Soyuz 11

Soyuz 11 (Russian: Союз 11, lit. 'Union 11') was the only crewed mission to board the world's first space station, Salyut 1. The crew, Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev, arrived at the space station on 7 June 1971, and departed on 29 June 1971. The mission ended in disaster when the crew capsule depressurised during preparations for re-entry, killing the three-person crew. The three crew members of Soyuz 11 are the only humans to have died in space.

The original prime crew for Soyuz 11 consisted of Alexei Leonov, Valery Kubasov, and Pyotr Kolodin. A medical X-ray examination four days before launch suggested that Kubasov might have tuberculosis, and according to the mission rules, the prime crew was replaced with the backup crew. For Dobrovolsky and Patsayev, this was to be their first space mission. After the failure of Salyut 2 to orbit, Kubasov and Leonov were reassigned to Soyuz 19 for the Apollo-Soyuz Test Project in 1975.^{[citation needed]}

The Soyuz 7K-OKS spacecraft was launched on 6 June 1971, from the Baikonur Cosmodrome in the central Kazakh Soviet Socialist Republic, and used the callsign Yantar (Amber). Several months earlier, the first mission to the Salyut, Soyuz 10, had failed to successfully dock with the station. During the first day of the flight, maneuvers were made to effect a rendezvous with the uncrewed Salyut (1971-032A). When Soyuz 11 was 6 to 7 kilometres (3.7 to 4.3 mi; 3.2 to 3.8 nmi) from Salyut, automatic devices took over, and in 24 minutes closed the gap between the two ships to 9 metres (30 ft) and reduced the relative speed difference to 0.2 metres per second (0.66 ft/s). Control of the ships went from automatic back to manual at 100 metres (330 ft). Docking took 3 hours 19 minutes to complete and involved making the connection mechanically rigid, engaging various electrical and hydraulic links, and establishing air-tight seals before locks could be opened. When the pressure was equalized between the ships, the locks were opened and all three members of the crew passed into Salyut 1. Soyuz 11 successfully docked with Salyut 1 on 7 June 1971 and the cosmonauts remained on board for 22 days, setting space endurance records that would hold until the American Skylab 2 mission in May and June 1973.

Upon first entering the station, the crew encountered a smoky and burnt atmosphere, and after replacing part of the ventilation system, spent the next day back in their Soyuz until the air cleared. Their stay in Salyut was productive, including live television broadcasts. A fire broke out on day 11 of their stay, causing mission planners to consider abandoning the station. The planned highlight of the mission was to have been the observation of an N1 rocket launch, but the launch was postponed. The crew also found that using the exercise treadmill, as they were required to twice a day, caused the whole station to vibrate. Pravda released news of the mission and regular updates while it was in progress.^{[citation needed]}

On 29 June 1971, the three cosmonauts loaded scientific specimens, films, tapes, and other gear into Soyuz 11, then transferred manual control back from Salyut 1 to Soyuz 11 and returned to their ferry craft, with undocking occurring at 18:28 GMT. Soyuz 11 flew co-orbit for a while before it retro-fired at 22:35 GMT in preparation for re-entry. Before re-entering Earth's atmosphere, both the work compartment and the service module were jettisoned. This occurred at about 22:47 GMT. Radio communications abruptly ended when the work compartment separated, well before the normal ionospheric blackout.

Almost 25 minutes later, Soyuz 11's automatic systems landed the craft at 23:16:52 GMT, 90 kilometres (56 mi; 49 nmi) southwest of Karazhal in Kazakhstan, after an abnormally silent return to Earth. The total flight duration of the crew had been 570.22 hours and involved 383 orbits—18 prior to docking, 362 docked, and three after undocking. When the recovery team opened the capsule of the Soyuz 11, they found all three men dead.

Kerim Kerimov, chair of the State Commission, recalled: "Outwardly, there was no damage whatsoever. They knocked on the side, but there was no response from within. On opening the hatch, they found all three men in their couches, motionless, with dark-blue patches on their faces and trails of blood from their noses and ears. They removed them from the descent module. Dobrovolsky was still warm. The doctors gave artificial respiration. Based on their reports, the cause of death was suffocation".

It quickly became apparent that the cosmonauts had asphyxiated. The fault was traced to a breathing ventilation valve, located between the orbital module and the descent module, that had been jolted open as the descent module separated from the service module, 12 minutes and 3 seconds after retrofire. The two modules were held together by explosive bolts designed to fire sequentially; in fact, they had fired simultaneously. The explosive force of the simultaneous bolt firing caused the internal mechanism of the pressure equalisation valve to loosen a seal that was usually discarded later and which normally allowed for automatic adjustment of the cabin pressure. The valve opened at an altitude of 168 kilometres (104 mi; 91 nmi), and the resultant loss of pressure was fatal in less than a minute. The valve was located beneath the seats and was impossible to find and block before the air was lost. Flight recorder data from the single cosmonaut outfitted with biomedical sensors showed cardiac arrest occurred within 40 seconds of pressure loss. By 15 minutes 35 seconds after retrofire, the cabin pressure was zero, and remained there until the capsule entered the Earth's atmosphere. Patsayev's body was found positioned near the valve, and he may have been attempting to close or block the valve at the time he lost consciousness. An extensive investigation was conducted to study all components and systems of Soyuz 11 that could have caused the accident, although doctors quickly concluded that the cosmonauts had died of asphyxiation.