Soyuz 7K-T No.39
Failed 1975 Soyuz launch; crew survived high-altitude abort.
In 1975, the Soviet Union launched a crewed Soyuz spacecraft that failed to reach orbit. Designated Soyuz 7K-T No.39, it is also known in some sources as Soyuz 18a, Soyuz 18-1, or the April 5 Anomaly. The mission was supposed to dock with the Salyut 4 space station, but a problem with the launch vehicle prevented the crew from achieving orbit. Commander Vasily Lazarev and flight engineer Oleg Makarov, a civilian, made up the crew. Though the flight was aborted and its goal unmet, the spacecraft crossed the boundary commonly accepted as space, making it a recognized sub-orbital spaceflight. Both men survived.
The mission was intended as the second crewed visit to Salyut 4, with a planned 60-day stay. Both cosmonauts were on their second flight; they had previously flown together on Soyuz 12 in September 1973, which tested a new Soyuz design after the fatal Soyuz 11 accident.
Launch went smoothly until 288.6 seconds after liftoff, at an altitude of 145 kilometers, when the second and third stages of the rocket began to separate. Only three of the six locks holding the stages together released. The third stage’s engine ignited while the second stage was still attached. The third stage’s thrust broke the remaining locks, freeing the second stage, but the strain caused the booster to veer off course. At 295 seconds, the Soyuz’s guidance system detected the deviation and triggered an automatic abort. Since the escape tower had already been jettisoned, the abort relied on the Soyuz’s own engines. This separated the spacecraft from the third stage, then split the orbital and service modules from the re-entry capsule. At that moment, the spacecraft was already pointing downward, accelerating its descent. Instead of the expected 15 g (147 m/s²) during such an emergency, the cosmonauts experienced up to 21.3 g (209 m/s²). Despite the extreme overload, the capsule’s parachutes deployed correctly, and it landed after a flight of just 21 minutes.
The capsule came down southwest of Gorno-Altaysk, 145 kilometers north of the Chinese border, on a snow-covered slope. It began rolling toward a 152-meter drop but was stopped when the parachutes snagged on vegetation. The cosmonauts landed in chest-deep snow at −7 °C (19 °F) and put on cold-weather survival gear.
Quick Facts
- Names List
- Soyuz 18a, Soyuz 18-1, / April 5th Anomaly
- Mission Type
- Docking with Salyut 4
- Operator
- Soviet space program
- Mission Duration
- 21 minutes 27 seconds / 60 days (planned)
- Orbits Completed
- Failed to orbit
- Suborbital Apogee
- 192.0 km (sub-orbital spaceflight)
- Spacecraft
- Soyuz 7K-T No.6
- Spacecraft Type
- Soyuz 7K-T
- Manufacturer
- OKB-1
- Launch Mass
- 6830 kg
- Landing Mass
- 1200 kg
- Launch Date
- 5 April 1975, 11:04:54 UTC
Facts from the source article.
Lore & Background
Soyuz 7K-T No.39 was intended to be the second mission to take cosmonauts to the Soviet Salyut 4 space station for a 60-day mission. Both cosmonauts were on their second mission and had flown their first mission together, Soyuz 12, in September 1973 to test a new type of Soyuz spacecraft after the fatal accident of Soyuz 11. The launch proceeded according to plan until T+288.6 seconds at an altitude of 145 km, when the second and third stages of the booster began separation. Only three of the six locks holding the stages together released and the third stage's engine ignited with the second stage still attached below it. The third stage's thrust broke the remaining locks, throwing the second stage free but putting the booster under unexpected strain that caused it to deviate from the proper trajectory.
Reader's Guide
The failed Soyuz mission was the only case of a crewed booster accident at high altitude until the accident with Soyuz MS-10 on 11 October 2018. The accident was partly disclosed by the normally secretive Soviets as it occurred during preparations for their joint Apollo-Soyuz Test Project with the United States which flew three months later. The United States requested a more detailed report, leading to a congressional inquiry. In the report the Soviets made to the Americans, the abort was referred to as the 'April 5th anomaly', and as this was the only term the Soviets ever used for the incident, that became the 'official' designation for years afterwards. The mission is referred to in some literature as Soyuz 18a or Soyuz 18-1, since the following Soyuz mission in May 1975 received the name Soyuz 18. The crew survived despite experiencing up to 21.3 g during abort, and were recovered after landing in deep snow near the Chinese border.
Did You Know?
- The crew experienced up to 21.3 g (209 m/s2) during the abort, far exceeding the expected 15 g.
- The capsule landed on a snow-covered slope and began rolling toward a 152 m drop before parachutes snagged on vegetation.
- The cosmonauts destroyed documents relating to a planned military experiment because they feared they had landed in China.
- The exact landing site remains debated among space historians, with some sources stating it occurred in Mongolia.
More in Suborbital human spaceflights 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced