Encyclopedia Astronautica
1968.11.10 - Zond 6

Test flight of manned circumlunar spacecraft. Successfully launched towards the moon with a scientific payload including cosmic-ray and micrometeoroid detectors, photography equipment, and a biological specimens. A midcourse correction on 12 November resulted in a loop around the moon at an altitude of 2,420 km on 14 November. Zond 6 took spectacular photos of the moon’s limb with the earth in the background. Photographs were also taken of the lunar near and far side with panchromatic film from distances of approximately 11,000 km and 3300 km. Each photo was 12.70 by 17.78 cm. Some of the views allowed for stereo pictures. On the return leg a gasket failed, leading to cabin depressurisation, which would have been fatal to a human crew. The 7K-L1 then made the first successful double skip trajectory, dipping into the earth's atmosphere over Antarctica, slowing from 11 km/sec to suborbital velocity, then skipping back out into space before making a final re-entry onto Soviet territory. The landing point was only 16 km from the pad from which it had been launched toward the moon. After the re-entry the main parachute ejected prematurely, ripping the main canopy, leading to the capsule being destroyed on impact with the ground. One negative was recovered from the camera container and a small victory obtained over the Americans. But the criteria for a manned flight had obviously not been met and Mishin's only hope to beet the Americans was a failure or delay in the Apollo 8 flight set for December. The next Zond test was set for January.

Zond 6 was the cover name for 7K-L1 s/n 12. It was supposed to photograph the moon in colour and black and white from 8000 km and 2600 km ranges, then return to earth, landing at Tyuratam only 16 km from the launch pad. It had been a long and difficult road to develop the L1 guidance system, but it worked perfectly this time. But trouble began on the sixth day of the flight. The capsule developed a leak, the pressure first dropping from 760 to 380 mm. It then continued to drop until it reached 25 mm by the time of re-entry. Due to the vacuum, static electricity built up in the spacecraft's electronics. A coronal discharge sent an erroneous signal, indicating that the gamma altimeter had sensed the approaching earth, even though the capsule was at 5300 m altitude. This tripped the soft landing rockets, followed by jettison of the parachute. The capsule plummeted to earth Luckily the APO self-destruct system did not explode when the capsule hit the ground, and Bushuyev was able to recover the film cartridges from the wreckage. The pictures of the earth and moon, similar to those of Apollo 8, were published and the world was told the mission was a complete success. A State Commission investigating the crash later determined that the coronal discharge effect which caused the parachute to jettison would only occur at the 25 mm capsule pressure. If the capsule had been completely depressurised to a high vacuum, the accident would not have occurred.

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