Zond 6, a formal member of the Soviet Zond program and unmanned version of Soyuz 7K-L1 manned moon-flyby spacecraft, was launched on a lunar flyby mission from a parent satellite (68-101B) in Earth parking orbit. The spacecraft, which carried scientific probes including cosmic ray and micrometeoroid detectors, photography equipment, and a biological payload, was a precursor to a manned circumlunar flight which the Soviets hoped could occur in December 1968, beating the American Apollo 8. However Zond 6 crashed due to a parachute failure.
Zond 6 was the official designation for Soyuz 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 that time.
Zond 6 flew around the moon on 14 November 1968, at a minimum distance of 2420 km. Photographs of the lunar near side and far side were obtained with panchromatic film. Each photo was 5 by 7 in (130 by 180 mm). Some of the views allowed for stereo pictures. The photos were taken from distances of approximately 11,000 km and 3300 km. However, only one negative was recovered from the camera container.
Zond 6 used a relatively uncommon technique called "skip reentry" to shed velocity upon returning to Earth. A few hours before reentry, on 17 November 1968, a faulty O-ring rubber gasket caused the cabin to depressurise, killing all the animal test subjects aboard. Zond 6's parachutes also deployed too early and it crashed in Kazakhstan, near the designated landing area.
For propaganda reasons the Soviets claimed the flight was a 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.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in brackets.