Description

Zond 5 was launched from a Tyazheliy Sputnik (68-076B) in Earth parking orbit to make scientific studies during a lunar flyby and to return to Earth. En route to the Moon the main stellar attitude control optical surface became contaminated and was rendered unusable. Backup sensors were used to guide the spacecraft. On September 18, 1968, the spacecraft flew around the Moon. The closest distance was 1,950 km. High quality photographs of the Earth were taken at a distance of 90,000 km. A biological payload of turtles, wine flies, meal worms, plants, seeds, bacteria, and other living matter was included in the flight. Additionally, according to the Russian Academy of Sciences, in the pilot's seat was a 175 cm tall, 70 kg mannequin containing radiation detectors.

Returning to Earth another attitude control sensor failed, making the planned guided entry onto Soviet territory impossible and forcing the spacecraft controllers to use a direct ballistic entry. On September 21, 1968, the reentry capsule entered the Earth's atmosphere, braked aerodynamically, and deployed parachutes at 7 km. The capsule splashed down in the backup area in the Indian Ocean at about 19:05 Moscow time at 32.63 degrees S, 65.55 degrees E, and was successfully recovered, safely returning the biological payload.

It was announced that the turtles (steppe tortoises) had lost about 10% of their body weight but remained active and showed no loss of appetite. The spacecraft was planned as a precursor to crewed lunar spacecraft. It represented the first successful Soviet circumlunar Earth-return mission. Transmissions of astronauts calling out readings of instruments from the spacecraft were received at Jodrell Bank, this led to the conclusion that cosmonauts at Yevpatoriya were relaying reports through the spacecraft as a training exercise, as was done on Zond 4.