Let us consider the function of the valve which was the technical cause of the loss of the Soyuz 11 crew. The limited capacity of the launch vehicle obliged Feoktistov and his design team to make the Soyuz descent module a very small vehicle - it is so cramped that it is right on the limit for accommodating the human body. In fact, the bell-shaped module stands 2.16 metres tall, has a maximum diameter at its base of 2.2 metres and weighs only 2.8 tonnes. Yet it had to contain couches for three cosmonauts and all the necessary life-support equipment, together with the systems to operate the spacecraft in space and two large parachutes for landing. The 'free volume' of the cabin is a mere 2.5 cubic metres, which is less room per cosmonaut than the Vostok capsule! The air in such a cramped module can support the lives of three men for only a short time - but this is viable because it operates autonomously only for the 30 minutes from the separation of the orbital and propulsion modules through re-entry and landing. Nevertheless, once the main parachute deployed at an altitude of approximately 5 km, two valves were to be opened to allow fresh air to enter the cabin; both to equalise the internal and external pressures and to eliminate the risk of the cosmonauts asphyxiating in the event of their having to remain inside for some time after landing, as might occur if the hatch were unable to be opened as a result of a technical problem or if the module were to land in water and the hatch was partially submerged.
The fact that both valves are closed during the majority of the mission and then opened only a few minutes prior to landing confused the State Commission. Surely the recovery team would open the hatch promptly, or if the module landed off target the cosmonauts would open it themselves! Given that the premature opening of one of the valves caused the deaths of three cosmonauts, what where the valves actually for? Was their inclusion a terrible error by the designers? The explanation from the TsKBEM of the risk of asphyxiation if for some reason the hatch was unable to be opened promptly was inconclusive. An additional confusion concerned the fact that each valve had two shutters. In fact, this aspect of the design would prove to be one of the most important factors in the Soyuz 11 tragedy.
To understand what happened, we must examine the valve's structure. The design was straightforward, involving a cylinder of cork with a rubber ring and a piston rod supported by a ball-lock shutter that was automatically controlled. The crew had no control over the automatic shutter, which would be opened by a pair of pyrotechnic charges after the deployment of the main parachute. Next to the automatic shutter was one that the cosmonauts could open manually by a small rotating knob. So long as at least one shutter remained closed, the valve ought to be shut. The valves were placed below the ring of the hatch: the No. 1 valve above Dobrovolskiy's couch and the No. 2 valve above Patsayev's couch, on opposite sides of the hatch so that if the module were to land on water there would be no chance of both of the valves being submerged. In the event of a splashdown, the manual shutters would be operated as required to prevent water ingress. This was the only circumstance in which the crew were to operate the manual shutters.
Why did the automatic valve open at an altitude of approximately 150 km, rather than at 5 km? The orbital and descent modules were connected by a dozen bolts in the ring that housed the hatch. During the assembly of the spacecraft, the bolts had been fastened using a special tool, then the joint was checked in an altitude chamber to ensure a hermetic seal. The combined force of all the bolts was about 100 tonnes. To separate the modules in space, the bolts had to be severed simultaneously. Hence each bolt incorporated a small explosive charge and an electric circuit. According to the programme, a timer would cause electricity to be supplied to the bolts in order to detonate the explosive charges and sever the bolts, applying a force of 100 tonnes for
a duration of one microsecond, in the process sending a shock wave across the metallic surface of the craft. The valves were located close alongside the connecting ring, and so would have been particularly sensitive to the propagation of this shock. In the case of Soyuz 11 this caused an automatic valve to pop open. The fact that particles of gunpowder were found inside one valve was conclusive proof that it had opened at the moment of separation.
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