Answer: Dogs

In the early days of space exploration and planning, animals were used to test safety conditions in order to pave the way for human occupied spacecraft. Among the earliest animals used were dogs due to their abundance, how easily they could be trained, and compared to the expense and complexity of handling mammals like chimps, the cost of dogs was trivial.

The most famous space dog, Laika–sent into space by the Soviets in 1957–never returned to Earth and her space capsule burned up in the atmosphere after its orbit degraded in 1958 (long after she would have died in the capsule). Later Soviet launches, however, yielded a return trip for the occupants. In 1960, two dogs (Belka and Strelka) successfully orbited the Earth and returned alive. Not only were the dogs celebrities in Russia, but one of Strelka’s puppies, Pushinka, became a gift for President John F. Kennedy’s daughter Caroline.

Although Belka and Strelka got the spotlight for their daring trip, it’s worth noting that the trip was a success for smaller creatures too–in addition to the high profile payload of two dogs, the spacecraft also carried a rabbit, 42 mice, two rats, a container of flies, several plants, and fungi.