Soyuz 18a

Soyuz 18 was a Soyuz spacecraft launched by the Soviet Union on April 5, 1975 at 11:03 AM GMT. It landed at 11:24.27 in the rocky region on the Mongolian-Chinese border (within Chinese territory), after a flight lasting 21 minutes and 27 seconds. The crew consisted of commander Vasily Lazarev[?], an Air Force major, and flight engineer Oleg Makarov (civilian).

The Soyuz 18 mission was supposed to be the second mission to take cosmonauts to the Soviet Salyut 4 space station. Both cosmonauts were on their second mission; they had flown their first mission together, Soyuz 12 in September 1973 to test a new type of Soyuz spacecraft. However, Soyuz 18 never achieved orbit.

The launch proceeded according to plan until T+288.6 seconds at an altitude of 192 kilometers, 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 an unanticipated strain that caused it to deviate from the standard trajectory. At T+295 seconds, the deviation became severe enough that an automatic safety system separated the Soyuz spacecraft from the third stage booster and then separated the orbital capsule of the spacecraft.

At the time when the safety system initiated separation the spacecraft was already pointed downward toward Earth, which accelerated its descent significantly. Instead of the pre-calculated load factor in such an emergency situation of 15 G, the cosmonauts experienced up to 21.3 G. Despite very high overloading, however, the landing parachutes opened properly and slowed the craft to a successful landing.

The capsule landed in a rocky area of the northwestern part of China, less than a mile from the Mongolian border and around 50 miles from the Soviet border. The crew was evacuated by Soviet helicopter a few hours after landing, without China being notified. In Brezhnev's time it was not typical to disclose anything about Soviet failures, and so the first publication about the realities of the flight was not made until 1983 in the Army newspaper "Red Banner".

The Souyz-18-1 flight was the only case of a booster accident at high altitude. The mission is referred to in the literature as Soyuz 18-1 or Soyuz 18a, since the following Soyuz mission was also numbered 18 to disguise the accident.