Soyuz-11 disaster: The largest tragedy in USSR's space exploration program

June 30, 1971, was the day when the largest tragedy in the history of Soviet cosmonautics took place. It was the day, when the entire crew of the Soyuz-11 spacecraft was killed during the return mission: Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsaev.

When returning to Earth, the crew of the Soyuz-11 spacecraft - Vladislav Volkov, Georgy Dobrovolsky and Viktor Patsaev - were killed as a result of the depressurization of the descent vehicle. The cosmonauts were buried underneath the Kremlin wall. This was the second and the last disaster in the history of manned space flight for both the USSR and Russia.

Soyuz comes to replace Gagarin's Vostok

Soyuz is a family of disposable manned transport spacecraft, which was designed and built by Design Bureau OKB-1 (currently known as Energia Rocket and Space Corporation named after Korolev). 

Soyuz spacecraft came to replace Vostok - the Soviet spacecraft of the first generation. First man in space Yury Gagarin orbited the Earth on board a Vostok spacecraft. 

The project for a manned flyby of the Moon was developed during the 1960s. Within the framework of this program (which was subsequently canceled), a manned spacecraft of a new type was developed - 7K-OK (later called Soyuz), which was designed to practice manoeuvring and docking operations in near-earth orbit.

The first manned launch of the 7K-OK (Soyuz-10) type spacecraft on April 23, 1967, ended with a disaster. The main braking parachute did not open up during landing, which caused the vehicle to crash into the ground at a speed of 50 meters per second. Cosmonaut Vladimir Komarov was killed. After the accident, the spaceship was redesigned. 

The development of the new spacecraft began in 1969. The new 7K-T spaceship was equipped with a docking manhole. Prior to that, cosmonauts had to move from one ship to another by spacewalking. The new ship could accommodate up to three cosmonauts (with no spacesuits on due to the size of the cabin).

The first manned launch of the 7K-T (Soyuz-10) modification spacecraft took place on April 23, 1971. The ship was launched to the Salyut-1 station, which was launched into orbit on April 19 of the same year and became the world's first orbital station. However, the crew failed to enter the space station due to the failure of the docking station. Two days later, the cosmonauts returned to Earth.

No flying from fate

The next flight to the Salyut-1 station was scheduled for June 1971. The crew of the first mission to the station included Alexei Leonov (captain), Valery Kubasov and Pyotr Kolodin. However, a few days before the flight, the crew was suspended from the flight due to Kubasov's suspected lung disease.

The crew was replaced with a backup one that consisted of:

1. 43-year-old Georgy Dobrovolsky (commander, first flight);
2. 35-year-old Vladislav Volkov (flight engineer, second flight);
3. 37-year-old Viktor Patsaev (flight engineer, first flight; during the flight he turned 38).

The flight program was designed for about three weeks. The main task of the mission was to successfully dock the station and conduct various scientific experiments there.

On June 6, 1971, the crew of Dobrovolsky, Volkov and Patsaev blasted off from Baikonur cosmodrome on board the Soyuz-11 spacecraft. A day later, on June 7, the spacecraft successfully docked the Salyut-1 orbital station.

The cosmonauts stayed on board the station until June 29 and fully completed the flight program. The total flight duration amounted to 23 days 18 hours and 21 minutes.

The Soyuz-11 undocked from the station successfully on June 29 at 21:28 Moscow time, all systems of the spacecraft were operating normally. 

On June 30, at 01:10, the ship's control system was switched on to direct the vehicle towards the Earth, the propulsion system was activated accordingly. The crew was reporting all details of the flight to Mission Control.

At the moment when the descent vehicle was separating from the instrument and orbital compartments at an altitude of about 150 km, radio communication with the cosmonauts was suddenly interrupted.

The descent vehicle, according to telemetry data, entered the dense layers of the atmosphere in a regular manner, the parachute system was activated accordingly too, the soft landing engines were activated, and the vehicle landed in the designated area. However, the search and rescue group, which arrived at the landing site almost immediately, found the cosmonauts on their seats dead. 

A preliminary conclusion said that the crew died from a sharp drop in pressure in the descent vehicle (the cosmonauts were not wearing rescue suits).

Later, a special government commission confirmed that the cosmonauts were killed due to the depressurization of the spacecraft descent vehicle as a result of the premature opening of one of the ventilation valves (to equalize the pressure during descent in the earth's atmosphere).
The cause of their death was identified as explosive decompression.

Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsaev were posthumously awarded the title of Hero of the Soviet Union (Volkov - for the second time). The urns with the ashes of the deceased cosmonauts are buried underneath the Kremlin wall on Red Square in Moscow.

Their names were assigned to research ships of the USSR Academy of Sciences, which were used to monitor space flights and maintain communication with ships in orbit.

Craters on the Moon and minor planets were named in honor of Dobrovolsky, Volkov and Patsaev - numbers 1789, 1790, 1791, respectively.

After the Soyuz-11 disaster, manned flights in the USSR were suspended for two years, until September 1973, when the Soyuz-12 spacecraft was launched. During the interval, Soviet scientists took a number of measures to improve the safety of the Soyuz spacecraft.

The 7K-T was upgraded, the crew was reduced to only two cosmonauts so that they could be staying inside the descent vehicle wearing rescue gear.

The last words from Soyuz-11

The transcript of the last communication of the crew with the Earth before the descent was published.

• Zarya: Amber, once again I remind the orientation - zero-one hundred and eighty degrees.
• Amber-2: Zero-one hundred and eighty degrees.
• Zarya: You got it correctly.
• Yantar-2: The "Descent" banner is on.
• Zarya: Let it be on. All's well. The connection ends. Good luck!

The last words that they heard from the cosmonaut was a joke from Vladislav Volkov: "We'll get together tomorrow, get some cognac ready!"

"I herewith confirm the authenticity of the recording of the negotiations," Colonel Gulyaev, the commander of military unit 26266, signed the document on December 27, 1971. Based on the markings made on the first page of the transcript, the record was declassified on April 10, 2013.

At the moment of separation of the descent vehicle from the instrument and orbital compartments at an altitude of about 150 km, radio communication with the cosmonauts was interrupted. Descent vehicle did not have telemetry systems back in the day, and no one on Earth knew what was happening to the crew at the moment.