Kosmos-496: Fixing Soyuz-11 flaws

On June 26, 1972, the Soviet space program made a major step on the difficult road to recovery from the Soyuz-11 disaster a year earlier. The upgraded version of the 7K-T vehicle orbited the Earth without crew in the autonomous flight under the name Kosmos-496.



Mission of Kosmos-496 at a glance:

Spacecraft designation
Soyuz, 7K-T No. 33A
Launch date
1972 June 26
Launch site
Landing date
1972 July 1
Autonomous test flight
Mission duration
Nearly 6 days

Original flight program

The Soyuz spacecraft, which would eventually become Kosmos-496, was the third flight-worthy vehicle within the 7K-T series, where “T” stood for “transport” denoting its role for delivering crews to space stations. This particular vehicle had factory number No. 33 and it was originally intended for delivering the second expedition to the Salyut space station, DOS-1. As of June 1971, Soviet cosmonauts Aleksei Leonov, Petr Kolodin and Nikolai Rukavishnikov were preparing to launch to Salyut aboard what was expected to be the Soyuz-12 mission. However, after the tragic loss of the Soyuz-11 crew on June 30, 1971, the follow-on expedition was grounded until the completion of the probe into the accident, which extended far beyond the life span of the Salyut-1 in orbit.

In the following months, the investigative team produced a list of recommendations that engineers at the TsKBEM design bureau incorporated into the design of the 7K-T variant.

No cosmonaut would ever be allowed to launch, land or conduct docking operations aboard Soyuz without wearing a protective spacesuit in case of depressurization. It was harder said than done, because all existing Soviet spacesuits were far too bulky to fit into the small Kazbek seat of the Soyuz spacecraft, which required cosmonauts to keep “an embryo” pose during launch and landing. To resolve the problem, engineers at the Zvezda enterprise urgently fashioned a special rubber-made Sokol-K rescue suit based on previous designs for military aircraft pilots. Although they managed to keep the mass of the Sokol-K at just 10 kilograms, the addition of an emergency air-supply kit into the already cramped descent module forced TsKBEM engineers to reduce the crew size onboard future Soyuz ships from three to two.

During a nominal flight, the Sokol-K suit would be ventilated with a cabin air, but in case of a sudden loss of cabin pressure, it would instantly switch to a supply of mixture of oxygen and nitrogen from an emergency kit. Cosmonauts were certified to wear Sokol for up to 30 hours under normal circumstances and up to two hours in an unpressurized cabin. This time was considered enough to make an emergency return to Earth. Sokol-K could even help cosmonauts to survive in the cold water, even though Soyuz crews would also have specialized Forel flotation suits in their safety kits.

In a drastic move to save mass, the Soyuz was stripped of its solar panels. Proponents of the measure argued that for short trips to the space station, onboard batteries would suffice.

The proposed changes were first implemented on the 7K-T vehicle No. 33, which after cancellation of the 2nd expedition to Salyut-1 was reconfigured for a test flight without crew. In the design documentation, it was designated 7K-T No. 33A, where "A" stood for "avtomaticheskiy" (automated).

The vehicle lifted off from Tyuratam on June 26, 1972, nearly a year after the Soyuz-11 tragedy. It successfully entered a 195 by 342-kilometer orbit with an inclination 51.6 degrees toward the Equator. Because the Soviet authorities wanted to avoid publicity around problems with Soyuz, the mission was hidden behind a generic announcement about the launch of Kosmos-496, with no details on the real nature of the flight. Kosmos-496 would not be officially identified as a Soyuz vehicle until 1985. (2)

The standard set of batteries aboard Kosmos-496 were probably able to sustain the unpiloted mission considerably longer than otherwise would be possible with the crew onboard and, as a result, the autonomous flight lasted for around six days instead of the nominal three for the 7K-T variant.

Following the successful landing on July 1, 1972, the stage was set for resuming piloted missions in the USSR, which was then expected within weeks after the launch of the second copy of the Salyut space station. (231)


Known technical specifications of the modified Soyuz 7K-T spacecraft:

2 people
Liftoff mass
6,800 kilograms
Descent Module mass
2,600 kilograms
Maximum length
7.94 meters
Habitable module diameter
2.2 meters
Returnable payload mass
Approximately 50 killograms
Launch vehicle
Autonomous flight duration
3 days
Flight duration jointly with space station
110 days
Flight altitude
200 - 350 kilometers
Orbital inclination
51.6 degrees
Orbital period
Approximately 89 minutes


The article and illustrations by Anatoly Zak; Last update: January 28, 2024

Page editor: Alain Chabot; Last edit: June 26, 2022

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Modified Soyuz 7K-T variant. Credit: RKK Energia


After the loss of the first crew of the Salyut space station during landing, the pressure suits (right) were introduced for launch, landing and docking operations. Standard Pinguin suits (left) were worn during the work inside the station. The shown equipment was used during the Interkosmos program in the late 1970s. Copyright © 2001 Anatoly Zak