It was the first spaceflight to send animals into orbit and return them safely back to Earth, including two Soviet space dogs, Belka and Strelka.

The first try on 28 July, carrying a pair named Bars (Snow Leopard aka Chaika (Seagull)) and Lisichka (Foxie), had been unsuccessful after the Blok G strap-on suffered a fire and breakdown in one of the combustion chambers, followed by its breaking off of the booster 19 seconds after launch.

Flight controllers sent a command to jettison the payload shroud and separate the descent module, but due to the low altitude, the parachutes only deployed partially, and the dogs were killed on impact with the ground.

All of the animals were recovered safely, and a year later Strelka had a litter of puppies, one of which, Pushinka, was sent to First Lady of the US Jacqueline Kennedy as a goodwill present from the Soviet Union.

President Kennedy's advisers initially opposed taking the dog for fear that the Soviets might have planted microphones in its body to listen in on national defense meetings.