To the complete surprise of the crew, the oscillations continued for seven seconds. The cosmonauts were concerned that they would lose the docking port. The swinging then subsided, but what exactly happened during the rest of the docking, the crew could not fully understand. The undocking, on another hand, was quiet, Shatalov said.
He also blamed the wild ride after the mechanical capture for excessive propellant usage. He claimed that ahead of the docking the pressure in the DPO thruster system was 220 atmospheres, but just 140 after the botched docking.
Chertok also cited Yeliseev as saying that while still in flight, he had come to the realization of what had gone wrong during docking. He blamed active DPO thrusters for their wild swings during docking. He was also surprised that they had not completely smashed the docking port in the process.
Yeliseev also said that he attempted to calibrate the emergency range finder, ARS, during the flight, because its indicator was fluctuating between readings.
Finally, Rukavishnikov said that with the temperature inside the cabin hovering at 20C degrees (68F), they were freezing and could not sleep for more than two or three hours, spending the rest of the time shivering, so sleeping bags would be needed.
Practically convinced in the reasons for the failure, Chertok and his colleagues went into some self-reflection on the way back from Star City. "What kind of patsies we got to be," he remembered Raushenbakh saying, "Nobody thought of shutting off the flight control system upon contact, let alone DPOs?!"
At the end of the same day, Chertok met with leading docking engineers Lev Vilnitsky, Viktor Kuzmin, Vladimir Syromyatnikov and Vsevolod Zhivoglotov, who drafted a list of necessary modifications to the mechanism. On the list were the manual control of the docking probe and other automated mechanisms, the retraction of the probe only after all oscillations had subsided, reducing the impact velocity to 0.2 meters per second, the installation of a special console inside Soyuz for docking control. But the most important (and most visible) addition to the docking port was a special "jabot" or a collar around the probe at the same level as the guidance levers. Made of a strong alloy, the device would reliably shield the delicate mechanisms of the levers from impacts during docking.
When the usual question was asked at the meeting about the deadline for the proposed designs, Vilnitsky replied that with some night work, the documents would be ready by the following evening! In turn, the processing shop was given a week to produce the modified hardware and the new instruments!
Chertok then called Mishin, who immediately approved the proposals but warned him that Ustinov and Serbin (Kremlin's officials) were scheduled to be at Hall 439 the next day (April 27), so Chertok would have to be ready with posters, a presentation and a docking demonstration (using the docking simulator). "All hands on deck," Chertok commanded to his associates, "We are moving to Hall 439."
In the meantime, right after their meeting with the specialists, the Soyuz-10 cosmonauts had a "press-conference." There, the flight program was presented as a test flight that showed the full reliability of all systems and that no transfer into the station had ever been planned. The official statements to the public and to the world went along the same lines. The fact of the docking system failure preventing the transfer of the crew aboard the station was officially recognized in the Cosmonautics Encyclopedia published in 1985. (2)
On April 29, Mishin chaired a technical meeting at the TsKBEM bureau in Podlipki on the status of the investigation. Chertok reported that nine (investigative) teams of engineers had been formed to cover the various problems encountered during the mission. He assured that all the telemetry information had been received and already processed. Apparently in reference to the undocking incident, Chertok said that the entire operational logic of the mechanism would have to be reworked despite its successes in previous flights. Chertok said that around 60 percent of experiments (in post-flight analysis) had been completed at the time.
In his notes, Mishin commented that the orbit correction failures during the initial rendezvous with the station had been attributed to the overlapping of commands in the onboard logic of the flight control system, leaving too little time to resolve the issue for the next opportunity during the 6th orbit.
However, the focus of the engineers was obviously on the botched docking. Mishin's deputy Eduard Korzhenevsky reminded that Soyuz-10 carried a different docking port and that not all the mechanical loads on various components of the system had been taken into account (before the flight). Konstantin Feoktistov added that there was a suspicion that the probe mechanism of the docking port had stalled.
A number of other issues encountered during the Soyuz-10 flight was also under investigation at the time.
There was an abnormal operation of the ion orientation sensor, likely due to contamination of the ion sensor.
In his notes, Mishin also recorded the need to clarify the operational sequence of the Igla rendezvous system, in particular, the timing for its deactivation during the final berthing, probably to avoid radio interference with other systems.
Clearly echoing Kamanin's account of the plans for the second docking attempt, Mishin wrote that Soyuz-10 came low on propellant in the tanks of the DPO maneuvering thrusters. Even though the main SKD engine had enough supplies, the lack of DPO propellant could prevent the second rendezvous attempt. Mishin also referred to the limitations in the resources of the life-support system (of the Soyuz spacecraft). (774)
Resolving root cause of failure
On May 10, 1971, Kamanin wrote in his diary that Chertok had announced the most likely route cause of the Soyuz-10 docking failure to the State Commission, whose members probably convened sometimes before Victory Day celebrations on May 9. The investigation found that a clutch in the shock-absorbing arms of the probe mechanism had broken under the excessive force of the docking process. The latest tests revealed that the clutch had disintegrated under loads reaching 130 kilograms, which would be exceeding the originally predicted loads during docking by around 60 percent. Due to relative motion of the spacecraft, the actual loads during the docking of Soyuz-10 with the station fluctuated between 160 and 200 kilograms.
Based on Chertok's proposals, the commission approved the redesign of the clutch for loads twice as high as the original and upgrading the docking mechanism with manual control of the probe movement, as well as manual operation of the rendezvous and docking thrusters DPOs. (774)
Further analysis eventually confirmed the source of excessive loads during docking to the ship's motion control system, which kept firing thrusters on Soyuz-10 after it had made initial contact with the station.
Crew of the Soyuz-10 spacecraft in front of a flight simulator of the 7K spacecraft, left to right: Aleksei Yeliseev, Nikolai Rukavishnikov and Vladimir Shatalov.
Crew of the Soyuz-10 spacecraft inside the flight simulator of the 7K spacecraft, left to right: Aleksei Yeliseev, Vladimir Shatalov and Nikolai Rukavishnikov.
Soyuz-10 during pre-launch processing in Tyuratam.
Soyuz-10 on the launch pad in Tyuratam.
Crew of Soyuz-10 arrives at the launch pad to board the rocket.
Crew of Soyuz-10 walks to the launch vehicle on the pad, left to right: Aleksei Yeliseev, Vladimir Shatalov, Nikolai Rukavishnikov.
Visualization of the docking between the Salyut and Soyuz spacecraft using scaled models.
A view of the Salyut space station through the navigation periscope of the Soyuz spacecraft during the rendezvous simulation on the ground.
A failure of the docking mechanism introduced with the Soyuz-10 mission prevented the transfer of the crew aboard the station. Copyright © 2000 Anatoly Zak
The probe of the active docking mechanism of the Soyuz spacecraft (top) positioned a few centimeters away from the mechanical capture by the passive cone on the Salyut space station during ground-based testing.
The front docking port of the Salyut space station during its pre-launch processing. It is partially blocked on the right by a folded rendezvous antenna.