In September 1968, the former Soviet Union launched the Zond 5 mission, a milestone in space exploration that marked not only the first time a spacecraft orbited the Moon in a circumlunar trajectory and returned to Earth but also the first time living beings did so. Onboard the spacecraft were two tortoises, becoming the first terrestrial beings to orbit our natural satellite.

The Zond 5 mission was part of the ambitious Soviet space program in the race to reach the moon in the 1960s. Following the success of the first manned spaceflight in 1961 with Yuri Gagarin, the USSR sought more ambitious goals, such as putting a man on the moon. The Zond missions were unmanned test flights to evaluate the technology that would later be used in manned missions.

Zond 5 was launched on September 14, 1968, from the Baikonur Cosmodrome in what is now Kazakhstan, aboard a Proton-K rocket. The 5.2-ton spacecraft consisted of a spherical descent module designed to carry cosmonauts, equipped with scientific instruments, the two tortoises, fruit fly eggs, bacteria, and some plants.

The tortoises were meticulously selected by Soviet scientists from various species of terrestrial turtles. They ultimately chose two Russian tortoises, Testudo horsfieldii of the Agrionesmys subspecies, a small species only 20 centimeters long that were easy to handle in the spacecraft. They were named Zond 5-1 and Zond 5-2.

Twelve days before launch, both tortoises were deprived of food and water, part of a pathomorphological and histochemical experiment. Sending living organisms aimed to measure the effect of cosmic radiation on them. A dummy with sensors was placed in the pilot’s seat.

The launch took place on September 14, 1968, at 9:42 UTC. Four days later, on September 18, the spacecraft completed a full orbit around the Moon, approaching to a distance of 1,950 kilometers from the surface, and then began the return to Earth.

The Zond 5 capsule splashed down in the Indian Ocean, where it was recovered by the Soviet ships Borovichy and Vasiliy Golovnin on September 21. The reentry would have been lethal if humans had been on board, but when scientists opened the capsule four days later, they found the tortoises healthy and unharmed, not having lost their appetite. They had demonstrated that living organisms could survive the rigors of spaceflight. At that moment, it was considered that the Soviet Union was ready to send cosmonauts to the Moon.

The Soviet Union did not announce that the mission had included live animals until November. By then, almost a month had passed since the tortoises had been dissected after 39 days without eating or drinking. During their space journey, they had lost 10 percent of their body weight.

The feat of Zond 5-1 and 5-2 demonstrated that with the appropriate technology, living beings could travel to space and survive in microgravity. The tortoises were the first Earthlings to complete a flight around the moon. Their unique journey was a small step for tortoises but a giant leap for terrestrial life.

This article was first published on our Spanish Edition on November 8, 2023. Puedes leer la versión en español en Dos tortugas fueron los primeros seres vivos en dar una vuelta completa a la Luna


Zond-5: A prototype of the Soviet crew capsule loops behind the Moon! (Russian Space Web) | Michael Cassutt, Red Moon | Zond 5 (NASA) | Wikipedia

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