During the 1950s and 1960s the Soviet space program used dogs for sub-orbital and orbital space flights to determine whether human spaceflight was feasible. The Soviet space program typically used female dogs due to their anatomical compatibility with the spacesuit. Similarly, they used mix-breed dogs due to their apparent hardiness.
In this period, the Soviet Union launched missions with passenger slots for at least 57 dogs. Some dogs flew more than once. Most survived; those that died were lost mostly through technical failures, according to the parameters of the test. Laika was an exception and was expected to die during her Earth-orbiting 3 November 1957 Sputnik 2.