Mission Type: Flyby
Launch Vehicle: 8K82K + Blok D (Proton-K no. 235-01 / Blok D no. 19)
Launch Site: Tyuratam (Baikonur Cosmodrome),, NIIP-5 / launch site 81L
Spacecraft Mass: about 5,375 kg
Spacecraft Instruments: 1) biological payload; 2) radiation detectors; 3) imaging system; 4) photo-emulsion camera and; 5) micrometeoroid detector
References:
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Monographs in Aerospace History No. 24, by Asif A. Siddiqi

National Space Science Data Center, http://nssdc.gsfc.nasa.gov/

Solar System Log by Andrew Wilson, published 1987 by Jane's Publishing Co. Ltd.

Zond 6 was the second spacecraft that the Soviets sent around the Moon.

Soon after translunar injection, ground controllers discovered that the vehicle's high-gain antenna had failed to deploy. Given that the main attitude- control sensor was installed on the antenna boom, controllers had to make plans to use a backup sensor for further attitude control.

The spacecraft circled the far side of the Moon at a range of 2,420 kilometers, once again taking black-and-white photographs of the Moon.

During the return flight, temperatures in a hydrogen peroxide tank for the attitude-control thrusters dropped far below acceptable levels. Engineers attempted to heat the tank by direct sunlight, but as they later discovered, such a procedure affected the weak pressurization seal of the main hatch and led to slow decompression of the main capsule.

Despite the failures, Zond 6 successfully carried a fully automated guided reentry into the primary landing zone in Kazakhstan.

A radio altimeter, not designed for work in depressurized spacecraft, issued an incorrect command to jettison the main parachutes. As a result, the spacecraft plummeted to the ground and was destroyed. Although the main biological payload was lost, rescuers salvaged film from the cameras.