Soyuz Salyut











Kosmos-573: re-confirming Soyuz fixes

On June 15, 1973, a heavily modified version of the Soyuz 7K-T spacecraft went into orbit without crew or much publicity on its second mission to ensure that all the lessons from the fatal Soyuz-11 accident in 1971 had been learned. In addition, the test flight sought to resolve problems encountered during the ill-fated launch of a Salyut space station a month earlier.


Kosmos-573 mission at a glance:

Soyuz 7K-T No. 36, Kosmos-573
Launch date
1973 June 15
Launch site
Landing date
1973 June 17
Autonomous test flight
209 by 268-kilometer orbit, inclination 51.55 deg., orbital period 89.2 minutes
Mission duration
2 days

Original flight program

The Soyuz 7K-T No. 36 was originally intended to be the first crew transport heading with two cosmonauts to the second Soviet space station, DOS-7K No. 3 (DOS-3), between two and 10 days after the launch of the orbital lab in 1973.

The construction of Vehicle No. 36 took much of 1972. As usual, the final assembly was conducted at the TsKBEM facility in Podlipki. Its head, Vasily Mishin indicated in his notes that the testing of Vehicle No. 36 was completed in early January 1973. The spacecraft was then shipped to Tyuratam on Jan. 27, 1973, and its integrated testing at the processing building at Site 2 was scheduled to be completed on Feb. 21, 1973. However, the spacecraft was still waiting for the delivery of its parachute system that had been modified after the loss of the Soyuz-11 crew in 1971.

As of March 1973, the launch of Soyuz 7K-T No. 36 to the DOS-3 station was penciled sometimes after May 2, 1973, but by mid-April 1973, the launch of DOS-3 and Soyuz 7K-T No. 36 drifted to May 6 and May 8, 1973, respectively.

All the testing of the Vehicle No. 36 had been completed at the launch site with flying colors by the middle of April 1973.

In the midst of DOS-3 launch campaign on the morning of May 7, 1973, when Mishin toured the processing building at Site 2, the Soyuz 7K-T No. 36 spacecraft was being prepared for integration with the payload fairing.

At 08:00 Moscow Time on May 11, 1973, (within hours after the launch of DOS-3), technical management met in Tyuratam and gave the green light to the rollout of an 11A511 rocket with the Soyuz 7K-T No. 36 crew vehicle to the launch pad. However, shortly thereafter, news came that DOS-3 had run in trouble and, suddenly, Vehicle No. 36 had no destination. (774)

New plan for a solo mission

After the loss of the DOS-3 station in May 1973, officials had to decide what to do with the three crew transport vehicles allocated to the orbital lab — Vehicles No. 34, 35 and 36, because the clock was ticking on the life span of their systems.

The question was obviously most burning for Vehicle No. 36, which had passed its irreversible operations, including fueling with hypergolic propellant. The solution was to launch it quickly without crew on another test of all the upgrades made in the wake of the Soyuz-11 accident which had first been tested during the Kosmos-496 mission in June 1972.

Moreover, serious problems with the new ion orientation sensor, discovered aboard DOS-3, had to be urgently addressed and Vehicle No. 36, which was equipped with a similar device, was a convenient testbed.

In the meantime, Vehicle No. 34 was sent to be reconfigured for an unpiloted two-month endurance test in orbit, while Vehicle No. 35 would be eventually dismantled and used for tests of the modified Emergency Escape System, SAS, which was developed in anticipation of the joint Apollo-Soyuz docking mission. (231)

Vehicle No. 36 completes a two-day flight

An 11A511 rocket carrying the Soyuz 7K-T vehicle No. 36 lifted off from Tyuratam on June 15, 1973. Less than nine minutes later, the spacecraft successfully entered a 209 by 268-kilometer orbit with an inclination 51.5 degrees toward the Equator.

Because the Soviet authorities wanted to keep the public attention away from post-accident test missions, which were ill-suited for propaganda purposes, Vehicle No. 36 was announced as Kosmos-573, without any mentioning of the link between this launch and the Soviet piloted space program. However observable orbital parameters of the spacecraft indicated its commonality with the previous Soyuz flights and that fact did not go unnoticed by the Western followers of the program.

On the second day of the mission, the spacecraft lowered its apogee, mimicking the behavior seen during the flight of Kosmos-496 almost a year earlier.

However, unlike Kosmos-496, which stayed in orbit for nearly six days, Kosmos-573 disappeared after just two days in orbit.

As it transpired later, on June 17, 1973, Vehicle No. 36 performed a planned braking maneuver and its Descent Module was successfully recovered. (50)

Results of the flight

Unknown to the general public, Vehicle No. 36 performed well during its autonomous flight, and even exceeded expectations of the engineers on the ground. According to Mishin, ion orientation flight experiments included firings of DO and DPO thrusters, providing data about the influence of engine exhaust on the sensitivity of the ion sensor, which had experienced fatal anomalies aboard DOS-3. (774)

On the morning of July 12, 1973, Dmitry Ustinov, who supervised the rocket and space industry for the Soviet government, opened a meeting on the status of the Soviet human space flight effort. In his remarks prepared for the event, Mishin reported that the results of the 7K-T No. 36 mission had confirmed one more time that the corrective measures and upgrades of the Soyuz 7K-T vehicle implemented after the Soyuz-11 accident had been effective. Mishin stressed that the objectives of the flight had been met with better than expected results. (774)

In 1985, a newly published Soviet space flight encyclopedia listed Kosmos-573 among the Soyuz test missions for the first time, finally acknowledging the nature of the flight. (2)


The article and illustration by Anatoly Zak; Last update: September 27, 2023

Page editor: Alain Chabot; Edit: June 15, 2023

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Launch vehicle and spacecraft processing building at Site 2 in Baikonur circa 1970s.