Encyclopedia Astronautica
1971.07.04 - Soyuz 11 failure investigation

This was a very difficult time for TsKBEM. All work at the bureaus came to a complete halt after the loss of Soyuz 11 and N1 6L. Simultaneous expert commissions investigated the loss of N1 6L and Soyuz 11. TsKBEM was seen as responsible for every failure. A virtually legal process ensued to fix guilt. Every design decision was examined and questioned.

Why didn't the crew wear spacesuits? It was a Korolev decision, the engineers replied, dating back to Voskhod. Only Kamanin had disputed the decision at the time. There had never been a problem with depressurisation in all previous Soyuz and Vostok flights. The valve in question normally would open automatically at an altitude of 2 to 3 km to allow fresh air into the capsule after the heat of re-entry. The valve was difficult to close - it was thought the only eventuality where the crew would need to close it was in the case of a landing in water. For the air to have vented into free space as it did, two valves had to have opened, which could only be actuated by separate electrical commands. The circuits were designed to be fail-safe, and it should have been impossible for them to both to have opened in a vacuum. The Mir magnetic tape system recorded the awful events. This showed the valves opened within only 0.06 seconds at 01:47:26.5 Moscow time. At that moment the cabin pressure was 915 mm. It took 115 seconds for the cabin to vent to 50 mm pressure, where it stabilised.

At separation of the orbital module after retrofire, Volkov was emotional - his pulse was 120. Patsayev's was at 92 to 106, and Dobrovolsky at 78-85. The average for cosmonauts at retrofire in earlier flights was 120, with Tereshkova setting the record at 160. A few seconds later, as the crew became aware of the leak, Drobrovlsky's pulse had increased to 114 and Volkov's to 180. 50 seconds after separation, Patsayev's pulse was down to 42, characteristic of someone suffering oxygen starvation. Dobrovolsky's quickly fell as well. At 110 seconds the hearts of all three men had stopped. Death came at 120 seconds after jettison.

The capsule, with the dead crew aboard, pulled the normal 3.3 G's during re-entry. It experienced a slow rotation due to the air venting through the open valve.

Many tests were conducted, including on a mock-up capsule in a large vacuum chamber at Star City, but the valve failure just could not b e duplicated. Ilya Lavrov, the designer of the environmental control system, became very distraught. He had tried to convince Korolev years earlier that if the spacesuits were deleted, at least the crew should be provided with aviation-style oxygen masks, which would give them at least 2 to 3 minutes time to act in case of cabin decompression. This would have given the crew enough time to have closed the valve (which should have taken 20 seconds according to the engineers, but had actually taken the cosmonauts 30 to 40 seconds during water recovery tests).

Gay Severin at Zvezda developed the lightweight Sokol spacesuits which all future Soyuz crews would be required to wear. An environmental control unit for these suits replaced the third crew position, reducing the Soyuz crew to two. This system would also flood the cabin with air in the case of a leak. The modifications to Soyuz were tested on unmanned flights on Cosmos 496 and Cosmos 573, then the manned Soyuz 12.

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