With over 140 crewed missions flown over the last half a century, the Russian Soyuz is the longest-serving and most-flown crewed spacecraft design of the Space Age. Only the now-retired American Space Shuttle, with 135 launches between 1981 and 2011, comes close to the impressive flight total of the Soyuz. Still used today to ferry crews to the International Space Station (ISS) and with any replacement still many years away from making its first flight, the Soyuz will continue to add to its impressive launch total for the foreseeable future.

While the Soyuz has earned an impressive record of reliability and safety, this has been the result of incremental improvements made over the decades to its various systems based on hard won experience and many early failures. Unfortunately, two of the failures during the first few years of the Soyuz program resulted in the loss of their crews. The first of these failures occurred on the first crewed flight of the earliest Soyuz variant, the 7K-OK. Under pressure to get back into the undeclared race to the Moon with the US, Soyuz 1 was launched on April 22, 1967 as part of an overly ambitious inaugural mission despite the fact that none of the previously flown unmanned test flights had been completely successful. After overcoming a number of problems during his single day in orbit, Vladimir Komarov died when the descent module of his spacecraft crashed due to a failure of its parachute to deploy properly (see “The Avoidable Tragedy of Soyuz 1”). Following this tragic loss, Soviet space officials embarked on a thorough review of the Soyuz design followed by a much more conservative test flight program with automated then crewed spaceflights as they continued to work their way up the steep learning curve for orbital crewed operations.

The second Soyuz mission fatalities occurred during the Soyuz 11 mission launched on June 6, 1971 with Georgi Dobrovolsky, Vladislav Volkov and Viktor Patsayev onboard. This was the second crewed flight of the new Soyuz 7K-OKS variant which was specifically designed to ferry crews to the new Salyut series of space stations – the ancestors of the Russian modules at the core of today’s ISS. After spending a very successful 23 days onboard Salyut 1, the crew of three died of asphyxiation when a pressure equalization valve failed during descent on June 29. This tragic loss resulted in another reevaluation of the Soyuz design, safety systems and a change in procedures including the requirement that the crew where space suits during launch and descent to avoid a repeat of this tragedy.

Following the return of the Soyuz into service in 1973 with the improved 7K-T variant, Soviet space authorities resumed crewed spaceflights. Not only did this include continued operations with subsequent versions of the Salyut space station, but plans to participate in joint US-USSR Apollo-Soyuz Test Project (ASTP) involving the docking of a Soyuz and Apollo spacecraft as part of a broader effort to improve relations between the Cold War rivals.

The Flight of “Soyuz 18”

As preparations were being made for the highly visible ASTP mission planned for launch in the summer of 1975, the Soviet Union quietly continued with a series of Soyuz missions to a succession of Salyut space stations as they gained much needed first-hand experience about how to live and work effectively in space. By the spring of 1975, preparations were well underway for what was to be called the flight of “Soyuz 18”. The objective of this mission was to send a crew of two cosmonauts to Salyut 4 for a 60-day mission which would build on the experience of the month-long Soyuz 17 flight launched the previous January.

The crew for this flight consisted of veteran cosmonauts Vasili Lazarev as the commander and Oleg Makarov as the flight engineer. These two cosmonauts had flown together earlier on Soyuz 12 launched on September 27, 1973. The purpose of the Soyuz 12 mission was to perform a two-day orbital flight test of the upgraded Soyuz 7K-T ferry to check out the modifications made after the loss of three cosmonauts at the end of the Soyuz 11 mission. The intent was to have the crew back on Earth before the launch of the upcoming Apollo-Soyuz Test Project (ASTP) mission in July.

The Soyuz 7K-T number 39 atop its Soyuz 11A511 launch vehicle serial number Kh15000-023 lifted off from Launch Area 1 at the Baikonur Cosomodrome (the same pad used by Yuri Gagarin) at 14:04:54 Moscow Time on April 5, 1975. At 120 seconds after launch, the four boosters of the Soyuz rocket were dropped as planned from the Blok A core followed 30 seconds later by the jettisoning of the launch escape system on top of the Soyuz fairing which was no longer needed to support an abort for the rest of the flight. At 288 seconds after launch, the Blok A shut down as planned. The Blok I upper stage was then suppose to separate and ignite sending the Soyuz into orbit. Instead the Blok I RD-461 engine ignited and the ascending craft began to roll and pitch heavily. This was followed by a “Booster Failure” alarm sounding in the Soyuz cockpit and the emergency shutdown of the RD-461 engine when automated safety systems detected that the attitude had deviated by more than the preset limit of 10° only four seconds after ignition.

With the automatic abort system triggered at an altitude of 145 kilometers (above the 100-kilometer Karman line which is widely regarded today as the threshold of space), the Soyuz’s descent and orbital modules separated from the now inert launch vehicle followed by the separation of the descent module in preparation for its emergency descent. After reaching a peak altitude of 192 kilometers and the crew experiencing about 400 seconds of weightlessness, the Soyuz automatically executed a high-G ballistic reentry with a peak braking load of 21.3 G instead of the normal 3 to 4 Gs owing to the non-lift reentry and a flight path that was steeper than a normal descent from orbit. The Soyuz descent module came down in the Altai Mountains 1,574 kilometers downrange after a flight of 21 minutes and 27 seconds. With the crew surviving its ordeal, the growing maturity of Soyuz and its safety systems had been proven. While unintentional, this was the first manned suborbital spaceflight since X-15 flight number 91 on August 22, 1963 (see “A History of Suborbital Crewed Spaceflights“).

The landing site of what became popularly known in the West as “Soyuz 18A”, a mountain called Teremok-3, was covered in chest-deep powdery snow at the time of landing. The descent module came to a stop just 150 meters shy of a sheer drop after rolling down the mountain’s steep slope before its parachute lines had become entangled in some vegetation. The cosmonauts donned their cold-weather survival gear and exited the capsule. Fearing that they might have come down in China, Lazarev burned documents having to do with a military experiment he was to perform on Salyut 4 relating to naked eye orbital reconnaissance. But soon the cosmonauts heard from the Soviet rescue teams on their radio – they had come down in Soviet territory 829 kilometers from the border. After much difficulty dealing with the mountainous terrain, the cosmonauts were rescued following a night spent on the mountain.

The Investigation & Aftermath

On April 7, after the cosmonauts had returned home and been checked out, Soviet officials broke the news of the launch abort. Naturally, the American partners of the ASTP were interested in the cause of the mishap and required an explanation. The investigation into the “April 5 anomaly”, as it was officially known in the Soviet Union, showed that excessive vibration during the ascent of the 11A511 launch vehicle had caused an electrical relay to close unexpectedly which prematurely detonated one of two sets of pyrotechnic charges that were used to split apart the lattice structure that held the Blok I upper stage to the Blok A core stage during ascent. This premature firing also severed the electrical connections to the remaining charges needed to fully separate the two stages. So when the time came for the Blok I stage to fire and pull away from the spent Blok A, the stages were still partially attached to each other causing the rocket to deviate off course and set off the automatic abort system. The upcoming ASTP mission (as well as subsequent crewed Soyuz missions for the next 27 years) would use the newer Soyuz-U 11A511U launch vehicle which, according to Soviet authorities, had a different separation system design that could not suffer from this sort of malfunction.

After this aborted flight, Makarov went on to fly on the Soyuz 27 and T-3 missions to Salyut 6 in 1977 and 1980, respectively. Reports indicate that Lazarev apparently had experienced internal injuries during the high-G emergency descent and he never returned to flight status after failing a flight physical in 1981. It would be another 43 years before Soyuz would experience a similar inflight abort during the launch of Soyuz MS-10 on October 11, 2018 which was to send Expedition 57 to the ISS. As with the “Soyuz 18A” abort, the maturity of the Soyuz design and its safety systems was proven with the safe recovery of its crew, Russian cosmonaut Aleksey Ovchinin and American astronaut Nick Hague, who went on to fly to the ISS on Soyuz MS-12 launched on March 14, 2019.

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Related Reading

“A History of Suborbital Crewed Spaceflights”, Drew Ex Machina, May 5, 2016 [Post]

“The Avoidable Tragedy of Soyuz 1”, Drew Ex Machina, April 26, 2017 [Post]

General References

Phillip Clark, The Soviet Manned Space Program, Orion Books, 1988

Edward Clinton Ezell and Linda Neuman Ezell, The Partnership: A NASA History of the Apollo-Soyuz Test Project, Dover Publications, 2010

Rex D. Hall and David J. Shayler, Soyuz: A Universal Spacecraft, Springer-Praxis, 2003