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Soyuz-11: Fatal return to Earth

Anatoly Zak, Spaceflight Correspondent
Apr 5, 2016, 3:14 UTC

Sen—After the failure of the Soyuz-10 crew to get aboard the Salyut-1 space station, the second expedition to the outpost blasted off from Tyuratam on June 6, 1971, at 07:55 Moscow Time. This time, cosmonauts Georgy Dobrovolsky, Vladislav Volkov and Viktor Patsaev had no problems either in rendezvous or docking.

Inside the spacious quarters of the Salyut, everything seemed normal except for a strong burning smell. Patsaev, who made a reconnaissance trip into the station, turned on the lights and found that two out of eight air fans had failed. Their burned wires probably left some smoke in the atmosphere. Patsaev activated the air-conditioning system, but the crew remained in their Soyuz for the first night.

Impressed with their new voluminous residence, the cosmonauts performed somersaults in front of a TV camera to the delight of flight controllers. Television images of the crew even made it beyond the secretive space organizations and onto the TV screens of Soviet citizens.

In the meantime, cosmonauts set out to a hectic program of onboard experiments with the strong emphasis on studying effects of weightlessness on the human body. They had to go through an unpleasant process of collecting frequent blood samples, taking seismocardiograms, measuring flow of blood and arterial pressure, checking the capacity of the respiratory system and the electrical activity of the heart.

In between, the crew had to constantly monitor and maintain the health of the station, take care of a miniature plant collection and conduct other experiments, as well as exercise. A special vacuum suit, known as Pingvin, was used to redistribute the flow of blood back toward the lower part of the body, thus counteracting the effect of weightlessness. The crew members even attempted to sleep in the bulky costume. Tired of their camper hygiene, Dobrovolsky and Volkov gave up shaving and grew considerable beards, while Patsaev stubbornly tried to maintain a civilized look.

Under an intense workload, the daily routine proved difficult for the crew, as mission controllers witnessed tension and misunderstanding onboard. Fellow cosmonauts, Nikolaev, Yeliseyev, Shatalov, Bykovsky and Gorbatko were taking turns at the flight manager console in the Crimean mission control, and had to spend considerable diplomatic effort reconciling frequent disagreements in orbit.

On June 16, during Shatalov’s shift as a flight manager, he received an urgent call from Volkov, reporting a strong smell of smoke onboard. An obvious command to prepare the Soyuz for evacuation followed, along with the attempt to establish the source of fire. As it turned out later, the smoke was caused by a broken electrical cable. Following a tense exchange with the ground, bordering panic, the crew switched to a backup power supply circuit and activated air filters. Without much supply of oxygen, flames apparently quickly died out. Relieved ground controllers called off the evacuation of the outpost after several hours of uncertainly. All unessential equipment onboard remained powered down for the time being. According to General Kamanin, in the wake of the incident, mission control was not particularly happy with Volkov’s performance, who came across as overly anxious and bossy.

In the following days, under careful watch from the ground, crew started turning on the station’s payloads one by one.

On June 24, the Soyuz-11 crew broke the flight-duration record, which was set just in the previous year by their fellow cosmonauts onboard Soyuz-9. However, the cost of this achievement continued mounting. While more than a week still remained in the 25-30-day flight program, the cosmonauts sounded exhausted to Kamanin. Doctors also warned that the crew had not being doing enough exercise to counteract the effects of weightlessness. In their defense, the cosmonauts complained that a poorly designed exercise machine was breaking down, causing a lot of noise and shaking the entire station, so that they could feel the vibration of solar panels and splashing of propellant in tanks… and all that when two other crew members were often trying to sleep! Remembering traumatic experience of Soyuz-9 cosmonauts, mission officials finally made a decision to prepare the crew for the return home early, after a 23-day flight.

On the evening of June 29, the cosmonauts finally got to their seats onboard Soyuz-11 and closed the hatch into the descent module. However the “open hatch” light on the flight control panel still remained on. Again, Volkov tensely demanded a solution from mission control. On the advice from a fellow cosmonaut, Aleksei Yeliseyev, the crew re-opened and re-closed the hatch, but the stubborn light remained on. For the cosmonauts, who had no protective suits, the problem of this sort was an extremely bad omen. The “hatch open” sign could easily indicate the depressurization of the capsule.

In the effort to resolve the issue, mission controllers advised the crew to check a sensor on the edge of the hatch. Dobrovolsky put a small piece of tape under the sensor and closed the hatch again. After the half-an-hour struggle, the warning light finally went off.

At 21:25 Moscow Time, Soyuz-11 undocked from Salyut-1. It was already 01:35 Moscow Time after midnight on June 30, as Soyuz-11 fired its engine to initiate a braking maneuver.

Some 12 minutes after the firing, the crew module of Soyuz-11 separated. Immediately thereafter the cosmonauts saw that the pressure inside the module started to plunge catastrophically.

Remembering all the troubles with the hatch, they probably rushed to check it first, but while it looked right, the swooshing sound of the air could be heard and the pressure kept dropping by every second. In the desperate effort to pinpoint the breach, they feverishly tried to turn off buzzing radios and ventilators. The doomed cosmonauts located the fateful valve under Dobrovolsky’s seat and unbuckled their seat belts in order to reach the area. It was theoretically possible to shut down the valve, however, all three lost consciousness from severe decompression 50-60 seconds after the breach occurred.

On the ground, unaware of the unfolding tragedy, mission controllers waited for the reports from orbit, which never came. Rescue helicopters crews spotted the spacecraft almost immediately afterwards and followed it to its planned landing site. While there was still no communication with the crew, the descent module touched down normally with the burst of soft-landing engines at 02:16 Moscow Time.

The first rescue crew landed nearby almost immediately and rushed to the capsule. It took them only a minute to open the hatch and discover the lifeless bodies of the three cosmonauts. Their seat belts were partially unbuckled. Rescue doctors tried in vane to resuscitate the crew.

The shocking news was quickly spreading around the USSR and the world. Four years after the loss of Vladimir Komarov and three years after the Apollo fire, spaceflight had claimed another three victims.

The investigation quickly established the cause of the tragedy—depressurization of the descent module in the upper atmosphere. One of the pair of valves, which were designed to equalize pressure inside the crew module with the surrounding atmosphere during the final phase of descent, was found to be the culprit. However it turned out much more difficult to pin point what caused the valve to open in the vacuum of space, immediately after the separation of the crew module.

A special investigation commission was tasked to find out the truth and to provide recommendations for the future. The most important information on the fateful descent came from the Mir autonomous register, essentially a “black box” recording the telemetry from the spacecraft’s various systems. Mir’s data showed that immediately after the separation of the descent module at an altitude of 150 kilometers, the air started venting out of the crew module, bringing the pressure down to almost a complete vacuum in just 115 seconds. By that time, medical data showed no signs of either pulse or breathing among the crew.

The rate of air loss matched precisely the opening in the valve for equalizing the cabin pressure. However the telemetry showed that a command to blew up a pyrotechnic device, which triggered the opening of the valve, had been issued exactly as planned, deep in the atmosphere.

During endless simulations on the ground, all efforts to open the valve by imitating the shock of separation between the spacecraft’s modules could not repoduce the fault. Only a combination of the separation shock with an almost completely improbable violations of the valve’s assembly and installation finally triggered the fatal opening. This scenario became an official explanation for the deadly accident.