In September 1968, the Soviet Union launched the space probe Zond 5 on a mission to orbit the moon and test conditions as a prelude to a possible lunar mission by cosmonauts. In addition to a life-size human mannequin equipped with radiation detectors, the spacecraft carried a number of living passengers, including a pair of Russian tortoises that newspaper reports initially described as "turtles." After a week in space, Zond 5 returned to Earth and, despite a failure of crucial altitude detectors, successfully splashed down in the Indian Ocean.

Along with the other creatures, the tortoises were rescued and brought back to the Soviet Union for study. The Soviets revealed that the tortoises had lost about 10 percent of their body weight, and showed an "excessive content" of glycogen and iron in their liver tissue and some changes in their spleens. Otherwise, though, the tortoises remained active and showed no loss of appetite, according to NASA.